workshop ceiling insulation suggestions for truss roof
Up front, thanks as always for everyone’s input. I always get thoughtful and creative answers from everyone.
Here’s my quandry: I have a new 24′ x 60′ garage built that uses trusses for the roof. The last 24′ (by 24′ deep) is my workshop. I have insulated and sheetrocked the walls to isolate it from the rest of the building, and plan on heating it only during the days when I’m working there in the winter (NH). The roof structure is a salt box, low to the ground, with the eves at 9′ at the front and 7′ at the back (so it blends in with the farm feel of the area). The trusses take up the whole “attic” space, and I’m trying to figure out the best way to insulate the ceiling in the workshop- doesn’t have to be pretty, just effective.
Couple of methods I’ve thought of:
1) Use craft faced fiberglass stapled up between the trusses, then 1″ of foil faced Iso screwed directly to the bottom of the trusses.
2) 3″ foil faced Iso screwed directly to the trusses.
3) Strap the trusses first, then one of the above solutions.
4) Where do I put a vapor barrier, if I don’t use the foil faced Iso?
5) If the trusses lift, is the seam taping of the 4×8 sheets of Iso insulation going to split/ tear?
6) What’s the likelyhood of the trusses lifting if the room is not heated for long periods of time (does the truss actually see any of the temperature change from the room?)
I only do antique home restoration, and after going to some of Gary Katz’s talks about wood movement, and reading about truss movement, I’ll stick with old wood!
Thanks again for any and all suggestions.
Sheridan
SAL Building Restoration
Replies
Not sure I have a clear picture here
but it sounds like you don't have a flat sheetrock ceiling with an attic space above, such that you could use blown-in insulation on top of the ceiling.
Of the solutions you listed above, my favorite would be the polyiso attached to the bottom of the truss chords. 3" is not really enough, you need more like 6". Two layers of 3" material with taped and staggered seams would be a helluva lid.
Is the roof vented?
I'm not sure I can understand why he couldn't rock it and blow insulation above. Don't quite have a picture of those saltbox trusses, though.
Picture of trusses
Here is a picture of the building under construction. In the end, it almost looks like a chicken coop or low carriage barn. If you can see, the ceiling inside slopes down considerably in the back 1/2 of the structure. I'm not sure that can work for blown-in, other than filling it up completely, with baffles to hold it away from the roof.
Again, roof venting
It looks like you're going to have a metal roof, judging by the purlins. Hopefully you're going to put nicely layered roofing felt down first, otherwise I would be concerned about condensation dripping from the bottom of the metal and getting the insulation and drywall wet.
Anyway, you could baffle between the trusses and then blow in insulation. It would fill the space near the eaves and there would be some airspace near the ridge. Or, you could go with some or all of it as rigid board under the trusses.
With large overhead doors, I think you're going to have a lot of air leakage, which will be your main problem in keeping the space warm.
Some thoughts:
Sheridan,
If you have eave vent intakes and a ridge vent outlet, you might want continuous baffles from the wall to the ridge in each truss bay. You could use purchased baffles that staple in to the trusses, or build your own out of polyiso insulation.
The baffles will not only keep the dirt and air out of the insulation layer, but they will also define the insulation space, acting as a cap to contain blown-in insulation. So, if you wanted say a foot of fiberglass or cellulose, you would install the baffles with their bottoms a foot above the bottom of the lower truss chords. Then you could blow in cellulose or fiberglass from below through a mesh and fill right up against the bottom of the baffles. At the low end, you might have to pinch down the insulation cavity by adjusting the baffles, so that your ventilation space gets through that choke point.
In the taller areas of the trusses, the baffles would be below the top chords, so you would also need to add some filler pieces of polyiso to block off the 1.5” wide gaps created by the trusses in the areas between their struts.
Then put a film vapor barrier on the bottoms of the truss chords and sheetrock over that.
Great ideas
Thanks everyone, I will look into the cellulose idea. May be tricky getting into the long slope to the back. Or I may see how much ceiling height there is to put up 3" of Iso and be done. Will follow up with the results. In the mean time, if I run into additional questions, I'll be back before the sheetrock is up!
Attached is the picture of the almost-finished project.
Sheridan