Add Joists Between Existing Floor Joists

My plan is to add 2x8 joist in between the existing joist for a total of 4 additional joist.

Add joists between existing floor joists.

Trex needs 12 to 16 between joists. 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. But it s usually best to run the sister joist over the entire span. Purchase the type of lumber that matches the width of the existing joist.

Generally newer home floor joists are made from 2x8s or new engineered i beams older homes however may have 2x6s instead. Measure the width and length of the existing joist. It s kind of old school. If the overall structure of the deck is still in good shape then yes you can add new joists between the existing.

Then attach the sister joist using three 16d common nails driven every 16 in. So i ve got 2 6 floor joists spanning 15 feet. 6 lift a sister joist into position. I would use construction adhesive on top of the joist to assure a gapless connection.

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. Driving 16d common nails in old hard wood is difficult. The adhesive strengthens the bond between the existing joist and its sister and it prevents the two boards from squeaking as they move. 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.

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. Nail the new joist to the existing joist with two rows of 10d to 16d nails spaced 6 in. I read it doesn t need cross ventilation. When the sagging joists are level apply a generous bead of construction adhesive to the existing joist.

This is the end that meets the existing house and is kind of poorly secured in my opionion. 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. Worse if a gap exists between joist and subfloor the floor may still flex. Close up of the far end resting probably 8 on the ledger or what ever it s called.

Most new construction uses 2 by 8 lumber for joists although 2 by 6. My crawlspace has six vents under the floor and i want to seal them up. Of the existing joist.