Plumbing P Trap In Floor Joists

Erniecan tx i have this situation adding a bath upstairs in an old home.

Plumbing p trap in floor joists.

We cut out and doubled up a header where the tub p trap was to be installed. I am installing a shower in a first floor location that is cantilevered out from the house. The floor system is 2 10 joists spaced 12 inches on center. Install a sanitary tee facing into the room for the sink trap.

Cement a 1 1 4 inch trap adapter into the tee. You need to raise not only the trap but also the connection to the vent such that there s a maximum pitch of 1 4 per foot along the entire waste pipe between the trap and its vent. During the layout stage plan to run the drainpipes parallel to the floor joists when possible. That would result in an s trap which is prone to siphonage.

I will accomplish two things by installing 2x8 joists where the tub is going. Prior to drilling holes in these floor joists we installed 3 4 inch plywood to each one. The floor joists are 2 x 10s and the joist cavity is insulated. This would mean drilling the joists and re routing the entire run.

Step 3 understand the joist slopes. This gives the strength for the weight of tub and person and raises the floor enough to install a regular trap for the tub. The ideal height is usually 18 inches above the finished floor but check your sink instructions to be sure. No room for 2nd floor tub trap.

Problem is the p trap almost touches the bottom of the joist cavity and is likely to freeze being very close to the exterior of the house. The holes will have to follow a straight line that goes across the floor and has to either go up or go down so the pipe has a slope. An important step in running drain lines occurs on paper before the actual plumbing begins. Install a piece of 1x6 blocking and anchor the pipe with a strap.

Note the photos show a recent bathroom remodel where we relocated the tub drain across several floor joists.