Article - Joist Repair

Joist and beam repair help

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Summary: Repair joists and other floor timbers - using our Joist End Repair Plates, Joist Splicing Plates or Timber-Resin Splice Kits.

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BM9 Joist End Repair Kit

Typical joist end repair kit with coach screws

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BRE Joist Spacing Table

BRE Notching and Drilling Holes in Joists


There are three main types of damage, but they are all caused by one problem - DAMP. Timber will start to decay at above 18% moisture content (in average softwood species, like an ordinary Pine), so elimination of dampness is our main concern.

1. Wet rot - does not spread beyond the area of wetness: it causes localised damage to timber

2. Dry rot - can spread well beyond the area of wetness and cause serious damage to timber

3. Insect attack - mostly in damp areas, can spread beyond, but mostly slow acting

Click to see timber decay treatments for wet rot, dry rot and woodworm attack.


Joist ends become damp because they rest inside or close to the support walls and easily absorb water from damp soil, humid air or water leaks. Any repair or treatment must include attention to the sub floor Air Bricks.

The easiest way to repair joist ends is to fit Joist End Repair Plates. These come as a pair of L shaped, metal plates complete with screws and instructions. They have the advantage that joists are extended back into or onto the original bearing, whereas repairs with bolted-on pieces of wood mean that you need a new bearing area, or a more complex solution using three pieces of wood.

Galvanised steel plate kit for rotted joist end repair

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These are usually larger section timbers than the joists and may not be suitable for the Joist Repair Plate system. If larger than 10 inch x 2 inch (250mm x 50mm) then you will need to use the Timber-Resin Splice system instead. This provides a new piece of timber, with bars pre-bonded into one end, ready for you to fit using the resins provided in the kit.

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Teignmouth, TQ14 9AE

T: 01626 872886


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Other Property Repair Systems Sites: - membranes for lining damp walls, floors, basements and cellars - epoxy resins for repairing wood, concrete, brick and stone - upgrade doors to 30 minutes fire resistance - our Home Site - treat steel with Intumescent Paint to provide fire protection - systems of repair, with step by step methods - how to repair timber beams

Site written by: David Moore

David Moore, B.A. (Hons.), C.T.I.S., C.R.D.S. Technical Author