The first step towards making accurate rafters is to take a look at the 3D plan to see what you’re shooting for. Turn your attention to the bottom right hand corner of the page, to the side view of the rafters you’ll need to make later. You’ll require 36 rafters in all, including 32 that span the cabin structure itself, and two more pairs that extend out past the walls to create the overhang past the porch and the back wall. Each rafter is made from a 14-foot long 2×6.
VIDEO: Cutting Rafters
Before you cut any rafters, mark rafter locations on the top edge of the side walls, beginning at the rear wall. The outside face of the first pair of rafters sits flush with the outside face of the rear wall studs. The next pair of rafters sits 5” in from this first pair, followed by 22 1/2” between the rest of the rafters until you get to the front wall. The last pair of rafters to sit on the front wall have the same arrangement as the pair that flank the rear wall. This means that the outer-most rafter pair is flush with the outer face of the wall frame, and the next pair 5” in from that. There’s crucial detail here to, so be sure to watch the next video before going on. It’s important.
VIDEO: Rafter Location Details
Now it’s time to mark rafter locations on the top of the walls. Use the same line-and-X marking scheme you did to lay out the location of top and bottom wall plates earlier, but be careful. Check and double-check that corresponding rafter marks are in the same location relative to each other on the two side walls. Each facing pair of rafters must align with each other or your rafters will go up at an angle. Also, while you’re at it, mark the location of the 6×8 loft beams you’ll be installing later. As you can see on the 3D plans, the loft beams always flank one pair of rafters. Mark the location of loft beams now, so you don’t forget which side of the line they go on. One side of the line is the rafter and the other side is the beam. Pay particular attention to how the last loft beam sits on the opposite side of the rafters, compared with all the others.
Tweaking Cabin Width
Next, measure the actual width of your building across the top of the side walls. It should measure 1 1/4” to 1 1/2” more than 16’, depending on the thickness of exterior sheathing you applied to the outside of the wall frames. Chances are good that your cabin width across the front and back walls will match this measurement, but maybe not across the middle. Bowed walls could easily add or take away an inch from overall building width, but that’s no problem. Take one or two spare planks, rest them across the top of the building and drive a deck screw to secure one end of each plank in place. Get some help wrestling the walls inwards or outwards (whichever is required to get a consistent building width), then spike the second end of your brace planks down. These planks will come off later, after the loft beams and rafters are added. That’s why it’s better to use screws than nails for securing them. These brace planks are only installed temporarily to make the building a consistent width while the rest of the structure takes shape. Also, make sure these temporary braces are well away from the rafter and beam locations you marked earlier. You don’t want them to get in the way of installing the rafters or beams as they go on next.