The short answer
The loft shows a leak before the ceilings do. Look for dark stains running down rafters and battens, insulation that is wet, flattened or discoloured, rusty nail tips, drips or damp patches on boards, and chinks of daylight in the covering. Check from the hatch or on boards, never by stepping between joists, and photograph what you find before you call a roofer.
Stains, damp and daylight
A good torch and a few minutes are all you need. Start at the hatch and sweep the light across the underside of the roof, then along the rafters, the battens and the ridge, looking for anything that is darker, wetter or out of place.
Water leaves a trail. Look for dark stains that run down a rafter or batten, often with a tide mark at the edge where a damp patch has dried and left a line of dirt. Timbers that are darker in one area than the rest, or that feel soft when pressed with a screwdriver, have been wet for some time.
Insulation is a good indicator. Wet insulation looks flattened, clumped or discoloured, and may smell musty. If it is heavy and compressed in one spot, water is probably dripping onto it from above.
Check the underlay, the membrane beneath the tiles, where you can see it. Tears, sagging sections and stains on the felt show where water has been getting past the covering.
Daylight is the simplest sign of all. Light coming through the roof where it should be dark means a gap, such as a missing or cracked tile. Do this check in the daytime, and note where any light enters so you can describe it to a roofer.
Nails, metal and the quiet signs
Some signs are easy to miss. Look at the nail points that come through the roof boards or battens. Rust, beads of water or a green or white crust on them can mean moisture is passing through repeatedly, either from a leak or from condensation.
Lead flashings and metal fittings can show white powder or corrosion where water has been sitting. Around the chimney, check the stack and the junction with the roof for damp patches, which may be the first sign that a flashing is failing.
A damp, musty smell in the loft is a warning even when nothing is visibly wet. Mould or fungal growth on timbers points to damp that has been there a while and may be spreading.
Watch for the difference between a leak and condensation. A leak leaves a local, defined stain, while condensation tends to spread widely, with beads of water and speckled mould along the roof's inner face. Our page on roof leak or condensation explains how to tell them apart.
Also look for droppings, nests or gnawed material, since pests can damage insulation and underlay and open routes for water.
Seasonal checks that catch problems early
A loft check once or twice a year is enough for most homes. Autumn is a sensible time, before the wet season, because you can spot problems that need fixing before the weather turns. A second look after the winter shows what the weather exposed.
It is also worth looking after any severe storm, or after heavy rain that was followed by wind. A single shifted tile or flashing can allow water in, and the signs appear quickly in the loft.
Keep a short log with dates and photographs. If you take a picture of the same area each time, you can see whether a stain is growing, which helps when you explain the situation to a roofer or an insurer.
Check safely. Step only on boards or joists, take a stable light, and do not lean on the ceiling between joists, since plasterboard will not take your weight. If the loft is cramped, full of stored items or has no boarding, ask someone to hold a torch from the hatch rather than going in.
Never go onto the roof itself to investigate. The loft side gives most of the information, and a roofer can look at the outside safely, with the right access.
What to do when you find something
Photograph the area, with a wide shot to show where it is and a close one to show the detail, and note the date. If water is dripping now, put a container beneath it and protect what is below.
Do not stuff the area with insulation or sealant to hide the problem. Covering a stain means you lose track of the source, and it can trap moisture against timber.
Then arrange a survey. A roofer traces the stain uphill and checks the covering above it, because the entry point is rarely directly over the stain. Photographs of the loft and the outside of the roof, plus measurements of the affected area, go with a plain-words explanation. The repair is then priced as a single written total.
If the leak is recent and small, the repair is often modest, such as replacing a tile or re-dressing a flashing. Acting early keeps it that way. If the timbers are soft or the covering is failing more widely, we show you the evidence and explain the options.
The find a roof leak page describes how the source is traced, and roof repairs covers the work we do. If the water is near wiring, read about a roof leak near a light fitting first.
