Rockwool Cavity Slabs

Rockwool Cavityprovides a completely reliable and cost effective method of insulating new masonry cavity walls.

The lightweight insulation batts considerably reduce heat loss without permitting water transmission from the outer to the inner leaf.

The risk of condensation is also reduced and intermittent heating systems will be more effective.

Advantages

BBA Agrément certified for all exposure zones

Water repellent

Excellent thermal and fire insulation

Superior fit against blockwork

Construction and installation guidance

The outer leaf is the first line of defence against rain. Its effectiveness will be improved if attention is paid to the following points:

The width of the cavity should be designed afterconsideration of the dimensional tolerances of the components which make up the wall. An extra 5mm above the nominal batt thickness will normally be sufficient.

Select porous bricks, which in periods of brief, heavyshowers will absorb the moisture. A non-absorbent brick will channel water into the mortar joints.

Select a lime mortar mix that does not containdetergent-type plasticisers, which reduce the water resistance of the joints.

Specify weather-struck, flush or bucket-handle joints. Recessed joints increase the risk of water penetration. Ensure all bed joints and perpend joints in the external wall are fully filled with mortar.

Cavity trays should incorporate stop ends and have weep holes at approximately 450 mm centres (max 900 mm centres).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cavity trays should be continuous across closely spaced openings (Figure 1) and stop ends provided.

Vertical DPCs at wall openings should project at least 25 mm into the cavity. (See Rockwool Cavity Closers Data Sheet for details.)

The use of Rockwool Cavity does not affect the choice of ties to BS 1243 (or DD140), which should be selected according to structural requirements.

Installing Rockwool Cavity

It is the installer’s responsibility to ensure that Rockwool Cavity is fitted in accordance with the recommendations of their data sheet.

The installation of the batts should commence below the DPC (preferably by at least150mm) with no risk of capillary action to minimise cold bridging. The bottom row of ties should be at 450 mm centres horizontally.

If necessary, the width of the first course of batts can be cut to suit the height of the next row of wall ties.

The width of cut batts should always be 5 mm greater than the width to be insulated, eg wall tie centres.

It is recommended that the external leaf be constructed ahead of the internal leaf so that any mortar protruding into the cavity space from the back of the external leaf can be cleaned off before installing the batts.

Build up a complete section of the leading leaf to one course above the next row of wall ties spaced at max. 900 mm horizontally.

Ensure that all mortar joints are properly filled, particularly the perpends.

Before installation of each course of batts, excess mortar must be removed from the inside face of the leading leaf and mortar droppings cleaned from the exposed edges of the batts. This is made easier by the use of a cavity board. This sequence should be maintained progressively up to wallplate (or cavity tray) level.

It is important that the insulation is carried to the highest level possible in either case.

Fit Rockwool Cavity by compressing between the two rows of wall ties to form a clean and tight butt jointed course. Wall tie drips should be located centrally in the Batts.

Ties must be inclined downwards towards the outer leaf. It is essential that all joints between Rockwool Cavity batts are clean and tightly butted. Raise the second leaf to the same level as the batts.The as-built cavity width must not exceed the following dimensions:

Nominal Batt thickness (mm)	Maximum as-built  clear cavity width (mm)
65	75
80	95
90	105
100	115
110	125

Repeat this sequence to the top of the wall. If not, protect the top of the batts with a cavity tray.

To prevent water penetration to the inner leaf during driving rain, it is essential that no gaps are left between the batts.

Cut the batts cleanly, using a sharp, long bladed knife and a straight edge.

Fit the batts closely around wall openings. Slit the batts neatly where additional wall ties occur. Do not impale or tear them.

At corner joints, edges must be cut accurately to ensure close butting.

Cut the batts accurately to fit between wall ties, if not conventionally coursed.

Ensure closely butted joints by cutting the batts 5 mm larger in size than the wall-tie centres. Avoid the build up of mortar on cavity trays.

Where make-up pieces have to be used, ensure that they are installed with the same direction of grain.

Protect the top of the cavity wall insulation at the end of the work period with a waterproof covering.

Store or cover Rockwool Cavity not in use and protect from site damage

External Walls - Masonry Cavity Walls – Full Fill – (Built-in)

Rockwool Cavity is extremely easy to install; cutting is simple (preferably with a long bladed knife and straight edge). The construction of the batts, and flexibility along their length and width, allows tight ‘knitted’ joints to be obtained easily on site. 

If a batt requires cutting, its width should always be 5mm greater than the width to be insulated, eg wall-tie centres, ensuring a tight/closely butted installation.  

The use of Rockwool Cavity does not affect the choice of ties to BS 1243 (or DD140), which should be selected according to structural requirements. It is the contractor’s responsibility to ensure that Rockwool Cavity is fitted in accordance with the recommendations on the data sheet for Rockwool Cavity.  

The installation of the batts should commence below the DPC to minimise cold bridging. The bottom row of ties should be at 450 mm centres. If necessary, the width of the first course of batts can be cut to suit the height of the next row of wall ties. The width of cut batts should always be 5 mm greater than the width to be insulated, eg wall tie centres.  

It is recommended that the external leaf be constructed ahead of the internal leaf so that any mortar protruding into the cavity space from the back of the external leaf can be cleaned off before installing the batts. Build up a complete section of the leading leaf to one.
Build up a complete section of the leading leaf to one course above the next row of wall ties spaced at max. 900 mm horizontally.

Ensure that all mortar joints are properly filled, particularly the perpends.  

Before installation of each course of batts, excess mortar must be removed from the inside face of the leading leaf and mortar droppings cleaned from the exposed edges of the batts. This is made easier by the use of a cavity board

This sequence should be maintained progressively up to wallplate (or cavity tray) level. It is important that the insulation is carried to the highest level possible in either case

Fit Rockwool Cavity by compressing between the two rows of wall ties to form a clean and tight butt jointed course  Wall tie drips should be located centrally in the batts. Ties must be inclined downwards towards the outer leaf.

It is essential that all joints between Rockwool Cavity batts are clean and tightly butted.  

Raise the second leaf to the same level as the batts.  

The as-built cavity width must not exceed the following dimensions: 

Nominal Batt thickness (mm)	Maximum as-built  clear cavity width (mm)
50	60
65	75
75	85
80	95
90	105
100	115

Repeat this sequence to the top of the wall. If not, protect the top of the batts with a cavity tray. Cavity trays should incorporate stop ends and have weep holes at approximately 450 mm centres. Cavity trays should be continuous across closely spaced openings.

Water resistance

Provided the batts are correctly installed and sound building techniques are applied to the cavity wall construction, any water penetrating the outer leaf will drain down the surface of the batts. The direction of the grain of the mineral wool ensures that the insulation will stop water crossing the cavity to the inner leaf.

Standards and approvals

Rockwool Cavity has been examined by the British Board of Agrément and granted BBA Certificate 94/3079 for use in all exposure zones for buildings up to 12 m in height and for buildings over 12 m and up to 25 m in height in zones where the exposure factor does not exceed 120.

To comply with the requirements of the Agrément Certificate, and to ensure trouble free performance, the masonry walls must be built in accordance with BS 5628:Part 3: 1985 or BS 5390: 1976, as appropriate, and the workmanship on site must comply with BS 8000: Part 3: 1989.

Rockwool Cavity conforms to BS EN 13162:2001 ‘Specification for factory-made mineral wool products’.

Manufacturer

Rockwool Limited, Pencoed, Bridgend, South Wales, CF35 6NY United Kingdom

Tel: 01656 862621 - Fax: 01656 862302 - Email: info@rockwool.co.uk

 

Page last updated Tuesday, June 1, 2010