Insulation question for attic of new home build.

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spray foam on inside roof and blow more in attic if possible.

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Ask for this, and then fire anyone willing to do it.


Foam in the attic:
You want to seal the space and make your house an air-tight capsule, basically. You will not get hot air coming into your attic. The cool air from the rest of your house (+/- an open air return) will cool the attic to temps much closer to regular temps in the home.

Most attics are designed to be vented. They have an intake (soffits) and an outflow (either a spinning fan or a ridge vent). Hot air rises, so you create a bit of a convection. Heat transfers well enough that you want to separate your surfaces that come into contact with the attic. This is what your blow-in does. You want your hot attic to not “intrude” on your conditioned space.

If you seal your attic and passively cool it, you do not need to separate the “hot” and the “conditioned portions of the home. They’re all conditioned (though some quite a bit more than others.

Now, if you want to seal it, there is debate whether removing the current blown-in is useful.
Pro: less material for rats/mice/etc to nest
Pro: far less material capable of holding moisture and growing mold. A sealed home is much more efficient. More efficient means less time the HVAC is running. Less HVAC means higher humidity. There are remedies (HVAC capable of “spinning down” to a lower setting/variable unit, separate dehumidifer, downsizing HVAC altogether so the otherwise undersized unit runs longer (don’t do that))
Con: more expensive/labor intensive, and some question whether the removal really makes a big difference, all other things being done properly. FIL has foamed in the attic on two different homes he has owned in a high-humidity part of the country.


So again, never ADD blow in and foam (unless maybe you decide to blow in, are dissatisfied with results, then decide to foam later. I suppose that’s at least logical/reasonable)
If you have blow in, you can consider foam. And it could be reasonable to leave what you have in there (best practice suggests removing it).

You can do that b ut it's not as good as foam. Foam will seal the attic. I had the fiberglass insulation vacuumed out of mine in the spring and replaced with foam. Cost is greater than cellulose or fiberglass but as usual-you get what you pay for.

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spray foam on the inside roof of attic?

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While I understand the concept and advantages of placing foam in-between the rafters next to the roof decking I (at least for myself) cannot wrap my mind around how to trouble shoot / locate any sort of roof leak that may occur under that foam layer. I have had enough sneaky roof leaks thru the years that would give me great pause for covering that area with foam. Maybe some of the more well versed contractors on this board can walk me away from this thought process. Or maybe the simple answer is I hire better roofing companies!

What level of blown-in do you have? R-30 or R-38? Blown-in is cheap and easy, doesn’t hurt to add a little more if you only have ~6”.

Have you looked at quotes for foam, including any modifications to equipment? If you have gas equipment, you will need to provide supplemental combustion air.

Don’t overreact to the high prices of an incredibly hot summer. Everybody’s bill is high(er).

Anecdotally, when I built my house, I priced out foam in the attic vs R-38 on the ceiling. It was roughly a $15k difference for me. It MIGHT could save me $100/mo during the summer months. <$50 the rest of the year. The math worked out to somewhere around 15-20 years for the simple return. It just wasn’t worth while, and you’d be much better off spending that money elsewhere.

I was actually looking into doing a radiant barrier in my attic when the temps cool down to help for next summers heat. Does anyone have any experience with it and is it worth the trouble?

LINK

Water should seep through open cell foam if you have a roof leak. I’d worry about undetected roof leaks if using closed cell on the deck though. Could also use adhesive I&W shield on top of the roof deck in the the leak prone areas for some extra insurance. Spray foam will void shingle warranty on most shingles, but not all. Probably pretty rare to actually use the shingle warranty anyways. Most of the time I’d bet issues are from installation errors and not manufacturer defects.

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Attic foil is fairly easy to install with a staple gun.

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I've watched some videos and it seems super easy with a partner, do you think it would be doable solo? If so any tips?

Good call removing the length of section needed off of the roll before apply. I was thinking that big roll will be hard to handle while you were also trying to staple it in to place.

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If you already have blown-in, then you might get more benefit ensuring you have good air seals on ceiling penetrations as opposed to just adding more blown-in.

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I agree this would be the best bang for your $ - seal attic/ceiling penetrations first, then if you have R-30, minimum required by code, increasing that to R-38/40 - recommended amount for our region, should offer some significant benefit. I plan to do this very thing this winter.

The radiant barrier, as also mentioned, is worth considering. It should reduce attic temperature 15-20 F.

Have fought this battle and here are my thoughts..

Have a recreation condo and gets full sun.. looked into foam and foil barrier on underside of roof.. big debate as to if this shortens the life of shingles .. I decided not because I did not want my roof of the complex to be different than rest and if it went bad early everyone would say now we all need to get new roofs and want me to pay

I.. took it to r49 …18 plus inches of blown and installed a attic zipper thing for where the ladder goes into the attic..this was in BR.

Hugh difference..

Got a crew coming over tomorrow here in katy to blow in another 11 inches on top of my old stuff. Should be 15 inches when done..

Recommended is 14 inches for southern states .. R38…. not what a new. Build usually put in..

Had a lot of bids for 10.5 inches of additional blown on top of my existing very old stuff there already… Ranged from 1300 to over 3000 dollars ..