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FAQ: Light Frame Construction

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A couple of questions about the structural loading of a back porch
Concerned writes:
I I am rebuilding a back porch on my house. The existing roof has a over hang and I am going to fasten a "sill plate" to the existing face board. Then I will use joist hangers to support 2 x 6 x 12' rafters. The rafters on the roof of the house are 2 x 10 s or 12 tappered from the bottom up to about 6" where the face board is that I am going to fasten the sill plate. jthe rafters on the porch are going to be on 2' centers. The rafters on the roof of the house are 16" centers. I am going to use lag bolts to fasten the sill plate. What size of bolts should I use and should I use 2 bolts for each rafter on the house, 16" centers. also I was considering fastening 2 x 6 x 12 together( 2 of them) for the header. is this enough or should I use three or 2 x 8 for the header. The up right supports will be every 10' and the porch is 60' long and 12 feet wide.

Paul Fisette answers:
I am sorry but we do not provide structural sizing advice through this service. Too many ways to go wrong without reviewing each situation carefully. You should have a competent design professional look at your application. However, something that comes to mind if I read your situation right..... If you can, why don't you remove the fascia board from the house and then sit the porch rafters right on top of the wall plate of the house. This will eliminate your need to construct a beam on the face of the rafters and you won't have to use joist hangers either. The wall will surely carry your load. Just nail the new rafters into the top plate and when the rafters fall along the side of the existing rafters, nail them together.

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A question about rafter spans.
M.W. writes:
What is the maximum rafter length that is sold. Probably a 2x8. I am designing my house where the width exceds 40'. Can the rafter be double up in order for it the span half that distance.

Paul Fisette answers:
All thing being equal doubling the rafter will double the stiffness and strength. The longest 2x8 available in my area is 16 foot long. You can get 20 footers on special order, but my recommendation is to go to engineered lumber (wood I-joists) for the longer spans.

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Concerns over metal studs and OSB over traditional framing.
L.B. writes:
I am having a house built in central Florida (Deltona,Volusia county > about thiry miles from the coast) > I would suggestions on materials to request from my builder > > 1.OSB vs plywood. What would you prefer? > 2.Metal studing for partion walls(non load bearing) is this Ok?

Dave Damery answers:
On the debate between OSB and Plywood we have an article covering this on our Features Page http://www.umass.edu/bmatwt/features.html. This should give you some info to help you decide. Personally I think you can save some money using OSB and it will perform equally with Plywood provided they have the same grade stamp rating. As far as metal studs go, my suggestion is to make sure your builder is familiar with them. They are rated to perform similar to wood studs, but could be installed quicker (with a properly trained building crew) and therefore could save you money on initial installation. They do conduct heat more readily than wood studs but since you are recommending use only on interior walls this should not be a consideration. Hope this helps, good luck.

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