SYSTEMS
INSTALLATION Through-wall systems may be installed by multiple contractors rather than a single contractor, and are commonly installed by the following contractors: • Specialist SFS framing contractor • Specialist drylining contractor • Specialist window/door contractor • Specialist façade contractor.
through the walls or ceiling, which could contribute to mould formation, structural damage, heat loss and increased energy costs. Effective sealing of the building envelope requires effective workmanship, the right choice of AVCL and good detailing. Water vapour, which can find many ways into the construction, from wet trades to occupier activity, is difficult to control and could result in risks to the building and its occupants. Any AVCL should be airtight. The degree of vapour diffusion, however, depends on the material composition. It can be distinguished by four different product technologies: solid polyethylene membranes, typically with high and fixed Sd-values; composite AVCL membranes with low to medium fixed Sd-values; reflective AVCL; and smart AVCL with adaptable Sd-values by means of humidity concentration. Further guidance can be sought from BS 5250: 2021 Management of moisture in buildings – Code of practice. See Specfinish May 2, 2014. specfinish.co.uk/insulation-air-and-vapour-control-in- modern-buildings/ “Effective sealing of the building envelope requires effective workmanship, the right choice of AVCL and good detailing.”
The designer should consider all these parameters during the design stage:
BREATHER MEMBRANES If these membranes are part of the certification, they cannot be substituted or removed. Breather membrane performance: • Located in the cavity to prevent water
penetration into the inner leaf • Has high vapour permeability • Typically requires UV resistance
• Other performance characteristics to BS EN 13859-2 Flexible sheets for waterproofing. Definitions and characteristics of underlays. Underlays for walls • Reaction to fire B-s3, d0 or better in relevant buildings (From B4 of Approved Document B 10.15a Volume 1: Dwellings). AIR AND VAPOUR CONTROL LAYER (AVCL) AVCL performance: • AVCL should be located on the warm side of insulation • Has low vapour permeability • Other performance characteristics to BS EN 13984 Flexible sheets for waterproofing. Plastic and rubber vapour control layers • Reaction to fire B-s3, d0 or better. WHY IS AN AVCL IS NECESSARY? An AVCL has two basic functions: controlling the amount of vapour that travels through the building envelope; and providing an airtight seal when properly installed and maintained. Various studies show that an AVCL is necessary to prevent moisture from the interior migrating
13
Powered by FlippingBook