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# Calculating rafter length

## Calculating rafter length

#1
04-23-08, 05:10 AM
Member
Join Date: Sep 2005
Location: USA
Posts: 125
Calculating rafter length

I am building a 12' X 16' storage shed (still in the planning stage) and have done all my calculations for rafter length, plumb cuts, etc. based on the framed size of 12' X 16'. Then I realized that I didn't take into acount the thickness of the siding (5/8" T-111) when determining the total span. Should I re-calculated rafter length and plumb cut at the "bids mouth" taking into account the 5/8" siding? This will make the total span 12' 1 1/4" (12 feet plus 5/8" on each side). Or should I shorten the building platform by 1 1/4" so that the finished span will be the 12' I initially calculated for?

What is the normal practice among builders?

I appreciate any input on this!
Thank You!

#2
04-23-08, 04:53 PM
Member
Join Date: Feb 2006
Location: USA
Posts: 6,413
Rafters

I would simply cut the bird's mouth 5/8 in. longer if the siding will go all the way to the top of the top plate.

You did not tell us the roof pitch or the amount of overhang. Making efficient use of materials can sometimes come into play in such decisions. A low roof pitch may mean you could stop the siding at the bottom edge of the rafters. If so, no need to lengthen the bird's mouth.

Be sure to let the siding cover a portion of the rim joist to prevent water from getting under the wall.

#3
04-24-08, 01:03 PM
Member
Join Date: Sep 2005
Location: USA
Posts: 125
Originally Posted by Wirepuller38
I would simply cut the bird's mouth 5/8 in. longer if the siding will go all the way to the top of the top plate.

You did not tell us the roof pitch or the amount of overhang. Making efficient use of materials can sometimes come into play in such decisions. A low roof pitch may mean you could stop the siding at the bottom edge of the rafters. If so, no need to lengthen the bird's mouth.

Be sure to let the siding cover a portion of the rim joist to prevent water from getting under the wall.

Makes perfect sense to me! The roof is a 10/12 pitch... I was planning to frame the walls and cover with T-111 before installing the rafters. I'll be using 10' 2x6 lumber for the rafters so the material is plenty long enough. As far as the overhang, I'm not sure yet. I need to figure out the optimum length so that building the soffits will not be unnecessarily difficult. Would you have any suggestions? I'm open to either plumb cut or square cut and any material.

Thanks again!