How long does a flat roof rebuild take?

A garage-sized flat roof taken back to the deck, re-boarded and re-covered in GRP with new fascia and gutter is usually a few days on site, depending on the size of the roof and the weather.

Why replace the deck instead of covering over it?

Laying a new covering over perished boards seals the damp and rot underneath a brand new surface, where it carries on quietly. Taking the roof back to the deck lets us replace what has failed and reset the falls, so the new covering sits on something sound.

What is GRP fibreglass?

GRP, or glass reinforced plastic, is a fibreglass covering laid over the timber deck as a single seamless laminate. It has no joints to fail, is walkable, and carries a long manufacturer warranty, which makes it ideal for flat roofs over garages and extensions.

Do you replace fascias and gutters too?

Yes. On this job we fitted a new treated fascia to the roof edge and a fresh gutter and downpipe, so the water leaving the new roof is carried cleanly away from the wall rather than running down the brickwork.

Case Study 04

Foxgate, Newport Pagnell: a flat roof rebuilt.

A tired garage flat roof taken back to the deck, rotten boards replaced, new fascias and a fresh gutter fitted, then re-covered watertight in GRP fibreglass.

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Foxgate garage flat roof re-boarded with a fresh timber deck ready for GRP

01/Project brief

Project brief

A small roof, done to a re-roof standard.

The owner had a garage flat roof that had quietly given up. Water was tracking through a perished covering, the timber below had gone soft in places, and the fascia line was rotten. The brief was not to patch it. It was to take the roof back to the deck, put the structure right, and re-cover it so it does not come back for a very long time.

DurationA few days
CoveringGRP fibreglass
ExtrasNew fascia + gutter

02/Project specification

Specification

The specification.

Every line item, on the record.

Finished Foxgate flat roof in grey GRP fibreglass with new black trim and white gutter — Project card
Foxgate Flat Roof Rebuild
A few days on site · GRP, fascia and gutter · Newport Pagnell

01 The brief

ClientPrivate residential ownerLocationNewport Pagnell, MK16PropertyResidential garage flat roofDurationA few days on site

02 The build

CoveringGRP fibreglass, laid over the deck as one laminateDeckPerished boards cut out, re-boarded in fresh treated timberFasciaNew treated fascia to the roof edgeGutterNew gutter and downpipe fitted

03 Sign-off

FallsFalls checked so water runs to the outlet, no pondingRecordWritten photographic recordRecordWritten photographic record throughout

Old flat roof covering stripped back to a worn timber deck before the rebuild

Finished grey GRP fibreglass flat roof with new black trim, fascia and gutter

03/ Before & after

A few days. A roof that sheds water again.

Before After

LocationNewport Pagnell

MaterialGRP fibreglass

TimeframeA few days

ScopeStrip, re-board, re-cover

04/Work breakdown

Stage by stage

Five stages, from strip to sign-off.

A flat roof is only as good as what is underneath it. The order of operations that took this one from leaking to watertight.

Old flat roof covering stripped off to reveal the worn, water-stained timber deck

Stage 01

01 Strip the covering

Strip the old covering.

The perished covering was stripped off entirely and the timber deck below exposed, so we could see exactly what we were working with rather than covering over the problem.

Soft, perished edge timber cut out from the roof edge above the old downpipe

Stage 02

02 Cut out rot

Cut out the perished timber.

Soft and rotten boards were cut out and the edge timbers checked. Anything past its life came off rather than getting buried under a new roof.

Flat roof re-boarded throughout in fresh treated timber, set to the falls

Stage 03

03 Re-board the deck

Re-board the deck.

The deck was re-boarded throughout in fresh treated timber, fixed down solid and set to the right falls so water runs to the outlet instead of sitting on the roof.

New white fascia, black trim and a fresh gutter and downpipe fitted to the roof edge

Stage 04

04 New fascia and gutter

New fascia and gutter.

A new treated fascia was fitted to the roof edge and a fresh gutter and downpipe hung, so the water leaving the new roof is actually carried away from the wall.

Finished grey GRP fibreglass flat roof laid as one seamless surface with dressed trims

Stage 05

05 Re-cover in GRP

Re-cover in GRP.

The roof was finished in GRP fibreglass, laid over the deck as a single seamless laminate with trims dressed into the edges. One continuous surface, no joints to fail.

05/Detail gallery

On site

The details that make the finish.

Finished GRP flat roof

New deck laid

Fresh treated timber

Perished fascia removed

06/Craft note

Why strip it back

Why we take a flat roof back to the deck.

The quick way to deal with a tired flat roof is to lay a new covering straight over the old one. It looks fine on the day and it is cheaper on the quote. The problem is that you have just sealed the perished timber and the old damp underneath a brand new surface, where it carries on quietly rotting out of sight.

Taking the roof back to the deck costs a little more up front and it is the only honest way to do it. You can see the timber, replace what has gone, fix the falls so water actually runs off, and know that the new covering is sitting on something sound. That is the difference between a roof that lasts a couple of years and one that lasts decades.

GRP fibreglass is the right finish for a job like this. It is laid as one continuous laminate with no seams, it is walkable, and it carries a long manufacturer warranty. For a small roof over a garage or an extension, it is hard to beat.