Replies

1. 
   Davo304 | Jul 16, 2002 07:22am | #1

   You're wasting time and money.

   Why form and pour a concrete foundation to simply install plastic decking on top? Where does the rain water drain to once it falls between the decking?

   If you want to build a porch deck, then build it like a deck. Attach a ledger board to your existing foundation, rent a post hole digger and set some 4X6 posts in the ground, run your joists, and install your decking.  No footers to mess with, save a bundle of time and money vs forming and pouring concrete footer/walls.

   Place your porch roof supports directly overtop your bottom posts, or simply use long enough posts to run from ground to porch header beam. (I prefer to run porch posts seperately, . I use the Simpson 4x4 anchor plates, install 4x4 treated posts, then cover with pine trim boards...to each his own) As long as the porch posts are directly in alignment above the deck posts, all loads are transferred directly to the posts ends buried in the ground.

   2 man, electric powered post hole auger with 12 inch dia bit cost $45 a day to rent. Can drill a 4 foot hole in matter of minutes.  Dig your holes below your frost line, pour a concrete punch pad (8 to 10 inches) then build your deck on top. Actually frame your deck before backfilling posts to ensure squareness of deck. Easier to bump a post into alignment BEFORE post is backfilled.

   HOWEVER,

   IF YOU ARE  SET ON GOING TO THE TROUBLE TO INSTALL A CONCRETE  WALL FOUNDATION, THEN GO THE REST OF THE WAY AND INSTALL A CONCRETE PORCH.

   Cheapest way is to dig your trench below frost line, and pour a footer, 8 inches thick X 16 inches wide. Install regular 8 X 16 inch concrete block up to within 4 inches of desired finished porch floor height.  install wood cross bucks, place galv metal overtop, with  a 1/2 inch rebar matt placed on top of this, then form and pour your floor.

   Just my 2 cents worth. Good luck on your project.

   Davo

1. 
   bobl | Jul 16, 2002 02:44pm | #2

   Check with your code officials

   here they wanted 10 or 12 inch concrete piers to put the posts on.  (I am not disagreeing with Davo, just talking about local code)bobl          Volo Non Voleo      Joe's cheat sheet

2. 
   bb2055 | Jul 16, 2002 06:30pm | #3

   Thanks much for all the info! Actually I would prefer a concrete deck, but can't figure out how to get the concrete slab to interface with the house. I would like the top of the slab to be about 3" below the front door threshold. That puts the concrete at the level of the rim joist of the house and I havn't figured out a way to deal with (1) water seeping/wicking from the concrete slab into the rim joist, and (2) termites getting up behind the concrete. Once the concrete slab seals off the ground below it access to even chack for termites is a problem.

   The porch is needed now ,in part, because the original front door had a concrete slab poured in direct contact with the rim joist. Rain draining down the side of the house seeped into the joint and rotted out the rim joist. I cut the rim joist out and replaced it with a CCA rim and mud sill but am very spooky about this concrete/wood contact in the new porch. The porch will have a roof but it's only 8' wide and rain/snow will still find its way to this contact.

   Any thoughts are much appreciated.

1. 
   JCarroll38 | Jul 16, 2002 07:38pm | #4

   Here in North Carolina termites are a major concern but masonry porches, such as the one you decribe, are common. My own front porch is concrete covered with brick pavers. The final height is the underside of the doorsill. Termites like moist soil and a covered path to their source of food, wood. By putting a roof over your structure, you are minimizing the amount of water that will get to the joint between the slab and the rim joist. However, I would still recommend that you coat the rim joist with stain or paint and install a layer of tarpaper or plastic. Then place an expansion joint between the rim joist and the slab. When the project is complete, of course, you need to fill the top of the joint with a flexible sealant. Also make sure you slope the slab at least one quarter inch per foot away from the house. To keep the area under the slab dry and to allow for periodic inspection for termites, pour a suspended slab and install vents in the walls of the porch foundation. A porch that sits against the frame of the house and is filled with soil is an invitation to termites. It gives them a protected path straight to the rim joist. It is not allowed by code here.

   If you're going to build a masonry porch (which I highly recommend), you need to pour a code-complying footing, which would be the equivalent of the footing for an enclosed addition. It would seem that you would need a wall or a series of piers along the wall of the house to carry the inside edge of the slab. Fill the slot between this wall or each pier and the foundation of the house solidly with mortar and, if you're using block, fill the top 8 inches of the wall with grout or concrete or cap the wall (or piers) with 8 inches of solid blocks. You can use eight-inch solid blocks or two courses of solid fours for this. The cores of block piers provide a protected path for termites and they need to be capped with solid masonry. This is required by code here.

   An alternate approach would be to move the piers a foot or so away from the existing foundation and then cantilever the slab. This would make a space that could be inspected for termite tunnels. By the way, you should provide access to this space. You can either cut an opening in the house foundation or build an access into the wall of the porch foundation.  

   You might also consider having an exterminator treat the soil along both the inside and outside of the foundation before you pour the slab. I think this is required by code here for porches; I know it's required for full additions.