Celotex Thermaclass Cavity Wall 21

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Get the best prices on Thermaclass 21 here! Thermaclass Boards are a quality product made up of a rigid polyisocyanurate (PIR) core with low emissivity foil facings bonded to each side of the board with tongue and groove profiles.

Celotex as a brand is renowned for its quality products and reliable services and has grown to become a go-to brand for builders and contractors across the construction industry. With a range of practical products at amazing prices, we can see why! The Celotex brand offers a wide material designed to suit every insulation need including, pitched roofs, flat roofs, walls, floors, and ceilings. Other Celotex products include Cavity wall boards, Insulated Plasterboards, and insulation boards.

Product Information

  • Thermaclass 21
  • 1190 x 450mm (installed) 1205 x 465mm (including tongue)
  • Range of thicknesses to choose from is between 90mm and 140mm.
  • The boards dimensions are designed for an easy fit when it comes to masonry wall applications.
  • The boards give a coverage of 0.53m2.
  • Celotex Thermaclass have an incredible thermal conductivity of 0.021W/mK. The low thermal conductivity reduces the heat levels travelling through the board.
  • Low emissivity foil facing provides improved thermal performance in sealed cavity air spaces, improving the achievable U-value.
  • With less heat escaping through the walls, your energy bills can be reduced by up to 35%.
  • Thermaclass 21 boards are also available in pallets.

Thermaclass 21 Size Guide

  • 90mm – Thermaclass 21 Thermal Resistance (R-Value): 4.25m2.K/W
  • 115mm – Thermaclass 21 Thermal Resistance (R-Value): 5.45m2.K/W
  • 140mm – Thermaclass 21 Thermal Resistance (R-Value): 6.65m2.K/W

Why Thermaclass Cavity Wall 21?

  • Save your time! Handling, cutting, and installing is made easy with this product due to the light weight and the easy application tongue and groove edges of the boards.
  • This high-quality long-lasting product will have a lifespan that lasts for as long as the building when installed correctly.
  • With a low thermal conductivity of just 0.021W/mK, less heat is allowed to pass through the walls and ceilings, keeping your heat where it should be – in your home!
  • Whilst you save you money on your bills, you also create a more energy efficient environment by reducing climate change and global warming levels by reducing heat loss.
  • Use Thermaclass in your new build, extensions, or to upgrade current building regulation standards.
  • The most used Cavity Board size is 90mm.

How do you cut and install Thermaclass boards?

  • Thermaclass boards can be cut by first measuring and marking the boards to size and cutting with a fine-toothed saw. They can also be cut by scoring one side of the board with a sharp blade, snapping the board over a hard edge, and scoring the other side of the board.
  • Protective gear such as gloves, masks, and goggles should be worn when cutting PIR boards to prevent irritation caused by the material fibres.
  • Please note this is a guide only. Always consult a building professional before insulation your domestic or non-domestic building. Installing the incorrect insulation materials or using an incorrect installation method can be a timely and costly mistake.
  • Full Fill Masonry Wall Applications – Cut the boards to size if necessary. The boards should be installed between the inner and outer leaf of the buildings structure as the wall is being built.

Build up the first section of the wall's inner leaf (concrete blocks).

Install the first row of wall ties at a minimum of one course of blockwork below the DPC – Damp Proof Course.

The Thermaclass Cavity Wall 21 boards should be positioned with the tongue at the top of the board. When planning the installation, the position should be decided for example, whether the tongue should appear on the ‘top and left’ or ‘top and right’ of the boards and maintain this defined orientation throughout the installation.

Before installing the Thermaclass Cavity Wall 21 insulation board: a. Identify where the wall ties will land on the tongue side of the board. b. Using a self-retracting knife, cut the facer then use a sharp specialist insulation saw to make the final small incision in the tongue profile, with a tilt to follow the downward facing direction from the inner leaf to the outer. c. The incision should not be more than 15mm deep. d. When there is a residual cavity, all ties should include a retaining clip or disc as appropriate to ensure boards are secured in place against the internal wall leaf.

The first row of the Thermaclass Cavity Wall 21 insulation boards should be supported by the first row of wall ties. Fit the boards flush against the internal leaf, maintaining up to a 10mm residual cavity where specified between the insulation board and the external wall leaf. The boards should be installed to an engineer’s requirement or to a minimum depth of 150mm below the damp proof course (DPC) to provide edge insulation to the floor and reduce thermal bridging at this junction. Ensure that the Thermaclass Cavity Wall 21 insulation boards are not in contact with the ground or that all board edges are sealed.

The next board can then be applied and fitted tightly to the previous board by positioning the tongue and groove edges together. This process is repeated for the first row of boards.

When installing the next rows, maintain a staggered pattern to have no continuous vertical joints – a staggering pattern of 600mm is recommended. The wall tie position should not coincide with a vertical joint. Please see further information in section 11 on starting the staggering pattern in corners.

Continue to construct the cavity wall and install insulation following the previous steps, ensuring excess mortar is removed from the cavity face and a cavity board is used to prevent mortar from dropping on the top edge of the insulation.

If the installation of the insulation boards is terminated below the highest level of the wall, the top edge of the insulation must be protected by a cavity tray and alternate perpend joints raked out, to provide adequate drainage of water from the tray.

Certifications and Safety

  • All Insulated plasterboards are CFC, HCFC and Formaldehyde Free with zero ozone depletion potential (ODP) and low global warming potential (GWP)
  • All Celotex products are manufactured under Environmental Management System – ISO 14001:2015.
  • Declaration of performance – covered by a harmonised standard: BS EN 13165:2012 + A2:2016
  • Achieves a BRE Green Guide A+ rating.
  • BBA approved – certificate 16/5343.
  • CE Marked (20.DOPCCT-01) to BS EN 13165.
  • Behaviour in relation to fire — the plasterboard face of the product has a reaction to fire classification of Class E to BS EN 13501-1 : 2007 and its use is restricted to the below.
  • In England, Wales and Northern Ireland, the product is unrestricted in terms of proximity to a boundary and, for constructions comprising two leaves of brick or concrete each at least 75 mm thick, and with cavities closed around openings and at the top of the wall (with cavity barriers in Northern Ireland), is unrestricted in terms of height, other than those described in section 9.2. For other constructions, the product should not be used in buildings with a floor more than 18 m above the ground and cavity barriers must be provided.
  • It is not classified as non-combustible or of limited combustibility.
  • Durability — the product is durable, rot-proof and sufficiently stable to remain effective for the life of the building in which it is installed.
  • The management system of Celotex has been assessed and registered as meeting the requirements of BS EN ISO 9001: 2015 and BS EN ISO 14001: 2015 by SGS UK Ltd (Certificates GB91/504 and GB11/83526 respectively).