Rockwool Comfortboard in attic?
Hi All,
I was hoping to get a sanity check on my idea.
A customer has asked me about enclosing the space around their air handler and ducts in their attic. They want to improve their efficiency to heat/cool their home but do not want to use any foam products as they are concerned about off-gassing and VOC’s.
The attic is vented and currently has fiberglass batts between the joists on top of the drywall. There is no top vent on the side walls, only the ridge vent.
After removing the current fiberglass insulation (havent done anything yet), my thought was to attach studs vertically from the rafters to the ceiling joists like a mini knee wall, then use Rockwool comfort board on the interior side of my proposed knee wall and on the interior side of the rafters all the way to the ridge, essetially creating a semi conditioned space for the air system while leaving space for the vents between the rafters. I would attach the rockwool to my new vertical studs and rafters in the same fashion as it would be installed as exterior insulation and offset/layer it up to meet code. Finally I would use custom sized pieces of rockwool batts for the spaces between the joists.
I normally focus my efforts on air sealing and insulating basements or crawlspaces so I am hoping to get some input on this before I commit to any one approach. Does this make sense and are the comfort boards appropriate for use in an attic?
Thanks for any help.
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Replies
Chris,
Your plan can work, but there are a lot of details that you need to get right. You may want to read this article on the topic: "Should I Build a Mechanical Room in My Attic?"
Thanks Martin, good reference. No lack of space in this case and unfortunately this isn't my house so the breadth of options vs cost is limited. I will do some more research on the pros/cons and my risk before proceeding.
Hi Chris,
I'm just a DIY guy but I've used a lot of roxul.
IMO, if you are building a kneewall, I would use the common and less expensive and (in my experience) less smelly comfortbatt. You can easily achieve R15 or double wall for R30 with staggered studs or even a between double stud cavity trapped comfortbatt (wood is cheap and carpenters are fast) for an affordable no foam setup. Achieve fire rating, if required, with wallboard or plywood (check code, but I believe 3/4" works)
In many areas of the country, roxul comfortboard is still only available by the pallet at a 3x+ markup per R. It's also hard to achieve tight fits with comfortboard.
I love roxul products but I think you'll be happier you went with in stud comfortbatt instead of some surface mounted comfortboard.
Of course, nothing to prevent you from doing comfortbatt in a single stud wall and skinning the outside with comfortboard (except cost).
Thanks Keith, you make some good points here. Ultimately the HO did not want to enclose the attic space, mainly due to cost of the options; I quoted both the rockwool & foam just for comparison. Instead I recommended a duct sealing service from another contractor so they should see at least a little benefit from that.
This might be a silly suggestion, but if the customer is due for a re-roof then I wonder if creating an unvented attic via exterior rigid foam on the roof deck would be a more reliable option?