rafter help

[forgeblast]

Nice day have most of my coop done and am ready to make the rafters for the roof......am having a brain freeze on how to do it.

i have the ridge/rafter board running down the middle of the coop, it is 12'' off the top of the walls, since it is in the middle it is 2' to the end of the rafter. I want to have about 1' over hang. the basic lenght of the board i want to use is 4' will make putting plywood on easier since the roof will then be 4'x8' on each side.

how the heck to i cut the birds mouth, how do i figure out where to start the birds mouth cut and what angle is the first cut that will be nailed to the ridge board.
any help quick is appreciated.

 

[smstonypoint]

Here's a source that will answer your questions.

Basic Roof Framing Techniques

 

[forgeblast]

Thanks, I ended up finding a template that was close and then i just cut and fit until it worked. Once i had one cut it was pretty easy to use the circular saw and clean up with my recip saw. thanks again.

 

[MikeD74T]

forgeblast, Having succeeded at this task you'll likely build again. The tool you should master is a framing square. It will perform almost any trigonometry function, which is what building is all about. New squares, i.e. from Stanley or Swanson, come with instructions for rafters, stairs, layout of pentagons, hexagons, etc. I looked at both websites & didn't find the instructions available but didn't ask them directly. Also do a web search for 'framing square instructions" if you already own a good square. Learning how to read a framing square eliminates the need for trial & error and is generally more accurate than using a pattern. MikeD74T

 

[smstonypoint]

The Swanson Speed Squares come packaged with "The Little Blue Book," a treasure trove of information for laying out rafters, stairs, etc.

 

[/pine]

Beware of cheap framing squares... cheap squares do not have the rafter tables that are paramount to "sticking" a roof...

Small triangle squares are handy and easy to use but they do not offer the accuracy of a standard framing square...

"speed squares" rely on a pivot point to mark angles...if the pivot point does not fall on a perfect spot on the material it can vastly throw off the angle...
This is especially evident when making seat,bottom or heel cuts

Ideally... you cut a pair of rafters and dry fit them...if they are right choose one with a bit of crown and use it (as a pattern) to mark all the other rafters... you always want to choose a board with "some" crown for the pattern because most of the other boards will have some crown...if you use a straight board as a pattern it makes it hard to mark boards with soem crown...

 

[2manyrocks]

The traditional L shaped carpenter's square has gone out of favor because it's so easily bent and because people don't understand how to use its features to compute rafter related problems. There was an article in Fine Homebuilding at one point that tried to describe how to really use it for the modern crowd. Today, people will refer to rafter tables, use a calculator or whatever, when the older guys probably just used their L carpenter's square to figure out all their rafter computations.

 

[forgeblast]

I have a small speed square, and a framing square. My problem was that since it was such a small run of rafter lenght that any examples that i saw threw me off.
But all is good now, i have the rafters in sheeting on and tarpaper on. I am working on the batton sides, nest boxes, and doors. should be done in a week or two depending on the weather.