# Deck Piers, yet again



## jar546 (Apr 26, 2019)

OK, another thread hit my hot button so I wanted to expand on it and bring it to the surface again.

The sizing of deck piers and adding a roof on it.  This is a major pet peeve because I use to get grief all the time because we would reject plans based on lack of adequate footing of the existing deck and would always hear: "I've built them all over the county like that and you are the first one to deny me"

Let us dive in.

Let's say for simple math we have a 10'x10' deck attached to a house with two piers, one on each corner.  A very simple setup.  Break it down:

10x10=100 square feet, 50% of  the load is carried by the house and the other half is split up between the two posts (assuming it is framed that way).  We have to charge a 10# sq/ft for dead load plus a design load of 40# sq/ft.  That sounds like 50# sq ft to me.  50lbs x 50sq' is 2500 pounds.

Without soil testing or confirmed that we are on solid rock, the code has us assume a 1500psf soil bearing capacity.  Here is why I love math.

Each of the posts much be capable of supporting 1,250 pounds by design.  A 12" sonotube is only 113 sq/inches so on a 1500 soil, that is only 1,170 pounds of bearing capacity. Even the DCA6 starts with an 18" sonotube or 16x16 x 7" thick footer.

My point is this.  Most decks have barely enough bearing capacity to support their own design load, let alone adding a roof on it with a snow load and dead load.


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## steveray (Apr 26, 2019)

Agreed....We typically use 2000#...but it is still tough....Same thing with 24x24 piers for the house main beam these days....


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## classicT (Apr 26, 2019)

This is why I run beam calculations on 90% of the decks that I review. We use the beam reaction to size footing.

(Beam reaction) / 1500psf = minimum area
Sq root of (Minimum area) x 12 = minimum dimension in inches for footing width

Footing depth for plain concrete = [ (footing width) - (post width) ] / 2


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## Glenn (Apr 26, 2019)

This link has the proposals for the 2021 IRC.  Proposal RB184-19 includes expanded tables for all deck framing components up to 50, 60, 70 psf snow loads, including footings.  The footings and posts tables are based directly on tributary area supported by each post or footing/pier.  Sizes accommodate a minimum 8" diameter pier for something as small as the corner of an intermediate stair landing, all the way up to enormous piers for large areas.  You could use these easily for decks with porch roofs because the table goes up so large in trib area.  Simply add the area of the roof supported with the area of the deck supported by each post and pier.  Then use the correct snow load table.

I will be at the hearings speaking for this proposal and other deck related proposals.  Ask me any questions you have.  Thanks.

http://media.iccsafe.org/code-development/group-b/IRC-B-compressed.pdf


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## TheCommish (Apr 27, 2019)

Decks are one  the most dangerous structures built, on Saturday or Sunday by people
armed with little knowledge, armed with advice from the Big Box Store that generate
pretty pictures and a stock list, or firmed by the experts in a can, ..Bud and Wiser.

Decks are used daily by a small number of people at low load condition, collapse
when the wedding, birthday or graduation party shows up, the participants do the hoky
poky and edged on by their friends Bud and Wiser, and the deck falls down.


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## rktect 1 (Apr 29, 2019)

You forgot the weight of the deck or maybe the weight of the roof.  But you forgot one of them.

Deck is 10# plus 40# = 50#/sf
Roof is 10#/15# plus snow load around here is 30# = 40#/sf

You need an architect for this.  It is not in the prescriptive code.


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## classicT (Apr 29, 2019)

rktect 1 said:


> You forgot the weight of the deck or maybe the weight of the roof.  But you forgot one of them.
> 
> Deck is 10# plus 40# = 50#/sf
> Roof is 10#/15# plus snow load around here is 30# = 40#/sf
> ...


Who forgot the dead load?

And no architect is necessary. AHJ's arbitrarily requiring design professionals as a scapegoat for their own lack of knowledge is one of the biggest plagues across building departments. The basic math provided above can be done by a grade school student, so why not a homeowner; why not a plans examiner?


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## jar546 (Apr 29, 2019)

rktect 1 said:


> You forgot the weight of the deck or maybe the weight of the roof.  But you forgot one of them.
> 
> Deck is 10# plus 40# = 50#/sf
> Roof is 10#/15# plus snow load around here is 30# = 40#/sf
> ...



Who forgot?


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## Glenn (Apr 29, 2019)

Ty J. said:


> Who forgot the dead load?
> 
> And no architect is necessary. AHJ's arbitrarily requiring design professionals as a scapegoat for their own lack of knowledge is one of the biggest plagues across building departments. The basic math provided above can be done by a grade school student, so why not a homeowner; why not a plans examiner?


This is why I am very happy to see "tributary area" being used in the IRC for the first time for prescriptive design.  (2018 IRC deck footing table).  The proposal I linked to above provides more tables for deck design that use tributary area.  Using that variable, prescriptive design tables, such as for decks, can be much more flexible.


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## Rick18071 (Apr 30, 2019)

I always used the AWC Prescriptive Residential Wood Deck Construction  Guide footing table. It assumes a 1,500 psf soil bearing and where I work is a rocky area where I the soil bearing capacity is much higher so I always let them build a roof on this size pier.



Ty J. said:


> (Beam reaction) / 1500psf = minimum area
> Sq root of (Minimum area) x 12 = minimum dimension in inches for footing width
> 
> Footing depth for plain concrete = [ (footing width) - (post width) ] / 2





Ty J. said:


> And no architect is necessary. AHJ's arbitrarily requiring design professionals as a scapegoat for their own lack of knowledge is one of the biggest plagues across building departments.



Where does this calculation come from? I am a plan reviewer but never saw it before. I always required the designer to do the calculations.


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## classicT (Apr 30, 2019)

Rick18071 said:


> I always used the AWC Prescriptive Residential Wood Deck Construction  Guide footing table. It assumes a 1,500 psf soil bearing and where I work is a rocky area where I the soil bearing capacity is much higher so I always let them build a roof on this size pier.
> 
> 
> 
> ...


I suppose you wont find it in the Codes, but it is the basic math for taking applied load from beam and sizing the footing for 1500psf bearing capacity.

For those that are unfamiliar with these calculations, are you reviewing engineered designs? Or do they get the rubber stamp automatically?

In all seriousness, I reject probably 1/3 of the engineered plans I see for some mistake or another. Engineers/architects are not saints that are immune from mistakes.


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## rktect 1 (Apr 30, 2019)

Ty J. said:


> Who forgot the dead load?
> 
> And no architect is necessary. AHJ's arbitrarily requiring design professionals as a scapegoat for their own lack of knowledge is one of the biggest plagues across building departments. The basic math provided above can be done by a grade school student, so why not a homeowner; why not a plans examiner?


Because, we at the city level, are not here to do your work for you nor take the responsibility or liability for possible mistakes.

Hire a design professional for the work you can not do legally per your own states regulations and/or the prescriptive code.


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## rktect 1 (Apr 30, 2019)

Ty J. said:


> In all seriousness, I reject probably 1/3 of the engineered plans I see for some mistake or another. Engineers/architects are not saints that are immune from mistakes.


You have no idea how many architects I have corrected for beam and column sizes in my 11 years at this.  But I don't design the beam or column for them just because I can.  I explain to them that something isn't correct with the loads and point them into the correct direction.  A couple fo times I have had them call me and thank me for it but usually not.  

DIY people, I point them into the correct direction as well.  Licensed design professionals.


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## classicT (Apr 30, 2019)

rktect 1 said:


> Because, we at the city level, are not here to do your work for you nor take the responsibility or liability for possible mistakes.
> 
> Hire a design professional for the work you can not do legally per your own states regulations and/or the prescriptive code.


You must work in a department where customer service is not a desire of your City Management/Council.

For me, I have the knowledge and am willing to help folks figure something out without blanket requiring a design professional. I'm willing to bet I can get better code compliance with this method than you do with blanket design professional requirements. _You catch more flies with honey than vinegar.
_
BTW, still interested in who missed the dead load.


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## Pcinspector1 (Apr 30, 2019)

I don't have any issues with the big box stores pretty pictures, material list, cut list, lay-outs and elevations. I still pull out the AWC and review the plans and check my little beam buddy calculations.

I do have issues with ink pen drawings and partially filled out applications and the dude wanting a pier inspection because its going to rain and he just submitted the half finished drawing on notebook paper. 

At the front counter last week:

 Me behind the bullet proof glass: Aw... "What size floor joist?" What do you mean? "What's the width?", "it's not on your notebook paper, 2x8?" Are you using joist hangers? Ya... I always use joist hangers!... can I use screws in the hangers? Man, your being hard to get along with, why so many Q's dude! ...I build decks all over and nobody asked all these Q's. Just wanting to make sure it's safe! You might want to have a big box store help you with your project or the local lumberyard? So I'm not going to get a permit?  I can't design it for ya!..oh.. I was just told you need a Business License and proof of workers comp... and the Police Department want's to know if that's your rusty red Ford parked in the handicap spot?I gotta go....


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## ADAguy (Apr 30, 2019)

You could do a TV show with comments like that (smiling). Sounds like a Bob Villa or Tim Allen monologue.


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## jar546 (Apr 30, 2019)

Rick18071 said:


> I always used the AWC Prescriptive Residential Wood Deck Construction  Guide footing table. It assumes a 1,500 psf soil bearing and where I work is a rocky area where I the soil bearing capacity is much higher so I always let them build a roof on this size pier.
> 
> 
> 
> ...



Without soil analysis, you have to assume the 1500psf by code.  I am familiar with most of NEPA and have reviewed soil analysis from many areas considered "rocky" whatever that means and in many instances they were required to bring in and compact engineered soil just to meet a minimum design criteria of 2000psf.


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## steveray (Apr 30, 2019)

jar546 said:


> Without soil analysis, you have to assume the 1500psf by code.  I am familiar with most of NEPA and have reviewed soil analysis from many areas considered "rocky" whatever that means and in many instances they were required to bring in and compact engineered soil just to meet a minimum design criteria of 2000psf.



No....
R401.4.1 Geotechnical evaluation. In lieu of a complete
geotechnical evaluation, the load-bearing values in Table
R401.4.1 shall be assumed.

It does not say that you have to use the minimum.....Just the table...


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## classicT (Apr 30, 2019)

steveray said:


> No....
> R401.4.1 Geotechnical evaluation. In lieu of a complete
> geotechnical evaluation, the load-bearing values in Table
> R401.4.1 shall be assumed.
> ...


I think what Jeff was getting towards is that most jurisdictions have variable soils and are unwilling to take the liability of determining or even approving a soil type without some documentation. Minimum documentation would be a soils analysis including a sieve analysis report (particle grain size analysis).


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## Keystone (Apr 30, 2019)

We assume 1500psf for all, despite 1500psf being complete garbage soil, soils report accepted but we have yet to see one provided for deck piers. Although with the 2015 IRC being newly adopted we are seeing them for house footings.

The vast majority of our plan rejections for decks, inadequate footing size.
The second most common issue is beam size.

After all this time I’ve had my first techno post installation and engineer report this year, such a simple system if you do not live in a new development that requires all types of underground drainage systems.

Decks with roofs, at first we required engineering or the deck built with its pier system and the roof built with its own pier system, skeleton. The skeleton system works great for applicants wanting to place a roof over an existing deck. Now we will run the calls but it’s up to the applicant to provide accurate details.

Also so other don’t misunderstand, A soil that sieves at a particulate size does not mean it achieves a particular PSF. Can it be used as an indicator toward that likelihood yes but either way this is outside most inspectors knowledge and even still would require a PE to provide the final details of its acceptance to achieve that PSF.


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## tmurray (May 1, 2019)

We started with deck blocks. The decks heaved with the frost, then fell off the houses when the fasteners withdrew from the ledger boards.

Then we moved onto sonotubes. 8" diameter concrete piles that went down below the frost. The decks heaved again, but this time is was frost jacking against the pile. Then they dropped. Dropped further than they installed it because the bearing pressure of the soil was exceeded. Again, the decks fell off the houses when the fasteners withdrew from the ledger boards.

Now, we use footings. Sized the same as if it were a part of the house. The enlarged footing area prevents frost jacking of the sonotube (10" diameter now) and provides sufficient area so that the bearing pressure of the soil is not exceeded. You want to put a roof on it? Great. It is already sized for it.


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## steveray (May 1, 2019)

We use 2000# as a default typically....Nothing wrong with a reasonably sized deck on 10" piers....Never heard of a failure around here for this non-issue....Rooms on piers are an entirely different animal, but we already have a code section for that...

R602.10.9 Braced wall panel support. Braced wall panel
support shall be provided as follows:
1. Cantilevered floor joists complying with Section
R502.3.3 shall be permitted to support braced wall
panels.
2. Raised floor system post or pier foundations supporting
braced wall panels shall be designed in
accordance with accepted engineering practice.


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## Rick18071 (May 1, 2019)

I see deck blocks around here but I don't  inspect them. In PA residential decks less than 30" above grade are except from a permit (except if part of a means of egress, which is the front door) even if attached to a house and the manufacturers instructions for the blocks are that they can only be used for a deck less than 30" above grade.


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## Pcinspector1 (May 1, 2019)

Keystone said:


> The vast majority of our plan rejections for decks, inadequate footing size.
> The second most common issue is beam size.



I would add to your list here:
3) No handrail
4) No flashing
5) No risers to prevent a 4-inch sphere from passing through
6) Stair issues, over cut stringer, rise and step width measurement issues
7) Wrong brand of beer at the job site.


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## Rick18071 (May 1, 2019)

Here's an inspection I just did yesterday:

Framing -- Failed
1. Post for top landing must be supported by a footing
2. All Posts must be on a 1 inch high standoff brackets
3. Main beam boards can not be apart, must be nailed together every 16 inches Staggered
4. Deck is supported by cantilever is beyond code. Must be engineered
5. Bolts in ledger board must be spaced not more than 12 inches and staggered
6. Deck must be connected to house by at least two lateral load tension devices within 2 feet of each end of
ledger board or at least 4 Simpson DTT1Z deck tension ties with two of them within 2 feet of end of ledger board
complying with manufacture instructions
7. Joist hangers not installed per manufacturers instructions. Cannot use screws. 10d x 1 1/2 required for ledger
connections and 16d for joists
8. Top of stair stingers to have support directly underneath or provide Approved brackets
9. Open risers between treads on stairway cannot have a opening larger than 4 inches
10. All risers on stairway must be within 3/8” of each other. Risers cannot be higher than 8 1/4 inch
11. The siding is not properly flashed behind ledger.
12. Edge of siding where cut out for deck needs to have proper J channel
13. A light is required for the stairway
14. A electrical receptacle is required on the deck


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## Rick18071 (May 1, 2019)

I built many decks in the past and always made them self supporting. It always seemed a lot easier and cheaper do do. Did not have to deal with ledgers with their hardware, siding, and flashing. If I rented something to dig the piers it didn't cost more or take much more time to put a few more holes in the ground. With a finished ceiling you didn't know what kind of rim board there was, some older houses I did not trust the rim board if it had one. Some times the ledger board did not line up with the rim board especially if the wanted different levels. Did a lot of decks for trailers too. Now that I am an inspector I am always surprised that I don't see more self supporting decks at a houses.


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## Keystone (May 1, 2019)

Rick18071 said:


> Here's an inspection I just did yesterday:
> 
> Framing -- Failed
> 1. Post for top landing must be supported by a footing
> ...



Your correction list looks the same as mine, must deal with same contractors.


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## rktect 1 (May 1, 2019)

Ty J. said:


> Who forgot the dead load?


Nobody technically did.  The deck description of the OP was deck only, not including the roof LL or DL.  I think his point was that a simple deck, if designed properly, cannot support the weight of a roof just being attached to it.  And I agree.


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## rktect 1 (May 1, 2019)

Ty J. said:


> I think what Jeff was getting towards is that most jurisdictions have variable soils and are unwilling to take the liability of determining or even approving a soil type without some documentation. Minimum documentation would be a soils analysis including a sieve analysis report (particle grain size analysis).


Not sure why you need this.  You have already figured out the loading for the beams and columns.  I would think that one final "resident friendly" determination of soil bearing capacity on your part would be in order.  Shot in the dark, best guess, or whatever but with that final tidbit of information, you can determine the pier size real quick and be done designing your residents deck or roofed over structure.  I wish you luck in court with your friendly resident if he or his family is ever injured.


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## classicT (May 1, 2019)

rktect 1 said:


> Not sure why you need this.  You have already figured out the loading for the beams and columns.  I would think that one final "resident friendly" determination of soil bearing capacity on your part would be in order.  Shot in the dark, best guess, or whatever but with that final tidbit of information, you can determine the pier size real quick and be done designing your residents deck or roofed over structure.  I wish you luck in court with your friendly resident if he or his family is ever injured.


How would a plans examiner know the soil capacity from the desk? A building inspector may be able to make the determination, but by that point the plans are reviewed and issued to the field. Does one provide footing sizes for each soil type? Sounds confusing at best.

And as for your bestowed luck in court, not sure as why we would need it. The methods outlined are all provided in the IRC already either directly or by reference. It would be an extremely brief case to show that the culpability lies with the AHJ; the AHJ who completed the review per the International Code.  Contractor or self-performing owner would ultimately be responsible for their design and construction.


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## jar546 (May 1, 2019)

rktect 1 said:


> Not sure why you need this.  You have already figured out the loading for the beams and columns.  I would think that one final "resident friendly" determination of soil bearing capacity on your part would be in order.  Shot in the dark, best guess, or whatever but with that final tidbit of information, you can determine the pier size real quick and be done designing your residents deck or roofed over structure.  I wish you luck in court with your friendly resident if he or his family is ever injured.



I am a little confused by your post.  In one part you are asking that the inspector/reviewer make the determination of soil bearing capacity (maybe I am wrong) and then you are wishing good luck in court if someone is injured.  Please clarify your answer.

Inspectors and plans examiners are not designers.  The liability is in poor judgement that is weak or lax.  If an plans examiner or inspector approves an installation that made no reference to soil bearing capacity and is acting on their own determination to approve a design or installation, they are taking on the liability.


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## steveray (May 2, 2019)

The building dept may know better than anyone what the soil is in a given area....Assume your typical (or whatever you want) and if the inspector sees differently in the field, then call it on inspection....


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## Rick18071 (May 2, 2019)

Keystone said:


> Your correction list looks the same as mine, must deal with same contractors.



It's not the contractors, it's the home owners (and his neighbor in this case) that build it. And when the plans were reviewed it did not indicate any cantilever.

I don't design the deck or pier size. I just attach the pier table in the AWC Prescriptive Residential Wood Deck Construction Guide footing table along with a list of other requirements to the plans. If they think the piers should be smaller they need to prove the soil bearing capacity to me.

When I plan review a deck I mostly just check the spans and will call the owner/contractor to suggest changes to comply and then red ink the changes. Then I attach my list to it. I will share my list here and I am open to suggestions for changes.

*                                    2015 IRC Residential Deck Requirements*

1.      For free download on how to build a deck to comply with code search on line  for:

AWC-DCA62015-DeckGuide-1804.pdf


2.      Decks are to be attached to piers/footings which are required to be at least 42” deep and is to comply with footing table at the end of these requirements. Stair stringers are to be supported and attached to at least 4” thick concrete pad. Posts are to be on stand-off brackets 1” above grade or concrete or on concrete piers that are at least 6” above grade. Otherwise posts that are on or in the ground or concrete are to be “ground contact type” (proof is required).


3.      Decks cannot be supported from cantilevers on the building. Decks can be self-supporting without support from the building


4.      Decks are required to be built out of preservative-treated or naturally durable wood.


5.      Ledger connection to band joist bolt spacing is to comply with IRC Table R502.2.2.1 or by the following:  ½” bolts with nuts and washers or lags with washers or FastenMaster LedgerLok Screws; staggered, 2” from the top and bottom edge, 2 to 5 inches from ledger board(s) ends, tip of lag bolts shall fully extend beyond inside face of band joist. Space fasteners by the following chart. Joist spans are from ledger to supporting beam:

Joist Span             6’     8’    10’     12’     14’    16’     18’

Bolt Spacing       36”  36”    34”    29”    24”    21”    19”

Lag spacing        30”   23”  18”    15”     13”    11”    10”

LedgerLok          12”    9”     7”      6”      5”      Not Used


6.      Each deck is required to connect to house by at least 2 lateral load tension devices within 2’ of end of ledger board or at least 4 Simpson DTT1Z deck tension ties with 2 within 2’ of end of ledger board, both complying with manufactures instructions.


7.      Flashing shall be installed properly under siding and over ledger to keep rain from getting between ledger board and house exterior wood (plywood/USB sheeting or framing)


8.      Boards making up beams are required to be fastened together every 16” staggered. Beams cannot be supported by ledgers. Beams are to be directly on top of posts, not attached to side of posts or use brackets that are tested for this.


9.      Beams and joists can only cantilever up to ¼ of the actual beam or joist span.


10.  Tops of guards (railings) are to be at least 36” above the floor or 34” above stair tread nosing where the deck floor, ramps, landings and stairs are more than 30” above a floor or grade.


11.  Graspable handrails are required on at least one side of a stair flight from top riser to bottom tread nosing with 4 or more risers. 2x 4’s and 2x 6’s, etc. are not graspable. If handrails are attached to side of guard (railing), return the hand rail to the guard so there is no space between the guard (railing) and ends of the handrail.

12.  Guards and handrails are required to withstand a concentrated 200 pound load applied in any direction at any point on the top by attachment bottom of guard posts to joists and band beam. Railing posts cannot be supported to ban beam only. Do not notch railing posts.


13.  Openings in guards cannot permit passage of a 4” (4-3/8 on stairway) diameter sphere. Opening between bottom of stairway guard and steps cannot permit a passage of a 6” diameter sphere.


14.  Maximum stair riser height is 8 ¼”. There may be no more than a 3/8” variation in riser heights within a flight of stairs. This includes highest stair tread to deck floor and bottom stair to ground or floor. Openings in stair riser cannot permit passage of a 4” diameter sphere. Minimum tread depth is 9”


15.  Top of stairway stringers are to be anchored to deck with metal connectors or supported underneath, not just by nails or screws. Stairway cannot be supported by deck cantilever.


16.  An electrical receptacle is required within the perimeter of the deck.


17.  Stairways are required to have a light at least near the top landing.







.


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## tmurray (May 2, 2019)

rktect 1 said:


> Not sure why you need this.  You have already figured out the loading for the beams and columns.  I would think that one final "resident friendly" determination of soil bearing capacity on your part would be in order.  Shot in the dark, best guess, or whatever but with that final tidbit of information, you can determine the pier size real quick and be done designing your residents deck or roofed over structure.  I wish you luck in court with your friendly resident if he or his family is ever injured.



There was a case here in Canada where a building inspection department was held partially liable (joint and several) for the settlement of the foundation of a building. The building was constructed in an area that was known to have poor soils. Rather than rely on a geotechincal report of the soils, the building inspection department stamped the plans with a disclaimer stating that soils had not been reviewed for proper bearing capacity. The judge ruled that the building inspection department owed a duty of care to investigate the soils as it was known to be an issue in that area. So, the question is: if the quality of the soils is not known to be poor, can the building inspection department be held liable if it does not investigate the quality of the soils?


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## Pcinspector1 (May 2, 2019)

Rick18071 said:


> 14. Maximum stair riser height is 8 ¼”.



Rick, where is this height listed in the AWC or IRC code or is it a local amendment. I use 7-3/4-inches

I must have missed this somewhere?


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## Rick18071 (May 2, 2019)

Pcinspector1 said:


> Rick, where is this height listed in the AWC or IRC code or is it a local amendment. I use 7-3/4-inches
> 
> I must have missed this somewhere?



This is a state amendment to the IRC


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## Pcinspector1 (May 2, 2019)

Rick,

I had a little heartburn with #16 GFCI recently went to do the framing inspection on a deck job and the homeowner was removing a double window and installing a patio door with out my knowledge. 

I think I know your answer, would you require the GFCI and exterior light, there's only two stair steps from deck to grade on that end of the deck?


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## Rick18071 (May 3, 2019)

Yes. I always herd that one step is the most dangerous so I guess two steps isn't much better.


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