1" sheet foam insulation?

[Darkside500]

I have an open ceiling shop about 20' x 30'. It gets pretty hot in the summer. I can't afford spray foam insulation. I saw this 1" sheet foam at Home Depot for about $10 a sheet. I figured 600 sq ft plus the pitch is around 20+ sheets. I was thinking I could cut into 22-1/2" strips and use liquid nails or the like to stick it up to the roof sheeting between the joists. My question for people with more knowledge about this stuff is, will 1" styrofoam make enough difference to be worth the effort? also it comes 1 side faced with mylar. should it be shiny side inward or facing the roof sheeting?

Thanks
Randy

 

[tfinniii]

Reflective side goes toward sheathing ,but should have space. Is your roof vented ?

 

[Darkside500]

yes, I have a couple of roof vents, I also have a high velocity gable fan

 

[Bert_]

Use it to close in the ceiling and it would make a huge difference. Up between the rafters, not as much.

 

[theoldwizard1]

Several different kinds of rigid insulation. Poly iso is the best and most expensive. Occasionally you can find it recycled.

IMHO 1" is a waste of time ! 4" !!

 

[TractorJeff]

Everybody has an opinion and mine is if you can create a ceiling, it would be better than nothing. If you are insistent (finance) to put it all the way up I believe you need to leave an air space as previously suggested in post 2.
All in All, if it reduces the Heat on your head a few degrees, then it is a Win, Win!

 

[metlmunchr]

I eventually insulated mine overhead with R19 batts stapled to the bottom chord of the trusses and insulated the 2 wood panel type overhead doors with R7 foil backed poly iso 1" sheet foam. But, back when I didn't spend more than 3 or 4 hours a week out there, I made a ceiling by stapling 6mil polyethylene sheet to the bottom of the trusses.

Anything like that stops thermal circulation where the roof heats air in the summer and cools it in the winter, and ultimately heats or cools the entire garage at times when you'd rather have the opposite. Since you already have a gable fan, and I assume a gable vent at the opposite end, my guess would be that a poly "ceiling" will do more toward making the garage comfortable than an inch of foam sheet on the underside of the roof during both winter and summer.

 

[Syberia]

We used the 1.5" styrofoam sheets cut up and glued between the rafters in my wife's animal shed. Combined with R-13 in the walls, it makes a huge difference, to the point that an 8k BTU window A/C keeps it cool when it didn't do anything before.

 

[PoorUB]

You really should not insulate directly to the underside of the roof.

Do you have truss rafters with a horizontal collar tie? You would be better off sheet rocking the ceiling and insulating on top of the sheet rock..

 

[Terry D]

You really need air flow to the underside of the roof sheeting. If not, you may create condensation and also shorten the life of your roof. You want to try and keep the underside cooler than the surface of the roof. Even with using a rolled insulation, they make air baffles that install first between the rafters and create a air space. With the combination of your ridge and soffit vents, there will be always air flow. You can use a ridgid foam board, but I would not glue it directly to the roof sheeting. I would install 2x2's the same direction of the rafters and glue it to them, then it will create a channel for the air to flow

 

[oilslick]

You really need air flow to the underside of the roof sheeting. If not, you may create condensation and also shorten the life of your roof. You want to try and keep the underside cooler than the surface of the roof. Even with using a rolled insulation, they make air baffles that install first between the rafters and create a air space. With the combination of your ridge and soffit vents, there will be always air flow. You can use a ridgid foam board, but I would not glue it directly to the roof sheeting. I would install 2x2's the same direction of the rafters and glue it to them, then it will create a channel for the air to flow

This is a good idea if all you have is the 1”

 

[NUTTSGT]

Putting an actual general location in your profile would help your fellow members give you better advice. What is done in Texas is different than what we do in Ohio.

I bought foil faced "seconds" polyiso and hung from the bottom of the trusses. Granted it covered R21, it did make a difference. Then I covered the polyiso with ribbed metal for the final ceiling.

 

[gungatim]

Several different kinds of rigid insulation. Poly iso is the best and most expensive. Occasionally you can find it recycled.

IMHO 1" is a waste of time ! 4" !!

LGR