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.