My single story rancher has a gable roof over the living room oriented perpendicular to the main roof. It has a 5 in 12 pitch, stick-framed with 6X8 doug fir rafters, 4′ on center, spanning 20′ with no collar ties. I’d like to extend this roof about 8′ to cover the entry on the front of the house. I plan to use 6X6 posts (or 8X8) to support 6X8 beams (or bigger) from the house wall to carry the weight of the new 6X8 rafters, still 4′ on center, plus a 2′ rake and 2X6 fly rafters. First question, are 6X8s big enough to carry the new roof load? Second question, since there are no collar ties, I want to use a beam between the posts to tie the frame together (keep the posts from spreading). Since the span is 20 ‘, is a 6X8 beam big enough, or should I increase to 6X10 or 6X12? I don’t want the beam to sag and I’d match the beams from the house to the posts the same size. Obviously, I want the frame to be structurally sound. We’re low elevation (500’, northern California), so average snowfall maybe once a year and doesn’t stick. Also, I like the timber frame look, so don’t mind a bit of over-building. I’d consider “timber framed trusses” instead of the beam between the posts, or maybe a steel colar tie between the end set of 6X8 rafters. What do you think?
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Replies
>> I'd like to extend this roof about 8' to cover the entry on the front of the house. <<
Sorry, I'm having a littel trouble following you. Is the extention going on the gable end or on the horozontal eve side of this living room roof?
Yeah Matt, the situation is easy to describe in person, but not so clear when writing it. The extension would be to the gable end, just a continuation of the roof.
Consider this post just a bump - which basically just puts you to the top of the current topic list.
So, you want to add a 20' wide x 8' deep porch to the front of your house by simply extending the existing gable end.
Basically this is post and beam type construction. The idea is to use 6x8 rafters that will span the 10' on either side of the ridge board and will be installed 48" O.C. 6x8-20' ceiling joists will tie the rafter pairs together. The proposed size of the porch headers are 6x8s which will span 8' on the 2 load bearing ends of the porch. The porch posts are to be 6x6s and there will be (how many of them?).
Here is the problem. We can't see your project from here and it would be irresponsible for us to give you specific lumber sizing recommendations. There are not that many post and beamers around here at BT, most of us build with dimensional lumber - 2x?s, although I'm sure there are people here with far more experience than I in this area. Further, being that you are in Calif, I assume you are working with Douglas fir - which we don't use here in the SE USA.
So, I'm not gonna answer your Qs, although I have some pretty good ideas of what would and would not work. None the less, start by looking at some span tables, like, this one that would probably cover your rafters. Maybe you can Google some more to cover your headers and ceiling joists, or likely this info is all contained in a code book for your area/state.
Thanks Matt. This is the first span table I've seen with lumber greater than 2X. I'll look again for more tables. This is my first time in the forum and you've helped a lot. Thanks again.