Windows and Doors for Passivhaus
Design which prioritises thermal efficiency and air tightness of the building envelope to minimise heat losses (Fabric First). Thermal comfort. Clean, fresh air. Health benefits. Less energy use. Low fuel bills and maintenance costs. Energy modelling and certification. Correct installation.
- Fabric First principles. Providing a thermally efficient building envelope (good levels of insulation) will minimise heat losses through the building fabric.
- Air tightness. Most PassivHaus projects fail to receive certification on the basis of failing to meet the air tightness requirements. Air tightness contributes to the thermal efficiency of the building by minimising heat losses.
- Good Orientation. Placing most glazing on the south facing elevation will maximise the solar heat gains for the building (windows can act as ‘radiators’ for PassivHaus projects). Poor orientation may lead to a 30% higher heating demand.
- Solar shading – designing solar shading is important to prevent overheating, especially on the Southerly elevation. Integrated blinds, solar control glazing and brise-soleil are commonly used.
All PassivHaus projects are energy modelled in the PassivHaus Planning Package (PHPP). This will determine that the building-as-designed meets the below requirements:
- Maximum space heating demand <15kWh per metre squared of floor area.
- Airtightness <0.6 air charges per hour (when tested at a constant pressure of 50Pa).
- Primary Energy Demand <120kWh per metre squared of floor area.
Before PassivHaus certification can be achieved, the constructed building will be subject to testing to ensure that the targets have been met.
- Ultra low fuel bills.
- Thermal comfort.
- Improved indoor air quality. It is necessary to install MVHR systems owing to the air tightness levels of the building – this will ensure a constant supply of fresh air to all rooms.
- 90% less energy use.
- Quieter (triple glazed windows provide acoustic benefits as well as thermal benefits)
- No radiators (the use of underfloor heating allows greater flexibility for the placement of furniture)
- Lower maintenance costs.
- 25-30% of energy loss in a building is through windows/ doors.
- Specifying triple glazed windows helps to reduce the temperature difference between the internal surface of the glazing and other internal surfaces, therefore contributing to the thermal comfort of occupants (humans are sensitive to temperature differences of 2oC and will feel uncomfortable when this difference reaches 4.2oC).
- The U Value and G Value of the window construction should be taken into account. The G Value represents the solar heat gain coefficient for the glazing (the percentage of radiation which passes through the glass into the building) and can be altered according to the needs of the project (to suit the building location and climate). In the UK, this is usually around 50/ 60%.
EcoHaus Internorm Technicalities
- EcoHaus Internorm windows can achieve a component U Value of between 0.62-0.64 W/m2K, which is below the 0.8W/m2K requirement for PassivHaus.
- Correct installation of windows is key to avoid the performance gap between designed and constructed U Values. For this reason, all EcoHaus windows are installed by their own installation team.
- Windows should be aligned with the building insulation – metal brackets are used to fix the window to the adjacent brickwork while minimising thermal bridging.
- Inward-opening windows are more common in Europe and in PassivHaus projects generally (all Internorm windows are inward opening). They provide an opportunity to cover the external fixed part of the frame with additional insulation, therefore benefitting the U Value.
- EcoHaus Internorm windows have a 30 year maintenance free period.
- In EcoHaus Internorm windows the glazing unit is bonded to the frame – this makes them very robust. Insulating packers between the glazing/ frame ensure that heat losses are minimised.
- Airtight membranes and weathertight sealing tape should be installed continuously around window fittings.
- A vapour open membrane should be used on the outside of the window frame (allows condensation to escape) while a vapour closed membrane should be used on the inside of the frame.
- Aluminium-clad timber windows and aluminium-clad uPVC windows are available. Identical profiles allow easy and undetectable mixing of timber/ PVC windows (PVC may be preferred in bathrooms or other areas of high humidity).
- Other EcoHaus products are available, but may not have the same PassivHaus benefits as the Internorm offering, eg. slimline and frameless (fixed frame) products.
- EcoHaus offer window products with integrated solar shading blinds (contained within their own separate compartment which can be opened and accessed for maintenance).
- EcoHaus offer windows with integrated MVHR function, which may be useful for refro-fit projects.