Extension on existing porch

[bill1952]

I plan to add an extension onto an existing wrap-around porch. It's roofed, and about 6'-8" deep, ledger on house, 6x6 pt posts to support deck, also approx 6'-8" on center, each with a 6" x 6" (5 1/4" actual) wood turned porch post roughly aligned with 6x6 pt. Extension is planned two bays -13'-4" - wide and 6'-8" deep. Porch was built in 1994 and the county has not saved the plans or there was a fire or something. I tried hard.

So the question is would you allow the extension - or half the dead and live loads of the extension - to be supported by the existing 6x6 pt posts and porch posts? I could support the deck separately but no nice way to support the additional roof load. I'm confident in porch posts, it's really the footings - if any - under the 6x6 pt.

And what's worst that could happen? Sinks a little? It's only about 36" above grade.

 

[TheCommish]

What is the capacity of the beam at the existing roof between the posts and if it has sufficient bearing capacity through the posts to appropriate footing in the ground.

What's the worst that could happen the porch could be overloaded the porch roof could be insufficient to support the snow load and it falls down and hurts someone.

 

[bill1952]

The beam between existing posts does not see increased load. Perpendicular to ridge on extension. But the posts see half the new room load based on the headers framing into them. And I will check posts - a ubiquitous porch post I can find data on.

In 5 years never seen anyone on porch in winter. And it's on windward side and rarely has any accumulation. While 60 PSF may make sense for most of county, we are so close to end of Lake Erie that we just don't see much accumulation. I know that is not permitted by code. It's really only the footing I consider as possibly undersized for extension, but it is all granular medium sand with very little silt.

 

[wwhitney]

As a novice at this sort of situation, I would have thought that the procedure would be to dig up enough soil around one or more of the footings to determine the as-built dimensions.

Cheers, Wayne

 

[bill1952]

Have thought about that. I worry that I'd find it's not deep enough and there are 11 of them.

Formulating a plan to dig and sister a second 6x6 to them. Worry about damage I could do. I'm just guessing but suspect just gravel at bottom.

 

[wwhitney]

Have thought about that. I worry that I'd find it's not deep enough and there are 11 of them.

Well, if that's the existing condition, it would need fixing, wouldn't it? At least for any of the footings to which you plan to add load.

I'm just guessing but suspect just gravel at bottom.

Is there not a provision for designing a gravel only footer?

Cheers, Wayne

 

[bill1952]

Well, if that's the existing condition, it would need fixing, wouldn't it? At least for any of the footings to which you plan to add load.

Is there not a provision for designing a gravel only footer?

Cheers, Wayne

Probably but how far can that go? Does 6" of gravel under a 6x6 constitute an 18" footing?

 

[wwhitney]

Probably but how far can that go? Does 6" of gravel under a 6x6 constitute an 18" footing?

Maybe? IRC Figure R403.1(2) and (3) have a detail for a strip footing, not sure if it can be adapted to an isolated footing for a post without engineering.

Cheers, Wayne

 

[bill1952]

Maybe? IRC Figure R403.1(2) and (3) have a detail for a strip footing, not sure if it can be adapted to an isolated footing for a post without engineering.

Cheers, Wayne

Worse one I need under 3000 pounds or 1 sf or less so probably fine with gravel.

Thanks to all that posted!