Add Joists Between Existing Floor Joists

Purchase the type of lumber that matches the width of the existing joist.

Add joists between existing floor joists.

I would use construction adhesive on top of the joist to assure a gapless connection. When the sagging joists are level apply a generous bead of construction adhesive to the existing joist. Worse if a gap exists between joist and subfloor the floor may still flex. 6 lift a sister joist into position.

If the overall structure of the deck is still in good shape then yes you can add new joists between the existing. Most new construction uses 2 by 8 lumber for joists although 2 by 6. This is the end that meets the existing house and is kind of poorly secured in my opionion. Of 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. Driving 16d common nails in old hard wood is difficult. 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. Close up of the far end resting probably 8 on the ledger or what ever it s called.

My crawlspace has six vents under the floor and i want to seal them up. Nail the new joist to the existing joist with two rows of 10d to 16d nails spaced 6 in. Then attach the sister joist using three 16d common nails driven every 16 in. It s kind of old school.

Measure the width and length of the existing joist. Trex needs 12 to 16 between joists. My plan is to add 2x8 joist in between the existing joist for a total of 4 additional joist. But it s usually best to run the sister joist over the entire span.

The problem is that the existing joists are 19 apart. So i ve got 2 6 floor joists spanning 15 feet. 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. 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. Generally newer home floor joists are made from 2x8s or new engineered i beams older homes however may have 2x6s instead. The adhesive strengthens the bond between the existing joist and its sister and it prevents the two boards from squeaking as they move.