# knee wall insulation help



## david szela (Jan 9, 2012)

Hi i need help on a insultion issue with my knee wall . they are complete and the drywall is hung. My question is the walls are insulated with vapor barrior with insulation on warm side like it should but my problem is I put rigid foam board on the cold side. I have acces in the wall. I read online before that it was ok to put it on cold side which i thought was incorrect. But doing some more research im getting conflicting answers. If it is wrong is it possible to leave up and drill holes in the foam in each cavity to help. I dont want to have to take it down if i dont have to. Thanks Dave


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## david szela (Jan 9, 2012)

*knee wall insulation question*

Hi i am remodeling my attic and have a question about my knee wall. I have put batt insulation on and i have also put foam rigid board on but on the cold side . I got conflicting answers about if that is correct. It is already installed and im concerned about moisture being trapped . I would like to know if its possible to leave up and drill holes in each cavity in the foam board. I have access back there but would be tough to get out now . Thanks for any thoughts . Dave


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## bubbler (Oct 18, 2010)

david szela said:


> Hi i am remodeling my attic and have a question about my knee wall. I have put batt insulation on and i have also put foam rigid board on but on the cold side . I got conflicting answers about if that is correct. It is already installed and im concerned about moisture being trapped . I would like to know if its possible to leave up and drill holes in each cavity in the foam board. I have access back there but would be tough to get out now . Thanks for any thoughts . Dave


What type of foam board is it? 

Is it rated to be exposed, or does it need to be sandwiched between two non-combustable surfaces?

These are some of the Q's I came up with when considering the same thing you did. I decided again the foam board... I installed batt insulation and then put house wrap on top of it--the house wrap blocks any wind in the space (since it's a vented attic space) which helps to retain the insulating properties of the batt (and also helps to make sure the batts stay in place).

I think drilling holes in the foam board would defeat the purpose of having the foam board at all...


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## Bob Mariani (Dec 1, 2008)

Will need some additional information here.

1) what is your concern exactly?

2) Where are you? Climate Zone? This will help address the vapor barrier issue

Some other issues.... Knee walls are rarely insulated correctly. The space under the Knee wall (bays in the floor) need to be air sealed completely. Without this the cold air will simply run through the floor joists cooling the room above and below this area.

Do not drill holes in the insulation..period! Air sealing is the most important thing. Use spray foam to seal all the edges of the foam board along the perimeter and tape the seams.

look at this web page to see what I mean with sealing under the knee walls. http://www.homedoctorofamerica.com/knee-walls


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## Bob Mariani (Dec 1, 2008)

Best to read this web page. Http://www.homedoctorofamerica.com/knee-walls

Batt insulation is only used when you need to be cheap. It is by far the least satisfactory installation.

Stopping the air leakage is the most important thing. do not drill holes:furious:


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## david szela (Jan 9, 2012)

thanks for your response . i live in pa and the knee wall is insulated properly.ohter than having the rigid foam board on the cold side of the wall my concern is that in the summer months. will i be causing myself issues with having two vapor barriers with moisture .its sealed well and on both sides and it will got hot back behind knee wall. I have r 13 and i wanted a little more so thats why i put the foam board up; its about another r 5 i think . i insultated way under the knee wall in each bay so there is no chance for air to get up under the knee wall . thats why i was thinking of puttin some holes between each stud in the foam board . it wouldnt affect my r 13 insultation at all.


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## Bob Mariani (Dec 1, 2008)

no holes.... it will effect the R-Value.

In your case you will have no issues with the double vapor barrier. If the foam is sealed completely as it should it will be fine. If you also used batt insulation simply do not use a vapor barrier with it.


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## david szela (Jan 9, 2012)

I do have my vapor barrier on my batt insulation . so i have drywall on, then r 13 batt with a vapor barrier in my 2 by 4 studs . vapor barrier on warm side and then i have my foam board over everything on cold side of the knee wall. thats why i was concerned about the moisture being possibly trapped between the two barriers. its already up . thanks again for any help Bob


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## bubbler (Oct 18, 2010)

david szela said:


> I do have my vapor barrier on my batt insulation . so i have drywall on, then r 13 batt with a vapor barrier in my 2 by 4 studs . vapor barrier on warm side and then i have my foam board over everything on cold side of the knee wall. thats why i was concerned about the moisture being possibly trapped between the two barriers. its already up . thanks again for any help Bob


Out of curiosity--how are your joists sealed at the knee wall? Is there wood blocking w/ spray foam? Dense packed cellulose? Foam board?


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## Bob Mariani (Dec 1, 2008)

2" foam board and the edges get spray foamed in place


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## david szela (Jan 9, 2012)

my joists are 2by 8 . i ran my batt r 19 insulation from the edge of house making sure not to block my soffits. but with a good seal and took it about three feet beyond my knee wall and then stopped it with blocking . I also on the cold side put another layer of inslutation on my joists right up against my rigid foam insualtion on my knee wall to make sure no way of air leaking thru. being an old house i doubled my joists for the attic. i used calking or spray foam between each joists . hope this helps . i dont even have the heat on in attic and its at least in the 60s up there and its goin down to about the mid twenties at night . it seems to be the trick . i also used foam board on the exterior. walls . which gets them to about r 18. it is a true pain in the ass putting drywall up over it being that your using long screws and into hard wood but its warm inside.


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## david szela (Jan 9, 2012)

any thoughts with the moisture issue bob or bubbler


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## Gary in WA (Mar 11, 2009)

Vapor barriers and vapor retarders are two different beasts: http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11810

If asphalt-coated paper (vapor retarder) on the insulation, it is vapor *variable *permeable; http://www.buildingscience.com/documents/reports/rr-0004-air-barriers-vs-vapor-barriers 

Your Zone requires a Class 1, or 2: R601.3 Vapor retarders. Class I or II vapor retarders are required on the interior side of frame walls in Zones 5, 6, 7, 8 and Marine 4.
It is not a vapor barrier- Class I: R601.3.2 Material vapor retarder class. The vapor retarder class shall be based on the manufacturer's certified testing or a tested assembly. 

The following shall be deemed to meet the class specified: 

Class I: Sheet polyethylene, unperforated aluminum foil. 

Class II: Kraft-faced fiberglass batts. 

Class III: Latex or enamel paint. *
*From: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_6_sec001_par005.htm*

*So any vapor from the inside will not condense due to the foam board (1") on the attic side. You don't even have one vapor barrier to "trap water". The foam board would need to be 9"or so thick to stop all moisture movement.*

*You want to stop air/moisture from getting to the cavity from the conditioned space (inside room):http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/*
*
Sounds as if it already done, at least air seal the drywall bottom edge to the floor- as per Code minimum, with caulking or canned foam; number 6: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec002_par021.htm*

*Gary*
*


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## AGWhitehouse (Jul 1, 2011)

GBR's got you covered on the vapor retarders...but...unless your code is different from the majority of others you *cannot* leave the foam exposed within the attic space. It is a fire hazard. It must be covered by either plywood, gwb, or sheet metal of adequate thickness to meet the code. This need for an additional layer is what likely drove bubbler to use tyvek instead.


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## bubbler (Oct 18, 2010)

AGWhitehouse said:


> GBR's got you covered on the vapor retarders...but...unless your code is different from the majority of others you *cannot* leave the foam exposed within the attic space. It is a fire hazard. It must be covered by either plywood, *gwb*, or sheet metal of adequate thickness to meet the code. This need for an additional layer is what likely drove bubbler to use tyvek instead.


gwb? gypsum wall board? Is that the same as drywall, or different?

BTW, I had a professional insulation company with very good reputation recommend leaving the foam board exposed in my attic... when I asked about flammability the guy looked at me cross eyed and said "yeah it's flammable, but so is wood"... I didn't hire them. Another company, the ones I used, also was prepared to leave the foam exposed--in fact they did use it for my access doors and left it exposed--this stuff has a tin-foil thick layer of reflective metal-like foil, it's printed right on the stuff that it is flammable and should not be left exposed, I think it says "to living space", but not sure... point is, pro companies are leaving this stuff exposed... I guess it's a lack of education in the industry, or maybe lack of inspection for work like this.


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## david szela (Jan 9, 2012)

thanks gary , ag and bubbler for your input im glad to know i can leave that up and its not goin to cause an issue. there is alot of conflicting info out there. also i agree with bubbler about exposed foam board . im sure it might b against code but i have wood all over the place exposed behind my knee wall. good pt on both sides thanks alot for your help


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## bubbler (Oct 18, 2010)

david szela said:


> also i agree with bubbler about exposed foam board . im sure it might b against code but i have wood all over the place exposed behind my knee wall.


Actually I wasn't intending it that way... I was actually intending to the give the impression of the OPPOSITE... I was pointing out that my potential installer had said that to me, and I was surprised to hear it, because although he's technically correct that they are both flammable, the foam board is much more flammable... It's like saying both a chopstick and a piece of paper are flammable... yes they are, both one is going to catch faster and burn faster...

Foam board ignites easily, burns fast, and releases toxic & choking fumes...

By comparison wood ignites with more difficultly, will probably burn slower, and will release smoke (but not nearly as acrid as the foam board).

I'm a believer that foam board should be covered--sandwiched between two less flammable substances.

In your case I think you could put plywood or drywall over the foam board to be code compliant as AGW mentioned, and it would reduce your risks if an ignition source were present in the attic space--like a workman's light held too close to it, a kid smoking a joint, or pyromaniac chipmunks...


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## AGWhitehouse (Jul 1, 2011)

It is specifically against most current building codes to leave foam exposed ANYWHERE within a building, even within an attic or crawl space. *Anyone who says you can leave it exposed is not adhering to the code.* Argue all they want, it's in black and white text (2003 International Residential Code: R314.1.2 pertains to living spaces, R314.2.3 pertains to attics and crawlspaces.)

It must be covered by 1/4" plywood, 3/8" particle board, 1/4" hardboard, 3/8" gwb (gypsum wall board, a.k.a. sheetrock), or 0.016" thick corrosion-resistant steel sheeting for use as an ignition and thermal barrier. The foil face that is on some foams is NOT considered an approved ignition barrier.

Yes, wood is flammable, but as bubbler noted it is not Extremely flammable and heavily toxic when burned like foam is.


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## david szela (Jan 9, 2012)

thanks guys and i will take your advice and cover it over . this is why these websites are great to have. i can see your point now. im all about saftey . I wonder if the bubbler would have left that like it was exposed , how many inspecters would have caught that. since both your contractors along with many others i guess wouldnt seem bothered by it.


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## bubbler (Oct 18, 2010)

david szela said:


> thanks guys and i will take your advice and cover it over . this is why these websites are great to have. i can see your point now. im all about saftey . I wonder if the bubbler would have left that like it was exposed , how many inspecters would have caught that. since both your contractors along with many others i guess wouldnt seem bothered by it.


I had two sets of pros come in, both of them were planning to install foam board WITHOUT covering it with a material like plywood, steel or "gwb". 

The first company wanted to cover the whole wall--same as you have.

The second company didn't offer that up (probably because I had a price ceiling that it didn't fit under), but did cover the backs of the access hatches to my knee wall attics with foam... it's the kind w/ the foil. As AGW points out, this isn't enough according to the code, it should be protected. So what I will be doing on my own is adding another layer of plywood and some 1x material to create a sort of sandwich that encloses the foam (in essence I'm making my own hollow door w/ foam inside).

In my area there were no permits required to do the insulation work I had done, and there was no town inspection process. 

Maybe a keen eyed home inspector might notice this at the time of sale and indicate to a buyer that this is unacceptable, but who knows... I know my home inspector walked right past major water damage when I was buying, he never saw it, frankly I didn't either, but I'm not a professional home inspector and in hind sight it was painfully obvious, particularly since there was evidence of water damage (staining) in the knee wall directly above...


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## david szela (Jan 9, 2012)

sorry to hear about the water damage and thanks again for your help good luck with your projects


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## Gary in WA (Mar 11, 2009)

In answer about the sneaky pros... The attic has to meet *certain requirements* to allow SPF or rigid foam board left uncovered. The SPF industry well knows this. The foam manufacturers have written amendments for their certain products, used as listed in attics. These are written by the “I” Code writers; IBC, IRC, and IECC. This explains it better: http://www.ncfi.com/Insulation/uploads/Evaluation%20Reports,%20Acceptence%20Criteria%20and%20the%20Building%20Codes%20SF0608L.pdf

Owen Corning pink board in attics: #4.2.1: http://commercial.owenscorning.com/assets/0/144/172/174/5deb06d2-43b4-44b2-b4ec-20579af27e5d.pdfI 

I am merely showing the reason spray foam professionals may not cover it, and if you are under an “I” Code, there is information you may be missing. I would cover it whenever convenient to do so, just for the fire safety issue.

Here is one from Dow, follow the other links/questions to learn more;
http://dow-styrofoam.custhelp.com/a...sion/L3RpbWUvMTMxODYwMjg4MS9zaWQvKkNueDl5R2s=

You may check the certain type listing: http://dow-styrofoam.custhelp.com/app/answers/detail/a_id/3891/~/what-are-the-astm-c578-classifications-for-styrofoam%E2%84%A2-brand-extruded

http://dow-styrofoam.custhelp.com/a...2LzEvdGltZS8xMzI2NDA0OTIzL3NpZC9ZNE9mbS1Oaw==

When using a foam board in the crawl space, check the type for application, this can be left uncovered, with the conditions listed: http://www.icc-es.org/reports/pdf_files/ICC-ES/ESR-2142.pdf
So the pros are not trying to sneak something by inspection, their livelihood depends on meeting code. One lawsuit is all it would take.

Gary


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## AGWhitehouse (Jul 1, 2011)

We've been through this before GBR...Here's an excerpt from the 2009 International Building Code:

*SECTION 2603 - FOAM PLASTIC INSULATION*

*2603.4 Thermal Barrier.* Except as provided for in Sections 2603.4.1 and 2603.9, foam plastic shall be separated from the interior of the building by an approved thermal barrier of 1/2-inch (12.7mm) gypsum wallboard or equivalent thermal barrier material that will limit the average temperature rise of the unexposed surface to not more than 250degF (102degC) after 15 minutes of fire exposure, complying with the standard time-temperature curve of ASTM E 119 or UL 263. The thermal barrier shall be installed in such a manner that it will remain in place for 15 minutes based on FM 4880, UL1040, NFPA 286 or UL 1715. Combustible concealed spaces shall comply with Section 717.

*2603.4.1 Thermal barrier not required.* The thermal barrier specified in Section 2603.4 is not required under the conditions set forth in Sections 2603.4.1.1 through 2603.4.1.13.

_(Sections 2603.4.1.1 -> 2603.4.1.5 and 2603.4.1.7 -> 2603.4.1.13 don't pertain to this topic)_

*2603.4.1.6 Attics and Crawl Spaces.* Within an attic or crawl space where entry is made only for service of utilities, foam plastic insulation shall be protected against ignition by 1 1/2-inch-thick (38mm) mineral fiber insulation; 1/4-inch-thick (6.4mm) wood structural panel, particleboard or hardboard; 3/8-inch-thick (9.5mm) gypsum wallboard, corrosion-resistant steel having a base metal thickness of 0.016 inch (0.4mm) or other approved material installed in such a manner that the foam plastic insulation is not exposed. The protective covering shall be consistent with the requirements for the type of construction.

*2603.9 Special approval.* Foam plastic shall not be required to comply with the requirements of Sections 2603.4 through 2603.7 where specifically approved based on large-scale tests such as, but not limited to, NFPA 286 (with the acceptance criteria of Section 803.2), FM 4880, UL 1040 or UL 1715. Such testing shall be related to the actual end-use configuration and be performed on the finished manufactured foam plastic assembly in the maximum thickness intended for use. Foam plastics that are used as interior finish on the basis of special tests shall also conform to the flame spread requirements of Chapter 8. Assemblies tested shall include seams, joints, and other typical details used in the installation of the assembly and shall be tested in the manner intended for use.

The evaluation reports you provided can only be administered under the direction of Section 2603.9 noted above. The homeowner/contractor would have to provide the evaluation reports along with documentation that the intended assembly meets the code derived requirements. Since most home attics are built of flammable wood, filled with flammable materials (boxes, etc.) and are not sprinklered, this is a difficult thing to have passed. Usually the inspectors have them paint it with an intumescent paint at minimum.

So, GBR, please inform people, correctly, that foam plastic insulation NEEDS TO BE COVERED per code, UNLESS THEY HAVE SPECIFIC WRITTEN APPROVAL FROM THEIR BUILDING OFFICIAL.


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## Windows on Wash (Aug 30, 2011)

There seems to be differing opinions on this.

The end all result is that you better have approval from the code enforcement officials in your area.

Here is a snippet from the ICC-ES: (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CEQQFjAA&url=http%3A%2F%2Fwww.icc-es.org%2FCriteria_Development%2F0805-pre%2Fmemos%2Fac12.pdf&ei=59kQT7-jFeK10QHPtay8BA&usg=AFQjCNEZN7oF1Y21ewBvpZArAG-2p0cSFA)

_4.5.11.5.1.1 Foam plastic insulation installed in attics where entry is made only for service of 
utilities shall be protected by an ignition barrier as set forth in IBC Section 2603.4.1.6, IRC 
Section R314.5.3 or Exception 4 of UBC Section 2602.4, except as noted in Section 
4.5.11.5.1.2. Utilities include, but are not limited to, mechanical equipment, electrical wiring, 
fans, plumbing, gas or electric hot water heaters, and gas or electric furnaces. 

4.5.11.5.1.2 The ignition barrier shall not be required when satisfactory testing is conducted in 
accordance with either Section 4.5.11.5.1.2.1 or 4.5.11.5.1.2.2. 


_


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## Windows on Wash (Aug 30, 2011)

FYI...it is always better to be safe than sorry.

Foam does not necessarily combust very readily but it does off gas pretty rapidly.


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