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# Notch at Bottom of Rafter

## Notch at Bottom of Rafter

#1
06-28-06, 07:49 AM
Member
Join Date: May 2004
Posts: 87
Notch at Bottom of Rafter

I apologize for not knowing all the terminology. I hope I can explain what I'm trying to accomplish anyway.

I built an 8 X 8 fort/tree house for my son. I want to put a roof on the structure. I'm not going to use a ridge beam (I think that's what it's called). Assuming this will be enough support for such a small roof I'm only going to use rafters notched at the base (to lay on top of the walls). I'll have a rise of 3 feet. If I did the calculations correctly, it's an 8-12 pitch. I'll want the rafter to stick out beyond the walls 3-4 inches. How do I determine where to cut the birds mouth on my rafters?

Last edited by WmHeffernan; 06-28-06 at 09:54 AM.
#2
06-28-06, 02:11 PM
Member
Join Date: May 2004
Posts: 87
Birds Mouth Calculator

Will this link (bottom right of page) give me what I'm trying to figure out? http://www.bradcosupply.com/lumber_math.aspx
I have no clue what I'm supposed to input to get my answer. I'm using 2 X 4 rafters. The tree house is 8' X 8'. I'm not using a ridge beam. I only want about 4" of over-hang off 2 sides of the tree house. Can someone tell me where I need to make the cut for the birds mouth?

Thanks

#3
06-28-06, 03:22 PM
Member
Join Date: Mar 2006
Location: Great Barrington MA
Posts: 496
For starters use a 2" X 6" ridge. Don't know why you want to leave that out or what method you think you can use in it's place. Instead of driving yourself crazy trying to calculate pitch etc. Hang the ridge to where it looks right (level to the walls!). Experiment with angles and your birdsmouth until you get one that looks about right. Then take that one that's right or close enough and use it as a template or pattern to trace the others with. Simple as I can think to explain it and sure, not how I would build a house but best way I can think of that doesn't take alot of complicated explanation

#4
06-28-06, 04:34 PM
Member
Join Date: Dec 2005
Posts: 61
Find the center of the sidewall of your building and draw a plumb vertical pencil line about a foot long. Cut the top plumb cut of a rafter and butt it to the line you made, then tack it to the wall. Using the side of the building as a full scale model, you can figure out total rafter length - including overhang and the birdsmouth from this using no math.

The little book that comes with a speed square has tables to figure it all out too.

Good luck

#5
06-28-06, 05:08 PM
Member
Join Date: Feb 2006
Location: USA
Posts: 6,402
Rafter for tree house

A 3 foot rise at the center of an 8 foot wall would be a 9/12 pitch.
You are creating a nice 3-4-5 right triangle. Rafter length will be 60 inches plus overhang minus 3/4" if you use a ridge beam. Cut a sample and lay it out on the garage floor. Good Luck.

#6
06-29-06, 05:36 AM
Member
Join Date: May 2004
Posts: 87
Thanks for the Information

I appreciate all the input. Should make the project easier.

#7
06-29-06, 06:57 AM
Member
Join Date: May 2004
Posts: 87
Ridge

Originally Posted by BuiLDPro68
For starters use a 2" X 6" ridge. Don't know why you want to leave that out or what method you think you can use in it's place. Instead of driving yourself crazy trying to calculate pitch etc. Hang the ridge to where it looks right (level to the walls!). Experiment with angles and your birdsmouth until you get one that looks about right. Then take that one that's right or close enough and use it as a template or pattern to trace the others with. Simple as I can think to explain it and sure, not how I would build a house but best way I can think of that doesn't take alot of complicated explanation
I built a storage barn a couple of years ago and didn't use a ridge. I don't recall why I chose not to use one then. I built trusses and secured them plumb/square to the tops of the walls and nailed my plywood down to the trusses. It seems to be solid. My barn is only 8 X 12.