Roof insulation

[The motor guy]

I was at my buddies house today and he was showing me how he had insulation added to the roof vs only in the floor joists and it was literally the same temp in the attic as inside the house. What's the purpose of having a 150 degree attic when you can block the heat before it even enters. The only issue I can see is if you have a leak.

Opinions?

 

[Nick1994]

I think the problem is that the roof shingles get super hot and don't last so long. I could be wrong though.

 

[meadows]

Insulating the roof is what they tend to do in Texas now .

 

[The motor guy]

He bought the house a couple years ago and had the insulation changed. Made the bill go from $400/month to $200

 

[The motor guy]

They keep it at 68 in the summer

 

[Food Scientist]

I'm confused - first you said the temperature is the same in the house and the attic, which was 150 degrees. Then you said they keep the house at 68.

 

[JC1]

Originally Posted by motor_oil_madman
I was at my buddies house today and he was showing me how he had insulation added to the roof vs only in the floor joists and it was literally the same temp in the attic as inside the house. What's the purpose of having a 150 degree attic when you can block the heat before it even enters. The only issue I can see is if you have a leak.

Opinions?



Would be nice to know how much insulation was in the floor joists (r value) versus the insulation in the roof (which I'm guessing is under the sheathing). What type of insulation is installed (fiberglass batts, spray foam, or something else)?

 

[Mad_Hatter]

Unless he's using the attic for living space, why insulate the roof if you've already layed down rolled/blown material between the ceiling joists? I suppose if you had vaulted ceilings like on an A frame you might insulate the roof with rigid foam board or between the rafters with a rolled insulation material behind wallboard, if there is wallboard and not an exposed construction.

 

[MParr]

If you don't have air flow between the roof decking and the insulation, you are setting yourself up for future problems.

 

[JHZR2]

Ive always heard the story that the shingles will get too hot. Not sure if that's absolutely true, or if they're rate for higher temperatures these days.

Walk-up attics with useful space are really a wonderful thing. People stand to gain so much if they can get roof life and that space.

Maybe solar shingles will be the answer?

 

[The motor guy]

Originally Posted by JC1
Originally Posted by motor_oil_madman
I was at my buddies house today and he was showing me how he had insulation added to the roof vs only in the floor joists and it was literally the same temp in the attic as inside the house. What's the purpose of having a 150 degree attic when you can block the heat before it even enters. The only issue I can see is if you have a leak.

Opinions?



Would be nice to know how much insulation was in the floor joists (r value) versus the insulation in the roof (which I'm guessing is under the sheathing). What type of insulation is installed (fiberglass batts, spray foam, or something else)?



They removed the insulation from the floor joists. It's only in roof rafters.

 

[kschachn]

Originally Posted by motor_oil_madman
They removed the insulation from the floor joists. It's only in roof rafters.

Oh okay that makes sense then why the attic space was cool. I couldn't figure that out based on your original post.

So now he is paying to cool the attic as well as the living space? Which is fine if you intend to use that space for something.

 

[SwampSurvivor]

Originally Posted by MParr
If you don't have air flow between the roof decking and the insulation, you are setting yourself up for future problems.


Hello rotten roof deck ...

 

[SZR48207]

It's perfectly acceptable to do:

https://www.nachi.org/inspecting-spray-foam-insulation-under-roof-sheathing.htm

 

[Cdn17Sport6MT]

You need a decent air gap between roof sheathing (plywood of roof) and the top of the insul layer + you need decent high point venting and unobstructed soffit vents. 1) keep asphalt roofing shingles cool by convective air flow means and 2) keep sheathing from rotting due to moisture / condensation. You also need at interval to vacuum the soffit vents cuz they get clogged with dust/debris with time due to their high airflow.

 

[ecotourist]

In Saskatchewan they used a thermostat controlled, powered fan (either on the roof itself or the gable end) to keep unused attic spaces cooler in summer.I don't have any experience with that method though.

I'm told that in Asia people lightly spray water on their roof (clay tiles I suppose) which evaporates and cools the roof.

Lots of ways to cool a roof.

 

[supton]

Originally Posted by Miller88
Originally Posted by MParr
If you don't have air flow between the roof decking and the insulation, you are setting yourself up for future problems.


Hello rotten roof deck ...

That's my opinion too. I know it's allowed, but, I think the drawbacks are too serious, along with the cost. Better to make a larger house and give up the attic to be an uncontrolled temperature zone than it is to hope you got all the details correct--way easier to spot a leak in an attic on a casual stroll than it is on a cathedral ceiling. Plus, and a bit of tin foil hattery here, sometimes the newest trend is found out, years later, to be a bad idea.

Maybe in a different climate zone but up here I would not pay to insulate a roof this way. I'd much rather go conventional.

 

[GoldDot40]

Originally Posted by ecotourist
In Saskatchewan they used a thermostat controlled, powered fan (either on the roof itself or the gable end) to keep unused attic spaces cooler in summer.I don't have any experience with that method though.
.

I have one of those in my attic. Have it on a thermostat switch that kicks it on at 110°F and blows the hot air out one end of the roof until the temp falls back to 95°F. I also have vents which allows heat to radiate up and out. I have it mounted on rubber insulators so I can't even hear it come on. A/C runs less in the Summer since I installed it. House was built in 2016 and it's well insulated. I even insulated the garage door too which made a huge difference inside there as well.

 

[Andrew1972]

Originally Posted by motor_oil_madman
He bought the house a couple years ago and had the insulation changed. Made the bill go from $400/month to $200


The likely case is the insulation is poor or your buddy may not be comparing apples to apples (temperature days). An insulation change would not lead to 50% reduction rate in power consumption unless it was so poor or nearly missing.

 

[alarmguy]

Originally Posted by GoldDot40
Originally Posted by ecotourist
In ...
.

I have one of those in my attic. Have it on a thermostat switch that kicks it on at 110°F and blows the hot air out one end of the roof until the temp falls back to 95°F. I also have vents which allows heat to radiate up and out. I have it mounted on rubber insulators so I can't even hear it come on. A/C runs less in the Summer since I installed it. House was built in 2016 and it's well insulated. I even insulated the garage door too which made a huge difference inside there as well.


-Im curious what "kit" you chose to do the garage door?
There are a couple of them out there or did you do your own thing?
I did insulate the garage ceiling in my DR Horton home last year, made a difference for sure, I have been at a lost as to which garage door insulation is best.

-I spent the day yesterday insulating a complicated part of a second floor room (correcting the builders mistake)It was rough crawling across rafters on a low part of the roof etc.
I dont blame them really and see by what the insulation people did how the mistake was made but I had about 8 feet or so of uninstalled wall, also above my Master Ceiling some areas were very shallow, again, because it was a trey ceiling it was the part that slopes down. The main part of the house is extremely well done for sure, where it is a flat ceiling all across. (that is another whole story though, when we moved in, I measured the ceiling insulation and it was short of what the contract called for, had them come back and add a lot more) they actually had a paper ruler showing the depth of the insulation, thing is, at the bottom of the ruler under the insulation, it was folded, making it look like there was more insulation then there was.

-In NY I had an attic fan, thought about adding one here in the south, our roof is so big I wonder how much difference it would make, in addition unlike NY this one is well ventilated.
I suspect it would make a big difference, we have two AC units and all the duct work up there. You know, if I knew someone who I know would do a 100% correct job cutting a hole in my roof I would be more tempted.

Anyway, really curious where you got the garage door kit. I know HD and Lowes sell them. I actually bought my own foam board some time ago, I gave up on the idea though, measuring and cutting isnt my thing and need it to look professional. I know many people can do that, I need a kit *L*