What roof covering should match my house extension?

Planning rules require materials similar in appearance to the existing house, so most post-war homes get concrete interlocking tiles, period properties get clay or natural slate, and flat sections use EPDM or GRP. Your roofer matches the existing profile and orders accordingly.

Why do most extension roof leaks happen at the lead flashing?

The abutment, where the new roof meets the existing house wall, is the most leak-prone junction on any extension. The tiles themselves rarely fail. Most leaks trace to missing soakers, the wrong lead code, or flashing dressed incorrectly for the tile profile.

What is patination oil and why does it matter?

Patination oil is a treatment brushed onto fresh lead flashing to stop white carbonate staining running down your brickwork and tiles. It must go on before the first rainfall after installation. It costs very little but prevents staining that is expensive to clean off later.

Is EPDM or GRP better for an extension flat roof?

EPDM rubber suits most extension flat roofs: it comes in a single jointless sheet and lasts 25 to 50 years. GRP fibreglass costs more and needs a specialist, but it cures to a walkable surface, so it is better for a flat roof that doubles as a balcony or needs regular access.

Can you still bed ridge tiles in mortar?

Not as the sole fixing. Since BS 5534 was updated in 2015, ridge, hip, and verge tiles need mechanical fixing through a dry ridge or dry verge system. Mortar alone failed too often, with widespread storm-related claims from tiles lifting.

When should building control inspect the roof covering?

Before the scaffold comes down. The officer needs to see the ridge, flashing, and tile fixing at close range from the platform. Once the scaffold is gone they are inspecting from the ground with binoculars, which they will not be happy about.

Back to Loft Conversion

Phase 4 · Structure · Task 05 of 07

Roof Covering for Your Loft Conversion

What goes on the roof once the structure is built: tiles, flat roof membranes, lead flashing, dry ridge, fascia, soffits and guttering, plus a pre-payment checklist.

19 min readUpdated 2026Premium

Process infographic showing the roof covering build sequence from breathable membrane through battens, tiles, ridge, flashing, fascia, soffit and guttering, with the extension becoming watertight at each stage

Prerequisites

Complete these first

Tiles are the easy bit. Any half-competent roofer can hang tiles and nail slates. What separates a roof that stays watertight for 50 years from one that leaks within 18 months is the stuff nobody photographs for Instagram: the lead flashing at abutments, the soakers under every tile course where roof meets wall, the patination oil that prevents white carbonate staining, and the dry ridge clips that stop ridge tiles lifting in a gale. Ten out of fourteen forum threads analysed for this guide were about leaks at the junction where extension roof meets existing house wall. The tiles were fine. The flashing wasn't.

Your roofer's job is to turn the bare timber frame (covered in breathable membrane from the roof structure stage) into a fully watertight envelope. Once that's done, your electrician, plumber, and plasterer can start work in a dry space. The weather stops being your enemy. But if the covering is rushed or the details are wrong, you'll be chasing leaks for years.

Do this first

Your roof structure must be complete with breathable membrane installed and inspected by building control before the roofer starts. If you have roof windows (Velux or similar), they should be on site before tiling begins. The roofer needs to tile around them, and the window manufacturer's flashing kit integrates with the tile courses. Missing windows means the roofer either leaves gaps (weather risk) or tiles over the opening (rework).

What this guide covers

01Choosing Your Covering: Pitched Roof
02Choosing Your Covering: Flat Roof
03Battens, Counter-Battens, and the Standards That Apply
04Lead Flashing: Where 90% of Extension Roof Leaks Start
05Dry Ridge and Dry Verge: Why Mortar No Longer Counts
06Fascia, Soffit, and Bargeboards
07Guttering and Rainwater
08The Roofer-Window Junction Problem
09What Building Control Checks
10What It Costs
11The Pre-Payment Inspection Checklist
12Timeline
13Building Regulations That Apply
14Common Problems and How to Spot Them
15What Comes Next

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General guidance for homeowners in England (and Wales where we say so), not professional advice. Every site is different: check anything that affects your build with a qualified professional, your local council or building control. Terms

Roof Covering for Your Loft Conversion

Complete these first

What this guide covers

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Frequently asked questions

Reference guides for this task

Tools

Materials

Background reading