Certified Passivhaus using our Passive Timber Frame System

Woodlands shows how a Passive timber frame system can be integrated with an exposed oak structure to achieve independently certified Passivhaus performance. At approximately 200m², this project provides real-world evidence of how precision off-site manufacture, a fabric-first approach and technical collaboration can translate demanding performance targets into a beautiful homme with low energy costs, providing a healthy living environment for the owners. 

The project set out to achieve certified Passivhaus performance while retaining the architectural expression of an exposed oak frame. The building envelope therefore needed to deliver exceptional thermal performance and airtightness, provide a thermal-bridge-free design and integrate effectively with the wider building services strategy, while keeping the design intent uncompromised. 

Our Passive Timber Frame System formed the basis of the project's fabric-first strategy. Precision-manufactured off-site, the wall and roof system were engineered to provide a continuous airtight layer around the building, connected to the insulation beneath the floor slab and sealed with airtight tape. The vapour-open construction and insulated panel build-up supported the stringent requirements of Passivhaus certification while integrating with the exposed oak structure. 

• Continuous thermal building envelope
• Cold bridge-free design 
• Wall U-value: 0.10 W/m²K
• Roof U-value: 0.10 W/m²K
• Airtightness: 0.50 ACH 
• Triple glazing: 0.75 W/m²K
• MVHR-system: high-efficiency heat recovery captures up to 90% of otherwise wasted heat energy, while also providing clean, filtered fresh air at a constant humidity
• Ground source heat pump provides domestic hot water and minimal space heating
• Passivhaus space heating demand: 13 kWh/(m²a)
• Heating demand: 13.2 lkWh/(m²a) 
• Overheating result: 0.1% 

In-use monitoring provides strong evidence of long-term performance. During 2020, outdoor temperatures ranged from 3.75°C to 33.09°C while indoor temperatures were almost aways stable between 22–24°C, dropping to 20–21°C overnight. 

During the July 2022 heatwave, indoor temperature rose from around 21°C to 25°C and exceeded 25°C for only one hour. In 2023, the indoor temperature exceeded 25°C for a total of 11.5 hours across the year (0.1% of the time). 

"We have now lived in a certified, self-build Passivhaus for five years. We would say that the continuous thermal comfort (irrespective of the time of year), coupled with a constant supply of 100% fresh air, and a total absence of draughts, providing a tranquil, relaxing, bright and open yet somehow also 'cosy' environment, is the most important, and pleasurable aspect. The fact that our heating costs are an estimated £273/year at January 2024 prices is an added bonus." Says Andrew, homeowner. Read more about their journey here.