Flat roofs are particularly vulnerable during winter. Standing water that freezes and thaws, surface deterioration, failed joints and storm damage all conspire to turn a sound flat roof into a leaking one. This article explains why flat roofs leak in winter and what to do about it.
Standing water and freeze-thaw
Flat roofs should drain, but many develop low spots where water ponds. In winter that standing water freezes and thaws repeatedly, widening splits and opening seams. Each freeze-thaw cycle does more damage than the last. Correcting the falls so water drains is essential to a lasting repair or replacement.
Visible surface deterioration
As a flat roof ages, the surface deteriorates — felt becomes brittle and cracked, GRP develops hairline cracks, and EPDM seams fail. Winter rain finds every weakness. A drone or physical inspection shows how far the deterioration has gone.
Failed joints and edge detailing
Joints between membrane sheets and edge trims are common leak points. If they have lifted or separated, wind-driven winter rain gets straight in. Edge detailing that has come away from the wall or upstand is another frequent cause.
Roof penetrations
Pipes, vents and roof lights that pass through a flat roof are sealed with flashings and trims that age and fail. A failed seal around a penetration is a common winter leak source that is easy to miss from inside.
Storm damage
High winds can tear and lift flat roofing materials, and falling branches can puncture them. After a winter storm, have any flat roof checked even if no leak is visible yet. See our storm damage roof repairs page.
Repair, maintenance or replacement?
Not every flat roof problem requires replacement. A sound deck with a localised split or failed seam can often be repaired. A roof with broad covering failure, a rotten deck, or persistent ponding may need replacing. An inspection determines the right answer — we will always advise honestly rather than defaulting to the most expensive option. See our flat roofing page and arrange a free drone roof survey.
Frequently asked questions
Can a flat roof be repaired during winter?
Yes, in many cases. We repair splits, failed seams and active leaks in flat roofs year-round, and can apply temporary weatherproofing where conditions prevent a permanent repair on the day. A leaking flat roof should not be left until spring.
Why is my flat roof leaking during winter?
Winter flat roof leaks are commonly caused by standing water that freezes and thaws, surface deterioration, failed joints, lifted edge detailing, and storm damage. An inspection determines whether repair, maintenance or replacement is the right answer.