Log Home Roof Reconstruction – Is This a Good Plan?
I’m fairly inexperienced, so excuse any ignorance that becomes apparent. My question is near the end. I’ll give as much background to this situation as I can.
N. Wisconsin, 60 psf ground snow load
Log Home
Full cathedral roof
24 square
2 valleys(2 parts of the home are perpendicular, T-shaped arrangement with gable ends)
no dormers or other complexities
10″ Log purlins on 5′ centers, perpendicular to log trusses
2×6 T&G pine perpendicular to the purlins are the ceiling
2×6 rafters with 4″ EPS, no vapor/air barrier, 3 tab shingles that require replacement
Ice dams are of epic proportions and there is log rot due to the poor roof and no water management.
I’m planning on a summer reconstruction of this roof. I’m tearing off everything down to the T&G and rebuilding. I’ve read many fine posts here and I will concentrate on a perfect air/vapor barrier, as much insulation as possible and venting.
What I’m considering now.
1) Vapor/air barrier – Cover T&G completely with Grace I&W. Reasons: All fastener holes may be self sealing, it will serve as a temporary roof, it is a very durable vapor/air barrier and seams are less susceptible to error. I won’t do this if I go with ccSPF.
2) Insulation – XPS, EPS or ccSPF to as high an R-value as I can get. I’m considering the board instead of the spray due to cost. The ccSPF will cost about $18,000 for 8″, R-48. The board will be $7900 for material for R-50 + $1700 for I&W + installation. When all is said and done, $18k for the ccSPF may be a better option. I want to put cross purlins on the T&G deck so that I can raise the framing up 1.5″ and apply a thermal break below it.
3) Venting – Make the roof cold, unless I do the ccSPF. According to what I’ve read, 8″ of SPF may make venting unnecessary. I’m not quite sure I want to risk it however.
Drawing of this plan available at: http://netcrafting.com/roofrebuild.jpg
In your opinion, is this a good plan?
Any other comments that you might have are welcome.
Thank you.
Rodger
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Replies
Rodger, Have you looked into PUR SIP possibility?
This may be easier with nailbase foam panels, and there are some vented panels on the market (Cool-Vent by Hunter Panels). But your plan sounds fine as long as the roof is vented to allow the roof deck to dry in the event of a leak.
You don't indicate what the roof sheathing or roofing will be, but the less breatheable those layers the more important the vent cavity becomes, particularly if you want to avoid any possibility of ice dams.
Thank you.
Roy) I have looked into SIPs, but the plate logs of this home are not level and SIPs need a square and level wall...at least that's what I've read/been told.
Robert) Sheathing will 5/8" T&G Plywood or OSB and 30 year architectural shingles. Thank you for the suggestions.
If the rafters are no more than 24" oc, there's no need for anything more than 1/2" square edge plywood, and I would recommend #15 felt as a roofing underlayment since it breathes better than any other (5 perm).