Porch Posts must be over pier?

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Old 06-17-16, 07:57 PM
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Porch Posts must be over pier?

Long time lurker, first time poster.

I'm building a 3 season porch (10 x 16) on the back of my house. Planning on using a beam with the joists cantilevering 18" built on 12" wide piers 4' below grade (I live in NH). My concern is if I need to have the roof supports directly over the piers, or the beam or the edge of the deck would be fine.

Thanks for any information.
perogi.
 
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Old 06-18-16, 05:04 AM
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Welcome to the forums! Cantilevering a deck is one thing. No vertical weight to speak of. Add a roof to the edge, then you open up another can of worms. The roof support should continue to footing. I would consult with an engineer to see if your choice of wood size and type would support the roof on cantilever.
 
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Old 06-18-16, 07:55 AM
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Thank you Chandler. That's what I figured - I will give an engineer a shout.

Looks like I might be losing a 2 feet or so of porch space or digging new holes :/

Got to love NH rocks!
 
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Old 06-18-16, 08:05 AM
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The type of roof will have a lot to do with whether it's okay or not. A gable roof would likely be ok if the gable was over the cantilever in front, because "most" of that weight would be on the sides of the structure that are not cantilevered, and the outside joists would likely be doubled or even tripled to handle that extra weight.

A hip or shed roof that has rafters bearing on the cantilevered portion would add extra weight and snow load potential, putting extra stress on the cantilever. Based on the size of your room, that might be ok or it might not. As Larry mentioned, you would need to have an engineer run the numbers to know for sure. Not something we can do here.

There are lots of houses that are built in the cantilevered style, so I don't think it is outside the realm of possibility. The size of the joists would just need to be sized accordingly... that's what an engineer would be able to tell you. Personally, I would probably just use 2x12's and go for it. ;-) If that front wall will have headers, they will be creating point loads, so you might need to engineer some additional support into the joists... such as tripling any joists that will have headers bearing near them.
 
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Old 06-18-16, 10:26 AM
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Thank you XSleeper. Good point about homes built with cantilevers - I tend to over engineer everything I build so I was already thinking 2x12 joists over an engineered beam.

There's a lumberyard near me that has engineers who are free if you purchase the lumber from them - I will give them a call.
 
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Old 07-15-16, 06:33 PM
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To wrap up this thread, I contacted the engineers at Brock's and he went punched up some numbers and gave me the correct sizes for the joists, beam and header/beam. Thanks for giving me the idea that it was possible.

For those who are interested, he calculated a triple LVL 11 7/8" x 1 3/4 for the header/beam, 3 - 2x10s for the beam and 4 - 2x10s for the unsupported side. 6x6 posts.
 
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Old 07-15-16, 08:40 PM
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Sounds about right. Thanks for posting back.
 
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