Use a Separate Pressure Treated Bottom Board on a Concrete Slab
Installing framing members on a slab requires use of a pressure treated bottom board to avoid wood rot. Concrete slabs will wick moisture between the underlying dirt base and the wood members sitting on top of the slab. If untreated wood is used for the bottom board, the high moisture level will promote rapid decay.
The obvious way to incorporate a pressure treated base board is to use one in lieu of a regular untreated board for the bottom member of the wall. This method is the least expensive because you only need to swap out the untreated bottom board for a pressure treated board, and build the wall just as you would using all regular studs.
An alternative to this method is to fasten a pressure treated board on the slab first using a powder actuated nailer, then build the walls using all untreated members and sit them on top of the pressure treated board. This method has several advantages and a few disadvantages. Overall, if offers a good solution for DIYers because, even though it costs a little more time and money, it simplifies the installation. A picture of a section of wall built in this manner is shown in the upper right of this article.
Advantages of a Separate Pressure Treated Bottom Board
- Easier Visualization. Fastening the pressure treated boards around the room first will allow you to better visualize the final room before you’ve built out the walls. If you decide to change anything about the room at this point, it is relatively simple to remove the bottom board and you haven’t wasted much wood.
- Easier Baseboard Installation. A separate pressure treated bottom board increases the nailing surface for baseboard installation. This is particularly helpful if you plan to install a floor with significant depth (like a radiant heated floor with a stone tile, which could be as tall a 1-1/4″.
- Walls are easier to move around the room before installation. Since the wall can be 1-1/2″ shorter than the height of the room, walls are easier to “scooch” around the room to their final location without worrying about hitting the ceiling. This is particularly valuable in rooms where the distance between the floor and ceiling varies by more than 1/4″ or so. This is also helpful if you don’t want to move your wall building station around the floor.
- Ease of Installation. It is easier to fasten the individual pressure treated boards using a powder actuated nailer than to do the same with an entire wall. If you misfire one of the nails using the powder nailer, or split the board, you need not worry about rebuilding the wall.
Disadvantges of a Separate Pressure Treated Bottom Board
- Increased Cost. The cost of the job is increased by the total cost of the additional untreated bottom board required for the walls. Lumber yeards are getting about $0.22 per linear foot at the time of this writing. This means an additional $22.00 / 100 feet of wall.
- Increased Installation Time. Fastening the pressure treated board first requires additional time because you must address each portion of the wall twice. There is some time savings that offsets this increased time, particularly if mistakes are avoided using the two-board method.
Tools Required to Fasten the Board
Fastening the pressure treated bottom board to the slab is simple. For the DIYer, a hammer drive powder actuated tool is your best bet. The Ramset Hammer Drive Tool is Available at the local Big Boxes for a decent price, as are the charges and nails you’ll need for this job.
You should buy approximately 1 nail and charge for every 2.5 feet of length of wall for the average room. (e.g. if you have 250 linear feet of wall, you should get 100 nails). You may also want to have 10-20 charges and nails spare in case of misfires/splits. Note that the charges required for the job vary by the type of surface your nailing into.
A Good Book on All Things Basement
Finally, if you’re looking for a great basement finishing book that provides more information on this topic and many more in great detail, check out Stanley’s Complete Basement Finishing Book. You can find it at the library or most online book stores.
We’re a big fan of Stanley books for their ease of use, clarity, and their step-by-step approach to projects. (It was just a cooincidence that the cover of the book shows this very topic using the single-board approach).
What do you think? Have you ever used this technique to frame on a slab? Leave a comment below and let us know if this helped!
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