Roof insulation for my 30x60 shop

[cgetsinger]

I have read many post on this and i still am lost as what is the right way to do this. My shop has a metal roof with a ridge vent. The purlins are 2x6 on their sides set even with the top of the trusses. The top cord of my trusses are 2x8's. How would i go about insulating this with out using spray foam. Would I need to put the insulation between the purlins, or simply below them or do something different. I hope i have explained this so everyone will know what im talking about. The attached picture is my roof. Thank you for any help in this. Chris

 

[BeezFun]

I think I'd put foam board between the roof purlins. You can cut it a little small and foam the edges to hold it. Whatever you do up there you'll end up with some moisture, but foam board will be fine. I wouldn't put fiberglass near the roof surface, it will collect any moisture and probably never dry out.

If it's an option, I'd hang framing from the bottom of those trusses and put in faced insulation just like on a house ceiling. You'd have to ventilate the new attic space. In your climate it's tough knowing which way to orient the insulation facing because of the seasonal temp change and humidity. If you plan to air condition it in summer I'd probably put the facing toward the attic not toward the living space. Otherwise probably put the facing toward living space as long as attic is well vented.

 

[cgetsinger]

The moisture is what i am trying to avoid. It is a open truss ceiling so there will be no attic. I will only be heating it during the winter with just fans during the summer for coolness.

 

[BeezFun]

This is a good application for spray foam, but you indicate you don't want to do that. There will always be some moisture condensing under a metal roof, particularly if you heat the interior. If you use foam board the moisture won't matter much, foam doesn't care about it. It will also help to block the raised channels in your roofing, to make sure it can't draw any interior air through the channel because that will really condense moisture.

Are you going to block off the ridge vent in the winter? If not, you'll draw the warm air in the building out the vent, negating the effect of adding insulation.

 

[michaelortiz]

Metal roofs are durable but they are poor insulators. Recently we have insulate our steel buildings colorado springs with fiberglass. Fiberglass insulation is best to avoid moisture problem. These fiberglass insulation with an attached vinyl or similar material as a built-in vapor barrier available in market which are particularly designed for metal roofs.

 

[Gary Fowler]

I am also thinking that sprayed foam would be the best and easiest to install. Otherwise you would be putting up scaffolding on the whole roof area to work off while stapling the bat insulation. You may also need to put some strips across the batting to hold it in place or else cover it with either 1/4" plywood after insulation. This would likely cost you more than spray foam.
I think there are places where you can rent the spray foam equipment to install it yourself if you want to save some money.

 

[ace10]

What's the spacing on the purlins?


I'm a huge fan of Roxul. Comfortbatts come in widths for 16" and 24" bays. No stapling, just friction fit. Even on a horizontal application. R15 or R23. I installed them in the floor joists of my crawl spaces. No need for vapor barrier. Really easy to work with. But it's not what one might consider a low-cost option.

$0.02