Unvented Attics

[Slaughter Construction Co]

I keep hearing about unvented attics where the insulation (sprayed foam) is applied to the bottom of the roof deck completly sealing it off from the outside air etc. In my part of the country (DFW) where the A/C units and ducts are ofter located in the hot vented attic, this seem like a good idea. As best I can determine there is nothing in the IRC building code (at least not the 2003 edition) and my local building department will not even discuss the pros and cons. of such a thing. Does the latter editions of the IRC code allow this or does anyone have any authoratative info/source reguarding this topic.

[Vinnie]

Re: Unvented Attics

I would also like to know if this is an good idea for heated only homes.

[Jim Coler]

Re: Unvented Attics

There are a number of sites from authorities in the building science industry who address this. I know it is becoming a common practice in many areas including Texas. Here are a couple of sites whihc may help answer your questions.

http://www.professionalroofing.net/p...2/feature2.asp
http://www.buildingscience.com/resou...ry_article.pdf

As far as the IRC and ICC codes, BioBased has ICC approval through testing.

[Slaughter Construction Co]

Re: Unvented Attics

Thanks Jim for you reply. My local building department here in Ft. Worth, Texas claim that they have never heard of such a thing as non vented attics. I don't think they do a lot of outside reading. I first read about it in the May 2005 issue of JLC which stated that it was to be OK'd in the 2006 version of the IRC.
Other than that the 2003 version of the IRC code book(which we are using) says that all attic spaces shall be vented, they claim that 1)if a roof leak were to occur you would not be aware of it because the water would be trapped between the roof deck and the foam insulation, 2)if you did discover a leak, you could not get the damaged roof deck off because it would be bonded to the foam insulation. I don't know if these are valid reasons or not, but I gave up and now the HVAC systems will have to burn up in the hot attic. Again, thanks for your time. Bruce Slaughter.

[R Factor]

Re: Unvented Attics

Demilec company is based in Dallas Fort Worth. They also have all of the ratings you were looking.
Your code people down there must be living in the dark ages. As Jim stated there are many studies done in this area with great results in either a hot climat or cold.

[R Factor]

Re: Unvented Attics

Bruce.
I didn't see the roof portion of your post. A leak with open cell foam will be detected as that style foam does have a perm rate. It will let the water from a leak go through and be detected. After the leak is fixed the water will in time wick out of the foam.

[Toolwhore]

Re: Unvented Attics

Slaughter, Vinnie and Jim;

Could you please fill-out your profiles? It helps to know who and where you are, the answers to questions vary greatly depending on what part of the country your in. Also, the abreviation DFW was something I was not familiar with. Until R Factor said Dallas Fort Worth, the only thing I could think of was Dela Friggin Ware. Some local abreviations aren't quite understood in other parts of the country.

Thank You,

[Slaughter Construction Co]

Re: Unvented Attics

Toolwhore Tom. Sorry about the profile. I get around the drawing board and the building site a lot better than I get around the computer. I will try to do the profile if this thing does'nt blow up. I have a hard time even logging on. They keep telling me that it's case sensitive. At one time I thought of getting a CAD but when they talk about a long learning curve I figured that I did'nt have that much time. One could say that I'm up in years. Bruce

[Toolwhore]

Re: Unvented Attics

Bruce;

Nice to meet you, and welcome to the forum. I too am "up there in years" and my first time on a computer was 4 mos. ago. It's been very frustrating at times, but it's just like anything else, the more you play with it, the easier it gets. I have AutoCad 14, Punch Platinum, and today Gary Katz gave downloads for SketchUp. This is some pretty wicked stuff for someone as computer illiterate as myself, and I've spent hours trying to figure it out, but next time I turn it on, it will be just like the first time. I won't have a clue! But I aint about to give up. One of these days it gonna just click.

I'll try to help you with the profile, if you like.

Scroll to the top of this thread.
Click on "private messages" in the upper right hand corner (under Wecolme Slaughter.....)
Then go to the left sidebar under "Control Panel" and click "Edit Profile"
It should talk you through the rest of the way.

Hope that helps,

[Vinnie]

Re: Unvented Attics

Slaughter,?

[elcalvo]

Re: Unvented Attics

There seems to be more than one question being tossed around here. It seems to me that if you spray foam between the rafters, you place the attic inside the insulation envelope and it becomes part of your conditioned space. I don't do this unless I am finishing the attic. In this scenario, the only vented space is the small area above the attic ceiling. The attic space is not vented. You could still use the vent chutes as long as they were compatible with the foam. This would allow the use of soffit vents and a ridge vent.

If you don't use the vent chutes, the question to me is, does this affect the shingle warranty or durability? The roof shingles above the rafters and the several inches on either side of the rafter do not have the ventilation chute underneath. I have never encountered strips of roof shingle failure above each rafter due to excess heat buildup, so it doesn't seem to me that this would cause a problem with the shingles. This would also eliminate the need to install soffit vents and a ridge vent.

You could still vent the relatively small area above the attic ceiling with gable end vents, roof vents, thermostatically controlled fan, etc.

[Vinnie]

Re: Unvented Attics

You could still vent the relatively small area above the attic ceiling with gable end vents, roof vents, thermostatically controlled fan, etc.
Yes.

[Vinnie]

Re: Unvented Attics

I would also like to know if this is an good idea for heated only homes.

The wet air of the houses may stop? We want it to stop out side the house. An attic that keeps heat in and water out may work for some of us. This is called a buffer zone. The problem is when the zones RH hits the dew point the air stops. RH Attic fans?

[Cseville]

Re: Unvented Attics

Unvented attics are becoming a much more standard method of construction and are approved in some form in most building codes and/or addenda. I have done a lot of work with Icynene and they can provide approval letters from code officials approving this installation method. I fully agree with the earlier posts about roof leakage - a closed cell foam will likely disguise a roof leak and lead to long term damage, however the open cell products will alllow water to drip through and let you locate the leak.

As to the comments about leaving the small section above the roof unconditioned and vented, there is really no reason to do this. If you are going to seal the roof, do the whole thing. It keeps dust and dirt out of the attic, if your HVAC is in this space it works more efficiently - I have even downsized systems by almost 50% in the southern US. You can also put in all the recessed lights you want and not worry about any air leakage out of your attic stairs or access hatch. I would never build a vented attic again if I could avoid it.

[andrewt]

Re: Unvented Attics

I'm just finishing up a new home in Houston built with unvented attic and SPF insulation (BioBase). A couple of thoughts...

The system seems to work. Attic is much cooler than a vented, unconditioned space. Great, big, large problem with humidity, though. We had to go back and add dehumidifiers to the system almost immediately. Local HVAC guys just don't quite know how to deal with this method of construction. They put 9 tons of air in 4,200 of living space; the thing cools down almost immediately, but humidity never drops below about 60%. Added the dehumidifiers, and humidity now stays in the mid-40's, house is very comfortable at 77 degrees (and we like it cold!).

Insulation has been a hassle. Although I'm happy with it, installation was a freaking unholy mess; the contractor BioBase referred me to wasn't exactly the bee's knees, and we're still going back and forth over backcharges nearly 7 months after installation (short version: they didn't shave the stuff completely down to the studs, the drywaller had to finish, trash guy had to clean up the mess, insulation on bricks / flatwork / windows, etc.). I may need to think about getting out of the homebuilding business and into the sprayed foam insulation business if this is the best they have to offer.

Attached garage. Unless you plan on insulating your entire garage, you better figure out early how to partition the attic space and seal it off. In my case, we just came back and built a non-bearing partition in the attic, sheathed it with thermo-ply, and sprayed the insulation into the cavities. I wish I'd thought this through more thoroughly, though. We ended up insulating part of the garage ceiling, roof and knee walls in order to have enough conditioned space to put the HVAC equipment in.

I'm happy to answer any questions anyone has about the process.