I’m pretty damned proud of myself right now. I did my annual roof inspection/gutter cleaning the week before Thanksgiving and discovered that a noticeable sag on one of the slopes of my roof was caused by two broken rafters. When I worked in construction, I learned how to fix a whole lot of things and build a lot of stuff new, but I’d never dealt with this before. So I did what any reasonably book-smart person with a basic level of competence would do: checked out some old books on carpentry and roofing from the library.
The section of my roof that needed repairs is over the oldest part of the house—construction that’s over 100 years old. The roof is shake-shingle with asphalt over that, so instead of plywood sheathing, there are 1X4′s running the length of the slope with shakes nailed to them, and modern shingles nailed into the shakes. While crawling around in the attic, I discovered a few repairs, where the shakes had been torn off and plywood nailed to the 1X4′s. That was a happy discovery—I hadn’t known that was kosher and thought I’d need to tear down to the rafters if serious repairs were needed.
So here’s what I did. I pre-drilled and screwed in two sisters apiece (or scabs, just lumber the same size as the existing, broken rafters) on both sides of the damaged rafters with the halfway point at the point of damage, so about four feet on each side of the break to make a rafter sandwich. Since the rafter was bent, I only screwed in on the upper halves and so the lower halves of the sisters were sticking out from the roof’s interior face.
I couldn’t find a good description of how to jack up a roof in this situation, so I kind of improvised. I screwed together two pieces of lumber perpendicularly lengthwise, so that I had a long piece shaped like an L on the ends and sawed another piece in half and did the same thing to make a short piece shaped like an L on each end. These are apparently called stiffbacks or troughs by people who know what they’re doing. I screwed the short piece into the sister rafters by where the original rafters had broken and screwed the long piece into the attic joists underneath the stiffback on the rafters and a little towards the outside of the house (fortunately close enough to a load-bearing wall that I wasn’t too concerned that I’d collapse the ceiling below). I eyeballed it so that the two were on a very slight angle towards the broken rafter in the middle of the sagged region. Then I angled in a piece of 2X4 so that it was resting between the two stiffbacks and pounded the bejeesus out of it with a sledgehammer until it was in straight, then pounded it down the two strongbacks. Since I’d angled them a little bit, the distance between them decreased as you move down the troughs, and so when I’d hammer the vertical piece of lumber along them, it would lift up the roof a little bit, with the weight dispersed from the sister rafters down into all the joists and into the load-bearing walls supporting them. Once I got it hammered down the stiffbacks a little ways, I angled in another 2X4 that my assistant had cut a bit longer than the first and did the same thing, hammering the two supports down the trough a little bit at a time. When I could, I angled in another 2X4 that was a bit longer still and kept going. After four of those supports where run down into the troughs (and the first one had fallen out) I had the roof jacked up perfectly straight since the sister rafters made contact with the 1X4 roof sheathing. I went outside to take a look and was extremely pleased to see that the roof was now perfectly straight.
After admiring the fruit of my labor, I climbed back into the attic to drill and screw the sisters to the old rafters below the break. Figured there’s no harm in leaving the supports where they are through the winter. Come Spring, I’ll have to carefully hammer them out and let the sisters start carry the full weight of the roof.
Now I’ll watch some Mizzou v. Oklahoma and get all the black boogers out of my nose.