Flat Roof Waterproofing Preston
Signs your flat roof isn't watertight
- Puddles that stay on the roof a day or two after rain.
- Splits, cracks or blisters in the covering.
- Edges lifting at the trims, or gaps where the roof meets a wall.
- Damp patches or drips on the ceiling underneath.
- A soft or spongy feel underfoot, a sign the deck below may be wet.
- Moss or plants growing on the roof or in the outlets.
- Gutters or outlets blocked, so water can't get off the roof.
Where flat roofs let water in
The surface
Sun, frost and standing water age a flat roof covering. Older felt roofs crack and blister; any covering can split where the deck underneath has moved.
Joints and laps
Where sheets of material overlap or join, the seal has to hold for years. Failed joints are one of the most common causes of flat roof leaks.
Upstands and abutments
Where a flat roof meets a wall, the covering turns up the wall and is sealed, usually with lead flashing above it. If that detail fails, water runs down behind the covering. See our leadwork roofing page.
Edges and outlets
Edge trims, drip details and outlets into the gutters or downpipes all need to be sealed and clear. A blocked outlet can turn a sound roof into a pond.
Ponding
A flat roof should never be truly flat. It needs a fall so water drains to the edge or an outlet. When a deck sags or was laid without enough fall, water sits on the roof and wears it out much faster.
Repair or re-cover?
| Situation | Usual answer |
|---|---|
| Deck sound, damage in one area | Targeted repair |
| A failed joint, upstand or edge | Repair that detail properly |
| Covering failing all over, many past patches | New covering |
| Deck soft, rotten or sagging | Replace the deck, then a new covering |
| Water ponding because there's no fall | Re-lay to proper falls |
We'll tell you honestly which applies to your roof. A repair on a roof that's failing everywhere only buys a little time.
The systems we use
| System | What it is | Good for |
|---|---|---|
| EPDM rubber | A single sheet of rubber membrane, with few or no joints | Extensions, garages and dormers |
| GRP fibreglass | A layered fibreglass finish laid in place, with no joints | Extensions, dormers and roofs that need a hard-wearing finish |
| Built-up felt | Layers of bituminous felt bonded to the deck | A traditional, cost-effective choice |
All three work well when they're fitted properly. The right one depends on the roof, how it's used and your budget. Our new flat roofs come with 20+ year guarantees. For more on each system, see our flat roofing in Preston page.
Getting the details right
Most flat roof failures start at a detail rather than in the middle of the roof. When we waterproof a flat roof, we pay particular attention to:
- Falls, so water drains away instead of sitting on the roof.
- Upstands, turned up the wall to the right height and properly sealed.
- Flashing above the upstands, tucked into the wall in lead.
- Edge trims and drips, so water runs into the gutter, not down the wall.
- Outlets, sized and sealed so they don't block or leak.
Flat roofs we waterproof
Across Preston and the surrounding towns, flat roofs turn up in the same places again and again: rear kitchen and back-room extensions on terraced and semi-detached houses, dormers added for loft rooms, single and double garages, porches and bay windows, and larger roofs on shops, offices and industrial units. Each has its own weak points. Extension roofs often leak where they meet the house wall, dormers at their edges and cheeks, and garage roofs across the whole surface once the old felt has aged. We look at the whole roof and its junctions, not just the area above the damp patch.
Insulation and building regulations
The Planning Portal says that in most situations, re-roofing needs building regulations approval, and re-covering a roof should also improve its thermal insulation. That can apply to flat roofs too. We'll explain what applies to your roof when we quote.
Flat roof leak, or something else?
Not every damp patch under a flat roof is a leak in the roof itself. Condensation can form under a poorly ventilated or poorly insulated flat roof and drip back down, and a failed wall junction or gutter can look like a roof leak from inside. We check before recommending a repair, so you don't pay for the wrong fix. For leaks elsewhere on the house, see our roof waterproofing page.
Frequently asked questions
Why does water sit on my flat roof?
Usually because the roof doesn't have enough fall, or the deck has sagged. Re-laying the roof to proper falls fixes it.
Can you repair my flat roof instead of replacing it?
Often, yes, if the deck is sound and the damage is in one area or one detail.
Which is best: EPDM, GRP or felt?
All three work well when fitted properly. We'll explain which suits your roof and budget.
Do your flat roofs come with a guarantee?
Our new flat roofs come with 20+ year guarantees. Ask us for the details when we quote.
Do you waterproof garage and dormer roofs?
Yes. See our garage and outbuilding roofing page for garages.
Are your quotes free?
Yes. Call 07742 720 236 for a free quote.
Leaking flat roof in Preston?
Call Danny on 07742 720 236 or request a free quote. We cover Preston, Leyland, Chorley, Penwortham and the surrounding area.