Walls - Partial Fill Cavity Wall Insulation

Walls

Issues to Consider - Masonry

Partial Fill Cavity Wall Insulation

Insulated Dry-Lining Plasterboard

Insulated Dry-Lining Plasterboard - Timber Frame

Issues to Consider - Timber Frame

Timber Frame Insulation

Walls - Partial Fill Cavity Wall Insulation

INTRODUCTION
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 Kingspan Kooltherm® K8 Cavity Board (premium performance CFC–free rigid phenolic insulation).

Figure 1

PRODUCT DATA

ACHIEVING U–VALUES

Kingspan Kooltherm® K8 Cavity Board
Board Size	1.2 x 0.45
Insulant Thickness(mm)	Refer to local distributor or Kingspan Insulation price list for current stock and non-stock sizes.
Facings	Composite Foil
Core	CFC/HCFC - free rigid phenolic

To select the correct thickness of
insulation to achieve a relevant U-value
please see design tables below.

Thermal Conductivity
(l-value) - K8®	25-44mm 0.023W/m.K 45mm 0.022 W/m.K

1 The l–value quoted is in accordance with the Harmonised European Standard BS EN 13166 (phenolic) using so called 90/90 principles. Comparison with alternative products may not be appropriate unless the same procedures have been followed.

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.
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).
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.

Figure 2

Figure 3

Use of a cavity board to
protect the cavity

Boards are installed as work
proceeds

Easily achieve your required thermal performance using Kingspan Kooltherm® K8 Cavity Board with any type of block.

For reasons of comparison the internal finish is taken as both 9.5 mm or 12.5 mm plasterboard on dabs and alternatively an internal finish of lightweight plaster. See footnotes 1 and 2.

The table below, lists all the main block manufacturers in the UK and the blocks they manufacture. To determine the thickness of insulation you will need to achieve your required U–value, select the appropriate block type and the corresponding thickness of insulation listed.

Dependent on the U–value required, the construction used for the purposes of these calculations a 100 mm block inner (of thermal conductivity shown in the table below), a minimum 50 mm cavity with either rendered dense blockwork outer leaf for Scotland or a brickwork outer leaf for England and Wales.

1 Add 5 mm to thickness of insulation if using a 13 mm layer of lightweight plaster as a substitute for the assumed 9.5 or 12.5 mm layer of plasterboard on dabs.

2 Add 5 mm to thickness of insulation if using a 13 mm layer of lightweight plaster or 9.5 mm plasterboard on dabs as a substitute for 12.5 mm layer of plasterboard on dabs.

3 For the purpose of these U–values we have assumed a rendered dense blockwork outer leaf.

4 For the purpose of these U–values we have assumed a brickwork outer leaf.

5 When calculating U–values to BS EN ISO 6946: 1997 the type of wall tie used may change the thickness of insulation required. These calculations assume a stainless steel double triangle tie 3.7 mm diameter, giving a cross sectional area of 10.75 mm². Contact the Kingspan Insulation Technical Services Department for project calculations.

6 For the purposes of these calculations the standard of workmanship has been assumed good and therefore the correction factor for air gaps ignored.