Insulating an Attached Garage

My neighbor recently purchased a prefab home and installed it on an adjacent lot next to me. Within the next six months she had a garage built which is attached to the house.

Now that summer is here she is finding that her bedroom, which is next to the garage, is much hotter then the rest of the house. The original home is well insulated but there is none in the garage except for the shared walled. The garage is of a typically "A" frame construction with approximately 20 foot ceiling at the peak (to match the house).

Now my question is how best to insulate;

Install drop ceiling (3/4" drywall) and insulate above it (if this is done she would she need some type of ventilation above this ceiling? If so which would be best; solar ventilator or dormer/sidewall vents. Not sure if she has soffit vents or not. There is not any roof ridge vents)

Install insulation in all three remaining wall and drywall (1/2").

Since it is not heated/cooled would she need the batt-face or open-faced insulation.

and anything else I missed........Tks guys for any help!


Forgot to add:, the roofing material is BLACK

since more than likely the roof area is what is causing isse since it is beside the wall of the bedroom ...

ventilate the attic FIRST !! get the 200 degree air out !

RIDGE vent and most important Soffit vents must be balanced ..

or

insulate the wall of the bedroom IN the attic ..

Inside and outside photos will help (if she will let you) and as Sump has mentioned ventilation is the key, a solar roof vent will help and save electrical cost, but should be installed by someone that knows how to do this or the roof could leak, and if it was built with a building permit there is a very good chance there are soffit vents unless they are not required in a garage or non-living area by code in your area.

You say it has a 20 foot ceiling, is that "A" shaped? If so how high are the cross members /_____\ from the floor of the garage and are they on 24" or 16" centers?

And in most areas 5/8" sheet-rock is code for a garage ceiling, (and any outside wall) this can be attached directly to the roof stringers with 1 5/8" sheet rock screws, the easiest way to do that is rent a sheet-rock jack if it's a do it your self job, run some electrical for lights too, and don't forget a ceiling scuttle to get up there.

Then roll insulation can be put down, this can also be done before the sheet-rock goes up, the kraft paper on one side insulation has a tab on each side to staple the insulation up to the rafters (paper side down) then the sheet-rock can go up.

Basically mostly what you guys are saying is what I thought. Insulate just pass the the point were the "dropped" ceiling will be installed, then drywall. Not sure if we need to insulate above the "dropped" ceiling if proper ventilation would keep it below 120'F. What do you guys think.

BTW the decking for the roofing, looking from underneath, looks like some form of a pressed wood, not plywood. I'll have to check when I see her at home again to see what the spacing is. I believe the garage walls are 24" OC, not sure about the rafters.

Question again about the paper facing on insulation; everything I read says that you apply the paper toward the heat/cooling side to form a vapor barrier. Since the garage is neither heated or cooled, do we need the vapor barrier.

BTW I don't mind hanging drywall as I have done it before. Don't like the overhead but the jack seems the ways to go. Guess I'll have to buy myself that new pink Dewalt......

Roof Vent that runs all the way down the peak of the roof I believe is the best way to vent the attic...

Most definately a venting issue.Roof vents are cheap to buy and easy to install.Shingling experience would be an asset at this point thou..Gl...

if the garage was added afterwards ...then the outside walls of the house are properly insulated...

the problem would be a ventilation issue...

it can be rectified by installing turbine vents on top of the garage roof... can't recall the adequate number of roof vents per square footage of area

also and intake vents at the bottom of the garage walls. or even the garage door

turbine vents have higher CFM (cubic feet per min.)

that would provide better air circulation...

so... no need to spend money on the garage insulation and drywall...

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Originally Posted by NOKIA

if the garage was added afterwards ...then the outside walls of the house are properly insulated...

the problem would be a ventilation issue...

it can be rectified by installing turbine vents on top of the garage roof... can't recall the adequate number of roof vents per square footage of area

also and intake vents at the bottom of the garage walls. or even the garage door

turbine vents have higher CFM (cubic feet per min.)

that would provide better air circulation...

so... no need to spend money on the garage insulation and drywall...

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Absolutely!!!No drop down ceiling required..And who makes 3/4 inch drywall????LOL>>

good points:thumbsup:

as Nokia says, no need to spend more money for insulation, just roof vents or side ventilation is all needed.

as Terryl suggest, a sheet-rock on garage ceiling and a ceiling scuttle for garage ladder to get up.

I've been thinking of solar roof vent when i have a courage to instal it myself.

When I built my garage it had only the outside siding, first summer it was very hot inside even with the AC powered roof vents, so I invested in sheet-rock and insulation for the walls and ceiling, it made a very big difference.

Made for a clean looking garage too...(it s a bit messy now)

Makes it a bit easier to get into a cooler car or truck.

But this is an added expense that some may not want to do.

Solar powered fans are nice to have, Costco sells the lowest priced ones

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I am using three on my house. Placement (southward) for the solar panels is critical, with no shade on them.

But for an "A" frame where would the lower intake vents be? "A" frames don't always have soffits.

If the lower section is insulated then she would need a space between the insulation and the outer wall/roof to allow for air flow upwards.

If she parks a car inside the garage then in the winter it will keep the garage warm. My own insulated garage normally doesn't go below freezing. So the insulation has plus factors year round.

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Originally Posted by Toddr

Absolutely!!!No drop down ceiling required..And who makes 3/4 inch drywall????LOL>>

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3/4" drywall .....

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It must be balanced is the important thing ..

with no soffit they make an edge metal that is vented for the plywood under the starter shingles on the soffit ...

or you can put box vents low on the roof for intake ...

IMHO the house is not insulated to take the heat generated by the attic air .. it was never designed too.

There's a million ways to skin a cat! I would handle like this:

1. Frame down the ceiling

2. Calculate the footage and see what proper venting is required. If you don't calculate and size your fan with venting you could cause negative pressure and this will make the venting and fan useless.

3. Install a a roof vent fan with appropriate CFM (do not use solar, use electrical, with a thermostat) Because we have sun in the winter it will run on a 30 degree, sunny day, and pull any heat OUT of the building.

4. Sheet rock ceiling 1/2" is fine. Glue it to the joists and seal all penetrations.

5. Insulate with blow in, try and get it to R-49, it only costs a few more dollars and difference is worth it.

6. Insulate the walls. Instead of bats use BIBS, it's a blown in dense pack insulation that will give you true R value. A properly installed bat might get you close, but they pretty much fail miserably.

7. Glue down drywall to walls and DONE!

Well guys got a lot of good ideas from reading your posts. Appreciate.

Neighbor still not home but I can see from my home that she does indeed have a partial ridge vent. By partial I mean that it is only in the middle of the roof so out of ~ 20 feet she has 12-14 feet of vent. She also soffit vents running the length of the garage, ~ 20 feet on two sides but they are the perforated kind so the actually vent area is cut back by probably a least a half.

Okay what I have learned is yes there is 3/4" rock and along with 5/8 is used in fireproofing and to span 24" OC ceilings and 12 feet vertical installations. (12' X 4' X 3/4"-believe that would be heavy).

90% of all DoITYourself sites and forums recommend a vapor barrier whether it is by the batt attached vapor barrier or installing plastic sheets over the entire area once you have completed the installation. The only exceptions are in areas that are very humid the year around and then there is a need for a vent space but that is a different install.

So it appears that we will probably install insulation with vapor barrier in the garage walls up to the soffit area and then using 1/2" rock cover the installation. If the garage ceiling-to-be is 18" OC then we will use 1/2" rock, if 24" OC, we will use 5/8". She then wants to wait and see if this will be okay but I believe if will need some sort of roof turbine eventually (or maybe ceiling insulation but I don't believe we will need it). I will also try to get her to insulate the garage door panels as this would be fairly cheap and easy installation.

Just by eyeing it appears the attic will be 17' X 20' X 25'/2 (A frame) = 4250 cu/ft.

BTW in the first post I mentioned that the adjacent wall to house is already done with 5/8" fireproof rock so we will only have 2 walls, ceiling and a little around the garage door.


So does this sound good to you guys?