Add Joists Between Existing Floor Joists

My crawlspace has six vents under the floor and i want to seal them up.

Add joists between existing floor joists.

Even if your joists already have a row of bridging at the center of the span adding a row on each side of the existing bridging will stiffen the floor. This is the end that meets the existing house and is kind of poorly secured in my opionion. This solution doesn t make the floor as stiff as the other solutions but since it s relatively easy and inexpensive you might want to try it first. The problem is that the existing joists are 19 apart.

Worse if a gap exists between joist and subfloor the floor may still flex. If you add joists between existing joists you have to make sure you get a good connection between the joist and subfloor or squeaking may result. Of the existing joist. Most new construction uses 2 by 8 lumber for joists although 2 by 6.

6 lift a sister joist into position. Nail the new joist to the existing joist with two rows of 10d to 16d nails spaced 6 in. While it is a good idea to replace rotted material with 2x8s it may require some notching to fit between the sub floor and ledger board. Measure the width and length of the existing joist.

When the sagging joists are level apply a generous bead of construction adhesive to the existing joist. Purchase the type of lumber that matches the width of the existing joist. Trex needs 12 to 16 between joists. I would use construction adhesive on top of the joist to assure a gapless connection.

The adhesive strengthens the bond between the existing joist and its sister and it prevents the two boards from squeaking as they move. Then attach the sister joist using three 16d common nails driven every 16 in. Generally newer home floor joists are made from 2x8s or new engineered i beams older homes however may have 2x6s instead. I read it doesn t need cross ventilation.

Driving 16d common nails in old hard wood is difficult. It s kind of old school. Close up of the far end resting probably 8 on the ledger or what ever it s called. But it s usually best to run the sister joist over the entire span.

If the overall structure of the deck is still in good shape then yes you can add new joists between the existing. My plan is to add 2x8 joist in between the existing joist for a total of 4 additional joist. If there is rot in the existing framing you re better off to start from scratch with all new materials.