What is the best way to anchor floor joist to a concrete block wall?

Asked By: jt145 on Tuesday, December 9, 2008
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Answer OK, here is my situation. I have a house in which the walls were make of concrete block. I am going to add a second floor over this and want to use wood floor joist over the block. When the house was built, the first floor joist were toe nailed into the block and after I removed the sub floor, the joist were very unsteady. How can I anchor the joist to the block before I put on the second floor? Also, the floor joist are not level. I want to raise up some of the joist and anchor them to the block. What kind of anchors should I use? Are tapcons alright to use? As you can see, I really need some advice. Thanks, JT


JT, I think I have the idea of what you are trying to achieve. First of all there are a couple of things you may want to try that will be helpful. Without seeing the job, I can only make suggestions based on similar situations that I have been in in the past when doing remodeling work for my clients.

So, you have taken up the sub floor and now the joist are exposed. You want to attach the joist to a cinder-block wall and level up the joist that are lower then what they should be. Hopefully I understand the matter correctly.

My first suggestion is this. Let's suppose the floor joists are made of 2 x 8 material and the joist space is 16" on center. This would mean that there is about 14 1/2" between the joist. Determine the height of where you want the joist to be and then take a 2 x 4 that will span across the width of the room over the joist. Place a level on top of the 2 x 4 and after it is level, draw a line under it at each end.

Next take a chalk line and hold it against the mark at one and have someone stretch it across the mark at the other end and then strike the line. This will act as the level line you want the top of your joist to come to.

Now, starting at one end cut 2 x 8 treated block 14 1/2" long or whatever the actual width between the joists is, and then you are going to attach it to the block wall, holding it up against the chalk line, with glue and tapcons. Once the block is in place, you can take the joist and nail and glue it against the end of the block.

Proceed to the next block and hold it tight against the joist you just installed and follow the same procedure. Keep adding the blocks making sure to keep them even with the level line and taking a new measurement between the joists each time to keep the correct spacing. With this method, you will not need joist hangers.

If you prefer, you can screw or bolt the joists into the block, but be sure to pre-drill holes as to avoid splitting the blocks. When you are done, you will have a very tight fit, strong floor frame. Just install the new sub floor and you are good to go.

The second method is similar to the first except for this. If you can cut 1 1/2" off the ends of the joist so that they are 1 1/2" short of the block wall, you can then take a 2 x 8 piece of treated lumber, or whatever the size of the existing joist are and insert it against the wall. Hold it up to the level line and fasten it to the wall using glue and tapcons.

After that you can proceed with the block method already described above, only this time you will nail the blocks into the 2 x 8 board you just installed, or you can use joist hangers which can be nailed against the board and install the joists that way. This is a good choice especially if it is required by the building code in your area.

Sorry this is so long. I hope this helps.  

Rick Maselli Founder of Showroom411.com

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