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Thread: how to Enclose a Pier n beam foundation

  1. #1

    Red face how to Enclose a Pier n beam foundation

    I live in a log home built 25 years ago and it has a pier and beam foundation. The under pinning is currently of treated plywood which has "bowed" in many places. The bowing has caused the joint where the two pieces of plywood meet horizontally to be out of alignment and now frogs, snakes and other critters can squeeze between there and get under the house. The underpinning is attached to the outside frame of the foundation at the top and dirt pushed up against the bottom of the plywood to hold it in place.

    How do I properly put in a correct underpinning? I was thinking about using a concrete board made my James hardie. I can attach the concrete board at the top of the foundation, but how do I handle the bottom of the board at the ground? Do I have to build some sort of frame? Do I try just burying the new board, or do I need to put some sort of footing down that the board will but up to at the ground? I don't want it to bow like the other underpinning did and more importantly I don't want anything to get under the house.

    It is really important that I do this right. I was bit by a copperhead snake that lived under the house by day and came out at night when it was cool and bit me on the foot.

    Can anyone help me with this project plan?

  2. #2
    Join Date
    May 2006
    Ottawa, Canada


    I am assuming when you say "pier and beam" you're referring to a "post and beam" construction. Either way...

    It all depends on how long you're expecting the wall to last. if your looking at 10-15yrs, then simply create a frame using treated 2X4 and face with the concrete board. You can also use treated plywood with a lattice tacked overtop. when painted it can actually look quite attractive (depending on what the rest of the building style is). Staining the wood will extend the life of the frame/face as well.

    make it as though you were making a regular wall inside, frame with studs running at 24" or 36" centers, depending of how high the wall is to be. have it sit on concrete block along the bottom to keep it drier. lasts much longer and keeps "things" from digging under the wall. don't shovel dirt up against the wood as this significantly shortens the life of the wall/wood.

    Make sure you add vents, small screened openings to vent moisture. have at least one on every side of the house, and if the house has a length of more than 15' then add a second along that length. they don't have to be too big, say 8" X 12".

    The venting of this moisture will significantly extend the life of your wall, as well as the life of the floor boards and beams of the house proper. you can block them in winter to keep the floor warm, but make sure you open them up in early spring to allow the runoff to dry out underneath.

  3. #3

    Default Ho to Enclose a Pier n beam foundation


    Thank you for getting back to me with such good information. Yes we have a post and beam foundation. I like the lattace idea! The concrete block under the underpinning should really help also.

    When I build the framing, what will anchor the frame to the ground, or is this necessary?

  4. #4


    Treated plywood will not last as long. I myself would use composite deck boards or the hardie plank.
    I would put pieces of 4 x 4 s into the dirt a little ways and pack good or use a some concrete. Toe nail with desk screws to cabin.
    You could put post every 2 ft or put 6 to 8 ft and between post build a frame of treated 2x4s with a stud every 16.

    You could also use a treated 4 x 4 laid sideways between each pier and bury in dirt with top edge even with ground level. Maybe a few steaks in back of it so will not move when you nail siding. Then this gives you something at bottom and you can now install 2 x 4 studs to this and the cabin. The put on whatever siding.
    The deck boards or hardie will hold up way better than plywood when part is covered by dirt.

  5. #5
    Join Date
    May 2006
    Ottawa, Canada


    rayh78 is quite correct, you can bury a 4X4 so that you can attach the bottom of the wall to something. Personally I would use cement block, it dries much faster and has less of a tendency to retain water, as well it gives you distance from the earth.

    As this wall is largely cosmetic, anchoring may not be that important to you. Anchoring at the bottom largely depends on how high the bottom log is from the ground. If you are over three feet high then it might be a necessity. Otherwise a well anchored wall at the top will stay in place with just a snug friction fit at the bottom.

    Other necessities may be in play as well. If you have a dog or have raccoons or skunks in the area that like to clamber underneath to nap, you may want to make sure that the wall can't be forced too easily. The simplest but least permanent solution is to drive long spikes into the earth through the openings of the cement block, behind the toe rail (or bottom board of the wall frame). This will act like a tent peg to prevent something from pushing it in, but may require regular checks (as in once a spring or fall). If you do this, make sure that you have easy access to the crawl space so you can check.

    Of course you could just lay cement block all the way to the top and have a board covering or other piece for looks. Again this will depend on how high the opening is.

    Remember that if the ground freezes in winter in your area, you will have frost heave, so either build in some flexibility or dig down 6' for a "heave-less" foundation.
    Last edited by Bumblerazz; September 4th, 2008 at 07:51 PM.

  6. #6
    Join Date
    Nov 2004
    Boston, MA


    My last house had cement board & plywood enclosing underneath. The cement board held up, plywood was falling apart
    DIY Homeowner...not a Pro or licensed electrician

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