Seal the Attic? The new Green?HVAC Loads?

[dogdoc]

So I am building a house on a lake in Alabama,I live in Atlanta and the info I am getting says the new technology is to "foam" the roof, etc and DO NOT put in any vents, soffits, etc?????? Then the guy tells me in many cases you can cut your HVAC equipment; for example before the envelope maybe you need a 3 ton; after this, maybe only a 2.5;and says I should use an electric heat pump for my upstairs; my builder is from the old school so he says he will do whatever but he will not be responsible; then I call a "certified" green builder I know and he says he agrees with the Insulation company but says you need "make up air", a simple 4 inch duct, like on a dryer just stuck in the wall and run into the attic; when the HVAC comes on it will pull outside air; BUT I thought the purpose was to SEAL the whole thing up, so while he agrees he says something else; I am way confused!!!!!!!a and finally the guy says to get a "J calc" but I hear no one wants to do them for if the system is sized wrong they dont want any finger pointing...so while I like the idea of foam I am not sure I can find a tech savvy guy in Alabama to do the HVAC part;calcualtion and all; the house is about 30minutes from Birmingham...THANKS!!!! PS I have 17 foot ceilings; one big open great room!! Cathedral like, dogdoc

[Carnak]

venting an attic is a dumb thing to do in a humid place, sealed attics is the way to go.

it will cut your energy load especially if you install your air handler and duct work in the attic. There will be no solar heat radiating your air handler and ducts and there will be less infiltration in your home with a sealed attic.

That make up air should get connected right to the return air duct of the air handler. 4 inch may be too small.

I built a small 4 unit apartment building in the tropics, I sealed the attics, it works great.

make sure it is 'open cell' foam

[watercop]

Sealed attic will almost certainly bring loads down, especially if ductwork is in attic.

We use closed cell since we like its extra strength and that it is a secondary vapor barrier

[Carnak]

what happens with a roof when some water makes it past the ice and water shield, then there is impermeable closed cell below the deck?

[dogdoc]

So I call Owens Corning and GAF; my builder does the same; we get the same response; when the shingles blister and they both assured me it will from the heat buildup(?) the shingles will curl; OC says they see this usually anywhere from 45 days to 6 months. The foam guys say GAF makes a shingle that is warranted regardless of APPLICATION...the website and I was told, it warrants manuf. defect regardless of vented attic or not BUT NOT due to application with an UNVENTED ATTIC; they got you there; they did recommend reflective type materials with perforation....so now how do I foam with a shingle that is backed by a warranty;I thought the foam and sealing should keep heat out but they say not true; my architecht says the truth is that the "green" tech. is ahead of the roofing industry and that is the problem: aaaaagggghhhhhh!!!! PS the local OWens Corning guy took my builders name and address of the site; he said PLEASE do not use our product; we will not stand behind it in this application....dogdoc

[Carnak]

When something can absorb 70% of what the sun throws at it, I have a hard time believing that if your house does not cool your shingles they will fail.

http://www.gaf.com/Content/GAF/COMM/...tral_POP1.html

Shingles reflecting away the sun would be a lot cooler.

We were hit with a major hurricane in 2004. So roof replacements are 5 years old. I have not noticed any blisters yet. Tropical location so hot year round has to be equal to 10 years 'heat build up' on top of the 5 years UV exposure.

I was on a flat roof a while back, it had an asphalt shingle membrane. The space below was not vented, it is in the tropics, 12 years old, it survived the hurricane.


So I guess it is a dilemma, on one hand save minimum 10% on your hvac bills and have low indoor humidity vs having to pay for the cost of replacement shingles 23 years down the line when the warranty for the material only (not the labour, the felt, the flashing) was good for 25 years

My own home has white standing seam as it is the most durable here for storms. Tiles are another 'non-disposable, no fossil fuel related' product a green person could use if he was concerned about an loophole in a warranty on something that is destined to fail in his lifetime anyways

[watercop]

what happens with a roof when some water makes it past the ice and water shield, then there is impermeable closed cell below the deck?

Would you prefer that water leaked into the attic?

If the water is absorbed by the sheathing wouldn't it then get cooked off when next the sun came out?

Is it a requirement that sheathing be able to dry inward / downward into the attic?

[Carnak]

i say it is a requirement to give water a path out if it gets in

I just took a secondary vapour barrier as a sandwich.

if the sheathing got wet, would not be end of the world if it could dry out to the dry attic air is my way of looking at it

[selfemployed]

icynene - local rep. can help you with all your questions and load Calc. It has a drainage path too.
http://www.icynene.com/

[slice]

All Bs my attic has been sealed for yrs shingles are fine been thru hurricane Ike no water leaks no nothing cut hvac load in 1/3 i have learned that fresh air make up is over rated how many times a day does the door open and close, i have one on my house and nvr use it....and the air is not stale or such....

3500 sq ft i use 3 1.5 tons heat pumps w/ variable speed ahu.. humidity @ 48 % . i used three small units so a 17 kw generator could start and run them...

[Carnak]

I believe it cuts the load,

I believe your theory on opening and closing doors is bs though

[watercop]

3400 SF conditioned with a single 038 dual stage in North Florida. Holds setpoints in any outside air temperature between 25-95 in stage one. Man J design temps 30 and 93

Closed cell spray foam is a big part of why it works that well

[alex_in_fl]

I am from Alabama so I understand the concerns expressed by those good ole boy HVAC contractors.

Here is a simple solution. Build the standard attic, and install radiant barriers. These are fairly cheap and are easy to install during construction. These will frequently provide significant insulation benefits.

Best of luck to you and ROLL TIDE !