# pressue blocking



## Jobsaver

Pressure blocking: allowed or not?


----------



## pyrguy

Saver

Please elaborate. I do not recognize that terminology.


----------



## ajweaver

It depends.

Ha. I learned that from the ICC.

Pressure blocking:

From my understanding, and this is folklore to me...before hangers-the pressure block would be cut larger than the gap between the ceiling joists and hammered into place then toenailed.

A lot of what I see is not pressure blocking, in that there is no pressure. I can see a gap.

Other times they face nail the block to a band joist, then nail the end of the face of the ceiling joist into the cut end of the block.

I always ask them first if there is a reason why a hanger cant go there?

My interpetation of the code is that floor joists require 1-1/2" of bearing per 502.6

And Ceiling joists per 802.6.

I interpet that to mean if they didnt have the min. req. bearing they would need a hanger.

I do not enforce this on short spans < 4' in closets etc..if there isnt significant load.

A MCP/CBO from this area refers to the "framing of openings" and doesnt require hangers until lengths exceed 6'.

But we both agree, always on floor joists.

I am curious too as to what people enforce.


----------



## Jobsaver

I am trying to pick-up on an old thread off the ICC bb archive having topic as Framing Anchors. There are good posts there with illustrations: I am not as good at describing things as many others in these forums, but basically in is a method of sideloading girders, beams, or walls with floor joists/ceiling joists by attaching blocking to girder, beams, or walls and then nailing the joists to the blocking.

Anybody out there good at posting illustrations?


----------



## Jobsaver

ajweaver: 802.6 - Where is the bearing of the top end of a common rafter? Against the ridge or on top of the ridge? This gos back to an unfinished debate: is bearing contact with another member or

does bearing require a member to set on top of the other?


----------



## Mark K

The code does not address the issue of pressure blocking.  Thus pressure blocking effectively cannot be used to show code compliance.


----------



## Code Neophyte

802.6, as Ajweaver said, is for ceiling joists, not rafters.  Rafters do not have the same requirement for bearing.


----------



## Jobsaver

Code Neophyte:

My book says:  R802.6 Bearing. The ends of each rafter or ceiling joist shall have not

less than 1 ½ inches of bearing on wood or metal . . .

Mark K:

R502.6.2 does allow for “approved framing anchors” as an alternative to ledger strips.

Under definitions, Section R202: Approved: Approved refers to approval by the building official as a result of investigation and tests conducted by him or her, or by reason of acceptable trade principles or tests by nationally recognized organizations.

I’m stupid. But, it seems to me that despite what many of the old timers on this and other forums say, BO’s can make a call on this either by acceptable trade principles, or, by tests conducted. In other words, traditional practice plus proven performance = prescription to the IRC.


----------



## Code Neophyte

You're correct.  A preceding section, R802.3, addressed rafter connection at ridge, hips, valleys.


----------



## Bootleg

I have approved pressure blocking if correctly applied instead of a hanger for floor and ceiling joist.


----------



## Jobsaver

Still. R802.6 applies to those same connections described in R802.3. So, what do they mean by bearing?



			
				Code Neophyte said:
			
		

> You're correct.  A preceding section, R802.3, addressed rafter connection at ridge, hips, valleys.


----------



## Jobsaver

Ditto.

I believe Simpson and the other framing connector manufacturers have duped our entire industry, including very very smart people using these forums, I don't get it.



			
				Bootleg said:
			
		

> I have approved pressure blocking if correctly applied instead of a hanger for floor and ceiling joist.


----------



## Code Neophyte

My 2-cent answer is that, going back to R102.1 "Where there is a conflict between a general requirement and a specific requirement, the specific requirement shall be applicable.", the upper end termination of a rafter is _specifically_ addressed in R802.3, so it would apply at that location.  In all other locations (i.e. lower end of the rafter), R802.6 would apply.


----------



## Jobsaver

Code neophyte:

Good answer. Thanks. What is your 2-cent answer to the legality of pressure blocking joists?


----------



## Mark K

The building official can approve alternates in accordance with Section R104.11.  From a practical point of view there are few limits on the building officials decision.

Neither Section 104.11 orthe defination of approved say anything about acceptable trade principles.  in my experience I have found a number of situations where what is presented as trade practices all to often has little foundation.  This does not necessarily mean that they are unsafe but I would be more careful when basing a decision on what I understand to be normal trade practices.

You can, and we have all done this, decide not to notice a code non-compliance.

Test data would be a good basis for making the decision.  I am not aware that there is any test data dealing with the effectiveness of pressure blocking.

While you could load test a particular situation.  I would be concerned that the performance would be dependent on workmanship thus making it difficult to extrapolate to other situations.


----------



## Code Neophyte

IF....I understand the concept correctly (so the floor or ceiling joists are side nailed into the end of a 1-1/2" block?), then I think it does not meet the prescriptive requirement of R802.6, and could not be accepted without engineering.  From a practical standpoint, however, I can't see how it is much different than the 2x2 ledger strip that's allowed by code to be used to provide bearing.  Both depend heavily on only a mechanical nail connection and no direct bearing loadpath.


----------



## Bootleg

Jobsaver,

I'm not sure what you question is but in framing you can use pressure blocking any where it is needed if done correctly.


----------



## Jobsaver

Mark K:

I stand corrected. The definition states "accepted principles" rather than "accepted trade principles".

I am now faced with the truth that I sometimes (accidentally) add or subtract a word here and there to try and get the code book to say what I want it to say.


----------



## Jobsaver

Code Neophyte said:
			
		

> IF....I understand the concept correctly (so the floor or ceiling joists are side nailed into the end of a 1-1/2" block?), then I think it does not meet the prescriptive requirement of R802.6, and could not be accepted without engineering.  From a practical standpoint, however, I can't see how it is much different than the 2x2 ledger strip that's allowed by code to be used to provide bearing.  Both depend heavily on only a mechanical nail connection and no direct bearing loadpath.


I understand and agree. An engineering study would be in order.


----------



## Bootleg

Jobsaver said:
			
		

> I understand and agree. An engineering study would be in order.


You would require an engineer to approve pressure blocking in SFR framing?

Is the house engineered?


----------



## Jobsaver

Bootleg:

I am probably not saying it right. I think it would be good if an engineering study could be done to establish, particularly in SFR, whether or not the practice of pressure blocking could be considered an alternative "accepted principle" to using hangers or a ledger to support joists.

Just about everybody in my state pressure-blocks. I haven't been personally exposed to any resultant failures. But, it remains the general consensus of many people in these forums more experienced than I that the practice of pressure-blocking does not meet code.

Further, there are apparently many places where nobody pressure blocks, and spends lots of $$ on metal. Seems like someone would want a study done.


----------



## Bootleg

Understood.


----------



## JBI

Jobsaver, Keep in mind that not meeting a prescriptive provision of the Code does not automatically mean non-compliance with the Code.

An Engineer could review and provide detail for only those elements of the project that are not prescriptive, or a contractor, owner etc could provide the Reference Standard that shows that detail, if it exists.

That a Code Official has broad discretion, does not mean it should be used too freely. Those accepted practices are usually accepted (Engineering) practices. Just because it's 'been done that way for XXX number of years doesn't necessarily mean it's a good idea.

I'm less convinced that Simpson, TECO, etc sold us a bill of goods. They sold us options, alternatives to traditional methods. And the Codes allow the flexibility to use a wide array of options in design and construction.


----------



## Rio

Legality aside, pressure blocking, as pointed out if done correctly, is one of the best and strongest ways to connect certain wood members such as rafters to ridge boards.


----------



## conarb

I learned to pressure block everything, the first metal we saw was Teco clips in the early 50s, when Simpson came out with joist hangers I was one of their first customers at their manufacturing plant by the Oakland Airport in 1957.  I didn't really trust the "flimsy tin" as the old guys referred to them, so we pressure blocked and added the joint hangers on top of the blocks. And by the way, I still won't use a rim joist, I solid block everything.

Now that steel construction is threatening to displace wood, Simpson has come out with their own line of bolt-together moment frames, obviously they are seeing so many moment frames in wood buildings that builders are going to think: "If I have a steel crew here welding moment frames together, why not do the whole thing in steel and eliminate the poor quality wood and all the metal connectors required to build a wood house? By providing bolt-together moment frames they can keep the carpenters building the house using their metal.


----------



## Jobsaver

Rio: Legality aside? That does hit the nail on the head when pressure-blocking!

JBI: Options are generally a good thing. Still. I paid for a training seminar recently based on the 2006 IRC advertised as sponsered by our Homebuildes's Association, but Simpson is serving the sandwiches an hour after the instructor is "requiring metal" based on the engineering behind the code. Do you know of any engineering studies that may have been done to research the effectiveness of pressure-blocking? I am not speaking of having a study done for particular elements of a particular project, rather, a study done to determine if prescriptive elements might be codified to allow pressure-blocking in typical wood framed SFHs.

conarb: I wasn't even a gleam in papa's eye in '57! You are gett'in old as dirt! Probably wise and experienced too ... do you know of any studies done to determine if prescriptive elements might be codified to allow pressure-blocking in typical wood framed SFHs? Maybe the guys selling gun nails, (Bostitch, Paslode, Hilti, etc.), might consider funding such a study.


----------



## Robert Ellenberg

Someone said they didn't see a difference in pressure blocking and using a 2x2 ledger strip.  It is possible that the code doesn't specifically allow pressure blocking because when you nail the end of the joists into the block, the nail is so close to the end of the joist that the nail would often split the grain, particularly if you are using SYP?  When nailing a 2x2 in place it's not likely to split unless you put the 3 required nails a little too close together.


----------



## Jobsaver

The combination of nailing the joist into the pressure block and toenailing into the girder makes for one heck of a hard to impossible connection to disassemble. My experience in the field is that 2x2 ledgers are prone to splitting if nailed securely enough with gun to "feel" secure. What is nailing pattern for ledgers? I can't find it in IRC.

Note: I am not the one to say I don't see the difference; pressure blocking is clearly better, but do agree both practices depend on the shear strength of the nails.


----------



## Mule

Haven't seen pressure blocking in a long long time. I've seen pressure blocking used for support and to keep the joists from twisting.


----------



## JayHawkInspector

I agree with Mule the main reason for pressure blocking is to prevent rotation or lateral displacement, just check out the WFCM (Wood Frame Construction Manual) page 21 Sections 2.3.1.3 & 2.3.1.4.


----------



## Jobsaver

Mule said:
			
		

> Haven't seen pressure blocking in a long long time. I've seen pressure blocking used for support and to keep the joists from twisting.


Do you think you would see more of it if it was codified?


----------



## mark handler

Due to the moisture of "green" lumber and the, Tangential and radial shrinkage values in the green lumber we cannot rely on just "good" construction and "Pressure blocking". The only way I would rely on "Pressure blocking" is if the lumber is oven dried and the moisture content is verified at the time of installation.

"Pressure blocking" should never be relied on for primary support members, or as a substitution for any steel clips, hangers, excreta.

Should Not be codified

All blocking should be tight fitting, with NO gaps, at the time of framing.


----------



## Jobsaver

Mark: Should not be codified?

I agree with some of your concerns, but believe those same concerns affect other codifed methods. I believe an engineering study could and should be performed, and the results commonly available, before the potential codification of the method of pressure blocking is marginilized.

I have read in the archived ICC posts that forum members commonly experienced this method being engineered into a particular project. It stands to reason that a prescription for codification can likewise be established.

Agreed: All blocking should be tight fitting, with No gaps, at time of framing. Would add to check for nail type and pattern if engineering prescriptions were available.


----------



## mark handler

If you want it codified answer this question:

How does wood shrinkage effect "Pressure blocking" and how do you "prescriptively" mitigate the effect?

With "green" lumber Pressure blocking is already marginalized.


----------



## Bootleg

Has anyone ever had pressure blocking fail?


----------



## conarb

Have to wonder how all our old buildings survived before joist hangers were invented, even Teco clips for that matter? The only building failures I've had in over a half century of building are the failures of the gang-nail plates in lightweight roof trusses, my homes with lightweight roof trusses with glued/nailed plywood gussets from the 50s are all doing fine, but several failures with the gang-nail plates popping off in my homes of the 60s and 70s, since I've always guaranteed my buildings for my life, I've rebuilt several roofs by now. Now I read that Australia is having an epidemic of gang-nail truss failures. I've had no pressure block failures, of course started adding Tecos and Joist hangers in the 50s. I've remodeled a lot of old Victorians and mansions in Piedmont and the pressure blocks are fine, all were built with green lumber.


----------



## Jobsaver

mark handler said:
			
		

> If you want it codified answer this question: How does wood shrinkage effect "Pressure blocking" and how do you "prescriptively" mitigate the effect?
> 
> With "green" lumber Pressure blocking is already marginalized.


The purpose of a study would be to answer the question you pose.

Can you give me a definition of "green lumber".


----------



## mark handler

Jobsaver said:
			
		

> Can you give me a definition of "green lumber".


Unseasoned or green lumber has a moisture content greater than 20 percent, shrinks and may warp as it dries.

Dry lumber has 19 percent, or less, moisture content

Dry lumber can cost 1/3 rd more over green lumber and needs to be protected on site to prevent the reintroduction of moisture.

And a side note, green lumber is a major cause of mold in buildings.


----------



## mark handler

conarb said:
			
		

> Have to wonder how all our old buildings survived before joist hangers were invented, even Teco clips for that matter? The only building failures I've had in over a half century of building are the failures of the gang-nail plates in lightweight roof trusses, my homes with lightweight roof trusses with glued/nailed plywood gussets from the 50s are all doing fine, but several failures with the gang-nail plates popping off in my homes of the 60s and 70s, since I've always guaranteed my buildings for my life, I've rebuilt several roofs by now. Now I read that Australia is having an epidemic of gang-nail truss failures. I've had no pressure block failures, of course started adding Tecos and Joist hangers in the 50s. I've remodeled a lot of old Victorians and mansions in Piedmont and the pressure blocks are fine, all were built with green lumber.


 Yeah "Pressure blocking" and green lumber helped this old building....


----------



## Jobsaver

Thanks, that is the same thing we call "green lumber" here. I thought we might have been talking about something else.

We don't have any around here that is grade stamped. Our yards carry primarily kiln dried, and some sun dried studs.

I never like to see a pile of wood or a frame exposed to the elements for too long, but believe all existing prescriptive codes must account for a measure of exposure, as would any proposed ones. Wood framing and framing connections depend on dimensional stability inherent to allowable lumber species.


----------



## Jobsaver

mark handler said:
			
		

> Yeah "Pressure blocking" and green lumber helped this old building....


C'mon.

Earthquake. Came from a geotech site. Probably rigid elements in the foundation.

Don't bs a bs'r.


----------



## mark handler

Jobsaver said:
			
		

> Came from a geotech site.


No, it came from Western Washington University, Yes it is earthquake related, central California, in response to Dicks comments on old buildings, not based on your comments.


----------



## Bootleg

Would it have been any different with joist hangers?

To me it look's like a positive connection failure.


----------



## mark handler

Bootleg said:
			
		

> Would it have been any different with joist hangers?To me it look's like a positive connection failure.


Probably, but probably no metal connectors either


----------



## Mark K

The reality is that the better a building is tied together the better it will survive earthquakes, hurricanes, or tornados.  This often means doing things that the contractors haven't done before.

Apparently on the East Coast where they have hurricanes they install steel rods that tie the roof framing to the foundation.  This the roof on and keeps the building from lifting off of the foundation.

The first step is to enforce the code.  Do not allow local trade practices when they are in conflict with the code.  The code provision may have been added in response to problems resulting from these trade practices.

We also need to recognize that when the IRC allows houses to be built without engineering that there will be a greater likelyhood of problems in extreme events.  I believe that the IRC is often applied to structures that differ from the idealized structure around which the provisions were written.  This has the potential of poor performance.


----------



## mark handler

Save a buck for no engineering, pay for it later when earthquakes, hurricanes, or tornados hit.


----------



## Robert Ellenberg

I thought I remembered 3 nails being specified somewhere (because I had put that in my file notes related to using 2x2s for bearing) but now I can't find it in the IRC and what I do find calls for 2.  R502.6 states the end of floor joists must bear on not less than 1.5" of wood and R802.6 states the same requirement for ceiling joists.  Both chapter 5 on floors and chapter 8 refer to the structural member fastening schedule in chapter 6 on walls, Table R602.3(1).  That table specifies for 2" planks that you must have 2-16d nails at each bearing.  I assume a 2" plank is the same thing as what I call a 2" ledger since it refers to bearing.

As to pressure blocking, I believe it is prohibited for floor joists by R502.6 where it states it shall have bearing unless using approved hangers. Pressure blocking, no matter how good it might be, doesn't meet either of these requirements.  Right below it in R502.6.2 where it describesf framing into the side of a girder it again states you must have a ledger or an approved anchor.


----------



## Architect1281

I would allow all the pressure blocking they could think of

as loong as

It was secured in accordance with the fastening schedule


----------



## Bootleg

Architect1281 said:
			
		

> I would allow all the pressure blocking they could think of as loong as
> 
> It was secured in accordance with the fastening schedule


I would agree.


----------



## conarb

Mark:

There is absolutely no evidence in your picture that pressure blocking was even used in that house, pressure blocking was rarely used, all joists rested on plates, we only pressure blocked in rare instances since all joists rested on plates, presure blocking was used in floors around stairway and fireplace head-outs, and in ceilings around access holes and  chimneys. At the time that house was built all lumber here in California was S2S meaning a full 2" thick, moisture content was never checked, the lumber was milled green and shipped down to sit around to dry until used, I never saw the stuff that squireted into your eye when you drove a nail into it until the tract home epidemic in the 50s and cheap apartments in the 60s.


----------



## JBI

Jobsaver, Have you researched the existing Reference Standards? The Codes cannot possibly provide every detail that exists for every type of construction in every possible combination. AF&PA provides the standards for most wood construction, nails are rated by recognized authorities, the Engineering is mostly already done.

Yes, material quality and workmanship are critical to traditional methods such as pressure blocking, but they are equally important to modern methods - the hanger manufacturers are pretty darn specific about how to install their hangers you know. The more we rely on Engineered products, like metal plate connected wood trusses, the more dilligent we need to be about the details. In modern construction, the devil is truly in the details.

When discussing things like shrinkage, warping, etc. you can't reasonably compare a 100 year old framing member to a modern one. We simply don't grow wood the way we used to. Those old buildings were built with wood milled from trees that grew at a natural rate into a mature tree. In my area it was almost all Oak and Hemlock 100 -150 years ago. Old Growth forrest. Todays lumber is milled from trees that have been selectively farmed for rapid growth and cut by the time they are 12" or less in diameter. Look at a cross section of an old 2x4 and compare it with todays.


----------



## Mark K

I believe that the biggest variations have to do with the definition of pressure blocking and variations in workmanship.   Untill you can address both of these It is impossible to know what the capacity of a pressure blocked connection.   The challenge in these situations is to make our decisions based on evidence.

Who has test data showing the capacity of pressure blocked connections?

I believe that it is harder for a carpenter to screw up with metal joist hangers.  With maybe rare exemptions a metal joist hanger will be stronger than pressure blocking.

I do not believe that the variation in shrinkage between species plays a big role.  Note that Oak is comparable to more common species.  for most of the country I believe that oak and hemlock are exotic lumber not used for beams and joists.

Percent of shrinkage from green to oven-dry moisture content:

                                   Radial shrinkage

Douglas Fir-Larch                   4.6%

Southern Pine                       4.8%

White Oak                            4.4%

Southern Red Oak                  4.7%

Eastern Hemlock                    3.0%

It is not clear why cutting trees 12" dia would increase shrinkage.  On the West Coast trees are much larger before they are cut for lumber.


----------



## DRP

Small fast growth trees contain a large percentage of juvenile wood. The cells of that wood are composed of fibrils oriented at an angle on a bias to the axis rather than in line with the axis as in mature wood of the same species. Shrinkage takes place after the free water has left the cell lumen. When the water bound to the cell wall begins to leave the fibrils move closer together in the cell walls. Mature wood with fibers oriented axially shrinks in width and thickness as it dries. Juvenile and reaction wood shrink lengthwise as well, I've had 16' lumber lose almost an inch of length. Think about the breaking strength difference of this fiber orientation vs the mature wood. Testing on tjuvenile wood has shown it to be highly variable and not for the better. Grading rules turn a pretty blind eye right here...

Shrinkage begins at "fiber saturation point" the point where all the free water is gone and the bound water is what remains. This point is also where most decay fungi cease activity. FSP for most species is around 25%. The wood is also getting harder and less appealing to insects below that point. A board at 45% will squirt in your eye, one at 20% cannot. Sap does not go down, it flows or not, cells die when they embolize.

Old growth ring porous woods like oak are structurally inferior to fast growth oak. They are dimensionally more stable but are lower density, more porous and weaker than fast grown ring porous hardwoods... that is one class of species. Hickory handle manufacturers recognize this and usually will not accept wood with more than 6 rings per inch, it breaks short and brash.

Softwood strength is usually more closely related to percentage of latewood than number of rings per inch, look for a healthy amount of dark rings and secondarily at the ring count, within reason ~6-40 RPI.

Wood does not stop drying and shrinking at 19%, it continues to dry and shrink until it hits "equilibrium moisture content" . EMC is "seasoned" when the wood is at balance with the humidity of the environment it is in. For me, on average, that 19% framing still has about 7% to go before it is at emc. There is no pressure or friction in these blocks, nails in shear from the NDS connections calc.

Timber framers notching beams for drop in joists make a similar argument sometimes, that the joist replaces the notched out material on the compression face and thus the beam is not weakened. The joist shrinks in width and the pressure is gone. I've seen dovetailed drop in oak joists withdraw enough to stuck my little finger in the gap.


----------



## Jobsaver

I appreciate all the info.

JBI:


----------



## Jobsaver

I appreciate the data and suggestions.

JBI:


----------



## Jobsaver

Having troubles. Sorry folks, not much of a blogger. More of an idiot, really.

JBI, I will try to obtain some info from the AF&PA. I went to the website. Good to know. Thanks!

Conarb,  we have a lot of old houses around here, like the one pictured, balloon frames out of full 2" thick virgin pine. You gotta be a pretty old dog to have framed with that material.

DRP, you are a scholar. Good stuff.


----------



## JBI

Jobsaver - Welcome by the way. Where the code stops, the Reference Standards begin... Where they stop, the Bulliten Board begins.


----------



## DRP

I appreciate it Jobsaver, just a wood nut.

I was looking for a picture for something else tonight and came across some that might go along with what I wrote before.

Look at the end of this rocking chair of a board. The heart is center top, the juvenile core is shrinking lengthwise, the mature growth rings are not shrinking lengthwise and the board is pulled into a bow as it dries.






This is from a forestry text, it is showing that in softwoods, specific gravity, or density/ strength, is not so much dependent on rings per inch as on percentage of latewood (the dark, thick cell walled rings)






This shows several meter readings and some squirting from some pretty green cypress. What can I say the salesman had plaid pants and white shoes. The end cut with a dry shell and a wet core is showing what the fiber saturation point is. The wet core has cells that have free water in the central cavity of the cell, the lumen. The outer shell has dried to the point where the free water is gone and the moisture that remains is bound within the cell walls. Only as that bound water leaves does shrinkage begin. Seeing free moisture in a cut end tells me the moisture content is over 25%.






This picture demonstrates "equilibrium moisture content". If you look up the emc of wood that is exposed to 65 degrees and 45% relative humidity, the moisture content of the wood will equalize to about 8% moisture content. The meter is confirming the framing here has acclimated to that environment.


----------



## texasbo

DRP: I had no reason to log in other than to tell you what excellent posts these are, and to thank you for your contributions. Great stuff.


----------



## RJJ

DRP: The rocking chair! Put it on the lawn over night, but flip it first. Next morning before the sun hits it nail it in place. Problem should be solved. As for the guy in plaid pants. Might have been a relative of mine.


----------



## beach

We used to pressure blocking all the time when I was framing, of course, I wouldn't allow it now if the plans showed a mechanical connection, like they usually do. It's amazing, really, how much of a load you can apply to pressure blocked joists if installed correctly and we didn't use kiln dried lumber.......


----------



## Bootleg

Beach,

I'm glad you replied, I didn't think there was any framers left from the old school.


----------



## beach

Old skool is cool!!!! When was the last time you saw an FHA style 1X6 let-in brace????


----------



## Bootleg

Summer of 1979 or so.


----------



## beach

'84/'85 was the last time I cut them in....... I think......


----------



## conarb

The plywood industry has done one Hell of a job selling us on the idea that all buildings have to be braced and sheathed with their product, the old carpenters who trained me always taught that all buildings had to breathe or they would rot out, they thought that when plywood came on the scene it was better for subfloors than 1x8s but a terrible idea on walls.  We absolutely never sheathed behind wood siding, and the 1x8s behind stucco had knots and was installed green so it shrank with ¼" gaps between the boards.

After the Vancouver condo crisis they made contractors drill holes in their plywood sheathing, eventually they mandated rain screens over sheathed walls. In the home I have in permit, with the steel frame, I have no sheathing whatsoever so my walls can breathe, a concept that's been lost and the reason for much of the building failure today with our new "green", "energy efficient" buildings. Of course this is all part of the NAHB "disposable house" program, and the main reason I dropped out of the NAHB in the early 70s.


----------



## Bootleg

After thinking about it,

You are right Beach.

I can remember cutting let in braces in 1983 in signal hill cailf.

We had some slow years in the early 80's and then when it pick in the mid 80's it seem to be more shear walls.


----------



## Bootleg

Conarb,

I know you are from the old school!

In fact I think you wrote the book for the old school.


----------



## DRP

The number I remember was that the exterior needs to breathe 5 times better than the interior. We wandered away from that but I think the gist of that is what Lstiburek and others talk about.

We let in 1x4's, cut in worthless metal straps or used plywood corners and celotex for the rest. My houses are certainly stronger now, more durable... I don't know.

Historically mill type construction sometimes used a 2x2 vertical block alongside of the joists. Bolts ran thru the block and beam and also through the block and joist.

The notched beam with drop in joists gave timberframers trouble from earliest times and evolved to designs that inserted a tennon into the beam's neutral axis. The tusk tennon from the late middle ages was probably the most elegant solution. It is inserted into the neutral axis of the timber and the upper compression edge of the beam is left intact. This also requires a set of hands on every joist as the beam is brought into place. CA Hewitt's "Historic English Carpentry" has an excellent commentary on this evolution.







Here we are with the fastest wood eating machines of all time trying to raise a block pinned to the rim and joist to some level of historical noteworthiness. I've seen mention of "properly" applied pressure blocking but haven't seen a description other than frail to fit. What makes it "proper". Are you suggesting that after drying in service it has some other strength beyond nails in shear?

Simpson and APA have done their homework. They have made it easy to use the product. AWC could take note, some basic prescriptive blocking and connection details and tables.


----------



## Bootleg

DRP,

I think it is the way we grew up doing it and it was a hell of alot of work to tear out pressure blocks that all.

Glory Days


----------



## conarb

DPR said:
			
		

> The number I remember was that the exterior needs to breathe 5 times better than the interior.


I never heard that ratio, but it makes sense. This knowledge is soon all going to be lost when we old guys die off and the Greenies and environmental wackos take over. View attachment 233

​When I started we used cut-in 2x4s, on higher quality jobs and in all underpinning we nipped the ends of the 45° cuts and ran 1x4s down to the bottom plate (or mudsill) and up to under the top plate.  Let-in 1x4s appeared in the late 50s, we always considered them inferior tract-style work, but they did take over by the 60s.  One of Simpson's less successful endeavors was the steel tension strap, you always had to install two of them, one in each direction in each direction, I see they still make them but limit their use to Seismic Zone 1.​​View attachment 233

​/monthly_2010_10/sim_brace.jpg.e053877c1afb3b755c4f4158be959f96.jpg


----------



## Bootleg

Conarb said:

This knowledge is soon all going to be lost when we old guys die off and the Greenies and environmental wackos take over.

This is very true.


----------



## Mark K

Let in braces are a lousy bracing system.  Not only is it weak compared to plywood the notches weaken the studs.  I have seen pictures of failures in the studs due to the notching.

Do not blame the rotting on the use of plywood.  A lot of the problem was the result of our efforts to make buildings tighter in response to the need to conserve energy.  The problem is that when we made buildings tighter we did not have a good scientific idea of how moisture flows through buildings.

It wasn’t until Lstiburek and his fellow researchers started applying science to the problem that we learned how to do it right.   And what is right in California on the coast is not the right way in Montana on the Canadian border.

Knowing how to do it right is only the first step.  The designers need to define what was needed and the trades need to learn how to do it per the plans.  We need to break old habits.  Doing it like you did it 40 years ago no longer cuts it.

Old timers can contribute a lot, but in order to do it effectively we need to embrace and understand the new technology.  If we do not keep up with the new knowledge we will rightfully be seen as irrelevant and will be ignored.  Get on the train or retire.

Sustainability is here to stay.  Rather than fight it we need to demand that the requirements be backed up with some objective thinking.  The objective should not be to go back to the old ways but rather to make sure that the new requirements are effective.


----------



## conarb

Mark:

There are better ways to brace walls than shear plywood without sealing the walls up,  are a good example.  In fact in one of Lstiburek's articles he shows himself as a young man driving shims under the lap siding of his parents home to release the water trapped and blistering the siding from nailing the siding right on plywood, he states briefly something about newer systems and showed a picture of a Hardy Frame¹, but then goes right on to say we have to brace homes so they won't fall down and use plywood, he then launched into his pitch for rain screens.  At this point from the rotted buildings I've seen I'm ready to say that any time you shear a wall you must use a rain screen. Before the 1998 CBC I avoided the problem by getting the engineer to approve putting the shear plywood on the interior behind the sheetrock, I doubt they would approve that now, engineers are requiring so much steel and Simpson products now that I am going to all steel frames. Furthermore, whenever there is shear plywood the green raters are putting in the G sheets OSB, that stuff is a disaster, by not having shear plywood they can't substitute OSB. In this addition the engineer still placed plywood on the walls, then the green rater substituted OSB to "clean up the forest floor" in the G sheets.



			
				Mark said:
			
		

> Sustainability is here to stay.


I was giving a talk to a Stanford Alumni group about Green Fraud and the Green Codes, I was asked what could be changed that would get me to buy into green codes, after thinking a minute I said that sustainability should be re-defined as building buildings that last hundreds of years instead of building sick buildings that are going to rot out in a few years.

¹ http://www.hardyframe.com/braceframes.htm


----------



## Jobsaver

DRP said:
			
		

> Simpson and APA have done their homework. They have made it easy to use the product. AWC could take note, some basic prescriptive blocking and connection details and tables.


I second that. Some basic prescriptive pressure-blocking and connection details and tables forthcoming.


----------



## Robert Ellenberg

conarb posted, "Before the 1998 CBC I avoided the problem by getting the engineer to approve putting the shear plywood on the interior behind the sheetrock, I doubt they would approve that now"

It is a very common practice in coastal Louisiana where the greatest concern is hurricane force winds.


----------



## beach

Hey Conarb, in the "old days".... did you use galvanized water pipe, transite (asbestos) ducts, asbestos interior plaster, lead paint, standard glass (not tempered) for showers and doors and parrafin wax on your 16d's?????

(Just messing with you, everyone did!!!!)


----------



## conarb

Beach:

Of course, we replaced the paraffin with soap powder in the late 60s, one day it rained in 1971 when the inspector was there on a 65 unit garden apartment complex, soap suds ran down the studs and legs of my carpenters. Nice inspector, he didn't say anything but gave me that "knowing look", damn good thing it wasn't Uncle Bob, I'd still be in jail.


----------



## beach

Never heard of the soap powder trick.... funny story! Don't rub your eyes!!!


----------



## conarb

Beach:

Another funny story, Cal Berkeley housed it's married students in Albany in a place called Codornices village, Codornices Village was old two story WWII army barracks, they were covered in stucco that was badly cracked from settling.  The Cal architecture people remodeled them and covered them in asbestos, my first job out of college was as a foreman on the carpentry crews stripping the stucco with 1x4s for the asbestos guys to cover the buildings.  It was only fitting that  Stanford guy's first job out of school was encasing Cal students in asbestos, and Big Game is coming up.


----------



## Jobsaver

DRP said:
			
		

> Simpson and APA have done their homework. They have made it easy to use the product. AWC could take note, some basic prescriptive blocking and connection details and tables.


Does anyone know if a study has ever been done?


----------



## Jobsaver

Conarb:

Nice post on the Dumas Residence in the foundation threads. Great pics! A couple of good examples of pressure-blocking there.


----------



## conarb

Jobs:

The Simpson products cost $35,000 on the Dumas Residence, and that did not include the structural steel.


----------



## Jobsaver

Okay. $35,000 worth of Simpson products and a couple of good examples of pressure-blocking.


----------



## Jobsaver

(RANT)

Construction Arbitrator: So. What is the deal. It is okay to employ the construction technique of pressure-blocking just so long you don't acknowledge it?

You have a depth of experience and possess personal capabilities that are enviable, and could be instrumental in furthering the idea that prescriptive codes for pressure-blocking, at least in limited circumstances, is a viable idea. But you appear to be too entrenced to even admit employing this technique on a limited basis.

We allow pressure-blocking in our ahj in limited circumstances, as do others that have responded to this thread. Then, there are those that criticize every inspector for allowing any deviation from the letter of the law of the code, sometimes pretending they don't . . . often, the same folks calling for reform and revolt against the ICC and the system of things.

Where do you stand? Are you saying you do or do not believe pressure-blocking should be accepted or rejected in all applications?


----------



## Bootleg

Jobsaver,

Accepted.


----------



## Belly John

Fronts occurr at interfaces between presure cells or air masses, and are not features of the global wind belts.


----------



## KZQuixote

Here in Oregon we call it power blocking. I've got to tell you it's great! Using power blocking gives the carpenter numerous angles and directions to toe nail and face nail a joist to a ledger without any worry about pushing the joist off of layout. All without having to deal with the thickness of the hanger messing with the drywall. If you've ever installed joists in joist hangers that utilize those 8 or 10d toe nails you know they're a joke.Course the carpenter doing the nail up lacks the engineering/insurance policy to back up his skill so most AHJ won't accept the personal responsibility to approve a very elegant carpentry technique.I'll edit this post to show some power blocking I've used on the addition I'm building to my own home.Bill

View attachment 255


View attachment 255


/monthly_2010_11/PowerBlock.jpg.e02d6011d9ad4f7cdf1cb9e6744504f0.jpg


----------



## DRP

> Does anyone know if a study has ever been done?





			
				KZQuixote said:
			
		

> Using power blocking gives the carpenter numerous angles and directions to toe nail and face nail a joist to a ledger without any worry about pushing the joist off of layout. Course the carpenter doing the nail up lacks the engineering/insurance policy to back up his skill so most AHJ won't accept the personal responsibility to approve a very elegant carpentry technique.


 NDS 11.5.4.2 Toe-Nail Factor would be the thing to use here. "When toe nails are used, reference lateral design values,_Z_, shall be multiplied by the toe nail factor, Ctn = 0.83."

Fig 11A shows the toe nail for that value. The nail is at a 30 degree angle to the joist and is started from a point 1/3 of nail length back from the end of the joist.

At 19% during installation and ~12% in service there is no pressure or friction to add to that in service. Not saying it doesn't work, those would be the design values I would check against. Elegant carpentry to me is to put the joist on the beam.


----------



## Jobsaver

KZ: Good illustration.

What is required is a study of the power-blocking, or pressure-blocking technique that would include numerous calculations including for toenailing, face-nailing, and allowable spans.

I The strongest connection is achieved by face nailing the joist to the pressure block, as well as toenailing the joist through the pressure-block into the beam.

Yes, the joist on beam is best where applicable. But, this application, like a joist hanger or notchiong for a ledger, is for the application where having the nailing surfaces of the joist and beam aligned is the desired result.

Based on this thread and a similar thread on the archived ICC bb, pressure-blocking is practiced throughout the United States, at least on a limited basis. I suspect it is more common than expressed.

For examples, pressure-blocking may can be established as a legal framing connection for ceiling joist spans up to 8', or floor joist spans up to 4', where uniform loading exists.


----------



## KZQuixote

Not sure where the term Pressure Blocking might have come from. Any carpenter who has nailed more than a few blocks knows the problem with not leaving some negative tolerance in the block length. Additionally, what might be tight at today's moisture content is certain to be loose once the building has dried out.

Jobsaver said: "The strongest connection is achieved by face nailing the joist to the pressure block, as well as toenailing the joist through the pressure-block into the beam."

Hi Jobsaver, Do not forget the back nails that the carpenter drives through the last joist into the newest block. This way the joist is face nailed from both faces as well as toenailed into the beam or ledger.

Power Blocking has got to be many times stronger than notching the joists onto a 2X2 face nailed ledger. Unfortunately, it'll never get published and accepted.

 The deep pockets of Simpson Strong Tie will see to that.

Bill


----------



## Jobsaver

KZQuixote said:
			
		

> Oh! If it could only be! Don't bet on it! The deep pockets of Simpson Strong Tie will see to that.Power Blocking has got to be many times stronger than notching the joists onto a 2X2 face nailed ledger.


Definitely on the ledger being weaker.

I am not sure that the Simpson Strong Tie pockets are deeper than the nail manufacturer's pockets combined with the lumber producer's pockets, both of which stand to benefit from prescriptive pressure-blocking.

Pressure-blocking? Power-blocking? Gotta find a new name that works for the engineering crowd . . . maybe Lateral Dimensional Lumber Framing Anchors? Carpenters can still call 'em blocks!


----------



## Robert Ellenberg

Is the opinion that pressure blocking is stronger than a ledger just that, an opinion, or is there a basis for that statement?


----------



## Jobsaver

Not a formal engineering basis, but it would be great to get one of the university labs to do some formal testing on various methods.

Its an opinion based on personal experience. Simple tests with simple tools building frames, and sometimes taking them apart. Ledgers work well too, but are prone to splitting using some species.

I am surprised that there is not more support for the idea of testing.


----------



## conarb

Jobsaver said:
			
		

> but it would be great to get one of the university labs to do some formal testing on various methods.


You're not going to get it from a university, universities work on grant money, there is Simpson grant money, but there is no pressure blocking industry to fund such a study, pressure blocks consume only scraps of lumber so their is no incentive for the lumber industry to fund such a study. Here is some information on drug studies, the same applies to building product studies.



			
				San Francisco Chronicle said:
			
		

> Money  talks  --  and very loudly when a drug company is funding a clinical  trial involving one of its products, according to a study released  Monday.
> 
> UCSF  researchers looked at nearly 200 head-to-head studies of widely  prescribed cholesterol-lowering medications, or statins, and found that  results were 20 times more likely to favor the drug made by the company  that sponsored the trial. "We have to be really, really skeptical of these  drug-company-sponsored studies," said Lisa Bero, the study's author and  professor of clinical pharmacy and health policy studies at the  university.
> 
> The research, reported in the online editions of PLoS Medicine, a  San Francisco medical journal, focused on studies of six statins  --   including Pfizer Inc.'s Lipitor, Merck & Co.'s Zocor and the generic drug Mevacor  --  that had already been approved by the Food and Drug Administration. The trials typically involved comparing the effectiveness of a drug to one or two other statins. "If I'm a clinician or funder of health care, I really want to  know within a class of drug which one works better," Bero said. "What  our study shows is that depends on who funds the study."
> 
> UCSF researchers also found that a study's conclusions  --  not  the actual research results but the trial investigators' impressions  --   are more than 35 times more likely to favor the test drug when that  trial is sponsored by the drug's maker.
> 
> Read more: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/06/05/DRUGS.TMP#ixzz15E2IFp3D
> ​


----------



## Jobsaver

Scraps of lumber . . . sounds like a good green idea to me.

How much energy is consumed producing one house's worth of unnecessary Simpson Products. What is the carbon footprint from burning the scraps of lumber? Obama will fund the study!

Kidding. But pressure-blocking consumes a lot of nails too. Nails cost money.


----------



## conarb

The last house I built consumed $35,000 worth of Simpson products, and their specialty nails cost more than common nails.


----------



## DRP

Jobsaver,

I haven't seen any resistance to your idea. Why do you feel this should be looked at differently than nails in shear. I think we've gotten past the warm fuzzies and magic dust our memory paints our own work and methods with. We've agreed there is nothing other than nails holding the members together. What I have seen is reference to "properly applied" which everyone seems to agree is critical... We've had alot of shyness posting descriptions of what that is and not full agreement amongst the posted methods. That says this is not as "common sense" as we might think.

The Simpson hanger is holding the nail the proper edge or end distance and giving proper penetration. It is going through a steel side plate, we are going through wood. Go to the AWC connections calc... there are the numbers for either. Doing it all in blocking simply means the carpenter needs to be aware of those distances and the capacity of the nails for the variables in the assembly. We can figure the allowable loads for Bill's blocking. The fact that we don't seem to know how to do that is the reason a wood industry group like the AWC needs to put out a flier with simplified typicals similar to a Simpson catalog. In that same vein, I can fold a piece of metal and use the NDS tables or connections calc to make my own plates and hangers. By third party testing Simpson has been able to broaden the applications and raise the allowable values. That is what any testing might be able to do for you.

I'd talk to Virginia Tech or Washington State, you might be suprised. If they cannot answer the question right off the bat those grad students always need a project.

You don't have the re-entrant corner at the inside of a notch like you would with a ledger, the block will not roll into withdrawal like a 2x2 can.


----------



## Jobsaver

Thanks. That is a good idea that I will pursue. Since joining this forum, I have become motivated and signed up to participate in our COAR, the body of code officials in our state that helps with revisions for our state building code. I have already talked to a couple of guys having influence in this group, and they are receptive to this idea. I believe the students, and a university, might be more reseptive to performing a study on behalf of legitimate organizations of building code professionals. *Who knows that the like-minded members of this forum can't pull together on this one and back me up on something tangible that can be accomplished despite the other lobbyists and special interest groups. I say we become our own special interest group advocating for common sense building methods that promote efficiency and building craft.*If there is anyone reading this that has experience approaching a university asking for such a study, I could use some pointers.


----------



## Jobsaver

Thanks. That is a good idea that I will pursue. Since joining this forum, I have become motivated and signed up to participate in our COAR, the body of code officials in our state that helps with revisions for our state building code. I have already talked to a couple of guys having influence in this group, and they are receptive to this idea. I believe the students, and a university, might be more receptive to performing a study on behalf of legitimate organizations of building code professionals. *Who knows that the like-minded members of this forum can't pull together on this one and back me up on something tangible that can be accomplished despite the other lobbyists and special interest groups. I say we become our own special interest group advocating for common sense building methods that promote efficiency and building craft.* If there is anyone reading this that has experience approaching a university asking for such a study, I could use some pointers.


----------

