About Mark Sundberg Expertise Architecture, structure, construction.
Experience 27 years licensed architect, work in 12 states. Currently working in Hawaii. Over 1000 buildings designed or worked on in a significant role
3 years quality control officer for Navy construction projects.
Education/Credentials Bachelor of Architecture, Cal Poly, San Luis Obispo, CA. 1977.
Question I'm in a double wide mobile home and i want to add on a screened in porch. i would like to install a roof system with a gable that's perpendicular to existing. the porch will be 12ft wide by 10ft. i want to use a ridge pole and rafters. my question is, can i use the existing exterior wall ( 2x6 const. ) to support / build from for the roof system. if i can't , and i need to install a support post for the roof.can these posts be set on top of an exsisting concrete pad. i believe the pad may only be 2 or 3 inches thick.the porch itself will be anchored with a ledger.or can the roof be completly supported by the porch via the ledger. i do have the room on the pad to use those "bases" like the ones used for a floating deck. i looked at these on line but couldn't find anything for them saying that they are capable of supporting a roof
Answer Hi Ron,
Assuming your ridge is running the 10' dimension with the 12' running parallel with the wall of the home, the load in the post bearing the ridge beam will be about 5x6x30 = 900#, at most. While that's not a lot, it is more than a little and I'd actually be surprised the walls of your home are 2x6. Might be if it's very new and well insulated, just they tend to be tight on area and one place they can save a bit is in the walls. People don't buy walls, they buy the space between them.
In any case, I'd not rely on that existing wall for the post supporting the ridge. I also wouldn't rely on a very thin concrete to support it as well. I'd suggest you dig out a space under the existing concrete that's 12" deep and 12" square and fill it with concrete. Then get one of those foundation blocks you describe, one for each end. An alternative that might look better would be to carefully chip out the concrete so the block fills the hole you dig below and just barely protrudes above the existing concrete slab, but make sure you lay about 2" of sand under the block and get it good and wet and wiggle that block into place and then compact dirt back around the sides well.
