Five materials that make a London home extension more sustainable

Material choice is the single biggest decision you’ll make in a sustainable extension. More than the glazing spec, more than the heating system, more than the renewable energy bolt-ons that often get added at the end. The materials you build with determine the carbon your extension carries for its entire lifetime before anyone has switched a light on.

Here are the five materials we reach for most often at New Makers Bureau; what they do, why we like them, and what to watch out for.

1. Reclaimed brick

Reclaimed brick is probably our most used and most loved material. Its carbon was spent when it was first fired, often a century or more ago. By reusing it, you’re not asking for new carbon to be emitted — you’re giving an existing material a second life and keeping it out of landfill.

Beyond the carbon argument, reclaimed brick just looks better. The variation in colour, the weathering, the slight imperfections — these are what give a brick its character. New bricks, however carefully matched, tend to look flat by comparison. A well-chosen reclaimed brick can make a new extension feel as if it’s always been there.

The challenges: it takes more effort to source, you need to find the right match for your existing building, and not all reclaimed bricks are suitable for external use. A good architect will know how to navigate this and can recommend salvage specialists with the right stock. The carbon saving: roughly 565 kg CO₂ eq/m³ for new brick, down to around 4.9 kg CO₂ eq/m³ for reclaimed is dramatic.

Downton Avenue reclaimed Suffolk White brick in a south London extension

2. Timber frame (SIPs and engineered timber)

Sustainably sourced timber is the only major structural material that stores carbon rather than releasing it. The tree absorbed CO₂ as it grew; that carbon stays locked in the timber as long as the building stands. Engineered timber products — cross-laminated timber (CLT), laminated veneer lumber (LVL), structurally insulated panels (SIPs) — take this further, making large, dimensionally stable structural elements from smaller, more sustainably managed trees.

For London extensions, SIPs are particularly useful. They combine structure and insulation in a single panel, build quickly, and achieve excellent airtightness. The speed is a real advantage: a timber frame extension builds faster than blockwork, involves fewer wet trades, and reduces programme time, which matters a great deal when you’re living in the house being extended. We also use zero carbon timber sheet materials fo rinternal joinery such as MDF and joinery.

3. Recycled wood fibre insulation

Most insulation on the market is made from petrochemical foam: rigid PIR or PUR boards. They perform well thermally but carry a significant embodied carbon cost and are difficult to recycle at end of life.

Wood fibre insulation is made from waste timber, stores carbon, and is breathable, which matters particularly in older London homes where moisture management is important. It performs excellently as both thermal and acoustic insulation, and works well with a timber frame structure. Hemp and cork are similarly good natural insulation options, each with slightly different performance profiles.

The honest caveat: natural insulations are typically thicker than foam boards for the same thermal performance. In a constrained London site, that can sometimes be a design challenge. It’s worth having the conversations early.

4. Lime mortar and breathable construction

London’s housing stock is predominantly Victorian and Edwardian: buildings designed to breathe. Repointing them with cement, or sealing them with impermeable modern materials, traps moisture and causes damage. Lime mortar is the historically correct and the technically appropriate material: it’s breathable, it’s softer than the bricks (so it takes the movement, not them), and it’s carbon-better than cement.

For a sustainable extension on an older London home, specifying lime mortar and understanding how the new extension needs to relate to the existing building in terms of breathability is essential. It’s a detail that gets overlooked surprisingly often.

5. Green roofs

A green roof isn’t a structural material, but it belongs on this list because of what it does. A well-specified sedum or biodiverse green roof manages rainwater runoff, provides insulation, extends the life of the roof membrane, supports urban biodiversity, and on a flat-roofed extension in London is often achievable without meaningful additional structural cost.

London’s drainage infrastructure is under increasing pressure as rainfall intensifies. Green roofs help. They’re also increasingly looked upon favourably in planning applications, particularly in boroughs with strong sustainability policies.

Questions to ask: what loading can the structure take? What’s the maintenance requirement? A simple sedum blanket requires very little attention; a wilder biodiverse roof requires a little more. Both are worth it.

What to ask your architect

When you’re appointing an architect for a sustainable extension, ask them specifically about these materials. Ask where they’ve used reclaimed brick before, how they specify timber frame, what their preferred insulation products are and why. The answers will tell you quickly whether they’re genuinely material-literate or just ticking a sustainability box.

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