Sustainable architecture in London: what it means for your home

Sustainability · Design

What sustainable architecture means for a London house, extension or retrofit: the features that make a difference, two of our projects with their insulation figures, heat pump grants, and what to look for in green architects.

Last updated: 2 November 2026 · Reviewed by Graham Sproul RIBA, Design & Operations Director

The figures here are approximate and meant to give you an idea, not a quote. Every house and brief is different, so your costs and programme will depend on your project.

What is sustainable architecture?

Sustainable architecture, also called green architecture or environmental architecture, is design that reduces a building’s impact on the environment across its whole life: the energy it uses to heat and run, and the carbon and resources that go into building it. For many London homeowners, that means architecture for green living in an existing house, because the house is already there, and adapting it well avoids the carbon of building a new one.

Environmentally friendly architecture on a house or extension comes down to a few decisions made early: where the new space goes and which way it faces, how well the walls, roof and floor hold heat, how the house is ventilated, and how it is heated. Materials and fittings follow from those.

Sustainable architecture features for a London house

These are the eco-friendly solutions in architecture that make a difference on a typical London house or extension, in roughly the order we’d tackle them.

Feature	What it does	Where it fits
Keeping and adapting the existing house	Avoids the carbon of demolition and new structure	Every project: extend and rework before replacing
Insulation to the walls, roof and floor	Cuts heat loss through the building fabric, measured as a U-value	New extensions to current Building Regulations; existing walls with care
Airtightness and ventilation	Stops draughts, while controlled ventilation keeps the air fresh and the building dry	New work and deep retrofits
Better windows, or repaired and secondary-glazed ones	Reduces heat loss and draughts at the weakest part of the wall	New glazing in extensions; repair and secondary glazing in period houses
Heat pumps	Low-carbon heat from the air or ground, run on electricity	Houses insulated well enough to run on lower flow temperatures
Solar panels	Generates electricity on site	Unshaded roofs; planning rules in conservation areas
Green roofs	Holds back rainwater and supports plants and insects on a flat roof	Flat roofs on extensions and garden buildings
Timber structure and natural materials	Timber stores carbon; lime and other breathable materials suit old walls	Glulam beams, timber frames, lime plasters and renders

Natural materials are part of this. Glue-laminated timber, called glulam, can span a large room while storing carbon in its structure, and lime mortars and plasters let old solid walls breathe. For interiors and finishes, our guide to sustainable interior design covers the choices inside the rooms.

Sustainable architecture examples: two of our projects

These two Hertfordshire extensions show what fabric-first design looks like on real houses. The figures come from the specification and Building Regulations drawings for each project.

Element	Project	Target	Specified
Arched roof	Toulmin Drive	0.13	0.13 (to target)
New walls	Toulmin Drive	Below 0.18	0.16
Green roof	Maple Lodge	Below 0.15	0.12

Worked example: what a lower U-value means

A U-value is the heat, in watts, that passes through one square metre of a wall or roof for each degree of difference between inside and outside. Multiply it by the area and the temperature difference and you get the heat lost. Here is the effect of the specified values on an illustrative 30 m² roof and 40 m² of wall, on a day 20°C colder outside than in.

Element	At the target	As specified	Difference
Roof, 30 m², Maple Lodge figures	0.15 × 30 × 20 = 90 W	0.12 × 30 × 20 = 72 W	18 W less, 20% (18 ÷ 90 = 0.2)
Walls, 40 m², Toulmin Drive figures	0.18 × 40 × 20 = 144 W	0.16 × 40 × 20 = 128 W	16 W less, 11.1% (16 ÷ 144 = 0.111)

Small numbers per element, but they apply every hour the heating is on, for the life of the building, and they let a heat pump run at lower temperatures.

Making an existing London home greener

Many older London houses have solid brick walls, which behave differently from modern cavity walls. Insulation in the wrong place, or the wrong material, can trap moisture in the wall. Where we use internal wall insulation on solid walls, the junction with the floor joists built into the wall needs its own detail, because the joist ends can become colder and damper behind the insulation, with a risk of condensation and rot.

Windows are often the easier win. Historic England’s research on sash windows found heat loss cut by “40 to 50%, simply by closing curtains or lowering plain blinds”, and by “over 60%” with low-emissivity secondary glazing (October 2009). The figures come from Research into the thermal performance of traditional windows: timber sash windows by C. Wood, B. Bordass and P. Baker (English Heritage, now Historic England). If your house is listed, our guide to renovating a listed building covers when energy works need consent.

Heat pumps and the Boiler Upgrade Scheme

The Boiler Upgrade Scheme gives a grant towards replacing a fossil fuel boiler with a heat pump. These are the current grants on GOV.UK. Until March 2027, a home heated by oil or LPG with no mains gas connection can get an extra £1,500 towards an air source or ground source heat pump.

System	Grant
Air-to-water air source heat pump	£7,500
Ground source heat pump	£7,500
Air-to-air heat pump	£2,500

The outdoor unit is the part to plan for. It makes some noise, and on a tight London plot it may sit close to a neighbour’s window. The government’s Planning Portal says that installing an air source heat pump on a house “is considered to be permitted development, not needing an application for planning permission”, within limits. The outdoor unit must be no larger than 1.5 cubic metres and the installation must meet the MCS 020a planning standard; the rights don’t apply within the curtilage of a listed building, and in a conservation area the unit can’t go on a wall or roof that fronts a highway. Where you do need permission, include a noise report: a recent AURA application in a London borough, for air conditioning units, was refused because it had no acoustic assessment. Our guide to why planning permission is refused explains how to avoid that. For new homes, the Future Homes Standard is the next step in the energy rules, and our guide to solar panels and the Future Homes Standard covers what it means for solar panels.

Sustainable architecture firms: what to look for in green architects in London

If you’re looking for eco friendly architects or sustainable home architects in London, ask to see the evidence on built projects. Useful questions:

• What U-values did your recent extensions achieve, and were they better than the Building Regulations targets?
• How do you insulate solid walls in a period house without trapping moisture?
• How do you plan for a heat pump, including where the outdoor unit goes and what the neighbours will hear?
• Which existing parts of my house would you keep, and how would that change the carbon of the project?

Our sustainable design service page sets out how we approach this on homes in London and the Home Counties.

FAQs

Sources