How to insulate attic with attic trusses?

[sevensandeights]

For some reason I just can't figure this out and I'm sure there is an easy solution but . . .

I am in the process of finishing up my garage build and am planning the insulation. It is 40x60x13 with 2x6 walls 16" OC. The trusses are attic trusses 2' OC with a 10" bottom cord that give me a 16' wide x 8' tall attic space .

I have radiant heat in the floor and plan to put R-19 batts in the walls and cover with OSB. For the ceiling, I plan to put the white metal siding up directly on the trusses and then blow in R-30 to R-38. My building has soffit and ridge vents so I will put baffles in.

My question is how do I insulate around the actual attic space? I planned to only put OSB on the inside surface of the attic trusses (both on the wall and ceiling). Can I just staple R-19 batts between the trusses all the way around the attic space?

My goal is to have reasonable temps in the attic so I can store a variety of things up there. I don't plan to heat the space but would like to avoid the temperature extremes like the attic in my house that gets up to 100+ degrees in the summer and down to 30 degrees in the winter.

 

[porschedude996TT]

I had mine (R30 ceiling/R19 walls) done by a pro, they did it in a day and I didn't itch a bit. The price was cheaper to have the pros do it.

 

[sevensandeights]

Your application looks like sissor trusses so I don't think it really applies to my application - looks good though, especially the skylights.

 

[Ray-CA]

If you want to keep the attic at reasonable temperatures, you will need to insulate the underside of the roof. Rolled insulation stapled to the roof trusses with the proper vapor barrier and allowances made for the vents will work. Then, if you want to insulate the attic floor/shop ceiling, that should be easy. Or, since the roof is done, you might just be able to deck over the attic floor to provide the storage space you want.

Ray

 

[thdewey]

I'm in the same situation and have been trying to figue something out. The problem with R-19 is the required space just isn't there. With 2X6 rafters, 1.5" baffles leaves you with 4" of actual space. Not enough for R-19, which I think is 5.5". You could sister a 2x 2 onto the rafters all the way down or what I was thinking was to use R-13 for this portion of the roof and use firring strips with 1.5" foam board to equal around R-19. I would put R-30 on the flat part of the ceiling.

 

[csp]

Some good info on radiant barrier in this thread. Allows necessary airflow through the top chord of the trusses.

http://www.garagejournal.com/forum/showthread.php?t=68632

 

[deepstuff]

Just looking at insulating my attic trusses. I have a 13.5' x 24' room. What are peoples thoughts on insulating the knee walls (so only room is insulated) vs. Insulating the full attic spaces including the storage spaces on the side of the room?

 

[MagKarl]

My bonus room trusses are insulated with batts on the bottom chord and outside of the knee walls, and rigid foam sheets to meet energy code on the upper portions that are only ~2x6 rafters. I have soffit and ridge vents.

Without some sort of airflow for the upper room it's still going to get hot up there. You need to think through how you want to handle the different spaces as far as air, temps, and fumes go.

 

[Firebrick43]

I am sorry but if you don't condition the space there is no way to avoid the extremes. It will happen slower but heat will build up.

To keep heat at bay in the attic I would put up some celotex between the rafters, even just 1/2" thick with the foil face up. I would then put a vent in one end and a fan on the other with a temp switch to keep ventilation going. Unfortunately this will work against you during the heating season. It's hard to have your cake and eat it to!

If you want max performance at not very much more price I would dense pack cellulose in the 10" space between the attic floor and ceiling. It involves putting up a netting and using a good blower to blow it in. Menards around here has a blower with high enough performance to do it. What ever you do make sure you place a well taped plastic air/vapor barrier to the inside. The paper vapor barrier is really useless except for attaching the batts.

Have you considered a liner panel for your ceiling/walls? For only a few cents more tha OSB it has better light reflectivity and is aleady painted and easier to install. Also leaks won't damage it like OSB.

 

[engineer2]

We use insulation trays when batts are going to be attached to the inside of the roof. Said to make the shingles last longer since it gives sun-driven heat a way to escape.

 

[finn]

Nail 2x2" spacers alongside the truss cord and then nail a piece of 1/4" osb or plywood to the spacers to create an air gap and flow path from thru soffit vent to the attic space / ridge vent area. You need the air gap and flow for proper venting and to keep the roof sheathing cool to prevent snow melt and ice buildup.

Insulate the area between your "proper vent" with bats, and maybe add foam sheets below that prior to finishing the ceiling with sheetrock.

Alternatively, have the cavity spray foamed, but don't omit the proper vent, or you won't have airflow from the soffit to the ridge.

 

[sierradmax]

scab an extra 2x4 to the trusses to gain another 3-1/2? You'll lose it in ceiling height.