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Sunroom Foundation Options

woodconcepts | Posted in Construction Techniques on March 26, 2009 11:33am

Hi all! I hope you can help me.

I tore a deck off my house because it was built so shoddy (the posts only went into the ground 16 inches) I was going to just rebuild the deck but I decided now that I would like to build a sunroom instead.

The house sort of makes an “L” shape around the proposed area and I can see just extending one roof over the deck with a beam and some rafters, then bringing the other roof over to it with some framing to make a valley.

The only thing I don’t know what to do with is the foundation.

Can I just put posts down 4foot like building a deck?
Should I dig bigger holes, like 12″ diameter, and pour concrete posts?
Should I pour concrete posts then make a “grade beam” to sit the floor on?
Should I dig a trench 8inches wide and 4foot deep and pour concrete?
Or do I need to excavate the whole area and make a proper footing and block foundation wall?

I live in south east michigan where the ground is all clay and digging is a real pain, so if I can avoid digging then I am happier. Digging posts holes is easy because my neighboor has a tractor with an auger…but no backhoe:(
I don’t have very much money to devote to this project, But figured that I could stretch it out over a long enough period to make it economical to me. i.e. just build the deck for now then add the roof later.

So what method is going to work but also be affordable?

I made a google drawing to give a sense of what I want to do.

Please help me!

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Replies

  1. User avater
    Dinosaur | Mar 27, 2009 02:13am | #1

    Should I pour concrete posts then make a "grade beam" to sit the floor on?

    Yes.

    Use your neighbour's tractor-mounted auger and go down below the frost line. Put in 8" Sonotubes, and pour the columns to a minimum of 4-6" above grade. Insert 12" x ¨ý" foundation bolts ('L-bolts') before the concrete sets up too hard and leave enough of the bolts sticking out to clear the top of the beam when you drill it and set it down over them.

    Dinosaur

    How now, Mighty Sauron, that thou art not brought
    low by this? For thine evil pales before that which
    foolish men call Justice....

  2. User avater
    EricPaulson | Mar 27, 2009 03:09am | #2

    You could build that on two ledgers attached to the existing structure and some number of piers.

    I'd get a PE involved. Don't you need a permit?

     

  3. gfretwell | Mar 27, 2009 06:36am | #3

    If you really want something that you will have for a while, dig a footer and build a stem wall. You don't want this to sag and screw up your roof line. "Sun rooms" tend to become "living space" after a while so why not build it like your house?

    1. woodconcepts | Mar 27, 2009 03:20pm | #4

      Wow, thanks for the quick responces!However, I got 3 different answers, so I am still pretty much where I started.I wasn't going to apply for a permit on the deck building portion of the project.
      I have never known anyone to pull a permit for a deck. Maybe that's regional.
      When I go to build the walls and roof, I will get the permit. I live in the sticks, inspectors are very lax around here.What is a PE? some sort of engineer I suppose. How much do they charge? I'd rather over guess by $1000 than hand that money to a number cruncher who is probably just going to tell me to do it the harder way anyway. That's been my experience with engineers.I'm starting to think of a trench wall, 4 foot deep. It wouldn't have a footing but it would be entirely below the frost line. Seems like a good compromise between all the suggestions.I'm still open to ideas though.

      1. TLE | Mar 28, 2009 06:43pm | #5

        I wasn't going to apply for a permit on the deck building portion of the project.

        When I go to build the walls and roof, I will get the permit.

        If your building department is like any other I have seen, They will require some proof that your foundation will support the additional wall and roof load. They might require that you excavate around your columns to prove their adequately sized.<!----><!----><!---->

        I would get a permit for the deck and state in the permit application the size of the footings, beams, and joists - making sure that the building inspector is satisfied that the size is adequate for your future plans.<!----><!---->

        You need to decide what your long term plans are for this room. Virtually every screened in porch I have ever done has morphed into at least a three season room and quite often set up for occasional year round use. That really requires some sort of full foundation w/crawl space to allow for insulation and heat runs.<!----><!---->

        If you are sure you will never want to condition the space, i would ledger board off the house and use 12" to 16" diameter footings to frost depth (I assume 42" for your area).<!----><!---->

        My own preference is to auger the holes (I have access to augers up to 24"), drop in a sauna tube the full diameter of the footing and pour it up to near ground level.  This gets the working conditions to set and align the posts up to a level that is handy to work at. And it is easier to just have a redi mix truck deliver a minimum sized load, rather then using bag mix of minimal quality that when you mix it by hand you have a tendency to have a thinner footer than is ideal (You just get tired of mixing, you end up throwing in rocks or busted concrete and calling it good)<!----><!---->

        That and having a full diameter column up to grade makes it easier to prove bearing at a later date if required.<!----><!---->

         <!----><!---->

        Terry<!----><!---->

         

      2. brownbagg | Mar 28, 2009 10:13pm | #6

        That's been my experience with engineers. and you dont know what a PE is?

        1. User avater
          Ted W. | Mar 28, 2009 11:50pm | #7

          I don't know either ;-)~ Ted W ~

          Tool Auctions - MyToolbox.netSee my work - TedsCarpentry.com

          1. User avater
            EricPaulson | Mar 29, 2009 03:39am | #8

            Professional Engineer 

  4. BUSTER | Mar 29, 2009 04:17am | #9

    Hi, speaking of inspectors, here in the Columbia Gorge area I am one of "those" loved ones! The advice you've received is very good!

    In Oregon you'd be getting a PE if you wanted to do anything other than a continous footing/foundation. The other issue I'd be addressing is lateral bracing. Also, are you "opening" any of the existing walls? If so you'll want to address your roof loads(which may cause enlarged ftings where your loads are coming down to.

    Have fun!!

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