Wet rot treatment in Glasgow

What wet rot is, what it looks like and how it is treated is on thenational wet rot page. This page is about where it hides in Glasgow property, which is overwhelmingly one place: the space under a ground floor.

Almost every pre-war building in the West, tenement or villa, has a suspended timber ground floor. The joists sit on low brick or stone sleeper walls with an air gap underneath, and that gap is meant to be ventilated from outside through airbricks, so that moisture rising off the ground is carried away rather than sitting against the wood. It is an elegant arrangement and it works perfectly well, right up until the airflow stops.

When it stops, humidity in the void climbs, the timber takes up moisture, and the cellar fungus gets to work on the joist ends nearest the damp. That is the job, in one sentence, for a large share of the ground floor flats and main door properties in this city.

What actually blocks an airbrick

Nobody sets out to seal a void. It happens by accident, in ways that all looked like improvements at the time.

• Decking. The single most common cause we meet in the suburbs and in main door flats. Timber decking laid across a back garden or a back court at or above the level of the airbricks, sometimes straight onto soil, seals the ventilation and holds water against the wall at the same time.
• Raised flowerbeds and planters. A bed built against the rear wall of a ground floor flat covers the airbricks and keeps damp soil in permanent contact with the masonry.
• Monoblock and paving. Drives and paths relaid over the years each add a layer, until the external ground level has risen above the internal floor level and the airbricks are effectively underground.
• Extensions and conservatories. Building across the back of a house closes off that whole elevation. Even where new airbricks were fitted through the extension, the cross-flow that used to run front to back is gone unless somebody deliberately ducted it through.
• Re-pointing and render. Airbricks disappear under a re-pointing job, a render coat or, remarkably often, several coats of masonry paint applied straight over the grille.
• Insulation and later floor coverings. Void insulation stuffed between joists without thought for airflow, or a sheet of impermeable underlay and laminate over the top, changes how the floor dries from above as well as below.

If your house has had a new drive, a deck, an extension or a re-point in the last twenty years and the floor has started to feel different since, that is a line worth following.

Back court drainage, and why ground floors get it worst

Glasgow back courts were built to drain, and after a century of resurfacing, bin stores, sheds and blocked gullies a lot of them no longer do. Water standing against the base of a rear wall wets the ground under the building, and a downpipe that discharges at ground level instead of into a gully puts hundreds of litres into the same spot every wet week.

That is why ground floor and basement flats in Govanhill, Partick, Dennistoun and the older parts of Paisley and Clydebank see far more of this than the flats above them. The upper flats are dealing with water coming down from a roof or a rone. The bottom flat is dealing with water coming up out of the ground, and it is the only one whose floor sits over it.

Basement and lower ground flats add one more difficulty: some of the floor may be solid rather than suspended, or the void may be so shallow that nobody can get into it. That does not change the diagnosis, but it does change how much has to come up to reach the timber.

What you can check yourself, tonight

Wet rot is one of the few things in this trade where a homeowner can do genuinely useful triage before phoning anyone.

1. Walk the outside wall. Find your airbricks. Count them, and see whether anything is in front of, over or above them. Look at where each downpipe ends.
2. Feel the floor near the outside walls. Springiness at the wall rather than in the middle of the room points at joist ends, which is exactly where wet rot starts.
3. Use your nose in the enclosed spaces. Cupboards, under the stairs, behind a kitchen kickboard.
4. Look, if you safely can. A lifted board near a suspect wall and a torch tells you more than any amount of guessing. Darkened, soft, stringy timber that you can push a screwdriver into is the finding.

What putting it right involves

The order matters more than the products. Dry the void first, or everything else is temporary.

• Clear or reinstate ventilation, so the void has cross-flow again
• Fix the water: the gully, the downpipe, the ground level, the leak
• Cut out the decayed timber and splice or replace the affected joist ends
• Isolate new timber from wet masonry where the detail allows it
• Reinstate the floor and let the void dry properly before covering it

• Blanket chemical treatment of sound timber that was never wet
• Replacing a whole floor because part of one end of it was soft
• Sealing the floor from above and calling the void somebody else's problem

For what drives the number up and down, see thewet rot cost page. If the timber under your floor has never been looked at, atimber survey covers rot and woodworm in the same visit, which matters here because a damp void is also the most likely place in a Glasgow flat to find beetle activity.