Sustainable construction is one of the most over-marketed and under-delivered areas of the UK building industry. Every product brochure promises Passivhaus performance, every contractor claims green credentials, and very few homeowners can tell what is actually worth specifying.
This is our honest take, based on what we install and what we measure on real projects in London.
Insulation: The Single Best Investment
Insulation is boring, invisible, and the single highest-impact sustainability measure on any London home. It is also the cheapest, when done as part of an existing build or refurbishment. Specifying high-performance insulation in walls, floors and roofs typically adds 5 to 8 percent to a build cost and reduces lifetime heating bills by 40 to 60 percent.
If you are doing any building work, do not compromise on insulation. The marginal cost is small. The lifetime saving is enormous.
MVHR: Worth It, with Caveats
Mechanical Ventilation with Heat Recovery (MVHR) brings fresh filtered air into the house while recovering 85 to 90 percent of the heat from the outgoing stale air. On a well-insulated, airtight home, MVHR reduces heat loss substantially and improves indoor air quality measurably.
The caveat: MVHR only works properly in a genuinely airtight house. Installing it in a draughty Victorian terrace without first sealing the building envelope is wasted money. Get the airtightness right first.
Air-Source Heat Pumps: Yes, with Realistic Expectations
An air-source heat pump (ASHP) running on the UK grid produces 60 to 75 percent less CO2 than a gas boiler, and the gap widens every year as the grid decarbonises. Running costs are now broadly comparable to gas and falling.
The realistic expectation: ASHPs work best at lower flow temperatures (35 to 45°C) than gas boilers (60 to 70°C). To get good comfort, you need either oversized radiators or, ideally, underfloor heating. Retrofitting an ASHP into an undersized system gives a poor result.
Solar PV: The Numbers Have Finally Crossed Over
Five years ago, solar PV on a London roof was a marginal proposition. Today, with panels at half their previous cost and electricity at three times its previous cost, a typical 4kW system pays back in 7 to 9 years and then provides free electricity for the remaining 15 to 20 years of its life.
If you are doing any roof work, the marginal cost of installing PV at the same time is low. We design every new build and major refurbishment to be PV-ready as standard.
What We Are Still Cautious About
Battery storage is improving fast but is still a 10 to 15 year payback for most homes, and the batteries themselves typically need replacement at the 10 to 15 year mark. The economics will improve. We do not currently recommend specifying batteries unless the client has a specific reason (off-grid resilience, time-of-use tariff arbitrage).
Hydrogen-ready boilers are mostly marketing. There is no domestic hydrogen network and no near-term plan to build one. Specifying a hydrogen-ready boiler today is essentially specifying a gas boiler.
"The rule of thumb is simple: insulate first, ventilate second, then think about generation. Get the fabric right and everything else gets easier." Daniel Carter, Site Foreman.