Hello all,
New to the Forum, but I have a question to pose to the accumulated wisdom of the minds assembled herein:
My wife and I recently moved into an old (c. 1900) Victorian house in upstate NY. The house has never been insulated, and given that it has been stated again and again that the attic is the source of the lion’s share of thermal loss in a house, we are going to start there. The semi-finished attic will be gutted down to rafters and kneewall studs, with an eye towards re-finishing the attic for living space. Here’s the problem: The existing rafters only leave a 5 1/2 inch deep space for insulation, and recommendations call for at least a 39 R-value for attic spaces in my zone (zone 5). The finished walls will follow the pitch of the roof for some 6 1/2 feet between the kneewall and the dropped (tray?) ceiling. How can I get the appropriate R-value for these sections of the attic wall? I am hoping to avoid sistering on new rafters, both for the cost and skill factor, as I am tackling this project on my own.
Just to save you all unnecessary typing, yes I am aware that there must be adequate ventilation along the roof sheathing, and I am planning to incorporate foam baffles beneath the insulation along the pitched portions of the wall.
I look forward to hearing your suggestions.
Thanks,
KJB
Replies
Assuming you really don't want to sister new rafters to the existing ones, you have few options. One option is sprayed-in-place polyurethane foam insulation. Not cheap, but it has the R-value per inch you need (R 7 per inch). If you need new roofing, you could consider installing some of your insulation on top of the roof sheathing (rigid foam insulation topped with another layer of roof sheathing -- plywood or OSB). If you go the latter route, you have to decide whether or not to include venting above the new rigid foam. That's a whole 'nother discussion (or controversy).
Thanks for the suggestions. I had thought about the foam, but knew it was expensive, and wasn't sure of the R-value. I just had the roof redone two years ago (we were not in residence at the time, living in Japan), and have realized that I blew that opportunity.
My brother, who works for a major construction firm, had suggested suspending lighter-weight wall framing between the kneewall and the ceiling joists to gain additional space. Any thoughts on whether that would work?
Please feel free to critique or suggest ideas freely. I want to have a very good idea as to what I'm doing before I get too deep into anything
Edited 11/22/2002 1:36:25 PM ET by IBKEVIN
You can attach 2x4s, for example, the to bottom edges of the rafters, by several methods, gaining 3.5 inches. (You can lag or screw or nail the 2x4s on edge to the rafter bottoms, either in the same line as the rafters or at 90 degress to the rafters.) But I thought you didn't want to lose the headroom. If you don't mind losing the headroom, you can also consider attaching rigid foam to the underside of the rafters -- 1 inch, 2 inches, 3 inches, whatever you want. The thicker the foam, the trickier the fastening, but anything is possible.
I don't consider a couple of inches of headroom on a portion of the side walls a huge loss. I had also thought about the rigid foam panels, but then, how do you hang drywall over the foam?
Thanks again for the thoughts.
KJB
You can screw through up to an inch of foam, but (1) it can be hard to find the framing with your screws, and (2) some compression of the foam is possible if you're not careful with your screw gun. But it is possible; I've done it. The thicker the foam, the better off you'll be installing strapping (1x3s at 16 inches on center) on top of the foam. The 1x3s get screwed to the rafters through the foam. Yes, you need long screws, and yes, it can be hard to find the rafters. Put people do it.
Can't find the bookmark I thought I had, but you can order the 2-part urethane foam to spray yourself (large returnable tanks). Anyone else have that link handy??
You may have already read these archived threads. They eventually degrade into attic insulation/venting discussions.
http://forums.taunton.com/tp-breaktime/messages?msg=1516.1
http://forums.taunton.com/tp-breaktime/messages?msg=20730.1
Thanks for the previous threads, Mongo. It's sure given me more to think about. I was only thinking about keeping heat in in winter, not keeping it out in summer!
You made a case in one of those previous threads for foil-faced poliso foam insulation to keep out radiant heat from the roof in summer, but I think you mentioned putting the foil facing out toward the sheathing. Doesn't this defeat the point of the facing as a vapor barrier? I understood that a vapor barrier should be faced toward the heated space. I see how that works in summer, but what about winter? Would you then need to add a vapor barrier over the poliso boards?
Another point made was that cellulose insulation is more resistant to radiant heat in summer. What about the expanding foam mentioned earlier in this thread? Anyone know about it's benefits in reduction of attic temps in summer?
Might as well do it right the first time. Can insulation be all things to all people in all seasons?
KJB
Edited 11/22/2002 6:33:45 PM ET by IBKEVIN
Edited 11/22/2002 6:53:17 PM ET by IBKEVIN
The foil-faced polyiso that I use (both TUFF-R and ULTRA-R) has foil on both faces. So as long as you don't install it on edge...<g>
Several inches of a spray on expanding foam would be an effective radiant barrier as well.
to IBKEVIN,
If you intend to use the attic for living space the r- value may not have to be as high if heat/ac is introduced into the space. The recommended r-value is tied to unheated or unfinished space above ceilings. I would think that adding R-19 insulation with kraft paper facing to the knee walls and blowing in fiberglass around the unused/unheated space at the recommended R-39 for your zone should be sufficient. Proper ventilation in the ceilings/rafters is critical as you mentioned, but reducing the size of your living space/headroom is not an option. some local codes require a minimum amount of headroom if it to be used as living space. If there are windows or dormers in the space, that will help with cross vetilation in the summer and provide necessary lighting for your finished area.
You seem to be on track and asking all of the right questions about ventilation and insulation but I would like to weigh in on convenience. If you are doing this job yourself there is only one answer and it is polyurethane foam. Why? Speed and permanence. Do you really want to hang off a ladder in your attic stapling up fiberglass for a few days and then go back over it with foam panels? I don't think so. The foam would in reality be necessary because the paper on the fiberglass WILL eventually tear and the fiberglass WILL eventually start to fall off and/or sag. With the foam you will be able to stand on the floor of the attic and spray from the floor to the peak. It will be the vapor barrier, will never sag or fall out. You will be finished in a few hours doing the job alone. In that respect, even if you are paying to have the attic renovated, you could still do the insulating and save that expense. Another consideration is if the rafters are not evenly spaced as they are not in my circa 1900 home. If they are not then you have doubled your work because of having to cut the fiberglass to properly fit each rafter bay.
Try the two part foam kits at http://www.fomo.com. They have refillable and disposable kits.
Foam has so many advantages that it is the only insulation I will ever use on my home.
Good luck.
I have a similar situation with a finished room in my attic, but in a better winter climate. While there is R19 fiberglass in the rafters over the finished area, there is still rockwool beneath the floor so there is an adequate amount of insulation between the second floor and the roof, and I am more concerned about keeping the heat on the second floor. For the area outside the kneewall, r39 cellulose would be the best bet. I have had to do my removal and replacement in spurts, and therefore went with fiberglass since I could reinsulate immediately each day. Ahh, a classic case of do as I say and not as I do. ;-) But had I done this in the summer, it would have been cellulose.
Here is something else I've been thinking about. I have 6" rafters that are not insulated, and we have had discussions about IR radiated heat from the roof down to the ceiling. Is there a reason one couldn't just staple heavy aluminum foil across the rafters, leaving air gaps at the top and bottom for ventilation? The foil would be pretty opaque, and could reflect IR in the correct direction for each season. I know people use that really expensive foam centered foil this way, but why not just AL foil since we've previously agreed the 1/4" of foam is pretty useless?
Thanks guys!
Here I thought my thread was dead. Thanks once more for all the great input.
Eschew, thanks for the link and the thoughts on the foam. I wouldn't have considered that as a DIY material. Your input makes that look very attractive. What's the learning curve like for applying the stuff? Any safety concerns (fumes, toxicity, etc.)? One problem is that I still come up short in the existing space. Even if we assume a best case scenario of R 7 per inch, I only come out to R 31.5 after leaving 1" of vent space, so I'm back to hanging foam panels over the rafters or trying to pad out the rafter space. Or could just call it good at that? As for the rafter spacing, a good 10' run (measured along the eaves) of the rafters are exposed in one storage area behind the existing walls in the attic, and these are all 16" o.c., so I feel pretty safe in assuming that the rest are as well.
Wood, as for your on-the-spot replacement process with the fiberglass, that immediacy is not really a concern, because there is nothing up there right now, so any insulation I add is an improvement. The foil idea sure sounds like it'd be cheap, but...
Another question: In one of the prior threads cited by Mongo, several people made mention of running vents and insulation all the way up to the attic ridge. Is this necessary for me if my finished space has a dropped ceiling? Can't I just insulate around and above the envelope of the finished spaces and leave the small crawl space in the peak exposed? This of course assumes that all of the area above the lower floors is covered. Is there a significant benefit to insulating along the full pitch of the roof vs. not?
Thanks again.
Kevin
There is no learning curve. The kit comes with all the stuff you need to get the job done. It is two part urethane that mixes in the supplied nozzle. If you need to stop you just remove the clogged nozzle and replace it. The give you about 10 disposible nozzles with the kit. If I were you I would spray out to the edge of the rafters and leave it. you can spray more where the walls stop. It might be cheaper to sptay the back sides of the walls instead of the rafters where the walls do not contact the roof. When you spray, give each rafter bay one good coating and then move on. Let the foam expand fully and then come back and add more where you like. You'll get the most expansion and the least waste (overspray that may need to be taken off) this way.
Good Luck