"Understanding Your Home" by Building Inspector Mark Visser
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Joist hangers were originally designed for regular 2"x8" or 2"x10" floor joists.
They are also used for "I" beam floor joists as shown above.


Joist hangers for 2"x8"

Main Floor Construction
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Floorjoists. "I" beam joists. Cross bridging. Joist hangers. Jack posts

Main Beam
. Many older homes have floors that are sagging and out of level. This is typical and can be expected. Adding more support will often prevent further movements but will not correct the problem Main beam deflections are mainly caused by undersized beams and/or not enough support posts or columns.
Sometimes floors can be adjusted by installing steel jack posts. The posts should be installed on solid footings and not just be standing on the concrete basement floor. The process is slow, 1/4 turn every two weeks. Walls above should be monitored for stress cracks. Doors will have to be adjusted or replaced. Always consult an expert before starting the work.
Cross Bridging. These are square pieces of wood which are nailed diagonally between floor joist or floor trusses in rows not further apart than 7 ft. (2.10 m.).

Each piece has an angle cut on both ends. Solid blocking is required where joists are spaced different than the normal 16" on center, and where heating ducts prevent the installation of bridging. Cross bridging will stiffen the floor and will lessen the 'bounce' in larger floor spans.
Cross bridging will not eliminate floor squeaks.

Joist Hangers are metal sleeves that are installed where a joist is framed into a beam. Tail joists that require a joist hanger are located around floor openings for stairways, chimneys, fireplaces, etc.
Joist Header Space. This area is located between the floor joists and above the foundation wall. There are five construction joints in this space between de foundation wall and bottom wall plate. The joist header area should be insulated and covered with a vapour barrier to prevent heat loss.

WARNING. If the joists are embedded in solid masonry, it is better not to seal the joist header space, insulation is ok but no vapour barrier! Studies indicate that sealing this space could lead to wood rot in the joist ends.

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