Sistering Structural Beams
We bought a brownstone in Crown Heights a few months ago and discovered some water damage to a structural beam between the garden and parlor floors. The beam is sagging and I want to see if we can add a sister beam to take some of the stress from it. Does anyone have any experience…
We bought a brownstone in Crown Heights a few months ago and discovered some water damage to a structural beam between the garden and parlor floors. The beam is sagging and I want to see if we can add a sister beam to take some of the stress from it. Does anyone have any experience dealing with this? Maybe a contractor referral and some idea of the expense?
Here’s advice a structural-engineer-in-training friend gave me about a broken joist we just discovered under our roof:
“The joist can probably be sistered. The sister should be as long as possible to make a good splint. If the splint only overlaps the break by a few feet, then the bolts will ‘torque’ a new split in the repaired member. I suggest at least a 12′ 2×10 sister. Use 3/8″ bolts with big washers staggered every 16″, no closer to the edge of the joist/sister than 2″. Individually, joists don’t take a lot of weight, but right now the joists on either side are taking 50% more weight than they’re supposed to. They will continue to do so (and be more likely to fail, themselves) unless the failed joist is jacked back up before the sister is put on. Make sure your carpenter understands this. If there is a stain on your roof, the joist has probably been going for some time.”
I’ve remodelled a number of old homes and have run in to this issue. In a lot of cases, I simply sister the existing beam by placing appropriate size beams on either side. Then, I drill all the way through the three beams, and join them with carriage bolts and washers. If it’s a particularly long span, I also sometimes add a layer of 3/4″ plywood on either side for rigidity, as it is less likely to bow over time. If there is sag in the existing beam, I use a lally column to push the beam back in to place before sistering, drilling, and joining.
You could also look in to replacing the beam with a modern structural beam. However, normally when I face this issue, because of the age of the buildings, the modern beams are too deep and would bump out in to the room and need to be boxed in