Message: Vinman, Sir;
I am to build a 250 sq ft deck in my yard. The area is presently concrete patio. The height of the concrete patio with respect to the door sills will allow a deck using 2X6 redwood grade “deck-heart” screwed to 2X4 PT sleepers (that is, laid on 3.5 inch side) at 90 degrees to the deck at two foot intervals. I will use some shims between the sleepers and the concrete since the concrete has many dips and slopes. I live in Mountain View, CA.
The sleepers will be in contact with the concrete in many places, although no more than 1/32 inch standing water in rain. Am I OK doing this or do I NEED NO CONTACT with the concrete.
Thanks for checking my project,
Curt
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Dear Curt,
I have been out of construction for some time, but the first decks I worked on , are as you describe-that is installed on sleepers over concrete patios. Before I give my answer, I notice you are from California. Your state, has some of the strictest building codes in the nation, including those for earthquake proofing. (I would strongly advise giving your local building department a call. Most of these big cities have handouts for specific types of homeowner construction including decks, and may also have some earthquake or other requirements, specific for your locality).
Mountain View, CA. Website
Mountain View Codes & Standards
Number one, PT-or pressure treated lumber or the “Heart” types of redwood are suitable for wood to concrete contact. (Check out my posts on the new types of pressure treated lumber and the post’s on different types of redwood). In my day, we would install the sleepers directly to the concrete with “Redheads,” or other wood to concrete fasteners such as Hilti Fasteners, provided we got enough penetration into the concrete. We didn’t worry about moisture as decks are typically sloped 1/4″ per foot, away from a house foundation. (Your area, may have some stricter requirements).
As far as shimming goes, the same applies. The shim needs to be PT or redwood. Typically redwood is a softwood, so has some give. We found it better to use PT later on, is it is typically treated Douglas Fir and harder than redwood. When construction adhesives came online, we liked to also glue the shims to the concrete and the sleepers to the shims along with our fasteners..This gave us a really secure platform for our deck. (I’m not up on the latest construction adhesives, but we used Commercial Grade Liquid Nails for wood to concrete use)
Over time, direct wood to concrete, especially in a wet climate, like my area,, was found lacking. Even if you use redwood or PT, all wood will decay over time. The last decks I completed, we raised them with shims so any water or moisture would weep out. This also allowed the area under the sleepers to air dry.
Another note on shims. I also had some decks over really bad concrete, like you describe. In some cases, I was able to rip 2×4 or PT blocks to the required thickness and in some cases the full thickness of a 2×4 block. (The wider a shim, the better off). I would rather rip the thickness of a shim out of 3.5 stock then 1.5, which gives more area for glue, and also prevents splitting. (Pre-drilling is recommended).
Another little trick, depending on the thickness of the shim, is to use a 2×4 block, say about six inches long. You can then notch the 1.5 inch joist space out of the block to set your 2x joist in. (Of course this takes some careful planning).
Click the following link, for a really good deck over concrete guide, by the California Redwood Association. I think it will help you quite a bit.
Thanks for your email, and good luck with your project!
Posted by Vinman | May 17, 2011, 9:07 PMFrom Curt,
Dear Vinman,
Thanks for the detailed response!!! What I plan to do is lay the sleepers on plastic door frame shims. This will allow me to adjust the sleeper to make it level and not have contact with the concrete (and associated water when it rains). I am leary of ripping the PT due to the poisons in the wood and the necessity to repaint the exposed wood.
Thanks again for your input
Posted by Vinman | May 17, 2011, 9:08 PMPlastic door shims would be perfect! They didn’t have those in my day, but what a perfect fit. As for ripping the PT wood, the chemicals are forced through the wood. You wouldn’t have to paint them, but breathing the chemicals is hazardous. We didn’t have those concerns way back then…as there wasn’t the information that there is today. Good luck with your project!
Posted by Vinman | May 17, 2011, 9:09 PM