How does rigid full fill cavity wall insulation work?

Traditionally, rigid insulation boards used in masonry cavity wall applications were offered only as a partial fill solution. Now, rigid full fill solutions for masonry cavity walls mean the clear air cavity can be significantly reduced or eliminated entirely.

By filling more of the wall cavity with thermally efficient polyisocyanurate (PIR) insulation, masonry cavity walls can achieve lower U-values with little or no increase in the overall thickness of the wall construction.

Using rigid full fill PIR cavity wall insulation to lower U-values

With a thermal conductivity as low as 0.021 W/m.K, a full fill PIR solution offers a more efficient way to insulate a cavity compared to partial fill solutions. It is also more thermally efficient than a corresponding full fill glass mineral wool product, making it ideal for projects that require both lower U-values and minimum wall thicknesses.

Masonry cavity walls featuring rigid full fill insulation products should be designed in accordance with the manufacturer’s details. For example, Thermaclass Cavity Wall 21 can be installed with a nominal 10mm cavity (which benefits from the low emissivity facing of the insulation board), or as a true full fill solution.

Using rigid full fill PIR cavity wall insulation to protect against moisture ingress

Rigid full fill PIR insulation boards typically have an engineered edge profile to help them ‘lock’ together when installed. A lap joint or tongue and groove profile acts as a barrier, stopping water from tracking across the joints between boards.

With no 50mm air cavity in the wall, the design of rigid full fill insulation boards has to guard against rainwater penetration, ensuring the cavity wall continues to fulfil its function of protecting the inside of the building.

Products are independently tested in a full ‘wet wall’ test rig, simulating heavy exposure to rain. The successful outcome of that test is incorporated into third-party certification, without which a product cannot be used in a masonry cavity wall application.

About Thermaclass Cavity Wall 21

Thermaclass Cavity Wall 21 is a BBA-certified, rigid full fill cavity wall insulation from Celotex. It has a low thermal conductivity of 0.021 W/m.K and features a tongue and groove board edge profile.

To find out more, download the product brochure or contact our technical support team to find out how Thermaclass Cavity Wall 21 could benefit your project.