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Cooling Down A House With No Attic.

Hi guys, first time here, so I want to thank you in advance for all your help...
Here's my situation, I live in Fremont, CA and I'm planning to buy the house I'm currently renting, but there's a problem, the house is "extremely hot" during the summer. It is 95 degrees inside. The house doesn't have an attic, it's a flat roof. When looking up to the ceiling, one can see the beams,etc and my wife happens to like that about the house. So, how can I fix the heat problem? In the winter, of course, the house is very cold. I have the suspicion that the house lacks insulation as well, but I can't tell. The floor is cement, litterally, the owners basically glued a layer of film that gives the floor a "wood floor" look to it, but it's not. I'm mentioning this, just in case in has anything to do with it. If the price of the house is right, I'll buyt it, but considering the cost of the solutions I'm looking for. I don't plan to do it all by myself either. Thanks.

Asked by J. Figaro
Posted Dec 11, 2012 12:03 PM ET


5 Answers

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Need to change something quickly...the roof isn't FLAT, it just doesn't have an attic, open space, etc. Thanks again.

Answered by J. Figaro
Posted Dec 11, 2012 12:16 PM ET


J. Figaro,
If you are not sure how to determine whether your walls, roof, or slab have insulation, you should hire an energy performance contractor or energy rater to perform a home energy audit. The investment is well worth it. In most cases, such audits include a blower-door test and infrared (thermal) inspection.

If your ceiling consists of exposed beams and roof sheathing boards, then the best way to add insulation to your roof is by adding a continuous layer of rigid foam on top of your existing roof sheathing, followed by new roofing.

Answered by Martin Holladay
Posted Dec 11, 2012 12:58 PM ET


It will likely require re-roofing to get summertime ceiling temps down, and when you do CA Title 24 will dictate both the insulating R values and minimum solar reflectace index (SRI) of the finish roofing. (A Title 24 code-min cathedral-ceiling is actually quite comfortable all year round.)

A truly high-R rigid foam solution can be quite expensive, but it's also possible to use reclaimed roofing foam from commercial re-roofing & demolition at about 1/4-1/3 the material cost, for a slight uptick in labor costs. A double layer of 3" polyisocyanurate (6" total) would hit code min with a bit of margin, 5" would be just scraping-by, but still fine, even 4" would be comfortable but you may have to argue the merits of continuous vs. rafter or joist insulation with the inspectors. Combined with a 50+ SRI finish roof the cooling loads would then be dominated by windows, not the roof.

Uninsulated slab floors are not a wintertime energy-disaster in your climate the way it might be in a colder climate, and it keeps the summertime cooling load lower, but clammy feet and a roasting head is not a prescription for comfort.

Answered by Dana Dorsett
Posted Dec 11, 2012 3:15 PM ET


I agree with Martin's suggestion for an energy audit, but for the roof/ceiling situation I think you want to talk to a roofer. You need someone who can strip the existing roofing down to the deck, install several inches of rigid foam over the deck, then install a new membrane. You want to look at something with high reflectance--get the manufacturers specs from the roofer and look up the SRI online.

If you have parapets, some work may be required on the insides and/or tops, and if you have scuppers through the parapets, they will have to move up, requiring changes to the leader boxes and downspouts.

But... it will be worth it all year long.

Answered by David Meiland
Posted Dec 11, 2012 4:54 PM ET


Take a look at installing spray foam roofing over your existing roof system, this should have the lowest cost/best performance...

Answered by Bill Clark
Posted Dec 12, 2012 6:32 PM ET

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