New garage, but it's too hot to work in it.

[tractchores]

Are you guys insulating directly below the roof? I.e fiberglass between the joists and right against the roof plywood? If so I may try that in my 30x50 garage, it has a full attic and putting insulation on the floor would cost me the storage space.

 

[ovrszd]

Are you guys insulating directly below the roof? I.e fiberglass between the joists and right against the roof plywood? If so I may try that in my 30x50 garage, it has a full attic and putting insulation on the floor would cost me the storage space.

In my opinion, whatever that's worth, I think insulation at the ceiling, leaving the air gap between the rafters/ceiling, would add some R factor. Additionally, you minimize the cubic feet of space being heated.

In my case my building is all metal and there's no air gap between my roof tin and the interior ceiling tin. Works for me.

 

[s219]

Are you guys insulating directly below the roof? I.e fiberglass between the joists and right against the roof plywood? If so I may try that in my 30x50 garage, it has a full attic and putting insulation on the floor would cost me the storage space.

You can do that, but you need to put foam baffle (channel) in there to allow airflow from eaves up to the ridge. Normally it's only done for cathedral ceilings.

There is another technique where spray foam is shot on the underside of the roof, but I don't know what they do about ventilation. Spray foam changes the dynamics of things, even on walls, so there may be a different way to handle ventilation. Maybe someone else knows. I bet Eddie Walker knows if he swings by this thread.

 

[Billrog]

It's my understanding that if you use closed cell foam it can be sprayed directly to the under side of the roof with no concern for ventilation as is a vapor barrier and there's no concern of moisture to cause condensation on the under side of the roof.

 

[Jim Timber]

If you insulate directly to the sheathing or steel, it's called a "hot roof" and no ventilation is needed.

Hot roofs, dense-packed insulated Cathedral Ceilings & Un-Vented Hot Roof Solutions: avoid condensation, leaks, attic mold, insulation mold, & structural damage to roof framing when roof venting is not possible

 

[Budweiser John]

I would put 3" of closed cell foam in the roof. It you plan to leave it exposed, I would also paint it white. This will add UV protection and brighten up your work area.

Ditto on the closed cell foam insulation. Re insulated my shop two years ago with foam. Yeasty warm in the winter and significantly cooler in the summer.

B John

 

[AGRIMAN]

Ditto on the closed cell foam insulation. Re insulated my shop two years ago with foam. Yeasty warm in the winter and significantly cooler in the summer.

B John

Yes sir, it's good stuff. It's amazing the difference that foam (closed or open) can made.

 

[AGRIMAN]

Ditto on the closed cell foam insulation. Re insulated my shop two years ago with foam. Yeasty warm in the winter and significantly cooler in the summer.

B John

Yes sir, it's good stuff. It's amazing the difference that foam (closed or open) can made.

 

[Jim Timber]

Foam makes a perfect gasket between all the members it's shot over. The best vapor barrier you can get. That's part of why it's so effective. No air can get through.

 

[brown40]

I have this in one of my buildings and I agree it's easy to install and does seem to work good. I was pleased with it for the first few years, but now I'm not and wouldn't recommend it.

After 5 or 6 years it started falling apart. The white backing material cracks/flakes off in little round circles (same size as the bubbles) and it looks bad. It's a never ending battle trying to keep it cleaned up.

There are several areas were it has started to pull apart and sag. I have also noticed that many of the bubbles have busted and I doubt it has much value any more.

I'm going to cut it out and replace it with foam.

Uh-oh! Mines only been up two years. I put prodex under the roof (not double bubble, but a foam sandwiched between foils) and infrastop (double bubble foil sandwich) on the walls. Do you recall what product you used?