Blown insulation over foam board?

[Huntinguy]

My garage is attached to my house but, is per code, " fire barrier isolated " from my house.

I did not have the garage ceiling sheetrocked or insulated. I had some things I wanted added in after we moved in.

Now I need to insulate now and since the garage doors are hung and openers are in, it would be a bit of work to sheetrock.

This brings me to my question. What is the downfall to putting faced rigid foam (foil down) onto of the top of the bottom (the side opposite where the sheetrock would go) of the rafters and blowing insulation on top?

The foam would have to be strong enough to support the loose insulation, would need to be screwed down and taped. Still working this out in my mind.

There's wiring running on top of the trusses in places....

What am I missing.... besides common sense?

I am about to do something similar to my pump house.

 

[gstrom99]

I wouldn't sandwich the wiring under the foamboard. I'd just do the drywall on the bottom of the rafters/trusses, even if it's a little "involved". You can spray foam (cans) to seal around the opener hardware if needed. It'll support the insulation better and look better in the end also.

 

[Roadworthy]

Have you considered having the garage door and opener taken down while the sheetrocking is being done? Of course just taking down the opener would greatly simplify the sheetrock job. Personally I wouldn't consider taking down a door by myself but removal and installation of the opener is a piece of cake.

 

[gstrom99]

Have you considered having the garage door and opener taken down while the sheetrocking is being done? Of course just taking down the opener would greatly simplify the sheetrock job. Personally I wouldn't consider taking down a door by myself but removal and installation of the opener is a piece of cake.

Take down the opener? Yes maybe, if the OP can't/won't work around it. No need to take down the door, at all.

 

[chim]

Like Roadworthy said, removing and reinstalling the opener isn't difficult. I'd take that route and drywall it.

The pole barn my BIL had built uses a heavy white plastic material fastened to the bottoms of the trusses, with insulation blown on top. There are heavier plastic straps that were installed under the white plastic for added support.

 

[KennyG]

As has been discussed before, using a finished panel on the ceiling makes sense when you look at the cost and time of finishing and painting a drywall ceiling. Look at the cost of metal liner panel vs. the total cost of drywall.

 

[Huntinguy]

I thought about drywalling the ceiling. It is not impossible to drop all the mounting hardware and putting it back. I could move all the mounting points up one hole on the hangers to compensate for the sheetrock. I do have access to a sheetrock lift.


The hard part would be clearing the floor space below. Then of course the taping... I don't like taping upside-down.

Finish pannels... never thought of that. I shall ponder that.

Originally I was going to use corrugated paels. They reflect light better and would brighten the garage more. Then I brainstormed just using foil faced rigid foam insulation boards. It seemed like a lightweight option.

I can cut channels around for the wiring.

Hmm, some things to ponder....

 

[paulsharvey]

Dont. The foil faced Styrofoam, or atleast the 1/2" 3/4" and 1" is already really floppy/saggy; before adding the blown insulation later. If you aren't sure if you want to sheet rock; there is a good option.

Rockwool, it's denser and more "grippy" and stays in place Far better than fiberglass bat insulation. I assume you trusses are at 24" OC, with a 2x4 bottom cord; get 24" 2x4 Rockwool, and insert from the bottom, between the truss bottom cord. It's fire proof, sound deadening, insulating, and pretty easy to work around the wires/garage door rails.

The downside; cause their is always one; Rockwool is worse than fiberglass as far as itchy, and when cutting/moving/installing, you want gloves, long sleeve (disposable) cloths, and a face mask.

Once installed, that's no longer an issue.

Then, I would still either install drywall, or atleast 1x2 boards every 16" perpendicular to the trusses, below the Rockwool, before even thinking of having the top blown. Blown insulation isn't heavy, But over say a 24 ft span, 24" wide; it does add up to several pounds, all pushing down on the rockwool.

Also; the Styrofoam option, if you want to drywall in future, you are fighting all that. You would need to adjust down any cieling outlets or lights, so the "lip" is flush with the new surface of the drywall; you would need to use atleast 1-3/4" drywall screws; and I think you would be facing an uphill battle to get a nice, smooth, even, drywall finish.

 

[EddieWalker]

How far apart are you trusses spaced from each other? Most common is 24 inches. If they are spaced 24 inches, you need 5/8's sheetrock so it doesn't sag between the trusses over time.

For my garage, I'm planning on using corrugated metal for the ceiling. I did it in my barn for our feed room and I really liked it. 12 foot long panels are easy enough to handle with a sheetrock lift, and once you install them, you are done. No taping, sanding, painting or anything else. Cost is a factor, but in my opinion, you get a better ceiling that you will never have to mess with again.

For insulation, my goal is to keep the heat out. Code is now R40 in East Texas. I went R60 in my parents garage and it was a huge improvement. R60 is just under 2 feet of blown insulation. I like Attic Cat. It doesn't itch, and you get to use the machine for free from Home Depot when you buy the insulation from them. It's an easy DIY job for two people. One in the attic to hold the hose, the other to feed the machine

Just remember, for insulation to work, you can NEVER go back into the attic. It has to look like fresh fallen snow to be the most effective.

 

[gstrom99]

I do have access to a sheetrock lift.

Originally I was going to use corrugated paels. They reflect light better and would brighten the garage more. Then I brainstormed just using foil faced rigid foam insulation boards. It seemed like a lightweight option.

I can cut channels around for the wiring.

I used steel roofing panels for my shop build (before electric - exposed conduit, or door openers went in though). You can order them to the exact length for your trusses - with a 3 or 4 inch overlap, if needed (I ordered 8' 4") I used a drywall lift to hoist 'em up.