Addendum concerning the use of vacuum insulation
The introduction of vacuum insulated panels (VIPs) represents an exciting development in the range of available insulation materials for buildings. Their relative slimness means that low U-values can be reached, even with very narrow wall constructions. This seems to be especially attractive for developers in locations where floor space is very expensive and must therefore be maximized, and also for retrofit schemes where the available space for the installation of insulation is limited.
On the other hand, the insulating properties of the panels are maintained only as long as the encapsulating membrane stays intact, which is difficult to guarantee over long periods of time, such as the typical building life cycle of 60 years. Failure can lead to low interior surface temperatures, which can, in turn, result in surface condensation and mould growth. In addition, the energy balance is disrupted, leading to a worse energy performance than design.
For these reasons, the Passive House Institute (PHI) recommends that this technology be used in a controlled manner, and only where standard, non-vacuum insulation materials cannot be installed or are not economical (under consideration of life cycle costs and shorter service life compared to standard insulation materials).
In cases where its use is unavoidable, the following recommendations are made:
- Panels should be tested by a notified body or other recognized testing institute according to the relevant guidelines in EN 17140:2020-12 (Thermal insulation products for buildings - Factory-made vacuum insulation panels (VIP)); performance should be guaranteed by the notified body or testing institute for at least 50 years.
- The rated/design thermal conductivity (lambda-R) should be established according to ISO 10456 (Building materials and products - Hygrothermal properties - Tabulated design values and procedures for determining declared and design thermal values) and should take into account the edges/joints between panels.
- The panels must be pre-fabricated in a controlled factory setting and must need minimal on-site processing (no cutting, minimal adhesion, etc.).
- The pre-fabrication process should, as far as possible, include pre-installation of services (electrical, plumbing, HVAC, etc.) or provide for the installation of services by sub-contractors at a later date by way of suitable gaskets, moldings, etc.
- The design of the panels should allow for easy mounting; there should be a documented method for installation of the panels by a suitably qualified craftsperson, including by third parties; the need for specialist training should be minimized.
- Where it is the case that services (electrical, plumbing, HVAC, etc.) have to be installed on-site, there should be a documented method for installation that ensures the panels are not damaged. Where services must be installed by third-party sub-contractors, only minimal further training should be needed.
- The panels should be easily accessible and inspectable via thermal camera to detect defects, e.g. behind a removable ventilated façade.
- Where defects are detected, there should be a documented method for panels to be replaced by a qualified craftsperson; again, the need for specialist training should be minimized.
- There must be a maintenance plan in place from the time of installation to monitor the performance of panels for the foreseeable future, unless it can be demonstrated that this would fall under national operation and maintenance requirements.
The Passive House Institute does not consider certification of construction systems that use VIPs as Passive House Components due to the reasons mentioned above.