Q. What is CavityTherm?

A.

Xtratherm CavityTherm wall insulation board is a high performance 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 unique 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.

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Q. What is the real benefit in using CavityTherm?

A.

Put simply, the U-values achieved by placing CavityTherm into your standard 100mm cavity achieves 2016 Fabric Energy Efficiency (FEES) minimum standards of 0.18 W/m²K. The FEES standard will most likely be written into the Building Regulations Part L 2013 and has already been adopted into the Code for Sustainable Homes. By keeping cavity widths at a reasonable 100-150mm wide, CavityTherm can achieve as low as 0.12 W/m²K without incurring all the additional costs of building a cavity over 150mm. It’s a very practical, affordable solution to low energy design.

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Q. What wall ties do I use with CavityTherm?

A.

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 0.15W/m²K is seen as optimum by regulations and Passive House.

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Q. What thicknesses of CavityTherm are available?

A.

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

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Q. Why slope the wall ties down to the outer face?

A.

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.

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Q. What building types can use CavityTherm?

A.

CavityTherm can be used in new external masonry cavity walls up to 25m in height in domestic and non-domestic buildings.

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Q. Can CavityTherm be used in all regions?

A.

CavityTherm can be used in any exposure zone. However, the use of the product does not preclude the need to apply an external render coat or other suitable finish in severe or very severe exposure zones where such application would be normal practice.

Tests by the BBA confirm that constructions built in accordance with BS 5628-3 : 2005 can resist rain penetration. Water penetrating the outer leaf of the wall, will drain down the cavity face of the outer leaf and the product will contribute to satisfying the national Building Regulations: England and Wales – Requirement C2(b) There are no restrictions on CavityTherm over and above standard full fill materials.

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Q. Can I get information on exposure zones?

A.

National Building Regulations: England and Wales – Requirement C2(b) gives information on wind driven rain exposure around the UK, but contact your local Building Control office, or NHBC inspector before commencing with a project for confirmation.

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Q. Do NHBC accept the use of CavityTherm?

A.

The CavityTherm BBA certificate 10/4786, in the ‘Non-regulatory information’ section, does say that the product can be used in accordance with Chapter 6.1 ‘External masonry walls’. Chapter 6.1 of NHBC Standards states that in England and Wales NHBC does not accept fully filled cavities where the outer leaf is fairfaced masonry in areas of very severe exposure to wind driven rain. In Scotland fully filled cavities are not accepted in any exposure.
Therefore in England and Wales NHBC accept the product in areas of exposure to wind driven rain up to and including severe.

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Q. CavityTherm has a lot of accessories as part of the ‘system’, what are they for?

A.

An excellent 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. CavityTherm is the only insulation system 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? Xtratherm have developed bespoke insulated pieces to ensure that these details are well insulated, so as to avoid thermal bridging and possible condensation/mould growth.

For the full range of accessories, see www.cavitytherm.com/what-is-cavitytherm/accessories/

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Q. CavityTherm addresses thermal bridging, but how do I use this in my SAP calculation?

A.

All the details available to download from the CavityTherm website have been based on the UK Accredited Details for Construction published by the DCLG. These are standard details that have been accounted for in SAP for over 5 years. What Xtratherm 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.
Xtratherm has fully BRE qualified thermal bridging assessors, and all our technical staff you will speak to on the phone are certified by the BBA to carry out U-value and condensation risk analysis.

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Q. Is there a benefit in the ‘Engineered edge detail’?

A.

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

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Q. When a board is cut what tape do I use to make the join?

A.

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 preparatory 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 as per Eurocode 6.

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Q. You recommend the use of a ‘Cavity Board’ – what is that?

A.

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.

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Q. Where do I get further information?

A.

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 the CavityTherm website.

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