CavityTherm

CavityTherm wall insulation board is a composite board of PIR core with a lambda value of 0.021 W/mK. The boards have gas tight facings with one face bonded to a profiled HIPS skin during manufacture to provide a drainage plane. CavityTherm’s profiled facing directs any moisture that might have penetrated the external wall down the protective facing and back onto the external leaf. The board includes specifically designed rebated edge detailing on all four edges to allow the system to tightly interlock when installed.

Put simply, CavityTherm builds as a system to ensure continuity. You can physically see that the procedures on site are being followed. It’s a solution to low energy design.

Standard S/S wire wall ties are used with CavityTherm. At up to 5 ties/m² the thermal impact is negligible because the cavity is kept to a reasonable width. Pushing the cavity wider and adding greater amounts of insulation will necessitate low conductivity ties, and result in worse thermal
bridging at junctions. It is for this reason that a U-value of around 0.15 W/m²K is seen as optimum by regulations and Passive House.

CavityTherm is manufactured for 100mm, 110mm, 125mm and 150mm cavities, and achieve U-values down to 0.12 W/m²K. Other thicknesses may be available subject to quantity and lead time.

This is not specific to CavityTherm, ALL wall ties in any construction should slope slightly down to prevent water travelling along the wall ties into the construction. WALL TIES MUST BE KEPT CLEAN AND FREE OF MORTAR.

Contact Unilin Insulation technical support for guidance suitability depending on building height

A wall U-value is not the only item that must be addressed to achieve a Low Carbon Fabric, airtightness and thermal bridging must be improved. Thermal Bridging is in fact just ‘good detailing’ and is accounted for in SAP. Unilin is the only insulation board manufacturer that addresses gaps or breaks within the continuity of the insulation layer. How do you detail insulation around stepped cavity trays, periscope vents in suspended floors, at corners or at meter boxes? Unilin has developed insulated pieces to ensure that these details are well insulated, so as to avoid Thermal Bridging and possible condensation/ mold growth.

All the details available to download from the unilininsulation.co.uk have been based on the UK Accredited Details For Construction published by the DLUHC. These are standard details that have been accounted for in SAP for over many years. What Unilin has done is just replaced the conventional insulation included within them with CavityTherm. This has
vastly improved the resultant thermal transmittance through all the specified junctions; corners, wall/ floor, reveals etc, and will deliver a Y-Value for most dwellings below the 0.05 target asked for under Part L. Unilin has fully BRE qualified Thermal Bridging assessors with the added assurance that the technical team members you speak with are fully trained.
U-Value and condensation risk analysis calculations are covered by the BBA/TIMSA competency scheme.

The Building Regulations now ask that insulation systems be ‘continuous’ and are installed in accordance with acceptable detailing. The jointing system in
Unilin products achieves this, encourages a more accurate build, and avoids the 0.01 U-Value penalty that should be applied when calculating to BR443.

When two abutting boards are to join, cut the profiled edge from each board and ensure
that they are closely butted. The joint should be sealed. When building the inner leaf first – seal
with a waterproof tape. The tape should be applied to a dry surface. When building from the inside a proprietary self adhesive jointing strip is available to insert over the join.

Any penetrations or small repairs can be made with the tape or sealant. Any services running through the insulation layer should be sloped to the outside. DPCs should be dressed
over services Contact the membrane manufacturer for further guidance on installation and best practice.

The use of a cavity board is recommended during construction, it is simply a board that is placed over the installed boards as the inner leaf is raised to catch any mortar drops that might fall. If mortar does fall onto the upper edge of the CavityTherm the HIPS skin is easily cleaned with a damp cloth.

Full details relating to compliance with Building Regulations, independently verified technical specification, assessment criteria and technical investigations, design considerations and installation guidance are available on www.unilininsulation.co.uk