Passivhaus Retrofit & Extensions, Sutton, Surrey

Futureproofing was central to renovating this spacious five-bedroom 1930s detached home in Sutton, Surrey, now complete with a luxurious heated outdoor swimming pool designed for year-round enjoyment and lasting value.

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Project Snapshot

Scope
Deep-fabric Passivhaus retrofit, full-width rear extension, pool-energy integration

Property
1930s five-bed detached house with outdoor swimming pool

Aesthetic
Heritage frontage + contemporary brick-banded extension

Programme
14 months on site

Services
On-site design development, engineering management, energy modelling, construction, airtightness testing

The Brief

Future-proof a period family home while preserving its character. The owners wanted a Passivhaus-level envelope to cut carbon footprint dramatically, reuse existing materials wherever possible, and create a bright, modern rear extension for family life.

Key Challenges

Retain fabric, improve performance – upgrade walls, roof and floors without wholesale demolition.
Blend old and new – a modern rear extension that feels at home alongside 1930s brickwork.
Integrate pool & house services – share heat efficiently between pool and dwelling.

Favourite Feature

A reclaimed-oak staircase framed by steel balustrades leads to a sun-soaked landing – marrying original craftsmanship with modern lines.

What We Delivered

Fabric-first retrofit – external walls over-wrapped, roof insulated, floors upgraded, all airtight to < 0.6 ACH.
Triple-glazed timber windows – period-style frames with Passivhaus-level performance, complete with airtight ironmongery.
Low-carbon materials – concrete with reduced cement content and lightweight low-carbon blocks throughout the new extension.
Full-width rear extension – open-plan kitchen-diner in glazed brick bands; structural knock-through links to the front sitting room.
Heritage elements restored – original doors, panelling and 1930s bathroom fittings stripped, repaired and reinstalled.
Renewable energy loop – solar-powered air-source heat pump for the house; pool heat pump linked so surplus energy can be shared both ways.
Concealed services & MVHR – ductwork hidden within new finishes; CO₂ consistently below 800 ppm indoors.

QUOTE

“We build with design in mind.”

— Valter da Silva, Managing Director

Outcome

The house now meets Passivhaus performance targets while retaining its 1930s charm. Space-heating demand is under 15 kWh/m²-year, slashing operational carbon. Airtightness achieved 0.42 ACH @ 50 Pa on first test, and the integrated renewable systems significantly reduce the home’s lifetime carbon footprint.

“Happy Building showed us you don’t need to knock down to build green. The house feels brand-new yet still ours.”
— Homeowner

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