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foam insulation, no venting

C

codeworks

Gold Member
Joined
Jun 12, 2011
Messages
579
Location
South Texas
i see more and more roofs down here being insulated with blown foam, directly to the underside of roof sheathing and encapsulating rafters with zero roof venting. i see this as a potential problem down the road, as i've seen this same practice up north, and it has led to rafter failure and sheathing failure and extensive, and expensive repair years down the road. the problem comes from what i would call dry rot. may not be "dry", actually. this appication leaves no way for the encapsulated strucure to breath. and any condensation that forms on the underside at night when it cools, gets trapped. any moisture in the wood componenets is trapped. over time, it will start to rot. i've torn a dozen roofs in vermont and had to reframe and resheath due to this very application. plywood temperature get too extreme, glue fail, which leads to delamination of the plyscore layers. blown foam was "BIG THING" in the early 70's there. not so much any more. buildings need to breath. i've taken houses apart that were built in the 1800's that had newsprint tacked up for "sheathing paper", prior to installation of clapboards or split shakes, that was installed over skip sheathing and that wood was as solid as the day it was built. anybody have any input. please, not the thermal barrier quotes and all that bs from the code book, we look at all that, ask for all that. rather i'm seeking insight or experince into how this will stand up over time. i don't see it as good. what i've posted is my experience.
 
Older houses breath better, no doubt. I also have torn into a few roof systems that were not vented in any fashion, vaulted ceilings for instance, where the sheathing had failed after only 15 years. Where, doing a real estate home inspection for an aquantence on a 100+ year old farm house, with no attic ventilation, it was solid as a rock. As far as the direct applied foam isulations, I guess time will tell, but I share your concerns.
 
Greetings

Yea I just looked at one this week. I had never seen one until about a year ago. That house, which is quite large has had minimal elect bills so I'm told. I don't expect to work here in this town long enough to see long term effects. Should be interesting though. The builder that did that house says he has done a few with no problems. Sure seems like the roof deck would take a pounding in our Tx climate.

BS
 
if there were end walls to provide venting, mybe it wouldn't be so bad, but this is all on multi hip/valley roofs, with no end walls, no place to install and end louver. odd. future work for someone.
 
done a few with no problems. yea, in the recent past. it's the older ones that will show the issues. these houses 8, 10, 15 yrs from now, will have bad roof sheathing at a minimum. looking to move? we need an inspector ! no bs (pun intended) lol!
 
codeworks,

Is your application an enclosed attic space, or a conditioned attic assembly?

(RE: Section R806 in the 2006 IRC)?

.
 
it's a conditioned attic assembly. still, presents potential for failure down the road.
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Thanks for the reply! I am not a fan of the spray foamed attics, and notreally of spray foam in general. I too believe that houses ought to breathe,

..a little bit anyway!

.
 
The purpose for the venting is to allow the sheathing to dry out from moisture, from water vapor in the air, that has condensed on the underside of the sheathing.

If the foam is closed-cell polyurethane, then the likelihood of moisture reaching the sheathing is almost nil, since closed-cell polyurethane is an excellent water and vapor retarder (low permeability). Thus, the need to vent between the foam insulation and sheathing is no longer present.

If the foam is open-cell polyurethane, then it will have a slightly higher vapor permeability than closed-cell, but it is still controlled, so the possibility of moisture reaching and condensing on the sheathing is low if provided in the recommended thickness. Thus, the need for ventilation is also not necessary.
 
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Both. Polyurethane foam has a high R-value. The closed-cell type has a greater R-value than the open-cell type. The foam also creates an efficient air barrier.
 
Foam technology has changed, I would venture the house done in the 70’s used formaldehyde foam that came and went quickly. I do not know the permeably of the formaldehyde foam or much about it.

The foams today are in my opinion much better.

The issue is moisture in the building and its condensation on cool surfaces, even if the house has fiberglass that can breathe excess moisture will condense on cold surfaces leading to rot. Sure the older buildings that breathed had no problems, just the dollars flying out the walls with the heat that was not keep in.

Building are a system and there is science involved it is unwise seal up a building to keep in the condition air and not deal with the moisture of everyday living and air quality through sensible controlled ventilation.
 
I asked ICC about this very issue and just got the response. I have had questions about the validity of whether it is acceptable to eliminate the air space along the underside of the roof sheathing in a vaulted rafter space. The ICC answer was that under no circumstance is it acceptable to eliminate the air space. I specifically asked about both spray foam and dense packed insulation. I also asked for a clear answer on whether the vaulted rafter was by definition not an attic assembly since that was the portion of the code that most SF companies are using to justify spraying directly to the sheathing. The answer was that a vaulted rafter was not an attic, therefore not a conditioned attic assembly. So now I have the ICC answer. Those answers may not apply to a true conditioned attic assembly but what I mostly see is the spray foam and dense pack in a vaulted rafter.
 
RLGA said:
The purpose for the venting is to allow the sheathing to dry out from moisture, from water vapor in the air, that has condensed on the underside of the sheathing. If the foam is closed-cell polyurethane, then the likelihood of moisture reaching the sheathing is almost nil, since closed-cell polyurethane is an excellent water and vapor retarder (low permeability). Thus, the need to vent between the foam insulation and sheathing is no longer present.

If the foam is open-cell polyurethane, then it will have a slightly higher vapor permeability than closed-cell, but it is still controlled, so the possibility of moisture reaching and condensing on the sheathing is low if provided in the recommended thickness. Thus, the need for ventilation is also not necessary.
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Does the moisture only come from the conditioned side of the sheathing?
 
Moisture, obviously, will come from both sides. The issue is the drying out process--if the wood cannot dryout, then rot and mold will set in.

The roofing membrane will protect the sheathing from liquid water (or it should, hopefully) and the water vapor in the air, if the roof assembly is properly insulated, will not condense on the exterior side of the roof.

On the interior side, water vapor can easily pass through fiberglass blankets and reach the sheathing. A vapor retarder can be installed to the warm-side of the insulation to prevent water vapor from reaching the sheathing, but the air already within the cavity can still condense and cause problems for the sheathing. Thus, the venting is required to allow the air to circulate, and if the water vapor does condense on the sheathing, the air circulation will allow the sheathing to dry.

Sprayed polyurethane foams, when properly installed, eliminate the air space completely and provides a barrier that prevents water vapor from reaching the sheathing. Thus, the venting is not necessary.

However, some roofing manufacturers, such as for asphalt shingles, may not warrant a roof if the insulation is installed directly to the underside of the sheathing for the reason that it builds up heat at the sheathing. This heat build-up tends to bake the shingles, thus reducing the performance of the roofing.

2009 IRC R806.4 (2012 IRC R806.5) allows the ventilation to be deleted if the insulation is air-impermeable insulation. Air-impermeable insulation is defined by the IRC as having an air permanence of 0.02 L/s-m2 at 75 Pa per ASTM E 2178 or ASTM E 283. If the insulation meets this, which most sprayed polyurethanes do, then ventilation is not required.
 
Codeworks

Maybe the problems you saw in the north where caused by moisture being "trapped" between the foam on the underside and the roof covering on the top. I have caught many a carpenter rolling out felt on a wet roof trying to get the house dryed in as quickly as possibleinstallinvetyour
 
Copied below is the Q&A response from ICC on this issue. It would seem that code does not permit the air space to be removed if an air impermiable insulation is used in a vaulted, enclosed rafter space. 806.4 refers to an attic space which a vaulted rafter is not.

September 13, 2012

Subject: 06 IRC R806.3

Q1: Without exception Section R806.3 requires a 1" air space between the insulation and the sheathing. Many installers are attempting to install insulation without this space in a vaulted rafter space by using Section R806.4 for a vented attic assembly. The contention is that the spray foam or the dense packed cellulose is air impermeable as noted in Section 806.4. Is the rafter space in a vaulted condition (rafter only) considered an attic space, especially in the context of Section R806.4?

A1: First of all, you incorrectly referred to the IBC; your questions should be referring to the 2006 IRC. Section R202 defines an Attic as “The unfinished space between the ceiling joists of the top story and the roof rafters.” Section R806.1 requires ventilation for two conditions 1) enclosed attics and 2) enclosed rafter spaces formed where ceilings are applied directly to underside of the roof rafters (vaulted ceiling condition).

The condition you describe is not an attic (no ceiling joists) and shall require ventilation as required for the second condition, vaulted ceiling condition. I have attached a page from the 2006 IBC to illustrate the intent of the air flow (ventilation) required in a vaulted ceiling condition (see Diagram C).

Q2: Is there any exception to Section R806.3 that would permit the air space to be omitted?

A2: No, the purpose of the air vent is to provide a way to reduce the moisture in the enclosed “attic” space and thereby avoiding the rotting and decay of the wood members caused by the moisture. It is interesting that for a “typical” dwelling of four-family members, the amount of moisture that can accumulate from cooking, laundering, and bathing can be, as much as, 25 pounds of water vapor per day on average, therefore, it is important to have air vents to keep the moisture down.
 
You are correct that the 2006 IRC does not permit it, but the 2009 and 2012 editions have changed that and now permit the exception in vaulted ceiling conditions when air-impermeable insulation is installed.
 
California still doesn't allow it:

2010 CBC R806]R806.1 Ventilation required. Enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof rafters shall have cross ventilation for each separate space by ventilating openings protected against theentrance of rain or snow.
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In Codeworks original post he stated " please, not the thermal barrier quotes and all that bs from the code book,", and of course was totally ignored.

These new wood chip and glue, foam houses are a shameful example of where this country is going. They are dangerous to the health and welfare of the inhabitants of the building. The main problem is that you don't see the problem until after the people living in them have become sick or contracted some form of allergy or other medical problems; and unfortunately that may never be attributed to the real cause which is a sealed box built with toxic materials and called a home.

The "only time will tell" is a poor excuse for allowing these toxic waste dumps to be called homes. While skilled, trained, knowledgeable tradesmen are a thing of the past and the manufacturers of these toxic products hide behind their installation instructions (which the installers couldn't read if they wanted to) for defense, the American people are being poisoned by their new home.

The ICC, who the governments have given carte blanche to determine what is and isn't acceptable, has sold out to the manufactures of these toxic materials and allows them to lead us in determining what is "good" for our built environment. The "green" train is running over the health and welfare of the people who have to live in these death cells we call new homes.
 
Sifu, would you mind writing back for an interp of the '09 and '12 codes on this issue? We have been having open cell foam applied to the underside of the roof sheathing without problems thus far.

My Dad was building unvented foam covered plank and beam roof assemblies in the 60's and 70's, there have to my knowledge been no moisture related problems. It was the latest hot tip at the time. We were using foil faced polyiso sheets and applying shingles directly over the foam with 3" roofers, there was no sheathing above the foam, ~r16, times have certainly changed. The problem that did surface was related to the shingles being cooked by the foil facing. He went back and strapped those roofs vertically, sheathed with ply and then reshingled, no problems after that. I've done several of those vented wrap and strap roofs, with much more foam, over the years since.

Mom made us all macrame' belts for our bellbottoms and string ties using pins and scraps of the foam to work on, we were stylin :)
 
 
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