• Welcome to the new GTAM. Have a look around and please post any issues in the Support Forum. Be sure to check out your profile settings to confirm all your settings.

Insulation into 2 foot drop ceiling in garage

Domon

Well-known member
Site Supporter
Hey guys so this fall I took apart my garage wall and ceiling (have a bedroom above garage. 3 wall of bedroom are exterior and floor is ceiling of garage.) So I got a company in to spray foam the joining wall and ceiling of garage but my garage has a drop ceiling it's about 2 to 3 feet below joist of floor above. So I wanted to blowin cellulose insulation into that cavity for extra insulation. The walls I have insulated with fiberglass and 6mil poly. I have put 6mill poly on ceiling and ready to blowin insulation but now my brother in law mentioned that I might be mold because there might be small areas of air leaks which I don't really feel. Wanted to know if anyone here does insulation for a living and can give me an idea if I should do the blow in insulation or just leave it with the spray foam on the joists (4inch 2 pound closed cell foam).

Pme for pics of garage.
 

JavaFan

Well-known member
Site Supporter
I'd just put fiberglass batts up in there in case you ever need to access the space for maintenance
 

Trials

Well-known member
In my experience; batt or blown insulated spaces need ventilation. Lack of ventilation in a relatively cool air space will cause moisture in the air to condense and water will collect in the insulation, that's what breeds the mold and mildew. If you want to add another layer of insulation that defines a virtually trapped air space you'd be better to continue with a closed cell type insulation, like silverboard (styrene covered with silver foil) it's impervious to the water just like your spray foam layer above it.

:D or you could heat the garage.
add: in floor heating for the room above a garage works really well, that's what I did with mine, takes advantage of heats nature to rise.
 

GreyGhost

Well-known member
Site Supporter
Ugh. If it was me, I would be sealing that register. Without a return, it won't function effectively (or if you are really lucky, the crappy door seals will pull the CO into your house).

I would not be using cellulose or poly in that space. The garage is the cold side of the floor and you already have a vapor barrier (spray foam). If you wanted more insulation, I would be using Roxul batts with drywall below.

Actually, I would probably be recovering most of that wasted space and pushing the drywall up. That single duct that presumably heats the bedroom would get a bulkhead which could also support the GDO.
 

Domon

Well-known member
Site Supporter
the bedroom above has two registers and i thought of raising the ceiling but because of the ducts, i would only get 6 to 10 inches. it wasn't worth the trouble. the garage has no access to house have to walk outside to get into house.
in the first picture the back wall which is spray foamed , the bottom half is the basement wall which im sealing with rigid foam and foam sealent around it to make it air tight.

so should i take out poly on ceiling and just put up drywall?

btw two side walls are insulated with fiberglass and 6mill poly over. these pic with no poly are old.

the room above garage is 2 degrees cooler then master which is on other side of house about 38 feet away

p.s garage is just for motorbikes and storage no cars go in there
 

nobbie48

Well-known member
Site Supporter
In my experience; batt or blown insulated spaces need ventilation. Lack of ventilation in a relatively cool air space will cause moisture in the air to condense and water will collect in the insulation, that's what breeds the mold and mildew. If you want to add another layer of insulation that defines a virtually trapped air space you'd be better to continue with a closed cell type insulation, like silverboard (styrene covered with silver foil) it's impervious to the water just like your spray foam layer above it.

:D or you could heat the garage.
add: in floor heating for the room above a garage works really well, that's what I did with mine, takes advantage of heats nature to rise.
A lot of high rise residential buildings put baseboard heaters in that two or three foot space to heat the floor above. It's a lot cheaper and trouble free than the in-floor cables / pipes. Totally different construction and the insulation sits on the ceiling, not stuck up against the floor. Without it the floors are always cold in winter.

It sounds like that option is no longer viable.
 

Baggsy

Well-known member
Site Supporter
How are you controlling moisture within the garage?
 

Domon

Well-known member
Site Supporter
There really isn't any moister in garage. Cars are not part in there nothing is wet. I spray foam all seals around framing and an holes that were made from builder on the black board.

I was thing of take that register that in garage and shooting it up and making any other hole in room above so it would have 3 registers.

Sent from my LG-H812 using GTAMotorcycle.com mobile app
 

GreyGhost

Well-known member
Site Supporter
There really isn't any moister in garage. Cars are not part in there nothing is wet. I spray foam all seals around framing and an holes that were made from builder on the black board.
Tons of moisture will come up through the slab and in with air exchanges through the garage door as the temperature in the garage changes. As well, that 2' space will suck moisture from the garage with temp changes as it can't suck from above as that should be well sealed with the spray foam. That's why the poly is a bad plan as it is going on the cold side of the insulation and I expect condensation.
 

Domon

Well-known member
Site Supporter
So should I just take out the poly on ceiling?


The humidity this last night in garage was 50 on a little temp guage I got from Amazon.
Sent from my LG-H812 using Tapatalk
 
Last edited:

Trials

Well-known member
So should I just take out the poly on ceiling?
You need the poly if you are going to drywall or plywood sheet it.
Would be so easy to economically heat your garage floor for just living space if you have natural gas hot water.
 

Domon

Well-known member
Site Supporter
Yeah I'm putting drywall, mud and paint.

I think I'm going to take the vent from garage and bring it up into ceiling and cut a hole along the wall and have 3 warm air outlets in bedroom above.

Then I'm just going to get a garage electric heater if I'm working inside in the winter on bikes.

Sent from my LG-H812 using GTAMotorcycle.com mobile app
 

Trials

Well-known member
;) I did my garage walls in thick plywood, looks very garage like but I can nail stuff anywhere.

First and most effective layer of the garage wall insulation is on the outside, even if it is a retrofit
Garage ceiling being a heat loss won't be a bad thing since there is living space above it.

The way you appear to have insulated the side garage walls are how you would insulate an interior wall for soundproofing, not correct for thermal insulation.

Good thing for your application is that electric heat is a very dry heat, cheapest to install, but sadly it is also the most expensive to operate. Heating it only periodically and then letting it cool will promote condensation somewhere.
 

GreyGhost

Well-known member
Site Supporter
What ceiling material was up before? Is a single layer of 5/8" Type X or C good enough for fire code? With all this talk about insulation, we can't forget that there is currently only sprayfoam and then plywood between flammable liquids and a bedroom.
 

Trials

Well-known member
I can relate to people wanting the garage space to be more of an extension of the living space.
But it needs to be built from ground up to do it right imho. a heated garage is awesome!
and yes code is a huge thing, but it still seems to be different from one area to another and over time. ymmv
 
Last edited:

Domon

Well-known member
Site Supporter
The house is 38 years old. It was plain 1/2 drywall. Nothing else.

Sent from my LG-H812 using Tapatalk
 

Trials

Well-known member
Are the walls to the left and right cold exposed or in contact with heated living space?

Code is kinda good because it makes you do it right ;)
 

Domon

Well-known member
Site Supporter
Left and right are brick walls. Back wall and ceiling is attached inner walls to house.

Sent from my LG-H812 using Tapatalk
 

Top Bottom