Following the pattern on the plans, cut one identical pair of rafters, and no more. Although they might fit just right on your cabin, it always pays to double-check before you make all the rafters you need. In fact, checking is essential.
The top ends of each rafter are best cut with a miter saw set to 45º. You could do this work with a hand-held circular saw or handsaw, but the results won’t be as accurate. The plans show an angled pocket near the bottom of each rafter where it rests on the cabin wall. This is called a birdsmouth. You can cut it with a hand-held circular saw, but because of the round shape of the blade, the two cuts required to complete each birdsmouth won’t quite meet in the corner. That’s fine and easily dealt with. Finish up these cuts with a handsaw to free the triangle of wood involved.Just remember, you’re only cutting two rafters at this stage. Before you do anything else, watch the next video.
VIDEO: Testing Rafters
To test the fit of the all-important first pair of rafters, tack a short scrap of 1 1/2”-thick construction lumber to the top end of one rafter, to simulate the thickness of the ridge board that will separate the top ends of the rafters on the completed roof later. Next, get some help temporarily hoisting the rafters up and leaning them against each other. No nails required. What you’re looking for is a gap-free fit where rafters meet the top of the walls, and where they come together at the simulated ridge board that sits between the rafters at their top ends. While you’re looking for gaps, be sure to test the location of the rafter pairs at various places across the building. If they fit in one place and not another, that’s a sign that the width of your cabin isn’t consistent after all. There’s not much you can do about it at this stage, and this is why it’s so important to get your cabin width consistent. If variation in cabin width at different places turns up now, the only thing you can do is make rafters of different widths to suit. It’s not ideal, but there’s no practical option.
Move Forward By Going Back
Nobody builds perfectly, but it’s how you deal with the inevitable errors that makes most of the difference. The natural tendency is to forge ahead even when errors show up, making whatever adjustments are needed in subsequent parts to make up for previous mistakes. And while this may be natural (and occasionally unavoidable), it’s not the way to build well. When you do find that something isn’t fitting together like it should, stop right there and find out what the real root of the problem is. It may help you to avoid getting upset if you realize that mistakes are made by builders all the time – even experienced builders. Only after going back and fixing the root issue should you move forward again. This moving-forward-by-going-back approach takes more patience, but it’s the way all good builders work. And of all the places in your cabin adventure you’re most likely to encounter problems of things not fitting properly, it’s testing the first two rafters you build. In cases like these (and others) moving backwards, finding the real reason why things don’t fit, then moving forward after it’s fixed is the single most important building skill you can cultivate.
Making All Your Rafters
When you’re satisfied with your pair of test rafter, and have adjusted their size or recut them if necessary to a gap-free fit, make the entire batch of 36 rafters you’ll need. Trace the top end and birdsmouth pocket of one of your test rafters over and over to maintain consistency as you work (rather than tracing second- and third-generation rafters). Don’t mark or cut the bottom ends of any rafters to length yet. Leave this operation until after rafter installation. I’ll explain why later.
Finish your rafter prep by drilling one 1/4” diameter hole through the top edge of the rafter, down into the birdsmouth pocket, as shown in the plans. This hole is for the 8”-long spike you’ll use to secure the bottom ends of the rafters to the top of the cabin walls. This is far better than driving smaller nails in through the side of the rafters by hand (an operation called toenailing). With all your rafters cut and drilled, you next need to add a special feature to just twelve of the rafters.
Rafter Cutting Tips
Consistency is key when it comes to cutting rafters, and this is why it makes sense to make them using specific tools in specific ways. The best option for cutting the top ends of each rafter is a miter saw (also called a chopsaw), swiveled over to create a 45º miter cut. You’ll need to support your rafters so they’re level with the rest of the saw, and site-cut wooden supports fastened to the subfloor of your cabin are one good option. Depending on your miter saw, you can cut the top end of two or three rafters with each chop. One way to cut the birdsmouth pockets at the bottom ends is with a hand-held jigsaw. The tool design lets you cut right into the top corner of the pocket. Just be sure to use a coarse blade. Also, apply even forward pressure on the saw to prevent the blade from angling to one side or another. Jigsaws tend to cut at an angle if uneven pressure on the tool causes the blade to bend left or right.
Cutting Rafters Notches
The plans show how you need to cut 1 1/2” x 3 1/2” notches along the top edge of some rafters to accept 2×4 rafter supports. These 2x4s strengthen the outer pair of rafters on each end of the cabin – the ones that create the overhang at the roof gable beyond the walls. They also give you something to climb on as you install the outermost rafters.
The best way to cut rafter support notches accurately and quickly is by temporarily clamping all 12 rafters together with a pipe clamp, precisely lining up all their top ends, marking notch positions as a group, then cutting the notches with multiple passes from a hand-held circular saw in the waste area, all at once. Make cuts defining the edges of the notches, then additional cuts n between every 1/4”. This approach makes it easy to knock out the slivers of remaining wood with a hammer and chisel. Besides superior speed, cutting in a group like this ensures that all notches are in the same line. Just be sure all rafters are aligned square with each other at their top end before sawing. Mark and cut the notches about 1/8” wider than needed to accommodate your 2x4s with a little bit of leeway. The next step involves marking the ridge board, and be sure to watch the video before you read about the process.
Marking the Ridge Board
The ridge board is the 2×10 that runs along the peak of the roof, providing a common point for the rafters to fasten to. Total length of the cabin’s ridge is 27’ 8” (25’ for the total length of the building and porch, plus a total of 2’ 8” of overhang). This means that the ridge board will have to be made in two lengths of 2x10s to make the one ridge. Although you can buy long lumber, standard lengths top out at 16 feet. Choose two straight, dry, well-behaved 16-foot long boards for ridge duty now. This is longer than they need to be, but there’s a reason for this. Lay the ridge boards down on top of the loft beams, end-to-end, and use the beam positions to mark the location of the rafters on the ridge boards. Remember, the plans show how each rafter flanks the side of a loft beam. You’ll find it easiest to mark the ridge boards accurately if you temporarily fasten the ends of them together with scrap wood and screws. You’ll also need to orient the joint between the ridge boards so it’s straddled by a pair of rafters. This is where the extra rafter length comes in. It allows you to move the ridge board pair one way or the other until the joint lands right in the middle of a rafter thickness. The loft beams will only act as a rafter location guide for part of the cabin. You’ll need to continue marking the ridge board by measurement only when you get out to that part of the cabin that has no loft beams. That’s the interior section that’s open from floor to roof at the door end of the structure, beyond the loft.
VIDEO: Marking the Roof Ridge Board
When it comes time to raise the rafters and ridge boards, do it one half of the roof at a time. Raise one pair of rafters that meet at the peak over one wall at the end of the cabin, and another pair of rafters in the middle, where one piece of the ridge board ends. Repeat the process for the other half of the roof and its ridge board, with another pair of rafters over the other wall to support it. You’ll find that the two-part process goes best with two and preferably three people on hand for the work. Are you concerned about the strength of two ridge boards instead of one? There’s no need to worry. The roof sheathing that comes after the rafters go up will join these two halves quite solidly.