The cellar in autumn: damp, cardboard, and the edges in between

Cellars, utility rooms and understairs cupboards fill up in autumn, and it is rarely bad luck. The three things insects are looking for are all down there: it is damp, it is dark, and there is cardboard.

Fix the conditions first

This is the part that does more than any spray. Silverfish in particular need humidity, and they leave when it drops.

• Run a dehumidifier, or ventilate properly on dry days.
• Replace cardboard storage boxes with sealed plastic ones. Cardboard holds damp and is food.
• Get stored items off the floor and away from the walls, so air moves and so you can see the edges.
• Fix the drip. A slow leak under a sink keeps a whole room habitable for things you do not want.

Then treat the edges

Once the room is dry and clear, treat the routes. In a cellar the routes are obvious once the boxes are out of the way.

• The floor to wall junction, all the way round.
• The frame and threshold of the door to the rest of the house.
• Around pipes and cable runs where they pass through a wall.
• Air brick and vent surrounds, and the frame of any window.
• The underside and back edge of fixed shelving.
• Behind and under the washing machine, the boiler and the freezer.

Clean the edges and let them dry first. Unpainted cement and old brick are porous, so try a small area and let it dry before doing the whole run.

A thin, even layer, overlapping slightly. Cracks and crevices in old masonry deserve the extra pass, because that is where the problem lives rather than on the open wall.

Drying takes longer down here

A cold, still cellar dries far more slowly than a warm room with a window open. Give it time, keep the door open and the dehumidifier running while it dries, and keep children and pets out until the surfaces are dry.

In a room that is not cleaned or handled much, that is realistic. Treat again if you wash the floor edges or after any building work.

And the way in from outside

Autumn traffic comes from the garden. Clear leaf litter away from the wall of the house, cut back anything touching the render, and check the seal around the cellar window and the air bricks. The treatment holds the edge; closing the gap is what ends the route.