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zachinqueens 11-11-2011 01:09 PM

Dealing with slightly rotted joists
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The foyer of my house is a pretty small area (about 5'x5') and it protrudes from the house. It has its own set of floor joists, that run about 8' through here and through the closet.

I recently tore up the circa-1928 mortar bed in here, as it had cracked badly. Planning on installing a plywood subfloor.

However, the joists here all show a little bit of rot toward the front door. The joists are huge and rough-cut (actual dimensions 2 1/2" x 10"), and the rot only extends through the top 2" or so.

My current plan is to sister with bolted 2x10s to alleviate the rot, then add ledger boards for the plywood to rest on. However, I can't sister the full length of the joist without tearing up the closet floor, which I'd rather not do (it's nice old hardwood supported by the remaining portion of the mortar bed).

Am I going to be sorry if I only sister the exposed 5' of the joist? The sister will rest on one bearing point, but not reach all the way to the end.

oh'mike 11-11-2011 02:10 PM

Hard to give you a firm answer without knowing the length of unsupported joists--and how sound the bottoms of the bad joists are.

A wishy washy answer is this--probably be fine with sisters---need more facts.

zachinqueens 11-11-2011 02:16 PM

Thanks Mike.

The joists are about 8' in total. The unsupported portion would be 5'. To me the bottoms look good, although I don't know how to verify their soundness. There's no visible rot past the top 3" of each, and the rot extends at most 2' along the length of the joists.

oh'mike 11-11-2011 02:28 PM

Sister them---do a careful job and fasten them together well ----you will be fine---

Have fun----Mike---

mnp13 11-11-2011 03:33 PM

We had a similar issue with the joists that are holding up our porch roof. I dug out all of the soft stuff until I found good wood, then use liquid resin to "harden" it, then put sister boards up. (We could not just replace the joists, as they run into the brick walls of the house.) Even if you protect them from further damage, rot tends to spread, so getting the bad wood out will help that. It will also answer the question "how far does the rot go."

forresth 11-11-2011 09:02 PM

I wouldn't bother with sistering in 2x10s. 5/4 deck boards would probably be enough.

whats under there? can you just fill it in?

zachinqueens 11-11-2011 09:33 PM

Under: It's about 3 inches to the fiberboard ceiling below. I considered replacing the mortar bed with another one, but sistering seemed simpler since I don't have much experience with that.

jimmy21 11-12-2011 01:21 AM

is it good practice to also treat the rot with something. OR is it enough to just remove the issue that was causing the rot?

mnp13 11-12-2011 08:14 AM

Remove the issue, or it will continue (obviously) but it is also good practice to remove all rotted material.

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