Non-vented attic

[dannyb]

I’m a builder in the boonies of East Texas. Around here new technology comes along a little later than in the bigger cities.

I recently heard of another builder in my area that is not ventilating his attics at all. He is using Icynene between the rafters. My HVAC contractor does his work and said that the attic was much cooler this past summer than in conventional ventilated attics.

Is this a new thing? Does it meet code? I don’t have the latest Code Check Book. In a trade magazine I was reading the other day something about a “closed attic system” was mentioned. I was wondering if that referred to this non-vented attic.

I know in the humidity of Texas this just doesn’t sound right.

[Carnak]

Most likely if you SEAL the attic, meaning no vents and taking care that air does not get in where the eaves meet the external walls, and insulate the underside of the pitch of your roof and possibly the gable end walls, codes may require you to condition the space.

The way some people do ductwork, probably duct leaks from ducts installed in the attics would suffice, but you would have to provide a small supply and return, to your attic

You need to check whatever building code you follow there.

[coolguysfl]

Different parts of the US need different rules on attic ventilation:

Go to

http://www.buildingscience.com/resources/mold/default.htm

I suggest buying the book Building Homes in Wet Climates, you're in for quite the education.

[Xavier]

Its called "Hot Roof" Here is a link that explains it: http://www.buildingscience.com/resources/roofs/roofs_unvented.htm

[mark beiser]

Check out the buildingscience.com site, it has the info you need.

It is a far more energy efficient way to go than the typical ventalated attic.
Foam insulation on the underside of the roof, no insulation in the cieling. The attic counts as part of the conditioned space for load calculations, but you don't actually have ducts to it, it will stay within a few degreese of the occupied space.

The main points of concern with this type of construction are the roof system, fuel burning appliances and mechanical ventalation.

You can't just lay typical roofing felt down on the roof deck and nail/staple shingles to it. They have specific recommendations depending on where the home is being built.

Fireplaces need to be direct vent type.

Water heaters and gas furnaces need to be sealed combustion with 100% outside air intake, basicly 2 pipe condensing furnaces. Alternativly they could be located outside the building envelope, but that would be just silly.

Mechanical ventalation will definatly be needed to insure proper air changes in the home and makeup for air exhausted by bathroom ventalators and kitchen vent hoods.

[Edited by mark beiser on 10-25-2006 at 07:06 PM]

[Carnak]

Being in a hot humid year round cooling environment, I am doing my best to avoid the hot roof.

I am just about finished building a four plex, I have sloping concrete roofs. On top of the roof, I have 1.5" of foam insulation, and then reflective, white standing seam roofing.

I insulated the inside of my gable walls and my attics are sealed. I was tempted to install an equailzair to vent my bathroom fans, with the flapper removed of course, but I could not bring myself to actually pay for three more for a consistent look in all four units.

I have not cut in the supplies to the attic spaces yet, I am going to monitor the attic spaces of the two middle units, Condition one and not the other and see what happens. I do not have to worry about ice dams here. So far the AC is not started up, and the attic space gets about 1 degree hotter than the day time high so far.

http://i32.photobucket.com/albums/d41/a_bee_normal/Apartments_October/Back.jpg

[Edited by Carnak on 10-26-2006 at 09:36 AM]

[too tall terry]

what brand are those units there big C? :D so this where you unloaded the furniture on Sunday huh?:D:D

[cem-bsee]

where is this?

did you install good gable bracing?

[pstu]

It is so rare to see someone actually build 4 similar housing units and try something different in each one to see what is the effect. Few people are in a position to experiment this way, I am awfully glad you chose to share this with us.

The term "Hot Roof" is not yet familiar to me, I though all roofs were hot<g>. Wonder if anyone in the USA has ever built a roof with external insulation and then written about it.


Best wishes -- Pstu

[Carnak]

Originally posted by too tall terry
what brand are those units there big C? :D so this where you unloaded the furniture on Sunday huh?:D:D

Luxaires, I had credit with them :)

[Carnak]

Originally posted by cem-bsee
where is this?

did you install good gable bracing?

The original owners started building in the late 90s and stopped construction in January 2001. We bought as is earlier this year and are finishing them off.

The gable walls of the two end units were up since Jan 2001, and the far end unit was actually occupied illegally for 5 years. In 2004 the gable walls withstood Category 4 strength winds and over 36 hours of troupical storm and hurricane force winds.

The gable walls are concrete block, there is rebar in every second core

Outside of the doors, windows, and the roof metal and insulation, the only other thing that is not concrete is the ceiling framing and the sheet rock ceiling.

[Carnak]

Originally posted by cem-bsee
where is this?

did you install good gable bracing?

Next time a storm goes over, the aerial photos won't look like some one spilled a load of toothpicks :)

These are down in the Caribbean cem

Front side photos a year ago.

http://i32.photobucket.com/albums/d41/a_bee_normal/1outof4.jpg

as bad as the one unit looks, if they would have had some expanded foam where the gable met the roof would have been zero damage from a major hurricane

the remaing 3, as they were, again from the front

http://i32.photobucket.com/albums/d41/a_bee_normal/tijuana.jpg

Under side of the roof in the unfinished one at the far end

http://i32.photobucket.com/albums/d41/a_bee_normal/Roof.jpg

shot of the roofs before the insulation

http://i32.photobucket.com/albums/d41/a_bee_normal/Apartments_April_11/Aug_13/concrete_roof.jpg

front of them now

http://i32.photobucket.com/albums/d41/a_bee_normal/Apartments_October/Front.jpg

Up 10 feet higher than the storm surge of a big one too