how much does drywall help??

[thammel]

I've got a fully insulated (R19 and R38) attic room above my garage. It's 12x32 with 7' ceilings. It's cooled and heated with its own mini split - a high efficiency mitsubishi 9kbtu unit. Darn thing couldn't keep up with the hot summer temp, when I had it set at 78. It would run all day. At first, I had the stairwell open to the garage, then I put up a plastic sheet to isolate it. I was getting cold air out - about 55F as I recall when it was 90+ outside.

I'm wondering how much drywall will help. I know there are small gaps at places with heat leaks. I'm guessing drywall will help a lot. Anyone have this experience? I also plan to put in an insulated wall at the top of the stairs with door to keep things isolated in the summer (garage below was fine with 18kbtu mini split).

If I have to I'll upgrade to a 15kbtu unit and someone will get a 9k system for a steal. It's the FH super high efficiency series.

Tom

Tom

 

[Empty Pockets]

There is no doubt that sheet rock would help. While it doesn't have massive insulating value, once installed, taped and mudded, not only will it plug the small gaps, it will look better than insulation just hanging there.

The insulated wall and door would likely be the key to keeping the room cool.

 

[54stude]

It will help a ton. My garage is 24x42', (r19 and r38), approximately 12' ceiling, and it rarely gets over 77-78 in the garage in the summer in MN.

 

[fastjohnny]

I've got a fully insulated (R19 and R38) attic room above my garage. It's 12x32 with 7' ceilings. It's cooled and heated with its own mini split - a high efficiency mitsubishi 9kbtu unit. Darn thing couldn't keep up with the hot summer temp, when I had it set at 78. It would run all day. At first, I had the stairwell open to the garage, then I put up a plastic sheet to isolate it. I was getting cold air out - about 55F as I recall when it was 90+ outside.

I'm wondering how much drywall will help. I know there are small gaps at places with heat leaks. I'm guessing drywall will help a lot. Anyone have this experience? I also plan to put in an insulated wall at the top of the stairs with door to keep things isolated in the summer (garage below was fine with 18kbtu mini split).

If I have to I'll upgrade to a 15kbtu unit and someone will get a 9k system for a steal. It's the FH super high efficiency series.

Tom

Tom

Get the 15kbtu. I'd be happy to steal your 9k system

In all seriousness, you've got radiant heat from the roof, rising heat from the inside, so it might be undersized, though the square footage seems appropriate for the 9k. Sealing up with sheetrock should help.

 

[finn]

Do you have soffit and ridge vents and an air gap between the roof and insulation?

Without proper roof venting, sheetrock won't help you.

If properly vented, it will help.

 

[lakeroadster]

How much help? Negligible. 1/2 inch Gypsum Board (Drywall or plasterboard) has an R value of 0.45.

https://www.e-education.psu.edu/egee102/node/2064

 

[toyotadriver]

Cover the fiberglass with foam sheets, then cover that with drywall. You've got a lot of heat coming in through the framing. Slow it down with rigid foam.

 

[Gerald O]

The main help from the sheetrock will be from the sealing against air flow with it being taped.
Is the garage below also insulated? The floor between? How often are you opening the garage doors?
I'm running a 12K btu unit in the loft over my 24 x 32 garage, and with the door at the top of the stairs open it will keep the garage at 74 and the loft at 70 with the outside temps in the 90s.
all walls are sheetrocked in the loft and the garage. R19 in garage walls, R15 in loft walls, and R30 to R38 in the loft ceiling. Loft roof is ventilated.

 

[csp]

The prevention of heat loss from air flow will definitely be noticeable. Fiberglass insulation alone does little to prevent heat loss because air goes right though it. Keep the air from moving and it allows the insulation to be relevant.

There's a lot more to heat loss than R-value alone.

 

[tyme2par4]

air sealing is as important if not more than insulation. Drywall will seriously help with air sealing if you mud and tape everything.

 

[larry4406]

If your attic has kneewalls, make sure the back side of the vertical insulated stud/truss bays is closed off with thermoply and sealed. Convective currents on the back side of insulation is a major loss.

 

[thammel]

Yes - I have ridge vents and soffit vents and styrofoam baffles so air can flow freely from soffit to ridge.

Yes, the garage below is fully insulated and the floor between is also insulated.

Yes, I'm thinking the key will be air sealing and that will make a huge difference.

Larry - hmmm...not clear. Yes, there are kneewalls (used attic trusses) and the vertical sides of the kneewall are insulated. But of course this triangular (roughly) section is open to the outside - via the soffits and the styrolfoam baffles at the top corner of the triangle allow the air to flow up to the ridge vent. Don't we want air flow (hence convection) in this region? How to prevent it?

Tom

 

[larry4406]

Larry - hmmm...not clear. Yes, there are kneewalls (used attic trusses) and the vertical sides of the kneewall are insulated. But of course this triangular (roughly) section is open to the outside - via the soffits and the styrolfoam baffles at the top corner of the triangle allow the air to flow up to the ridge vent. Don't we want air flow (hence convection) in this region? How to prevent it?

The back side of the vertical kneewall portion of the attic trusses you should cover with thermoply and tape the seams. You don't want the convective currents scrubbing the back side of the vertical insulation. At the top of the kneewall truss bay, it sounds like you have insulation baffles to allow the soffit vents to breath to the ridge vent. These vertical kneewalls turn into huge radiators of heat from the ambient conditions.