Compound mitered birdhouse roofs

There are many ways to design polygonal structures but this is the path I have chosen for small bird feeders and bird houses. It relies on simple materials and a repeatable jig that makes cutting the sections very easy. You can apply the same technique to a structure of as many sides as you have patience for.

I want to show you one method to construct a polygonal raised roof for small structure like a birdhouse or bird feeder.
Generally speaking, to keep the costs down, most guys and gals I know purchase 1 x 6 or 1 x 4 cedar or spruce fence material. It's rough cut and generally varies in and around three quarters of an inch thick by 5 1/2 inches wide.
In this case, I wanted a roof with approximately a 35° pitch and a 10 inch diameter to cover a small birdhouse.
By using a small free program from the Internet called Miter calculations I was able to feed in information I didn't know and the program calculated the information I needed to set my saw angle.
http://jansson.us/jcompound.html
I decided that the slope of the roof would work fine at approximately 45°. From this information I was able to determine that I needed a solid level on my miter saw off somewhere around 15° ( 15.53) for the purists
I set the length of the slope or my roof pieces add 8 1/2 inches long and proceeded to cut equal lengths.
Using one of the pieces, I then constructed a jig using a 1/2 inch piece of OSB and some cleats to hold the roof blanks at the exact position required to cut the bevels.

From octagonal roof - birdhouse

Doing it this way requires that the saw only be set for the bevel required and does not require setting for the miter. In other words the saw blade remains at 90° and the jig is adjusted to the preferred angle
.

From octagonal roof - birdhouse

By making use of the laser guide I was quickly able to determine the exact position for the miter cut and from that also set my bevel cut.

From octagonal roof - birdhouse

From octagonal roof - birdhouse

This particular saw that I am using allows me to adjust the depth of cut so I was able to build my jig on top of the OSB and proceed to cut the blanks without cutting through the supporting OSB panel.
This picture shows one of the panels set in my jig ready to be angled and beveled

From octagonal roof - birdhouse

From octagonal roof - birdhouse

With the jig flipped 180° I'm able to duplicate the bevel on the other side as shown here.

From octagonal roof - birdhouse

Here's a picture of the panel showing both sides removed.

From octagonal roof - birdhouse

Now I just repeat the process seven more times for the octagon.
The last picture shows the eight pieces temporarily set up to check for fit and held together with blue painter's tape.

From octagonal roof - birdhouse

. When the final fitting is satisfactory I will flip the triangles over and fill their seams with waterproof glue. I have used Tite bond III for this procedure but I prefer polyurethane glues similar to Gorilla glue or Elmer's etc. because the porous cedar has a tendency to swell up in wet weather and when it freezes here, it will expand and pop the joints. I have pin nailed them on occasion with varying success.