Rafters and Blocking

I'm starting to get a sense of space inside my tiny house, thanks to the latest big addition: rafters!

Remember when I said I was going to use Western red cedar for my rafters, since it's so much lighter than Douglas fir? Since I'm using 2x8s for added insulation space, weight is more of an issue than strength, and my online sources indicated that cedar is "moderately priced" and only 2/3 the density of Douglas fir. Good plan, huh?

Cut to: the lumberyard. I'm standing next to the Western red cedar dimensional lumber with my dad and the guy who is helping us. I explain what I'm looking for and why, and ask how the price compares. 


Guy: "Price check, Douglas fir 2x8, ten foot, versus cedar 2x8, ten foot."
Guy's walkie-talkie: "Looking at a $20 difference. Douglas fir, $8.10 per board, cedar $28."
Guy: "C-c-c-c-c-c-copy!"

 So, Douglas fir it is, then. And next time someone tells me a price is "moderate," I'll ask them: compared to what? Teak? Ebony...? 

Anyway.

Hurricane ties installed 24" on center to receive the rafters

In theory, installing the rafters ought to be easy. Cut the notches, called birdsmouths, to allow them to sit flush against the tops of the walls. Cut them to length so the overhang is right. Attach them to the walls using a metal bracket called a hurricane tie (or clip) and nails. Finally, add blocking in between to keep them steady and hold in the insulation.

I used an online birdsmouth calculator to find out the angles and measurements for all the cuts needed. I was also reminded that another name for my shed roof style is skillion roof. Ha! That's a much easier term to Google when I need to look up details, since the results won't come back with a bunch of roofs on actual sheds.

Of course, nothing is ever as easy as it's supposed to be, especially if you've never done it before. Hell, Dad has installed rafters on at least two occasions before this and it was still a bear!

The first problem we encountered is that somehow, somehow, the walls of the house are not 8' apart all along the length of the house. In fact, they are closer to 8' 1/4" and as much as 8' 1/2" apart. Yay, extra quarter to half inch of interior space; boo uneven measurements!

Which meant that when we cut the birdsmouths, sometimes we had to make the cuts closer together or farther apart than the last one. Which meant that we couldn't just bang out a bunch of copies of the one model rafter that we cut initially. We had to take some care to customize each one.

You're supposed to be able to just copy the measurements for all the rafters...

It also meant that if we make all the rafters the same length, the overhang length will vary a little across the length of the house. If we try to make the overhang length equal everywhere, some rafters will need to be shorter than others. We weren't sure what to do, so we installed the rafters and left the lower tails long on most of them, to cut later.

When we measured the diagonals, to see where to cut the rafters to make the roof square, we discovered that... oh geez... that measurement didn't match up to anything else we were expecting, either.

We did know that the end rafters were parallel to each other, however. We decided to make the rafters all the same length, and worry about getting the plywood sheathing square when we get to that step.

I just have to keep telling myself, every house that has ever been built is full of little imperfections and inconsistencies and fudges, and it almost always turns out okay!

We are now about 70% done with installing the blocking between the rafters. Theoretically, there should be exactly 22.5" between each rafter, since they're 1.5" thick and spaced 24" on center. However, those hurricane ties and the nails used to affix them take up space, so each piece of blocking needs to be 22 3/8" or 22 1/4" or so to actually fit. Got to adapt.

The next steps are to prepare the trim pieces--the fascia and verge rafters--and install the outriggers, that is, the pieces that stick out over the end of the gable walls to create the roof overhang there. (I've decided to have a 12" overhang on both ends of the house rather than the lopsided 24" overhang off the back.) I ordered 1x cedar for the trim and intend to give it the shou sugi ban (AKA yakisugi) charred treatment. Update on that when it happens!