Tripple-glazing – step 3
This is possibly the single most expensive additional investment needed to achieve the Passivhaus standard. Fine tuning the window specification is an important part of achieving the Passivhaus standard and the window specification may not be finalised until late in the design process. Because lead times for manufacture and delivery of glazing and doors can be long it is advisable to place orders as early as possible to avoid delays on site.
Ensuring that the correct glazing specification has been delivered to site is the first step in ensuring proper installation in accordance with the design. This involves comprehensively checking the order. Not only should the window dimensions and reference codes be checked off but so should the product specification to ensure a mistake has not been made at the factory.
Each window and door should be uniquely coded with the following information:
- Frame type and UF-value (EN 10077)
- Glazing type and UG-value (EN 673)
- Solar energy transmission g-value (EN 410)
- Daylight transmission (EN 9050)
- Glazing and gap dimensions
- Spacer type used
- Special low emissivity coatings
- Inert gas fill type
It is likely that the designer has specified a unique g-value for the glazing of each façade, and possibly for each opening as this is a way of fine tuning the useful solar gains that enter the building. It is therefore possible that two windows which appear to be identical with respect to frame type and dimensions are actually intended for different openings. It is essential that the windows are correctly coded for each opening in line with the designer’s window specification.
Correctly installing Passivhaus glazing and doors is a specialist job and technical support and training from the manufacturer is needed. Triple glazed systems are particularly heavy and special lifting equipment may be needed to lift larger windows and doors in to place. Prior to installation the window openings should be inspected and cleaned of any dust or debris. Priming of the reveal surfaces may also be required if proprietary air tight tapes are being fixed to masonry.
To achieve a thermal bridge free window connection windows may be designed to ‘float’ in the opening which is subsequently back filled with foam insulation once the window is in place. Air cushions and other positioning devices will allow the installer to works closely to the designer’s drawings at this stage where millimetre tolerances may make the difference between a bridged and a bridge free connection.
Air pressure test
The final critical aspect of glazing installation is the air tightness of the units once installed, and this can only be checked on site during the air pressure test. It is therefore important that an experienced installer is on site during the pressure test to make any additional adjustments to the window and door gearing necessary. Sufficient time should be allocated in the pressure testing and air leakage detection schedule for this procedure.
Read about steps one, two, three, four and five in our next articles.
Excerpt from “Passivhaus primer: Contractor’s guide. So you’ve been asked to build a Passivhaus?” by BRE.