Bonus Room Insulation Thoughts

[tuccillo]

While not really an HVAC question, I thought I would toss this out there to the knowledgeable folks of the forum. Our bonus room (room above the garage) essentially is at the attic level and is surrounded by attic air. We have a foamed attic so the attic temperature is around 85F or so on hot sunny days. The bonus room has no additional insulation on its ceiling or knee-walls. Above the ceiling, the underside of the roof sheathing is foamed. Effectively the bonus roon sits in the unventilated attic. The floor of the bonus room is the ceiling of the garage and that is foamed. Effectively the only thing separating the bonus room from the attic is 1/2" drywall.

It seems to be that insulation on the ceiling and kneewalls would result in a lower heat load in the bonus room. Any thoughts? If so, what sort of insulation? I can get to the ceiling and kneewalls.

[BaldLoonie]

Foam the sucker!

But for price reasons, I'd probably go with batts if you want to DIY. 3.5" batts are R13 and easy to do. If you have 2x6 studs, R19 is even better.

I put a tiny system in for a bonus room. Stat on an outside wall which is about all there is. Stat reads 5+ degrees higher than the room is from heat penetrating the wall. They were gonna foam but for budget reasons, didn't.

[paul42]

It doesn't make sense to add insulation between the rest of the house and the attic, so it won't make sense to add it to the bonus room either.

It is just not a good place to add insulation. Spend your dollars on a blower door test to find air leaks instead. the payback will be much shorter.

[tuccillo]

BaldLoonie,

Thanks for you post. A bit more info. The ceiling is sloped on the sides and the middle is flat as follows:

______________
/ \
/ \
/ \
| |
| |
| |


The sloped part follows the roof and there is about 3 inches of space between the drywall and the foam on the underside of the roof sheathing (essentially a catherdral). The flat part in the middle has space to crawl into ( about 3 feet high ). The sides are kneewall that I can get to. What would recommend for the sloped part - I can get to it from the kneewalls and the flat part of the ceiling but it is a series of 4 foot tunnels through the joists, if you will. Cant really stuff batts in there. What you suggest for the flat part also? Do you think blowing insulation in would be worthwhile? I can blow down the sloped sides (not easily but it can be done ). Thanks.



Originally posted by BaldLoonie
Foam the sucker!

But for price reasons, I'd probably go with batts if you want to DIY. 3.5" batts are R13 and easy to do. If you have 2x6 studs, R19 is even better.

[tuccillo]

Hi Paul42,

I have thought about that. I think the issue may be that the rest of the house is below the attic (and also separated from the attic by only 1/2" drywall ) but the temperature stratification with hot air rising and cold air sinking probably means there is little heat transfer from the attic to the rest of the house during the cooling season ( the heating season would be different). The bonus room is different in that it is at the same level as the attic, actually it effectively sits in the attic, if you will, and is surrounded by 85F air. Thoughts?


Originally posted by paul42
It doesn't make sense to add insulation between the rest of the house and the attic, so it won't make sense to add it to the bonus room either.

It is just not a good place to add insulation. Spend your dollars on a blower door test to find air leaks instead. the payback will be much shorter.

[BaldLoonie]

So this room is surrounded by foamed attic? Yea, then you probably don't need any more surrounding the room. I must not have read it very carefully.

[tuccillo]

Hi Bald Loonies,

Yes, the bonus room is surrounded by a foamed attic - closed cell, about 3 inches, attic goes up to about 85F or so on hot sunny days. It winds up taking a lot of AC to keep the bonus room at 76F. Proably 10F gradient across the 1/2" drywall.


Originally posted by BaldLoonie
So this room is surrounded by foamed attic? Yea, then you probably don't need any more surrounding the room. I must not have read it very carefully.

[paul42]

There will be very little temperature stratification in a house, typically less than 2 degrees from floor to ceiling. Hot air rises, but heat goes from hot to cold regardless of the direction.

Sealing off any air leaks between the attic and the outside will do a lot more good than trying to insulate around the bonus room.

[tuccillo]

Hi Paul42,

The attic is sealed from the outside - the whole thing is foamed right down to the ICF walls. I watched that part of the construction carefully and had the foam guys go back and refoam areas that looked a little thin or didnt extend to the ICF walls. I guess my real question is as follows: Is a 10F temperature gradient across the bonus room drywall worth insulating for? It sound like the answer is no.


Originally posted by paul42
There will be very little temperature stratification in a house, typically less than 2 degrees from floor to ceiling. Hot air rises, but heat goes from hot to cold regardless of the direction.

Sealing off any air leaks between the attic and the outside will do a lot more good than trying to insulate around the bonus room.

[paul42]

Your numbers would lead me to believe that there is an air leak or leaks somewhere.

With the foam in the roof, and the sheetrock in the ceiling, then the temperature differential across each should be roughly proportional to the R Factor of each.

If you have black shingles, the roof temperature on a typical summer day might hit 135. With no air leaks, the total heat coming through the roof is the same amount coming in through the ceiling and bonus room sheetrock.

To do the math correctly, you would also need to include the relative number of square feet of the foamed roof vs the sheetrock of the ceiling and bonus room, but as an approximation we will call them about the same surface area.

If you are getting a 10 degree temperature differential across the sheet rock (something you might want to actually measure) and the sheet rock has an R factor of about .5, then a 50 degree temperature differential across the foam insulated roof implies that it has five times the R-Factor of 1/2 inch of sheet rock.

I cannot believe that you have an R2.5 foamed roof, so either there is an air leak somewhere, or the temperature differential across the sheet rock is much less than 10 degrees for at least most of the house.

[tuccillo]

Hi Paul42,

I am not sure I follow you. Basicly, the attic reaches a temperature of about 85F. The only thing separating the bonus room from the attic air is 1/2" drywall on 3 wall and the ceiling (the 4th wall is the front of the house and it is insulated with foam). If we keep the bonus room at 76F then we will have approximately a 10F gradient across the drywall. My original question was whether folks thought it was worthwhile putting insulation on the backside of the bonus room drywall (attic side) for a 10F temperature gradient.


Originally posted by paul42
Your numbers would lead me to believe that there is an air leak or leaks somewhere.

With the foam in the roof, and the sheetrock in the ceiling, then the temperature differential across each should be roughly proportional to the R Factor of each.

If you have black shingles, the roof temperature on a typical summer day might hit 135. With no air leaks, the total heat coming through the roof is the same amount coming in through the ceiling and bonus room sheetrock.

To do the math correctly, you would also need to include the relative number of square feet of the foamed roof vs the sheetrock of the ceiling and bonus room, but as an approximation we will call them about the same surface area.

If you are getting a 10 degree temperature differential across the sheet rock (something you might want to actually measure) and the sheet rock has an R factor of about .5, then a 50 degree temperature differential across the foam insulated roof implies that it has five times the R-Factor of 1/2 inch of sheet rock.

I cannot believe that you have an R2.5 foamed roof, so either there is an air leak somewhere, or the temperature differential across the sheet rock is much less than 10 degrees for at least most of the house.