Why joists fail
Floor joists carry the weight of the floor, furniture and people. They can weaken when timber stays damp, leading to rot, or when insects attack the wood. Joist ends built into damp walls are especially vulnerable, as are timbers beneath leaking bathrooms, kitchens and pipework.
Signs of trouble
- Floors that feel bouncy, soft or sloping
- Boards that crumble or feel spongy underfoot
- A musty smell or visible fungal growth
- Gaps opening between skirting and floor
- Furniture that wobbles or tilts
- Small exit holes or dust from insect activity
Fix the cause first
Replacing joists without stopping the source of moisture just means the problem returns. Typical causes are blocked air bricks, leaking pipes, failed gutters, high external ground levels, damp walls and defective drains. We trace these and deal with them as part of the job, see subfloor ventilation improvements and underground drainage repairs.
Repair options
The right repair depends on how much of the timber is affected:
- Cutting out and replacing the affected length of joist, jointed to sound timber
- Sistering, where a new joist is bolted alongside a weakened one
- Replacing joist ends using support plates or joist hangers, so they are no longer embedded in damp masonry
- Full replacement of joists that are beyond repair
Timber used should be appropriate in species and size, and treated where suitable. Floorboards are lifted carefully so they can be refitted, which matters in period homes where the boards themselves have character.
Older properties
Victorian and Edwardian terraces in Newcastle and Tynemouth often have original timber floors built into solid walls, and coastal exposure can add to damp problems. Tyneside flats can have floor structures that serve two homes, so care is needed over which areas are involved.
Regulations
Replacing a large number of joists can be notifiable under Building Regulations; see GOV.UK. If damp is a wider issue, see rainwater penetration remedial works.
Frequently asked questions
Can rotten joists be repaired, or must they all be replaced?
Often only the damaged part needs replacing. Where decay is limited, a new section or a reinforcing joist can be fitted. Severely decayed joists are replaced completely.
Will I need to lift all my floors?
Only the affected areas usually, but we may need to open up more floor to find the extent of the decay. Boards are lifted carefully so they can be reused where possible.
