Is it ever okay to cut roof rafters without installing headers?

Question

We just had a roofer install a skylight on our sloped ceiling of our third floor. (The third floor is basically a finished attic in the peak of the roof.) The installer just cut away two rafters (16 inches apart) in order to fit in the skylight. He did not install any headers on these cut rafters.

I asked him about it since I thought you should always put headers on when you cut like that but he said it was fine to leave it without headers. He's a roofer so I thought he must know and I didn't argue, but now I can't stop thinking that this is not right. I was surprised actually that the rafters are only two by fours. Our house is over a 100 years old.

Any advice, please?

Answer 1

We could use more detail about the roof framing for confident answers, but here are some thoughts.

• A house that old has a few things going for it. One is heavy, old-growth lumber. Another is heavy roof decking (probably 7/8" thick solid wood boards 8-14" wide). Yet another is beefy nails. For that reason, the roof as a system is probably still ok.

• Yes, I would've headed off those rafters. There's stress on them in one direction or another, depending on overall framing design, and that should be managed to avoid sagging, etc.

• No, roofers don't necessarily know (or care). They're in a square-foot-per-hour business with thin margins. Any delay could cost them their entire profit margin. Therefore, delays and distractions are minimized. This might be a reason to hire a carpenter who knows some roofing rather than the inverse for this job.

• Many rafters are still "only 2x4s", even with engineered trusses of considerable span. They do the job perfectly well when used properly. My guess is that your attic has 1x4 webbing in several locations on each rafter reducing local spans.

At this point I'd get a good look into the attic and take a walk on the roof. I'd want to know the exact framing strategy and what the deck feels like under load. There may be repair to be done.

Update after new information... The solution here is fairly simple, I think. Open the drywall and install double 2x4 headers between the adjacent rafters using suitable joist hangers. Just toenailing the headers in place doesn't provide enough shear support, in my opinion. It might be ok if 4 nails can be driven from the outside face of the rafters, though. Still, hangers are dirt cheap.

Answer 2

tl;dr - you need the headers if that window is in a span of more than a few feet in any direction. That section of roof will probably never collapse, but it will definitely sag over time and create leaks around the skylight, which will lead to mold and water damage of the structure and your belongings. Call them back to finish the job properly.

Explanation
The section of roof above the cut rafters, both in view and behind the camera, no longer has end support, so it is hanging from the adjacent rafters. These now have carry roughly twice their original load. An engineer would have them go beyond headers and first install "sister" joists to the uncut ones on each side, as would be done if this was a new build (along with metal hangers at every connection).

While the deck sheeting does spread the load out enough that the severed section won't cave in, it is much weaker under vertical load than joists, and will bend differently from the rest of the roof. Over time* it will gradually warp out of plane without the missing joist support, especially with the heavy snow load and seasonal temperature swings in Toronto. The differential flex and/or sag will eventually breach the waterproofing around the skylight, and if the got bad enough, the displacement could impede the window's operation or even crack it if the frame was sufficiently squeezed or twisted. Perhaps under a record snowfall while you're away on vacation.

*months to years to decades, depending on the sheeting, surrounding framing and spans which we can't see, etc.