Roof Support Birdsmouth

Large 8 x 8 posts are necessary for the use of supporting a porch roof.

Roof support birdsmouth.

With the ripped strip installation there would be no horizontal bearing surface to resist that force. A bird s mouth cut lets a rafter sit squarely down on the top of the wall rather than resting against it at an angle. The actual indentation or cut is known as the birdsmouth while the birdsmouth plumb is the depth of the cut out. This is usually the edge of the mauerlat on the external side of the wall.

A lot of force is transferred down the length of the rafter and the seat cut on the birdsmouth transfers that force directly to the top plate. One important point to note in terms of roof construction and this type of joint is that the birdsmouth is only used when constructing a traditional cut roof it is not to be used in the installation of roof trusses due to the fact that they are pre fabricated to engineers specifications and any cuts could serious affect their. A rafter tie can help to keep the joists from pushing out and down against the wall. Here the birdsmouth plumb is 76 37 inches.

If you re framing a gable roof on a new house or building a shed or even a doghouse with a gable roof you ll need to cut a number of roof rafters. For the rafter to fit correctly you need to cut the bird s mouth exactly where the rafter will meet the wall. Roof overhang the distance from the edge of the wall to the edge of the roof. If the wall framing is 2x6 that birdsmouth horizontal dimension will be 5 5 inches.

The roof height is the distance from the level of the floor of the attic to the roof ridge. Roof width distance between the points of support of the rafters. Your subfascia spec in your roof defaults guide chief to making the rafter cuts outside the wall line. There are other ways to support the weight of the roof aside from these joint cuts.

Before you cut your boards you ll need to measure the width of your building and calculate the exact length of each rafter. The roof rafters provide integral structural support to the roof. I typically gang cut my rafters and 90 percent of the time i set the saw to 3 inches to make the seat cut for both 2x10 and 2x12 rafters. While many like to use the smaller 4 x 4 posts they can tend.

Birdsmouth plumb if you study the diagram carefully you will see that there is an indentation in the roof rafter where it meets the exterior wall of the building. For larger porches such as wrap around porches you will want to make sure that the support is more than you need. Of course this all depends on how big your roof is going to be. If they spec a roof frame of 2x10s the roof plane is positioned so the 2x10 framing members get a full seat bearing on your wall framing.

Birdsmouth joint notched onto wallplate showing seat and heel cuts. The larger the roof is the more support that you are going to need.