Renewing Floor Joists

Filed Under: Do it yourself, Home repair, Remodeling    by: ITC

You may find that a problem floor is simply due to one or two joists having become twisted and this can be cured by toe-nailing tight fitting wooden struts between them. However, if the wood is being eaten away by insects or rot, you will have no option but to replace every affected piece.

Lever up a sufficient number of floorboards to get at the affected joists, using a claw-headed hammer with a wooden batten to help leverage. Pull out all the nails and stack the boards so that you can replace them in the same order.

If only a small section of a joist is damaged, the affected area can easily be sawn out and replaced. However, for safety, make sure that the cuts are at least 24in beyond the damage.

Removal of a complete joist will mean levering it from its wall plates at each end, and also any intermediate wall plates. If the ends are set in sockets in the wall, cut through the joist just short of the wall and pull the stubs out. Brick up the sockets, cementing metal hangers into the top joints.

If only a section of joist has been removed, cut a new piece of joist to the same size plus extra wood so that it will overlap the ends by at least 18in. Bolt this to the old joist with two carriage bolts at each end.

If a complete joist is to be fitted, trim back its ends to a taper so that there is no chance of it touching the external walls. Toe-nail the joist to its wall-plates.

If the wall plates themselves are affected, replace them at the same time, simply laying them on top of the sleeper walls. Make sure you prevent contact with the masonry by laying a strip of flexible flashing along the wall first. It is recommended that pressure treated lumber be used for replacement sections.

Something to watch out for are pipe and cable runs below the floor. Pipes are usually set in shallow-cut notches in the tops of the joists and cables pass through holes drilled in them.

Always remove the fuse, or flip the circuit breaker, controlling any underfloor electrical circuit before work begins. Cut the cable out of the old joist by making two saw cuts down to the hole. Make similar cuts in the new joist and glue the offcut back for added protection. Alternatively, disconnect the cable from the nearest fitting and thread it through the holes.

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