Rafters

RAFTERS FOR SINGLE PLANE, SLOPED ROOFS:

Skillion -- Roof Scribing Rafters (This video presents a simple procedure for creating the bird's mouths on your rafters.)

Birds Mouth and Perlins Cutting the Roof; Chicken Coop Build Part 4 (This video also walks you through the creation of rafters on a shed-like structure).

Birdsmouths

NOTE this is how we did birdsmouths for the house with the tall wall and short wall flipped sides. For the house you're working on it might be helpful to find a small scrap piece of wood to help visualize where and how the birdsmouths angles should be cut. This might be the hardest part of building the tiny home so take all the time necessary to make them well. Make sure the birdsmouths are smooth enough so the rafters rest on the walls without shaking.

A birdsmouth is a notch cut in a rafter so that the angled rafter has an edge that will lay flat (and thus securely) upon the top plate of the wall. Because the angle for this shelter is not severe, the notch is hard to see in the picture, but it is there.

First understand which way you want the angle to go. For our house the tall wall was on the left so if we were looking at it, the rafters should have a right triangle cut out of it with the piece that is touching the top plate to the left of the line cut into the rafter parallel to the studs. This is called a birdsmouth.

Begin by laying an UNCUT rafter up on the walls. Ensure the rafter overhangs the wall enough on both ends. Next, use a level or some other straightedge to mark where the uncut rafter hits each wall.

Now it's time to find the angle of the line parallel to the studs to mark the rafter. Use a sliding T bevel to draw new lines "uphill on the rafter at both original lines. Usually the sliding T-bevel will be adjusted at the correct angle while the uncut rafter is resting between the walls.

Now a right triangle can be used to mark the birdsmouth to be cut out. Blue tape has been added to the triangle so that a mark can be placed on the tape that is 3.5" away from the right edge of the triangle in the picture. The 3.5" corresponds to the wall thickness. This is how the birdsmouth needs to be to rest flat on top of each wall. In a real house, this would be a larger number -- likely 5.5".

With this mark, slide the right edge of the triangle along the second angled line you placed with the slideing T-bevel. Move the triangle until the 3.5" mark on the tape resides at the bottom edge of the rafter. Hold the triangle in place, and draw a line from the mark on the tape to the angled line.

The highlighted right triangle represents the material to be removed for the birdsmouth. Usually a jigsaw will be used to cut this triangular piece out of the rafter.

DO NOT CUT THE RAFTERS TO SIZE BEFORE CUTTING THE BIRDSMOUTHS. The rafter tails will be cut to a uniform length AFTER the rafters are installed. It is much easier to get all of the rafter ends to line-up by cutting them all later. It is especially difficult to line them up as you go when multiple people and periods are involved in rafter placement.

For locating the birdsmouths, the best way probably described above -- set the rafter on the walls and mark locations. At this time, be sure to make sure the walls are parallel over their entire length. If they are not, you will either need to adjust the walls, or rafters will need to be made one at a time and birdsmouth location will vary with each rafter.

If you wish to use measurements to locate birdsmouths on a single rafter, Before marking for a birdsmouth, ensure you will have at least six inches of overhang beyond the wall. Once the rafters are installed the rafter tails will be cut to 6", so any extra leeway will make life a lot easier. Once the first birdsmouth is marked and cut, measure and mark the distance between the two birdsmouths either using a tap measure between the top plates, the Pythagorean theorem, or by putting the rafter up and marking the location with a pencil. This only has to be done for the first rafter because all rafters should be identical. Once the other birdsmouth is cut, put the rafter up and check the fit. If the rafter fits well, use it as a template to cut the other rafters. When cutting take care to ensure the jigsaw blade doesn't bend or get too hot.

Installing Rafters (Toe nailing technique)

Once the birdsmouths are cut, the rafters can get installed onto the walls. First lay the rafter in the correct spot (ideally, rafters should be placed right above each wall stud). Next, screw a 3" screw part-way into the top plate that is touching the rafter. This screw is meant to prevent the rafter from sliding when you screw into the rafter from the other side.

Once a screw is in place on one side, install a screw in the other side of the rafter at an angle. First screw parallel with the top plates and then remove the screw. Then, using the hole created in the previous step, orient the screw at an angle so that it secures the rafter to the top plate. This method is called toenailing and should allow the screw to be installed at an angle without sliding down.

Next, remove the first screw that was installed to keep the rafter in its proper location and use it to toenail in on the other side. You don't need a large angle since the screw can go through both top plates.

Hurricane Ties

Use the palm nailer and the Teco (short) nails to install the hurricane ties.

There are two types of hurricane ties. One is stamped H3-R and the other is H3-L. Make sure the front, rear, and double rafters each have their necessary-sided hurricane tie. Then lay out the rest.

We put the hangers on the outside because we already put plywood on the inside. One problem with hurricane ties on the outside however is that they will interfere with the installation of soffit blocking needed between the rafters. To avoid this, place the hurricane ties (one on each end of each rafter, so two per rafter) between the rafters and the interior side of the framed wall. The wall sheathing can be installed over the ties.

Ideally, the hangers would get four nails on the rafter and then two on each top plate but your main priority should have no extra metal where the hardiboard or plywood is going to go. This will entail putting the hurricane ties fairly high up so no metal gets in the way later on.

Cutting Rafter Tails

Rafter tails are the pieces of the rafters that hang outside the top plates. Ideally the horizontal distance should be 6" from the exterior edge of the top plate to the end of the rafter. It doesn't matter if the distance is shorter as long as its uniform. First measure the distance on every rafter tail to find the shortest rafter tail. If the shortest is still greater then 6" then mark all of the rafter tails at 6". If less then 6" then mark at that distance. Use a tape measure, pencil, and speed square to mark 6" from the top plate on the bottom of every rafter. There is also a technique of finding the shortest rafter and then marking that distance at the ends. Then put in a screw and tie a tight string across all the rafters, this way the length of the rafters is more likely to be equal. Then use a sliding T bevel to draw a line on every rafter tail that is parallel to the walls (so vertical). Then use the circular saw or jig saw to cut on that line.

Notice how the rafter on the left side of the shelter are uneven. It is better to cut them after they are installed to ensure they are even.

The rafter with the shortest overhang is identified and marked.

A string is used to ensure all rafter cuts are inline. There are a number of ways to attach a string to the rafters temporarily. A second method would be to simply screw in a screw at the location and tie one end of the string to a screw.

The final product should look something like this, even and ready for facia

Lookouts

At the rear of the shelter, the roof extends 24" beyond the rear wall to help protect the heat pump to be installed in the wall from the weather. To help support the portion of a roof that extends out beyond the rear wall, "lookouts" are used. In this case, 4x4 material was used for our two lookouts, but in general 2x4" material is often used. The process involves cutting the lookout so that one end is nailed to one rafter in from the rear wall, it passes through notches that are cut in the rafter over the rear wall, and terminates the distance away from the rear wall so that a "fly" rafter (a rafter that is not supported by walls) can be installed and supported by the lookouts.

Measure the cross section of the 4x4 to determine the exact dimensions to cut out of the rafter above the rear wall. Mark the square that is to be cut out on the rafter. Lookout location along the rear rafter should be placed as uniformly as possible. The exact location is not crucial. In this case, the rafter was divided into thirds.

Cut the notches out of the rear wall rafter using a jigsaw for the rough dimension and the multitool to clean up the cut. Measure the distance between the last and second to last rafter and add that to the dimesnions the 4x4 hangs out as specified in the drawing to find the length of the 4x4 lookout. Us the chop saw to cut each lookout to size.

Install each lookout using 3" star bit screws. 4 screws go through the second to last rafter and into the 4x4. Then 2 screws on each side go through the rafter above the rear wall into the 4x4 at an angle.

Facia

Facia is the equivalent of capping off the rafters. Be careful, this will be seen as part of the finished product. Also, DOUBLE CHECK THE ANGLE OF THE RAFTER PLEASE.

THE ROUGH SIDE OF THE FACIA IS WHAT SHOULD BE SHOWING. Nail into the rafters. It will take two people to nail in the facia. It is helpful to start at one side, make sure it is exact and flush with the top of the rafter. Then as you move across the wall the other person can adjust their end to make sure the facia is flush, the board is flexible enough for this (within reason).

Generally the front and rear pieces of facia get installed first (and they will have angles cut on each end -- take care, double measure, and hold the fascia up to the shelter before making any cuts. We have miscut these in the past.

Once the front and rear pieces of facia are installed, the side pieces can be cut and installed by installing three nails through the facia board into each rafter (and fascia) tail.

Report abuse