proper method to repair section of joist.

[Walker]

I have a 4 foot section of a 2x8 joist damaged by water. Rotted out. The cause of the damage has been fixed.

I removed the damaged section. The free ends of the good part are being supported by jacks now. What is the proper way to repair this section?

I considered attaching a 10 foot 2x8 to the side of the joist but am not sure of what to use to secure them together. Walker1940

[Chris Perdue]

check with a local contractor or the local inspector....some allow nails, some want carriage bolts, etc, when you sister a joist.....the three foot overlap you have should be sufficient also....but wouldn't hurt to inquire with the locals that know the codes...

[B]

Use about two nails to put the "sister" in place, then pre-drill maybe 15

3-inch screws on each end. Pre-drilling releases the pressure on the board that might be caused by putting in as many fasteners as you will want for strength. What I have described is somewhere between sufficient and overkill, which is good.

-B

[Neil Covington]

Hi Walker.

I recently went through a very similar repair. There are a lot of things to consider that your post did not mention. Since you said the joist was rotted out from water, I am led to wonder if the joist is a roof support truss on a flat poured tar roof.

Is the joist that you are replacing identical to modern 2x8 lumber, or are you referring to the sawmill sizes that were common up until somewhere around the 30's or 40's? If it's an old sawmill joist, chances are it's more like a 2.5 by 8.5 in today's lumber sizes. It may also be made of a much higher quality of wood than the pine you may be getting at your local home improvement store.

In any case, you need to consider how much weight is to be on this joist. If we're talking about a 1920's poured tar roof (which is what I was dealing with on my truss replacement), you're talking about a potentially tremendous amount of weight. Think about how many layers of tar are on that roof, and then recall how heavy one of those

5-gallon buckets of cold-app roofing tar are. Then add the weight of the sheathing, any repairs, and the consderation that the original roof was likely 3-5 layers of tar and tar paper, then top that off with a large snowfall, and you've got the potential for disaster.

Yes, in many circumstances a quantity of screws or bolts will work. But this is not the method that I would choose. Instead, I would try to replace or supplement the entire length of the joist. If you can install your new joist such that it rests on the load-bearing elements that the existing joist rests upon, you have a much more reliable and safe repair.

In the house that I am rehabbing, I actually built a jacking assembly out of floor jacks and a wooden frame of 2x8s and 2x4s to create a new load bearing assembly to lift the roof back to its proper location, then up a little higher. I completely removed the old truss, and seated a new 16 foot 2x8 between the opening in the brick wall and the center girder. The new truss was shimmed up to compensate for its slight difference in size from the original truss. Then the roof was lowered back down onto the new truss.

This technique worked out very well for me. I also don't have to worry about a pieced-together truss breaking in the future, nor do I have the concern of pieces of old rotted truss breaking loose, or the potential that a small split developing in the wood could have very bad consequences.

It's also worth noting that the garage with this house was repaired a long time ago by the previous owner using the joist bolting technique. This joist, however, was a main girder to support all the trusses at their center point. Apparently after some snow, the entire roof collapsed in because it was enough weight to split one of the bolted together 2x8s.

On the other hand, if we're talking about a regular floor joist over an unfinished basement, that changes a lot. It'll be accessible to be watched or repaired in the future, and it's not going to be holding a massive load. Here bolting in a new joist would be fine. However, I would still get the new joist segment as close as you can to whatever elements are supporting the existing joist, that way you have more room for spreading out the bolts over the length of the joist run, and it minimizes the potential of the joist assembly flexing under a large load or sagging over time.

This is just a bunch of information I have put together from my experience with some similar situations. I am by no means an expert, just another homeowner hoping to provide some intellectual stimulation through the communication of my ideas and experiences.

-R. Neil Covington [e-mail]

[default]

Shove the jacks up an extra 1/4" or less, coat the overlapping sections of joist with a non-creeping construction adhesive, and nail. Drive 8-penny (2 3/4") nails every 16" along the top edge, and along the bottom edge also every

16" but offset 8" so they don't line up vertically. Then do it again from the other side.

[Walker1940]

Thanks to everyone who replyed. A big help.

Incidently, I should have mentioned that this was a floor joist. Easily accessible by a crawl space.