Adding Wood Decking on Top of Concrete Porch
Our craftsman style house was built in 1923 and currently has an 8' x 30' concrete slab porch, 6" thick. The porch rests on a block foundation. I'd like to have a wooden porch. Since it will be too expensive to remove the existing concrete porch, I am looking for a way to apply wood decking on top of the concrete. We only have about 1.5" from the top of the slab to the door's threshold. Would like use real wood (T&G)not a composite material. Any ideas on how to construct this so that the wood will not rot from the bottom? Thanks for any ideas!
Re: Adding Wood Decking on Top of Concrete Porch
I installed a deck for my parents several years ago, in a similar scenario. There was an existing concrete patio, and I put the deck over it.
One important consideration is drainage. Check the existing patio to make sure it has a slight pitch away from the house. If not, then a deck built on top will not drain properly, no matter how it is installed. If the patio is perfectly flat, then it's probably a bad idea to build a deck over it. Standing water will just create more problems.
There must be some space between the deck boards and the concrete, to allow moisture to escape/run off. Use composite deck boards as runners underneath (like the joists under a floor), and attach the wood decking to them. Cut grooves through the runners where they contact the concrete, for drainage. Glue the runners down to the concrete, to prevent the deck boards from curling and warping the deck. I made the mistake of not doing this on my parents' deck, but the deck was large enough that the boards did not warp enough to notice.
As for the low clearance by the door, it will require a step up/down planned into the deck design. Leave a large area of clear patio by the door, and build up the deck from there.
There was a similar deck installation procedure on a TOH episode a couple of years ago -- a deck built on a roof, but the solution was the same. Don't remember which season, but I think it was 2005. Check it out.