Double Floor Joist Under Wall

This sample table gives minimum floor joist sizes for joists spaced at 16 inches and 24 inches on center o c for 2 grade lumber with 10 pounds per square foot of dead load and 40 pounds of live load which is typical of normal residential construction.

Double floor joist under wall. However the floor joists must also be adequate to support the additional load from the wall. Floor joists align with the wall studs which align with the first story floor joists. Make sure not to install joists so they run parallel to and directly under walls where you intend to install ductwork. They re least obtrusive when run along an outside wall or center beam.

The main reason for doubling up floor joists is to double the strength of a single floor joist. But for nonbearing walls why do any extra joists at all. This allows you to install a supporting post off the double floor joist to hold a second storey or a roof beam. So instead of having a post run all the way from the roof to the ground it can stop at the double floor joist.

With timber or metal frame walls it is normally acceptable to support them on the existing floor joists not the floor boards either by providing a double floor joist underneath if they run parallel or across the existing joists if the floor joists run at 90 to the wall. Nonetheless this does not ensure good floor performance. When i draw plans i locate joists under bearing walls only for parallel walls off layout but i do it with two joists spaced apart the depth of wallplates above. Finally if all else fails drop your pipes and ducts down below the joists and box them in with wood framed soffits.

True floor joist span calculations can only be made by a structural engineer or contractor. Hi if the wall is not crossing several floor joists and only sitting on the floor boards it will need a new floor joist putting under it to take the weight of the wall that is what the inspector wants you could just put several knoggings form joist to joist down the length of the wall at 400mm centres to solve this problem. Framing for floor openings a staircase is essential for commuting between floors but it creates an opening in the second floor so you can t run the joists from one side of the house to the other without interruption. For better performance the designer may wish to add a joist or blocking panels below the non bearing wall.