Add Joists Between Existing Floor Joists

Then attach the sister joist using three 16d common nails driven every 16 in.

Add joists between existing floor joists.

Trex needs 12 to 16 between joists. It s kind of old school. Nail the new joist to the existing joist with two rows of 10d to 16d nails spaced 6 in. Worse if a gap exists between joist and subfloor the floor may still flex.

Driving 16d common nails in old hard wood is difficult. When the sagging joists are level apply a generous bead of construction adhesive to the existing joist. 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. If the overall structure of the deck is still in good shape then yes you can add new joists between the existing.

But it s usually best to run the sister joist over the entire span. Generally newer home floor joists are made from 2x8s or new engineered i beams older homes however may have 2x6s instead. If there is rot in the existing framing you re better off to start from scratch with all new materials. The adhesive strengthens the bond between the existing joist and its sister and it prevents the two boards from squeaking as they move.

My plan is to add 2x8 joist in between the existing joist for a total of 4 additional joist. Use a sledgehammer or a pry bar to force the bottom of the new joist along the mudsill and center support beam of the floor system or the opposite mudsill on short spans until it s flat against the existing joist. I read it doesn t need cross ventilation. My crawlspace has six vents under the floor and i want to seal them up.

6 lift a sister joist into position. Purchase the type of lumber that matches the width of the existing joist. 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. Most new construction uses 2 by 8 lumber for joists although 2 by 6.

Of the existing joist. Close up of the far end resting probably 8 on the ledger or what ever it s called. And i d like to know if i rip some inch plywood and sister it up against the 2x6s and glue and screw it if that would be sufficient. This is the end that meets the existing house and is kind of poorly secured in my opionion.

So i ve got 2 6 floor joists spanning 15 feet. The problem is that the existing joists are 19 apart. I would use construction adhesive on top of the joist to assure a gapless connection.