# vent craw space



## Rick18071 (Mar 13, 2013)

Doing alterations. Have a 15'x10' 18" high crawl space. My inspector said I have to vent it. If I put plastic down and fill the crawl space completely with insulation do I still need to vent it?


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## steveray (Mar 13, 2013)

Rick18071 said:
			
		

> Doing alterations. Have a 15'x10' 18" high crawl space. My inspector said I have to vent it. If I put plastic down and fill the crawl space completely with insulation do I still need to vent it?


   No......you can replace the floor system in 10 years instead!....The problem that the ventillation is trying to address is the removal of water vapor from the space...If you get some condensation (which you will) if it dries, no biggie, if it can't because there is nowhere for it to go it sits and rots.....That is why code requires ventilation...


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## Gregg Harris (Mar 13, 2013)

Rick18071 said:
			
		

> Doing alterations. Have a 15'x10' 18" high crawl space. My inspector said I have to vent it. If I put plastic down and fill the crawl space completely with insulation do I still need to vent it?


Take a look at IRC 408.3 for alternatives


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## steveray (Mar 13, 2013)

Thanks Gregg...that is a better answer....I didn't have any books (and my sarcasm levels must've been high) when I answered...


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## tmurray (Mar 13, 2013)

steveray said:
			
		

> No......you can replace the floor system in 10 years instead!....The problem that the ventillation is trying to address is the removal of water vapor from the space...If you get some condensation (which you will) if it dries, no biggie, if it can't because there is nowhere for it to go it sits and rots.....That is why code requires ventilation...


If he installs a vapour barrier at the ground level and seals it well the only moisture will be migrating through the floor system from the building above. We have them all the time up here and don't see any problems with rotting. It also provides a much warmer floor.


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## Francis Vineyard (Mar 13, 2013)

How could an alteration make it worst if it wasn't required to be vented in the first place?

Quite an expense; what model code and what kind of alterations triggered the requirement for ventilation?

*R102.7 Existing structures. *

The legal occupancy of any structure existing on the date of adoption of this code shall be permitted to continue without change, except as is specifically covered in this code, the _International Property Maintenance Code _or the _International Fire Code,_ or as is deemed necessary by the _building official _for the general safety and welfare of the occupants and the public.

*R102.7.1 Additions, alterations or repairs. *

_Additions,_ _alterations _or repairs to any structure shall conform to the requirements for a new structure without requiring the existing structure to comply with all of the requirements of this code, unless otherwise stated._ Additions,_ _alterations_ or repairs shall not cause an existing structure to become unsafe or adversely affect the performance of the building.

Francis


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## ICE (Mar 13, 2013)

R408.3 Unvented crawl space.

Ventilation openings in under-floor spaces specified in Sections R408.1 and R408.2 shall not be required where:

1. Exposed earth is covered with a continuous Class I vapor retarder. Joints of the vapor retarder shall overlap by 6

inches (152 mm) and shall be sealed or taped. The edges of the vapor retarder shall extend at least 6 inches (152

mm) up the stem wall and shall be attached and sealed to the stem wall; *and*

2. One of the following is provided for the under-floor space:

2.1. Continuously operated mechanical exhaust ventilation

at a rate equal to 1 cubic foot per minute

(0.47 L/s) for each 50 square feet (4.7m2) of

crawlspace floor area, including an air pathway

to the common area (such as a duct or transfer

grille). Crawl space perimeter walls shall be

insulated in accordance with the minimum insulation

requirements established in the California

Energy Code. Crawl space insulation shall be

permanently fastened to the wall and extend

downward from the floor to the finished grade

level and then vertically and/or horizontally for

at least an additional 24 inches (610 mm).

2.2. Conditioned air supply sized to deliver at a rate

equal to 1 cubic foot per minute (0.47 L/s) for

each 50 square feet (4.7 m2) of under-floor area,

including a return air pathway to the common

area (such as a duct or transfer grille). Crawl

space perimeter walls shall be insulated in accordance

with the minimum insulation requirements

established in the California Energy Code.

Crawl space insulation shall be permanently fastened

to the wall and extend downward from the

floor to the finished grade level and then vertically

and/or horizontally for at least an additional

24 inches (610 mm).

2.3. Plenum in structures complying with the California

Mechanical Code, if under-floor space is

used as a plenum.


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## Rick18071 (Mar 14, 2013)

How can you ventilte this floor if there realy is no space? The 18" crawl space is all filled in with insulation. Is it still considered "under floor space" if there is no space?

In the other half of this same room there there is a concret slab which was part of a garage at a higher elevation. To make my floor level I have 2x6 joists siting on plastic that is right on the concret slab with bats of insulation between them. How do I vent this under floor space? Or is this not considered a "under floor space"


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## Gregg Harris (Mar 14, 2013)

Rick18071 said:
			
		

> How can you ventilte this floor if there realy is no space? The 18" crawl space is all filled in with insulation. Is it still considered "under floor space" if there is no space? In the other half of this same room there there is a concret slab which was part of a garage at a higher elevation. To make my floor level I have 2x6 joists siting on plastic that is right on the concret slab with bats of insulation between them. How do I vent this under floor space? Or is this not considered a "under floor space"


 As long as the ground is covered with vapor barrier as noted in 408.3 there is no ventilation requirement


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## Francis Vineyard (Mar 14, 2013)

Rick it is now apparent this is an addition; to avoid vent openings need to have the barrier and insualtion up the stem wall and air movement to remove the possiblity of condensation.

Since there are sleepers I would have suggested section R504.

Francis


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## Rick18071 (Mar 14, 2013)

i don't understand how section 504 have to do with it. I am not laying the Joists on the ground, but on a slab that used to be part of the garage.

How can I use section 408 (unvented crawl space) mechancal ventailtion in my crawl space if there is no space, it's filled with insulation?

This is not an addition, I tore out the floor in an small existing addition between the house and garage, and going into part of the exsiting garage to make this new room. There is no way I could vent under the floor from the ouside in this area and I want to overinsulate the floor and not need to do mechancal ventailtion too. It is only a 10x15' area with only 18" to 10" from the plastic on the ground to the bottom of the joists. The rest of the room (10x15) is over the existing garage floor.


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## Francis Vineyard (Mar 14, 2013)

I refer back to my original post where the existing crawl space had no ventilation is not required and where the floor is extended over the garage slab does not lower the existing performance.

R504 concept does not require ventilation with the barrier using decay resistant joist and subfloor, and (impermeable) insulation installed as applicable along the exterior perimeter.

Overfilling the space with insulation is not an option prescribed in the code.

Crawl space openings installed that are not located diagonally across would make matters worse.

Francis


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## jar546 (Mar 14, 2013)

What kind of insulation?

How are the joists clear span or is there a beam too?

It is still a crawlspace.

For the record, I have inspected thousands of crawlspaces in Pennsylvania in existing homes and I would never, ever, ever build a house with a crawlspace.  Way too many problems due to poor, no ventilation, high water table areas, no access, falling insulation, wet insulation, failed vapor barriers, improperly installed vapor barriers, rusted out junction boxes, mice haven, carpenter ant, termite haven, etc, etc, etc.

What you are trying to do will eventually bite you in the *** or the next owner.


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## Rick18071 (Mar 15, 2013)

What do you suggest I do. Fill the crawl space with dirt and cover with plastic?


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## Francis Vineyard (Mar 15, 2013)

Rick18071 said:
			
		

> What do you suggest I do. Fill the crawl space with dirt and cover with plastic?


That would not change the fact for pressure treated or decay resistant wood and impermeable insulation.

Francis


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## jar546 (Mar 15, 2013)

There is simply not enough information and I asked two questions already unanswered.  Here are more:

Is the crawlspace fully, partially or not below grade at all?

The floor joist bay cavity will be filled with insulation, not the space below the joists.........I assume

Will this be a block foundation or concrete?

The best crawlspaces that I have ever been in had a concrete floor so you can lay on a mechanics creeper and move around for inspection.  This way there was a vapor barrier below.

The best crawlspaces that I have ever been in were not below grade at all.

The best crawlspaces that I have ever been in were either extremely well ventilated or conditioned.  By conditioned, I mean they were not vented but either had a radon fan being used to remove and the air IAE the code OR had a dehumidifier permanently installed with an automatic setting and the condensate was sent to a sump pump or to the exterior.

I have not been in many really great crawlspaces, probably less than 20-30 out of the 10,000 or so that I have inspected.  Most of them had rotted sill plates, rotted rim board (especially where the deck attached or there was a slider or door above due to improper pan flashing and a lack of ventilation to remove condensation.  The less below grade the crawlspace, the less the likelihood of problems.

As you can tell, I have a really big issue with crawlspaces, probably because I spent so much time crawling, squatting, hunched over and sweating in crawlspaces and seen first hand the problem they cause.  I actually wrote an article about them about 9 years ago.   Here is an old, short version from 2004:  Crawlspaces and Moisture Problems


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## Coder (Mar 15, 2013)

Gregg Harris said:
			
		

> As long as the ground is covered with vapor barrier as noted in 408.3 there is no ventilation requirement


Sorry to hi-jack the thread. I have a duplex I am about to go do a final inspection on. Crawl consists of ICF walls, closed cell spray foam rim joist, R19 batts in floor joists, nicely installed reinf 6 mil poly vapor barrier with radon reduction system underneath. NO ventilation to crawlspace. Thinking I need to at least make him put  a floor register in somewhere to create a little air movement. Keeping in mind that it is dry as a bone here with little chance of the relative humidity ever getting above 30-40% down there.

Any comments


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## Min&Max (Mar 15, 2013)

We have had excellant results with crawlspaces once we did away with venting them. We now treat a crawl space in much the same way you treat a basement. We require a 3" thick concrete floor. Insulate walls to a minimum of R-10. No insulation required in floor joists. At least one supply and one return air located remotely from each other. Radon vent.


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## Gregg Harris (Mar 15, 2013)

Mr.Inspector said:
			
		

> Sorry to hi-jack the thread. I have a duplex I am about to go do a final inspection on. Crawl consists of ICF walls, closed cell spray foam rim joist, R19 batts in floor joists, nicely installed reinf 6 mil poly vapor barrier with radon reduction system underneath. NO ventilation to crawlspace. Thinking I need to at least make him put  a floor register in somewhere to create a little air movement. Keeping in mind that it is dry as a bone here with little chance of the relative humidity ever getting above 30-40% down there.Any comments


408.3 any of 2.1--2.2-- or 2.3


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## Coder (Mar 15, 2013)

Thanks for those codes sections Gregg. despite what it says about mechanical ventilation, I still have a problem with communicating the crawlspace air with the house air.  Mostly because of all the foam plastics that are now allowed down there (ICF evaluation reports not requiring a thermal barrier for certain ICF's and rim joist spray foam allowances). That and a dirt floor with plastic over it and the exposed fiberglass batts in the floor joists all spell poor indoor air quality to me. Maybe I will start another thread so I am not being rude to the gent who started this one. :cheers


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## Francis Vineyard (Mar 15, 2013)

I have no problems with highjacks as much as I do with this interpretation: R408.3 Unvented Crawl Space IRC Interpretation

Francis


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## Coder (Mar 16, 2013)

This subject is always going to be controversial. I don't nescessarily have the answer but, I am not sold on the language in the current code either. Granted, I am obligated to enforce what it says. I still don't have to agree with it!  I would like to see the code folks come to some sort of a compromise some day.


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## Rick18071 (Mar 16, 2013)

JAR546, I have installed insulation under and inbetween the floor joists. Remeber it is only 12" to 18" between the josts and the plastic on the ground. There no way to get into the crawl space and there is nothing there to service. There was a exsiting crawl space there before mosly filled with a built-in hot tub that I took out. It was easyer to take out the old floor, start with a new floor, re-level, than to fill in the hole where the hot tub was. Hard to tell if it is below the grade beause it doesn't make it to an exteior wall, it is surounded by house and garage that is on a hill. one 15' side is next to the garge foundation and it's 12" below that. A 10' side is where I put in sleepers on part of the garage floor to extend the room. The other two sides are where it connects to two moble homes that where connected together 35 years ago, rebuilt into what looks like a house, and the crawl space was closed off at the time. Here it looks like it is level or higher than grade.

Since I could not vent to the outside I want to avoid mecanacal ventalation since it is such a small space and can't run any ducts to it.

I don't understand if I don't need ventalation where the sleepers are why is this filled crawl space any differnt? Instead of concret or dirt it has insulation under the joists.


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## Robert Ellenberg (Mar 20, 2013)

In 2005 I built a model home (that I ended up living in) which was my first sealed-insulated crawlspace. It was in the Southwest at 7,200' so a fairly cold winter climate.  HVAC was forced air through uninsulated ducts in the crawlspace.  The system was efficient because it is so much easier to seal the perimeter crawlspace walls than all the holes in the floor system.  It also provided heated floors in the winter without the expense of radiant heat pipes/coils.  I do not know of any disadvantages and would never do another crawlspace anyway other than sealed/conditioned.


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