adding joists will go a whole lot easier with the decking removed. crown the lumber so that the bow goes up. the new joists may need to be notched slightly or the hangers installed a bit lower to account for the difference in material height from old to new.
adding a beam placing a beam perpendicular to the joists at mid-span effectively shortens their length and eliminates flex. tom makes the beam out of two 2x8s or 2x10s glued and nailed together with 10d nails in a staggered pattern 12 inches on center.
the foundation for the addition is three sided, with the fourth side being the existing foundation. there are two support foundation pillars under the middle section, but none under the sunroom or bedroom both are 15 x 15 the addition floor joists run perpendicular to the existing foundation, and thus needs to be attached to it.
how to add joist to fix sagging floor joist house framing repairs of how you can add additional joist or even larger materials to repair a sagging floor after it has been jacked up into a
re: reinforcement of the floor joists hi henry. thanks for response. i was considering your approach as one of the alternatives where 2x4 or 2x6 will be 'sistered' on both sides of the existing floor joists. the problem here is to fit 2x4 or 2x6 15' long around the existing wires, pipes, and ducts.
when the sagging joists are level, apply a generous bead of construction adhesive to the existing joist. then attach the sister joist using three 16d common nails driven every 16 in. driving 16d common nails in old, hard wood is difficult. predrill and drive 3/8-in. x 3-in. lag screws if youre having trouble nailing.
floor joists if you stand in an unfinished basement and look up, those pieces of wood running parallel to each other are the floor joists. they hold up your floor. they hold up your floor. your floor joists rest on the sill plate and dead end into the rim joist at the end of the house.
nail the new joist to the existing joist with two rows of 10d to 16d nails spaced 6 in. on center. for additional stiffness, sister joists can be applied to both sides of a joist. an alternative to adding full- length sister joists is to ap- ply two layers of plywood to one side of the bouncy joists.
bridging: if the existing joist system is very close to being sufficient to support a new attic flooring, the addition of bridging between the joists may be all thats required. bridging
i'd suggest you first run a continuous 1-by or 2-by plate across the ends of the existing joists to provide a stable base for the new joists. that also gives you a fighting chance at a level floor. if you simply set the new joists on the old they probably won't mate well, and any slope in the old floor will translate through to the new.
build a standard frame with a new rim joist on both sides and nail the new rim joist to existing rim joist. structural details: the new area is 12 feet by 4 feet, pretty narrow. so we are using 2x6s for the joists.
1 - make a couple of small ledgers 11' between existing joists with offcut of 2x8, bolt to wall with a couple of m10 bolts and stick joist on hanger. 2 - cut extra slots in existing brick and breeze block and rest on wall as per existing joists.