Damaged and Deteriorating Floor Joists

Recently, I’ve been called out to do a couple of special inspections of damaged and deteriorating floor joists in Maryland and DC. Floor joists, in case you don’t know, are the horizontal “beams” just under the floor. Put another way: the floor rests on the floor joists. Floor joists can be either 2 by lumber, such as 2 by 10s, or sometimes they are engineered joists (part plywood) or trusses. In older homes, it’s always 2 by lumber.

So what do you do if you have a damaged joist? Well, a lot of people here in Montgomery County Maryland take this project on themselves and do what I would describe as “non-standard” repair work. It’s a nice way of saying sloppy repairs. Often, I seen 2 by 4s nailed alongside the damaged joist, or I see a 2 by 4 post beneath it. The concept of repairs like this is correct, but the selected timbers are undersized, the techniques and workmanship is often lacking. More often than not the repairs are structurally inadequate. The correct repair is normally installing a new joist that is equivalent in size and strength to the bad joist. This is best done by sistering an identical joist alongside the original. And there is no reason why an informed homeowner can’t do a repair like this on their own.

It’s a good idea to inspect your floor joists from time, particularly if you notice new squeaks in the floor or movement of the floor. Unless you have an unfinished basement, access is often limited. Sometimes you can see the joists under the stairs or in a closet. Sometimes a basement laundry room allows access to the joists. At minimum take a flash light and look at every joist you can see. Do you see any splits in the wood? Do you see water damage? If you do, take a hammer and gently tap the problem area, or use a pick to see if the wood is sound. If you have partial damage or deterioration to one joist, and there are no other signs of problems such as settling of the floor, then monitoring the situation is usually sufficient. But if you find more than that, it’s a good idea to have it professionally inspected by a skilled home inspector or engineer.  And if you find any repair work there already, look at it and determine if the new joist is equivalent to the original joist. If not, consider calling a home inspector.




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  1. Hi Greg, I am in the process of buying a house that is being renovated. Built in the mid-1950’s, it feels pretty sound however in the past several years, the occupant did not take care of the home. One of the tub drains fell off and shower/tub water poured into the crawlspace for who knows how long. When we had the crawlspace inspected, the floor insulation was “raining” and there was a large puddle of water in one of the corners of the house and right below the bathroom. The insulation has been removed and everything dried out and we now have had the opportunity to check out the joist situation. I took a nail under the house and did some testing, poking and proding to see what I could penetrate just with pushing on the nail. It looks like half of the joists are pretty soft on the bottom 1″ to 1.5″ of the joist. Some I could only get the nail in about 1/2″, and a few, all the way through. I didn’t have too much concern here, understanding that we would have to sister some joists in the near future. HOWEVER, the HVAC contractor was just under the house attaching straps for the new ductwork, and he is quite concerned because he is noticing the drywall screws he is using are not gripping, but just stripping out, unless he attaches closer to the top of the joists. What is your unofficial opinion on the integrity of these joists? Do we need to restructure the entire floor system? Sister the joists? Or rip all the old ones out and replace with new? We still have an option to get out of buying this house and need to be sure we are willing to take on whatever is required if we decide to proceed with the purchase. Sorry for the length email. Would love to hear your unofficial opinion! Thank you!

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