Home Insulation- Any Experts Here?

[Minor Axis]

I'm thinking about putting more insulation in my attic. The possibilities are more insulation on the floor of the attic, spray foam or cellulose, or radiant barrier under the roof deck.

Several weeks ago I got an estimate: $3700 to spray 5" of open foam up under the roof deck. This is supposed to keep the attic about 10° warmer than the house. Wow, sounds great because the attic becomes a more usable storage space instead of baking stuff at 140°F! However when I called another contractor, I was told that open/closed foam was not allowed with gas water heater/furnace in the attic. (That's how they do it in Houston, no basement, furnace and water heater in the attic, although I'd prefer it in my garage but those are not big enough to put them there). So that's why this contractor offered cellulose insulation. And then there is radiant barriers, aluminum foil stabled to the bottom of the rafters that keeps heat out of the attic.

Anyone familiar? I'm about to launch some net research to educate myself, but thought I'd ask here.

 

[The Man]

I would get the ceiling insulated rather than the roof.
An attic is supposed to be a ventilated area...so why insulate the roof unless you have money to burn.

Additionally roof decking lives in a hostile environment ...minor water penetration is common..it cant dry out if it is foamed over.

Future work of re shingling the roof {about every thirty years} could involve a few sheets of roof decking { is common especially the perimeter pieces}..this would cause your foam barrier to be damaged during such.

You will get more benefit by insulating the ceiling as this is the area closest to your living area....if we insulated the roof and was able to change the attic a few degrees we still dont get the benefit that we would if we insulated the attic which had the greatest temp difference.

Lets say the attic is 130
The house is 70 inside .....that's a 60 degree difference.
If we insulated the roof and brought the attic down to 120..we still have a 50 degree difference.

You best bang for the buck here by far is to further insulate the attic.

 

[Jackass master]

I would insulate the attic floor with blow in cellulose. You can get the blower at Lowes to use to blow it up to the attic. I did this to my place when we first set it. The R-value is much enhanced and lowers heating and cooling costs. I would not insulate under the roof rafter. A good gable ventilater fan will do wonders to help your A/C by cooling the attic.

 

[Joe the meek]

A good gable ventilater fan will do wonders to help your A/C by cooling the attic.

There is nothing wrong with having cross ventilation in a hot attic, but if you're inducing a negative pressure in your attic, you can cause more harm than good IMO.