Saving the Old Look of an Exposed Ceiling
My husband and I are buying an old farm house. Part of the second floor was never finished so when you look at the ceiling you see the original boards that were used to construct the roof. I want to preserve them but the house needs a new roof desperately. My husband says we can build a roof over the original but that we'd have to insulate it. Can this be done?
A few years ago I visited a cottage on Nantucket that was brand new but made to look old. Inside, both structural framing and the board sheathing had been left exposed.
The effect was charming, as if this rustic and inviting cottage had not been touched for generations. Nothing could have been further from the truth. In reality the cottage was very well insulated, thanks to a second layer of materials that enveloped the outside of the building.
And, with a couple of caveats, a similar strategy could work for you.
First step: Check your existing roof carefully
You can, in effect, built an entirely new (and insulated) roof system over what's already there. But a first and important step is to determine whether the existing roof is up to the task.
As much as we'd like to believe otherwise, old houses were not always well built. Carpenters then, like carpenters now, sometimes took shortcuts or used materials that were not as robust as they should have been. Time and gravity take their toll as well.
So inspect your roof carefully. If the framing is under-sized and sagging, re-think this plan. Look for signs of insect infestation. Use an ice pick or sharp pocket knife to probe both framing and sheathing to make sure it's sound.
If you have any doubts, call in an experienced builder or even an engineer. But let's assume the roof framing is strong enough and there are no other problems.
New rafters, insulation and sheathing
The next step is to build a new roof atop the old.
Start with dimensional lumber set on edge and spaced at 16 inches on center. These new rafters run from ridge to eave.
Insulation is next. Even though fiberglass batt insulation is relatively cheap and readily available at your local big box store, this isn't the place for it.
There are two reasons. First, fiberglass won't provide high enough R-values. The Department of Energy suggests a cathedral ceiling in the northern tier of the country be rated at R-38. That takes a layer of fiberglass a foot thick. (For complete recommendations, checkhttp://www.ornl.gov/sci/roofs+walls/insulation ).
Second, fiberglass batts allow way too many air leaks - and the last thing you want is warm air making its way up through the roof.
Your best bet is to hire a contractor to spray closed-cell polyurethane foam into the rafter bays. With an R-value of nearly 6 per inch, you can pack a lot of insulation between 2x6 or 2x8 rafters. And you won't have any air leaks.
Follow this with plywood sheathing and a layer of tarpaper.
One more layer to vent the roof
Whether a roof should be vented (that's a "cold" roof) or un-vented (a "hot" roof) is a point of contention in the building trades. You'll find plenty of advocates on both sides of the fence.
Check with your local building inspector to find out what local ordinances require. And discuss the options with your builder.
But assume for the moment that you go the traditional route -- a roof with vents at both the soffit and the ridge. In that case, add 2x4s on the flat to what you've already built, then a second layer of sheathing to create an air space. Finally, cover the whole thing with tarpaper and then shingles
Whew! That's a lot of effort, and there will be a few details to work out as you go. Trim, for instance.
But if you want to preserve that old-time look on the inside of the house, it's going to take this kind of effort.
An accomplished woodworker and carpenter, Scott Gibson is the former editor of Fine Woodworking magazine, and a former editor at Today's Homeowner and Fine Homebuilding magazines. He also is former managing editor of the Kennebec Journal, a daily newspaper in Maine.