Raise the roof to expose the old sheath?
My wife and I are knee deep in our first home, a 100+ year old church in the Midwest. Hot, humid summers, cold windy winters. Plenty of rain, too. We’re focused on the roof/ceiling, which was plaster and lath and has been torn out. The structure has a nice dry roof in place, as of 3-4 years ago. Lately I’ve been planning on using Icynene at the ceiling height (it’s a scissor truss system). However, the original old roof sheathing is now visible after removing the old ceiling, and it’s pretty attractive.
My wife wants to know if we can keep the whole thing exposed on the interior – which means insulating on the outside, via (I’m guessing) building up the roof.
In my head, I imagine this requires a *lot* of effort. Strip the old shingles down to sheathing, build up some sort of 3-4 inch thick framing, spray the Icynene, put down another layer of sheathing, then felt paper, then new shingles. Don’t forget you need to build some sort of weatherproof edge around it .. All of this on a roof pitch that is just a bit scary.
So I’m wondering what the correct term is for this technique (other than “so expensive you’ll cry”), and whether it’s even a reasonable option. Also, am I way off base about how it works?
Thanks for your help.
banned from the nail gun
Replies
You might investigate having SIPS laid flat over the old sheating rather than going through all the effort of building up framing. When I was looking at a SIP house, the supplier I was dealing with offered something they called "nailbase panels" which were basically SIPS with OSB skin on only one side. They were made for exactly what you're doing.
None of that, of course, speaks to any loading concerns...
did
did;
I had to do a little googling to understand SIPs, but see your point. It would reduce the work of building the roof up, for sure. I guess that still leaves the essential question of "Is it so difficult and expensive that I'll probably throw up?"------------------------
banned from the nail gun
That's not such a bad idea. Is your roof in decent shape at all?
AFAIK, you would rip off the roof down to sheathing, put rigid foam insulation on top of that, then sheathe over that with OSB or plywood, and then reroof.
As far as SIPs go, I can't see much advantage to using SIPs rather than rigid foam and one layer of ply. SIPs are much stronger of course, but if the sheathing on there is good, it doesn't really matter.
You might want to look into roof shingles that still have a warranty when installed on a hot roof- I think Certainteed and Elk have partial warranties. Then again, shingle warranties never seem valuable to me- the cost of a roof is mainly labor.
4" rigid foam should be cheaper than icynene, from what I've heard of icy prices.
I think there are some people here that have done this, so hopefully you'll get some more informed advice than mine.
zak
"so it goes"
Good points zak;One big question is: will it be enough insulation to do much good? As I recall, rigid foam is about R4 per inch, so 4 inches is a whole r16?What's considered a "good" R factor for ceilings and/or roofs?------------------------
banned from the nail gun
Yeah, 4" is probably not enough. Foam R-values vary. EPS is around 4/inch, XPS around 5/inch, Polyisocyanurate around 6.5/inch.
I don't know how much energy codes vary around the country, I think ours here is R-39 for roof/ceiling insulation. I may be wrong about that. My ceiling is currently about R-5 (4-5 inches of sawdust), so my view is that R-20 or so would be a major improvement, and I believe that foam performs better than it's R-value indicates, because of the way it stops air infiltration.zak
"so it goes"
EPS at R5
Polyiso foil surfaced R-7per inch
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Have you considered over head lights and wires? That is MY issue. Do you mind working with a plumbing stack vent exposed?
Wider Fascia, ext. cornice details, and wall trimming to the sheathing on the inside all propose a complete study.
You CAN do it, you CAN do it on the fly cheaply, but it may well haunt you.
"midwest" can be Minnesota, or Oklahoma...I am in KY, And I'd refer to that as the midwest sorta..so any thing less than a 30 ciel/roof insul. is better than zero, but not ideal.
Replicating the interior view of the sheathing may be better.
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Just a thought--not my area of expertise--but what about a sprayed on polyurethane roof? This can be sprayed on as thick as necessary to acheive proper R value--It is done in a 3lb foam (I believe) so it is very tough...something to think about.
If it's scissor trusses just put the treatment you want on the bottom chord of your trusses and insulate the roof however you want.
That's the way I would do it instead of tearing the roof off and dealing with it that way. Probably be whole lot cheaper as well.
I only golf on days that end with a "Y".
Insulating your roof from above is probably not too much more expensive than doing it from below. The main extra expense is reroofing and you will end up with a new roof. It is possible that you will need this in the not too distant future anyway.
The main problem as I see it is that you will increase the thickness of the roof and that this could look very weird from the outside. Most of the old churches appeal is a quaint aesthetic and this could be ruined by messing with the roof thickness. It is possible to disguise this or even rebuild the overhangs but this could be a very difficult and expensive process. In any event it deserves serious design consideration.
Good luck in whatever you decide.
Here's a link to a company making nailbase. I'm sure there are others as well. They offer up to 4" of foam insulation and also can get venting channels.
http://www.atlasroofing.com/residential_roof_deck/index.asp
I"m thinking about these for my finished but unused attic which I will be bringing up to speed over the next year or so. It has low cathedral ceilings and the rafters are 3x4's without insulation. 4" is not much space for insulation. Which has led me to these nail base (SIP) panels.
The more I think about it, giving a couple of inches on the inside for insulation will be substantially faster and cheaper than the nail base panels and the frightening possibilities of reworking the roof perimeter.
I've done a bunch of searching and found little info on re-roof application of these panels.
good luck
splat