A partial fill cavity wall application provides the most effective barrier to rain penetration by allowing the traditional wall cavity to be maintained. The insulation is fixed to the inner leaf of the wall construction, maintaining a clear cavity which avoids the problems associated with full cavity fill. For this application we recommend the use of either Kingspan Thermawall TW50 zero ODP (high performance CFC/HCFCfree rigid urethane insulation) or Kingspan Kooltherm K8 Cavity Board (premium performance CFCfree rigid phenolic insulation).

FIXING DETAILS

* Determine the overall cavity width by adding the thickness of insulation required to the residual cavity width (50 mm minimum).

* Install the first row of wall ties at 600 mm horizontal centres to the inner leaf, one course of blockwork below the d.p.c. Install the next course of blockwork to secure the ties.

* Wall ties should include a retaining disc/clip and be of double drip type, installed drip downward.

* Continue constructing the inner leaf up to the next wall tie course (450 mm above the first usually 2 block courses). Position the next course of wall ties at the usual 900 mm horizontal centres and install the next course of blockwork to secure the ties.

* The first row of insulation boards should now be installed, ensuring each insulation board is retained tight against the inner leaf at three points (this includes cut boards at details), See figure 3 on page 9 of the Structural Users Guide.

* Repeat the process described in the previous 2 bullet points.

* Take care to remove excess mortar and protect the insulation board edges from mortar snots by using a cavity board. See figure 2 on page 9 of the Structural Users Guide.

* Always ensure accurate trimming to achieve close butting joints and continuity of insulation.

* A vertical damp proof course should be installed at window and door openings. The insulation boards can be used to prevent a cold bridge at details. Refer to Limiting thermal bridging and air leakage: Robust construction details for dwellings and similar buildings, available from the Stationery Office.

* When insulating to ceiling height at a gable, wall boards should be continued 250 mm beyond the ceiling and a cavity tray installed above the insulation.

* Boards should be cut using a sharp knife or a fine toothed saw.