Home / Low / Flat Pitch Roofs

Flat and low-pitch roofs, built as complete systems.

Most flat roof failures aren't the membrane — they're poor falls, missing vapour control and weak upstand detailing. We design and install the whole build-up, not just the top layer.

Systems: EPDM · GRP · Felt
Pitch range: 1:80 to 10°
Life expectancy: 25–50 years
Build-up: Warm deck

01Overview

A flat roof is only as good as what sits beneath the membrane.

A 'flat' roof is never truly flat. It needs a designed fall so water drains to an outlet or gutter instead of sitting on the surface. Ponding water accelerates membrane ageing, adds load to the structure and finds any weakness at a lap or upstand. We set falls with tapered insulation or firrings so the finished roof drains at 1:80 or better.

We build almost every new flat roof as a warm deck: the insulation sits above the timber or concrete deck, so the structure stays at room temperature and condensation can't form inside it. A vapour control layer on the warm side and a fully bonded membrane on top complete the system.

On refurbishments we survey the existing deck, take core samples where needed and check moisture levels before recommending an overlay or a full strip. Where a cold roof can't be converted, we show you how to ventilate it properly.

Each project finishes with upstands, outlets, rooflight kerbs, drip trims and wall abutments detailed to the manufacturer's system, so the guarantee covers the whole roof.

02Where it's used

Typical applications

a.
Rear & side extensions
Warm roofs with rooflights, tied into existing walls with proper abutment flashings.
b.
Dormers & garages
Small-area roofs where neat trims and drips matter as much as the membrane.
c.
Balconies & terraces
Inverted or paved build-ups with walkable finishes over occupied space.
d.
Commercial & retail
Large-area felt or single-ply systems with tapered schemes and internal outlets.
e.
Green & blue roofs
Root-resistant membranes and drainage layers for sedum or attenuation roofs.
f.
Refurbishment
Strip, survey and upgrade older roofs to current insulation standards.

Finished EPDM flat roof with rooflight on an extension — a.Single-sheet EPDM warm roof with a flush rooflight and edge trims.

Flat canopy roof over a front entrance at dusk — b.The same warm-roof build-up, finished behind an aluminium fascia.

03Systems

Choosing the right membrane

System	How it's laid	Best for	Typical life	Watch-outs
EPDM rubber	Single sheet, fully bonded, few or no seams	Extensions, dormers, garages	40–50 yrs	Needs care at complex details; plain matt finish
GRP fibreglass	Resin and glass matting laid wet, seamless	Balconies, walkways, intricate shapes	25–35 yrs	Weather-sensitive install; deck must be stable
Torch-on felt	Two or three bonded bitumen layers	Commercial, large areas	20–30 yrs	Hot works permit; fire-safe detailing at edges
Liquid systems	Cold-applied coating with reinforcement	Refurb overlays, awkward penetrations	15–25 yrs	Only over a sound, dry substrate

04Detail

How it's built

Warm flat roof build-up

Insulation sits above the deck, keeping the structure warm and dry.

1
Waterproof membrane
EPDM, GRP or felt — the weathering layer, bonded to the insulation.
2
PIR insulation to falls
Sits above the deck so the timber stays at room temperature. Tapered boards create the fall.
3
Vapour control layer
Stops warm, moist indoor air reaching the cold side of the insulation.
4
Deck
18mm OSB3 or plywood — the base the system is bonded to.
5
Joists
Structure sized by the engineer for span and load.

Common failure points

Ponding water from inadequate falls
Missing or punctured vapour control layer
Upstands lower than 150mm at walls and door thresholds
Outlets undersized or set above membrane level

05Process

From survey to handover

01
Survey
Measure, check the deck, outlets and wall abutments, and agree access.
02
Design
Falls layout, insulation thickness to the target U-value, outlet sizing.
03
Install
Deck, vapour control, tapered insulation and membrane in sequence.
04
Handover
Flood test where specified, photos of every stage, guarantee registration.

06Specification

Notes for architects & QS

Falls: Design to 1:40 to achieve a minimum finished fall of 1:80, allowing for deflection and tolerances.
Upstands: Minimum 150mm above finished roof surface at walls, rooflights and plant kerbs.
Thermal: Insulation thickness calculated to current Part L elemental U-value; calculation supplied per project.
Condensation: Warm deck preferred. Condensation risk analysis (BS EN ISO 13788) available on request.
Standards: BS 6229 Flat roofs with continuously supported flexible waterproof coverings.
Fire: System classification to suit boundary distance; Broof(t4) systems available.

Guidance figures only — final details are confirmed against manufacturer literature and the project engineer's design.

07FAQ

Common questions

How long does a flat roof last?

A well-designed EPDM or GRP warm roof should last 30–50 years. Most early failures come from poor falls or detailing rather than the membrane.

Can you lay a new roof over the old one?

Sometimes. If the deck is dry and sound, an overlay can save cost. We check moisture levels and deck condition first and only recommend it when it's safe.

Which is better, EPDM or GRP?

EPDM is the better choice for most extensions: a single sheet, very durable, quick to lay. GRP suits roofs you'll walk on or with lots of complex shapes.

Do I need to insulate when replacing a flat roof?

Replacing more than 25% of a roof usually triggers the Building Regulations requirement to upgrade insulation. We include it in the price as standard.

How long will the work take?

A typical extension roof takes 2–4 days, weather permitting. We keep the building weathertight overnight throughout.

Have drawings or a roof that needs attention?

Send plans, photos or a short description. We'll review it, visit if needed, and come back with an itemised price and programme.

Request a quote 087 000 0000