attic truss design
attic truss design
(OP)
I'm in the process of having a home built and the roof system has created some debate. The plans call for a traditional rafter and floor joist systems by request to create an open space in the attic for storage and potential future living space. The builder has been pressing hard to go with an attic truss. I asked around and read online and agree this seems to be the best way to go weighing costs and time to get the house weather tight. The house is a simple rectangle (30'x40' outside dimensions) with a designed 5.25/12 pitch gable roof. I've realized after the fact the pitch is far to shallow to achieve the center room desired height of between 6'6" and 7'. What I have read online thusfar seems to point to a 9/12 pitch being typical for attic trusses. I fully intend (since its required by the BI) to have the system engineered and certified, but my questions are: given the outside dimensions of the house (plus a 12" overhang if its important to know), what should be the minimum pitch of the roof to achieve the 6'6" to 7' center room height? and what is the interior width of the space?





RE: attic truss design
Garth Dreger PE
AZ Phoenix area
RE: attic truss design
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: attic truss design
If you want to create storage area, a scissor truss will not help.
Assuming your truss will span the short distance, you will need a pitch of 5.5/12 to 6/12 to achieve the height you want at the ridge.
RE: attic truss design
Garth Dreger PE
AZ Phoenix area
RE: attic truss design
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: attic truss design
RE: attic truss design
At least ask. BTW - this type of construction has been used for well over 20 years and is most cost effective and gives good value.
RE: attic truss design
The information has proven very informative and useful. The exterior wall construction of the house is ICF and there is a centerline bearing wall that carries down to steel girders in the basement.
A raised heel had been discussed, but in coordination with an open floor truss. The builder's idea is to lay two more courses of ICF (32" of increased height) and construct a knee-wall to the floor framing to tie everything together. The way I understand it from the posts, a typical attic truss with a raised heel can be engineered to achieve what is desired without having to frame a traditional floor (i-joist or dimensional), thus reducing cost due to more concrete and floor framing.
I appreciate the feedback and advisements; I think I can speak a lot more intelligently about what it is we want and possible methods to achieve it.
RE: attic truss design
Jim Houlette PE
Web: www.evstudio.us
Online Magazine: www.evstudio.info
RE: attic truss design
RE: attic truss design
Also, we often see or design attic trusses with a 2x6 top cord and then add an packer along the cord for the depth needed to hold the insulation as was mentioned above.
RE: attic truss design