Summer beam repair is the structural repair of a decayed main beam in a historic building, keeping as much original timber as possible. In practice it nearly always concerns the beam end built into the external wall: that is where damp and lack of ventilation have rotted the timber away, while the rest of the beam is perfectly sound.
Replacing the whole beam is rarely the first choice in a listed building. It is expensive, means major disturbance to the masonry, and destroys material with historic value. Repairing only the affected section is usually both better and cheaper.
First: remove the cause
Any repair is pointless if the moisture stays. Start with the source:
- A leaking gutter, verge or downpipe above the beam end
- Penetrating damp or cracks in the masonry
- Rising damp where the floor sits low
- A beam pocket packed solid with no ventilation space
- Cement render or a vapour-tight internal lining that seals the timber in
Measure the moisture content. Persistently above roughly 20 per cent is the zone in which fungi stay active; below that the attack stops.
Repair methods
| Method | When to use |
|---|---|
| Timber splice (prosthesis) | The rotten end is cut away and a new piece of the same species is spliced on with a scarf joint, dowels or glued joints. The most common and most reversible solution |
| Resin repair with reinforcement | The decayed timber is cut out, stainless or glass-fibre rods are set in, and the whole is cast with epoxy mortar. Invisible, but vapour-tight and hard to reverse |
| Steel flitch plates or beam shoe | Two steel plates or a let-in flat take over the beam end. Fast and strong, but visible and prone to condensation |
| Relieving the beam | A new bearing is created: a steel corbel, a joist hanger or a new wall plate, so that the load no longer passes through the decayed end |
| Full replacement | Only where the beam is decayed over its whole length or too badly deformed |
Points to watch
- Consent. On a listed building, listed building consent is required. Discuss it with the conservation officer beforehand; they often set conditions on the method
- Ventilate the new beam end. Leave an air space around the beam end in the masonry. Never build it in solid or set it in expanding foam
- Do not tar or seal it. A vapour-tight coating traps moisture in the timber
- Prop first. Support the floor before cutting — the beam carries the floor and sometimes walls above
- Use the same species and a comparable grade; timbers that move differently will crack open at the splice
- Treat active beetle separately. A structural repair kills no larvae
Always have the splice or prosthesis designed by a structural engineer. The joint has to carry the same forces as the original timber.
Related terms
- Summer beam
- Beam end
- Common joist
- Wet rot
- Deathwatch beetle
- Restoration
- Listed building
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