Proper ventilation is essential in timber frame buildings. It protects both the building fabric and occupant health by managing internal moisture, regulating air quality, and supporting energy-efficient performance. In well-sealed timber structures, ventilation becomes a critical part of the overall building strategy, not just an add-on.
Timber Frame and Airtightness
Modern timber frame construction delivers excellent airtightness thanks to precision manufacturing, taped membranes, and service voids. Air permeability levels below 3 m³/m²·h @ 50 Pa are achievable as standard, with sub-1.0 figures possible for homes targeting Passivhaus or AECB performance.
This high level of airtightness significantly reduces uncontrolled air leakage and improves thermal efficiency. But it also removes the incidental ventilation that older homes relied on. Without proper mechanical ventilation, this can lead to a build-up of internal humidity, poor air quality, and a risk of condensation within the structure.
Why Ventilation Strategy Matters
Timber performs optimally in environments with controlled humidity and stable conditions. In buildings constructed to high levels of airtightness, uncontrolled internal moisture can lead to interstitial condensation, which reduces thermal performance and compromises the durability of structural elements.
Natural ventilation is insufficient in these scenarios. A defined ventilation strategy is essential to safeguard both occupant health and the building fabric. This strategy must be considered early in the design process and coordinated with airtightness detailing, SAP calculations, and thermal specifications.
The chosen ventilation system should reflect the building’s permeability level, energy targets, and intended use, ensuring compliance with Approved Document F and supporting the long-term integrity of the timber frame structure.
Ventilation requirements for new homes in the UK are defined by the following:
- Approved Document F (England and Wales)
- Section 3.14 of the Scottish Technical Standards
- Technical Booklet K (Northern Ireland)
Key compliance areas include:
- Minimum ventilation rates by room function and occupancy
- Effective moisture control to prevent condensation and mould risk
- Alignment with SAP assessments and accurate EPC ratings
- Integration with Part L (energy efficiency requirements)
Mechanical Ventilation with Heat Recovery (MVHR)
MVHR is the recommended ventilation method for airtight timber frame buildings. It combines fresh air supply and stale air extraction with a heat exchanger that recovers up to 90% of outgoing heat.
MVHR Benefits in Timber Frame Projects:
Timber frame buildings are especially well-suited to MVHR, as duct runs can be planned into service zones or pre-formed voids in panel systems. SIPCO provides layout assistance to simplify integration and avoid site clashes.
Alternative Ventilation Options
Where full MVHR isn’t viable, other options may be used depending on the building’s airtightness level:
Intermittent Extract Ventilation (IEV): For homes with air permeability above 5 m³/m²·h. Uses fans in wet rooms and trickle vents. Unsuitable for high-performance builds.
Mechanical Extract Ventilation (MEV): Centralised extraction for multiple rooms. Simple but lacks heat recovery.
Positive Input Ventilation (PIV): Sometimes used in retrofit. Pressurises the building with filtered loft air. Offers limited humidity or temperature control.
Passive Stack Ventilation (PSV): Not reliable in airtight homes. Relies on natural pressure differentials, which are inconsistent in modern fabric-first designs.
Each method must suit the building’s airtightness level, thermal performance, and intended use, while still meeting regulatory requirements.
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