FULL FILL CAVITY

Full fill insulation simply fills the entire gap between outer and inner wall rather than leaving the traditional air void. Cavity insulation slabs fit closely against the brick and block of the wall construction. It means you’ll no longer have a void in the cavity to prevent moisture getting across to the inner leaf of the wall. The thickness of insulation to be fitted is dictated by the cavity width (typically 75mm or less). Full-fill built-in insulation solutions are installed as the walls are built, with slabs being friction-fitted between the inner and outer leaves of the wall and in between wall ties. There is a variety of products available for full fill cavity insulation: PIR, Glass Mineral Wool and Blown Insulation. This method of insulating has become more popular as insulation manufacturers have adopted new technology and methods to produce moisture resistant and suitable insulation for full fill cavity walls. Full-fill insulation can be slightly quicker to fit, as there’s less need to focus on how the material is held in place. It will also offer slightly better thermal performance over partial-fill for the same wall thickness. Put simply, with a 150mm cavity you’ll be able to include a full 150mm thickness of insulation; which is likely to net you a U-value of around 0.20 W/m2K on a typical brick and block setup when using a product such as Superwall 36 slab from Superglass. 

TYPES OF FULL FILL CAVITY INSULATION

Most common types of full fill cavity wall insulation are:

Phenolic core

It is a premium performance insulation with a fibre-free rigid thermoset phenolic core. Kingspan predicts a result of around 0.15-0.17 W/m2K when using 100mm of Kooltherm K106 in a 150mm cavity. However, rigid products are more expensive up front and installation can require more attention to detail on site.

Products:

Kingspan Kooltherm K106 Cavity Board

PIR core

PIR boards are made by mixing chemicals with a blowing agent. This forms large rigid blocks which are low density, closed cell insulation sheets. PIR boards tend to offer the optimum performance vs price ratio as they’re pretty close to phenolic boards when it comes to r-value and yet they’re cheaper. Although you will need a slightly thicker board to achieve the same r-value. 

Products:

Recticel Eurowall Plus Cavity Insulation Board ǀ Xtratherm CT/PIR CavityTherm Thin-R 

Mineral wool core

Cavity full fill insulation batts are non-combustible and contain water repellent additives which prevent moisture transmission between the outer and inner leaf. Mineral wool cavity insulation is not only waterproof, but lets the walls breathe deterring any unwanted moisture. The batts are simple to install and provide a close fit against brick and blockwork. 

Products:

ROCKWOOL® Full Fill Cavity Batts 

Superglass Superwall 32 Cavity Wall Batt

Superglass Superwall 36 Cavity Wall Batt

DriTherm 32 Knauf Ultimate Cavity Insulation Slab

DriTherm 34 Knauf Super Cavity Insulation Slab

DriTherm 37 Knauf Standard Cavity Insulation Slab

FULL FILL CAVITY SIZES

All boards are designed to fit between wall ties. Typically they are installed at 900mm horizontal x 450mm. For this reason all boards are made in standard size of 450mm/455mm x1200mm.
Cavity Slabs are available in a range of thicknesses: 50mm, 65mm, 75mm, 85mm, 90mm, 100mm, 115mm, 125mm, 140mm and 150mm.
 

FULL FILL CAVITY WALL INSULATION

· For cavities up to 100mm, install wall ties in the inner leaf at maximum 900mm horizontal centres and 450mm vertical centres, with additional ties around openings and at corners.

· For cavities greater than 100mm, wall ties should be installed at reduced centres.

· Wall ties must slope down from the inner leaf in order to shed water into the cavity.

· Continue building the inner leaf as you install wall ties, with ties secured by the next row of blockwork.

· Ensure the blockwork structure is kept clean as you build. The faces of masonry must be kept clean and clear of mortar snots and droppings.

· Once the wall ties are secured, the full fill insulation boards can be installed. Wall insulation boards must extend 150mm below the upper edge of floor insulation to prevent thermal bridging at the floor perimeter.

· Boards should be fitted tightly against the leading leaf of masonry supported on the first row of wall ties. The higher side of the rebated edge should always be against the inner leaf.

· Ensure each insulation board is fitted tight against the inner leaf and joints are tightly butted. Each board should be secured by wall ties at a minimum of three points.

· At corner junctions, the rebated edge should be carefully removed with a handsaw or knife to allow a straight butt joint with no gaps. The corner joint should be staggered and the exposed edge of the board should be protected by a vertical DPC of an appropriate width.

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