Building for the future: North Somerset’s approach to Passivhaus

As the UK moves toward higher performance requirements through the Future Homes Standard, and local authorities face increasing pressure to deliver climate action and more affordable homes, Elm Grove demonstrates how Passivhaus can be delivered at scale through a proven and reliable route to compliance

Elm Grove in Nailsea is a 52 home new build development, delivered across 20 blocks and comprising 44 houses and 8 bungalows. The scheme represents a major step forward for North Somerset Council’s ambition to embed Passivhaus into their future housing delivery.

Designed to respond sensitively to its ecologically rich setting, more than half of the site’s existing green space has been retained, with community gardens, orchards, foraging paths and ecological corridors woven throughout. In total, 56% of the site is dedicated to landscape and biodiversity, delivering a measurable biodiversity net gain.

Key stats

Construction: Timber frame
Number of homes: 52
Property type: Detached, semi-detached (including bungalows) and terrace
Occupancy: 2-7 persons
TFA: 57.57 m2 – 146.61 m2 per dwelling m²
Build start date: 2024
Completed: 2025
Certified: 2026 Passivhaus Classic (41 houses), Passivhaus Plus (3 houses) & PHI Low Energy Building (8 bungalows)

This development shows what’s possible when local authorities take a proactive role and work with local partners to facilitate housing delivery. Elm Grove offers much-needed affordable homes for sale and rent, all built to the highest energy efficiency standards. North Somerset Council’s Development Strategy looks to deliver homes and jobs that meet the needs our community now and in the future. These are the building blocks of thriving local communities, which is why it’s critical these sustainable Passivhaus homes are affordable and of quality.

Councillor Mark Canniford, North Somerset Council

Construction

A Passivhaus‑certified timber frame provided low embodied carbon, predictable thermal performance and suitability for rapid, high‑quality installation. Because the system’s U‑values and thermal bridge details were pre‑calculated, early‑stage modelling was simplified and uncertainty reduced.

Form factors across the development range from 2.56 to 3.99. The bungalows sit at the higher end, explaining their PHI Low Energy certification. Although they follow the same construction specification as the houses, their less favourable form factor results in a higher heating demand.

Elm Grove, Nailsea Credit Greengauge

U-values

Roof: 0.096 W/m²K

150 mm mineral wool between joists + 300 mm above; some houses insulated at rafter level with insulated panel + service void.

Wall: 0.105 W/m²K

Passivhaus‑certified timber frame: 235 mm mineral wool in panel + 50 mm internal service void + 50 mm externally.

Floor: 0.106 W/m²K

300 mm XPS; thermal bridging mitigated using aerated concrete block and cavity insulation at slab edge

Further information can be found at the International Passivhaus Database listing - Block Q

Building performance

Across the development, space heating demand ranges from 14–30 kWh/m².a, reflecting differences in form factor and certification level.

Measured energy performance
Airtightness n₅₀ (≤ 0.6ACH @ 50 Pa)	0.34 - 0.87 @ 50 Pa (Dwellings exceeding 0.6 ACH were certified to PHI Low Energy Building standard)
Space Heating Demand (≤ 15 kWh/m².a)	14 - 30 kWh/m².a
Heating Load (≤ 10 W/m²)	8 - 14 W/m²
Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)	49 - 83 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Elm Grove, Nailsea, Credit Rebecca Faith

Services

All dwellings are equipped with Passivhaus‑certified MVHR units with high heat‑recovery efficiency and summer bypass. Space‑heating demand is extremely low, so air‑source heat pumps were not required. Instead, heating is provided by direct electric radiators, with hot water supplied by an individual hot‑water heat‑pump cylinder in each dwelling.

Each home also includes 3.44–6.075 kWp of solar PV, providing at least 90% of predicted energy demand. Two blocks achieved Passivhaus Plus certification due to their larger PV arrays.

Dynamic overheating modelling informed the summer comfort strategy, which includes modest glazing areas to limit solar gain- natural ventilation through openable windows and MVHR with summer bypass

Elm Grove, Nailsea, Water heater, Credit Greengauge

Elm Grove, Nailsea, MVHR, Credit Greengauge

Lessons learned

Delivering Passivhaus at this scale within local authority constraints required careful coordination of design, procurement and construction. The project benefitted from an integrated approach. This enabled simple, cost‑effective solutions that supported certification across all blocks.

Early optimisation pays off: The near north–south orientation optimises winter solar gain while limiting summer overheating, reducing space‑heating demand and avoiding the need for excessive insulation thicknesses.
Choose high‑quality, Passivhaus‑ready products early: Having certified or well‑modelled components allowed accurate energy modelling from the outset.
Keep systems simple: With minimal heating demand, direct electric radiators and hot‑water heat pump cylinders proved efficient and cost‑effective.

It has been great to be able to offer an integrated approach, combining both building physics and mechanical services design for the project. Greengauge has been able to help provide simple and cost-effective solutions for the development.

Mitch Finn, Greengauge

Key team

Client: North Somerset Council/ Stonewood Homes
Architect: Mikhail Riches/ APG Architecture
M&E Design & Passivhaus Consultant: Greengauge
Contractor: Stonewood Homes
Environmental Consultants: Johns Associates, Seed, Vectos
Structural Engineer: JDL Consultants
Passivhaus Certifier: Etude

Elm Grove demonstrates how local authorities can deliver certified Passivhaus homes at scale, combining high performance, comfort and affordability, while addressing both the climate emergency and local housing need.