The short answer
Check for light showing through the roof, dark stains and drips on timbers and underlay, damp or flattened insulation, soft or discoloured wood, and blocked ventilation at the eaves. Use a torch, stay on boards or look from the hatch, and record what you see with dated photographs. Anything that looks wet, soft or open to the sky is worth showing to a roofer.
Before you go up
Start with safety, because the loft floor is usually a ceiling. Plasterboard between the joists will not carry your weight, and a single step in the wrong place ends in a hole and a hospital trip. If the loft is boarded, stay on the boards. If it is not, you can usually see most of what matters from the top of the ladder with your head and shoulders through the hatch.
Take a bright torch rather than relying on the light, and wear a dust mask if there is old insulation or visible mould. Open the hatch on a bright day first. Light creeping in is the very thing you are looking for, and it shows best when the loft is dark and the sun is high.
Do not go into a loft that holds asbestos-looking material, damaged board or anything you cannot identify. HSE advises treating any property built or refurbished before 2000 as one that may contain asbestos, so leave suspect material untouched and ask for advice before you disturb it.
Tell someone you are going up, keep a phone in your pocket, and never use the loft as a place to stand on a chair or a stack of boxes. A mobile light on a clip or a head torch leaves both hands free for the ladder.
Why a loft check is worth doing
The loft is the one part of the roof an owner can inspect safely and for free. Water that gets through the covering leaves its trail on the underlay and timbers long before it reaches a ceiling, so a regular look catches a problem while it is still a small repair. It also gives you a baseline, a set of photographs of how the roof space looks when all is well, to compare against after bad weather. The wider service sits under roof inspections and surveys.
Daylight and stains
Switch the torch off, let your eyes adjust, and study the slopes above you. Pinpricks and slivers of light mean gaps: slipped or broken tiles, a displaced slate, a hole round a pipe. A tile that has slipped by a few centimetres can let in water in driving rain without ever showing from the road.
Then look for stains. Tide marks on the underlay or the rafters show where water has run, and the highest point of a stain is nearer the source than the lowest. Check round the chimney, where the roof meets a party wall, beneath valleys and around any roof window or flue pipe, since those are the places where the covering gives way to lead or sealant and where leaks most often begin. A fresh, damp patch is a current problem. A dry brown ring may be old and still worth noting.
Dark spots on the timber can mean mould from condensation. Our page on damp in a loft helps you tell leaks from condensation.
Felt, underlay and timbers
Look closely at the underlay, the membrane or felt that lies under the battens. On older roofs it may be bitumen felt that has become brittle, torn or missing; on newer roofs it is a breathable membrane. Sagging felt can hold water, and torn felt at the eaves can let wind-blown rain in.
Then look at the timber. Rafters, purlins and joists should be dry, pale and firm. A screwdriver tip pressed gently into the wood tells you quickly whether it is soft. Dark, crumbling or cracked timber, white fungal threads, a musty smell or fine dust beneath a timber with small round holes are all reasons to ask for a specialist opinion rather than guess. Our roof timber survey page covers those.
Check that nothing has moved: a rafter that has dropped, a sagging ridge or a joint that has opened up. Movement is a structural question and not a job for do-it-yourself fixes.
Insulation and ventilation
Insulation should lie evenly across the ceiling joists and stop short of the eaves, leaving a clear gap for air to enter. If it is pushed hard into the corners, flattened, wet or missing in patches, the loft will be colder and the ceilings below may sweat. Marley's guidance, which cites BS 5250, describes continuous eaves ventilation for a cold roof, so check that the vents or gaps at the eaves are open rather than blocked with insulation.
Look at what vents into the loft too. A bathroom or kitchen extractor discharging into the roof space is a common cause of damp, and it should be ducted outside. Check water tanks and pipes for lagging and for signs of dripping.
Finally, note what is stored. Boxes pushed against the eaves restrict airflow and hide faults. A tidy loft is easier to inspect, and a record of what you saw is useful if you later need to compare.
What to do with what you find
Write down what you see, with dated photographs and a note of where it is. A simple sketch of the loft with the chimney, hatch and problem areas marked is more useful than a long description, and it helps us find the spot on the outside. Our guide to roof inspection photos explains how we record what we find.
If everything is dry, firm and dark, check again after the next storm and once a year. If you find daylight, wet timber or a stain that is growing, ring us on 01793 626096 or send photographs on WhatsApp. We prioritise leaks, make a leaking roof safe first and price the proper repair in a written quote after the survey.
Buying a new home with a boarded loft, or one built recently? New build roof snagging lists faults to look for in newer houses, and roof inspection methods covers how a roofer checks what you cannot reach.