I agree, it is now inside the buildings insulated envelope and should be conditioned as such.
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Hi Les. I think there has been little change in building standards since then. In my opinion what I posted is still current info. Do you think differently? I would like to know your opinion. Thanks
Hey Brian. Yes, these are pretty rare in the southeast as you know, but the garage I’m building has a conditioned attic. I don’t want my stored items to get moldy or overheated so I insulated my roof. Pretty rare around here. I have only inspected a handful of attics built this way.
Blower door test after insulation was 1.4 ACH
I haven’t even done drywall yet. I will have it tested again after drywall and interior trim are complete (in a month or two I hope).
I am considering SPF my hip roof. However, I do not want to condition the space because of my HVAC configuration (it is in the crawl). But I would love to have a clean, conditioned space for light storage.
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My garage has closed cell sprayed on the concrete blocks (CMU) and upstairs is open cell. 5.5" thick in the stud walls, 9.5" thick under the roof. It’s very quiet inside the upstairs rooms. I’m looking forward to low energy bills. (hardly anybody around here builds like this)
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For an unconditioned attic, you’r right, Bert.
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Revisiting this post: It would be great to have some professional info on this topic. I would guess that it would have to be an exponential effect. The hotter/colder it gets the more differential change in temp you get. It would be great to have a Chart to reference. Like at 70 - 85 is good, at 100 - 135 is good etc. Whatever that number is anyway. I’m sure this would be all based on max sun exposure and outside temp etc.
There are too many variables to give you what you are asking for.
Here are a few real world examples.
Our rental property was built in 1971, has a low slope shingle roof and originally relied on soffit vents and two gable vents for ventilation. The attic temp was around 160 degrees in the summer. I installed a ridge vent which immediately dropped the temperature by about 20 degrees. It made a difference on the interior of the home as well. Then, through a bizarre series of events, (hurricane Irma, insurance claim, etc…) I was forced to coat the entire roof with a white elastic coating. The temperature dropped in the attic by at least another 20 degrees. The insulation in the attic was old, blown in and didn’t even cover the two by four beams. The interior temperature did drop more which helped with the electric bills. The final attic temperature in the summer when it is 96-100 degrees out is around 110 degrees. Which I would consider acceptable for that type of home.
The home that we live in was built in 1999 and has a very large attic. When we replaced the original tile roof with another tile roof, we added an extra layer of underlayment and also added 4 additional vents to the two we had. This home has soffit vents and the aforementioned 6 gooseneck 12 x 12 vents. The attic temperature has never gotten above 90 degrees since we redid the roof. Add in the R-19 batts insulation and the interior of the home never gets above 80 degrees even if we shut the a/c off.
The third home is my wifes parents home in Clermont, Fl. It is a two-story home with a black shingle roof. It has spray-foam on the underside of the attic and is not vented at all. I have been in the attic in the summer where it was 100 degrees out and the temperature in the attic was the same as the interior of the home (78 degrees).
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When there is no more room in hell zombie threads will walk the bulletin boards!
Replying to necro threads is fun for me because I didn’t see them the first time round.
I’ll just say that in the latest new homes that I’ve inspected that have half a dozen or more passive vents on the roof and ridge vents where possible, it’s quite pleasant in the attics even when it’s 97 outside.
I’m quite sure there’s some ideal amount of upper venting versus the amount of soffit venting, but as far as I can tell, most older homes don’t have anywhere near enough of it.
I get in one of these 15 year old homes with just ridge vents and by 10am, it’s 120 up there. I’ve done a few wind mits in the afternoon on those homes and holy cow, it’s like sticking your head in an oven set on broil.
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I agree with the first response that it depends on many factors as well as the method you are using to cool your attic. Is the reason for that question to determine what temperature will shorten the life of the roof before it fails or to decide if it is safe for the inspector to go into the attic. I saw that one of the respondents said 20F difference between the outside and in the attic. That may be true but as the weather gets to be warmer that gap between the outside and inside will have to get smaller until we get to a point when both for the safety of the inspector and the life of the roof some kind of mechanical cooling system will be necessary.