Damp Patch After a Roof Repair: Still a Leak, or Something Else?

You pay for a roof repair, the leak stops, and then a brown patch appears on a ceiling or a bedroom wall. Or the patch was always there and now seems worse. It is worth sorting out quickly, because the repair may have missed the real fault, or it may have changed how the roof space breathes.

Rung 1: Read the pattern (free)

• Note when the patch changes. Does it darken or grow after rain, or on cold mornings with no rain? The Property Care Association says penetrating damp is rainwater that passes through the walls or roof of a building, so a rain-linked patch points that way.
• Look in the loft with a torch, standing only on the joists. Look for damp timber, wet insulation, drips or rusty nail tips on the underside of the roof.
• Walk round the outside. The Property Care Association lists missing, broken, displaced or loose tiles, faulty flashing around chimneys, defective valley gutters and flat roof surfacing, and blocked gutters in hidden valleys as roof causes.
• Trace the water. The same page says the progress of water through the building should be traced, because the stain may be some way from the entry point.

Rung 2: Record it and keep the air moving (free)

• Take dated photos of the patch and the loft. The Energy Saving Trust suggests photos before and after any professional works, and they help if you need to go back to the roofer.
• Do not block loft vents, grilles or airbricks. The Energy Saving Trust says warm air trapped in a loft can lead to condensation, damp, mould and rot in roof timber.
• Keep moisture out of the loft: shut the hatch, keep the bathroom fan working and vented outside, and do not dry washing under the hatch. Our guide to loft condensation and ventilation covers this.

Rung 3: Go back and fix the cause (cheap to moderate)

If the patch is rain-linked, give the roofer your photos and ask them to check flashings, valleys and gutters as well as the original repair spot. If you cannot get a straight answer, the Property Care Association suggests a trained and competent specialist to diagnose penetrating damp. Fix the cause before redecorating, and check our leaking gutters and downpipes guide if the stain runs down a wall.

Rung 4: When mechanical help makes sense

If the roof is sound and the loft vents are clear, but the home still holds moisture, controlling humidity can help. A loft-mounted dehumidifier such as Dryzen is one option for owner-occupied homes with a loft, with insulated ductwork to the central area or stairway. It helps stop the conditions mould and dust mites need. It does not stop a leak, it will not remove existing mould, which must be cleaned off, and it is not suitable for rented homes unless the landlord authorises the changes.

Mistakes that make it worse

• Painting over the stain before it has dried and before the leak is traced.
• Adding loft insulation over damp. The Energy Saving Trust says to fix damp first.
• Covering the eaves vents or airbricks with insulation or stored boxes.
• Having foam sprayed onto a leaking roof, which the Energy Saving Trust does not recommend.
• Assuming the stain is the entry point. Water can travel before it shows.

In Chatham and the Medway Towns

Medway Council's planning data lists 24 conservation areas, so check with the council before changing roof materials or chimneys if your street might be in one. Our pages for Brompton and Rochester cover older streets where roofs and chimneys are often the first thing to look at.

Questions we are asked

Related guides

• Loft Condensation and Ventilation
• Leaking Gutters and Downpipes: Damp Walls Explained
• Rising, Penetrating or Condensation Damp? How to Tell
• Cracked Render and Failed Pointing: Damp Through Walls
• Chimney Breast Damp

Local help

• Damp, mould and condensation help in Brompton
• Damp, mould and condensation help in Rochester
• Damp, mould and condensation help in Strood

Sources: Property Care Association: Penetrating damp; Energy Saving Trust: Roof and loft insulation; GOV.UK: Understanding and addressing the health risks of damp and mould in the home; Planning data: Medway Council conservation areas.