I have a 1921 1 1/2 story bungalow in MPLS. There are three attic areas, all of which are vented by one vent near the floor level apx 8″ by 8″, and a power roof fan. I think some of the roof fans may have siezed. Anyway, the spaces are under vented. The insulation is blown in celluose under the floor and fiberglass batts under the roof decking. Thats right, it is vented and has insulation on the roof. I think that was an attempt to stop ice damns. In 2 of the 3 attic spaces there are short runs of HVAC ducts (say, 3-4 feet).
I would strongly consider bringing the attic “inside the envelope” and insulating the roof but there is one problem… I don’t have acces to the entire roof due to the finished areas of the upstairs. The ceiling upstairs folows the roof line part way up and then has a flat spot across the top. I think there is blown-in insulation above the ceiling, but can’t really see up there. So, baring a major re-do upstairs, I don’ think that is an option. So what I really need to do is increase the venting in the attic and seal off the conditioned area of the house as best as possible, right? I could put some sort of enclosure over the ducts to bring them “inside the envelope”
As for type of venting, I guess I could put ridge vents in… You don’t need access to the inside of the house to do that, do you? Then I could add some of those small circular vents between each rafter tail.
What do you guys think? Any advice?
Also, the house has central AC, but the upsairs is pretty hot. I’m sure a good part of that is the attic heat, but also the vents upstairs have very little air flow. There are return vents in each room and I have shut off some of the vents downsairs to force more upstairs, but the run is quite long and not very large cross section. Any ideas on how to get more air up there? I say a “booster fan” that goes in the ductwork at home depot the other day. Made by “suncoast” (sp?). Otherwise I suppose we could put a window a/c unit up there, but I hate to do that.
Thanks,
erik
Replies
Yep, ridge vents and some sort of eave vent is the way to go. Unfortunately, with the eave vents you may run into trouble with the cellulose being in the way -- some invention required.
You'll probably need new cap shingles for the ridge vent, of course. Generally you don't need a perfect match with existing shingles for it to look OK, though.
I was looking at 3" circular vents, since I cant do contiuous soffit vents (exposed rafter tails, no soffit). So those should have an effective venting area something less than 7 sq in. I read that you should always have at LEAST as much effective area for the intake as the exhaust (I suppose so you don't create a vacum sucking air from the inside of the house). The ridge vents I see are 13 sq in effective venting area per linear foot. So would I just use the vent on part of the ridge to equalize the effective venting area?
Thanks,Erik
I don't think it's necessary to balance in and out that closely. You'll probably never be able to get as much eave venting as the ridge vents will supply, so just get as much as you can. If air is drawn from the house as a result that simply means you need to seal those air leaks.Besides, it'll look really crappy if you only use ridge vent on part of the roof.