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.
 
1) 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.
 
2) 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.

3) 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 (Figure 1). Ensure that all mortar joints are properly filled, particularly the perpends.

4) 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 (Figure 2).

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 (Figure 3).

9) Repeat this sequence to the top of the wall (see Fig 3). 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’.
 
CE Mark & Kitemark


Note: Rockwool Cavity may be used above the BBA certified height, subject to an assessment by the BBA of the building in question.
  
Use in tall buildings

Agrément Certificate No. 94/3079 covers the use of Rockwool Cavity in buildings up to 12 m in height, and permits the use of Rockwool Cavity in buildings from 12m to 25 m in height, provided the exposure factor does not exceed 120, and subject to a detailed project assessment by Rockwool Limited in association with the architect.
 
A written approval form is to be completed and returned to Rockwool, together with an on-site examination of the work in progress by Rockwool Limited.
 
Above-average site supervision is recommended during construction.
 
Building Regulations In the opinion of the British Board of Agrément, Rockwool Cavity will satisfy the following requirements of the 2000 Building Regulations:
 
B3 (4): Resistance to fire spread between and within cavities. Rockwool Cavity is non-combustible and therefore may be used in buildings of every purpose group. They may also be considered as a cavity barrier when tightly fitted between masonry leaves where an insulated wall connects with the cavity of a wall without cavity insulation.
 
Approved Document C (2004 edition): Resistance to weather and ground moisture. Rockwool Cavity does not absorb water by capillary action and may therefore be used in situations where they bridge the DPC, providing the construction is in accordance with technical solution 4.4.
 
Para 5.15 allows Rockwool Cavity to fully fill the cavity of masonry walls (brick, block or dressed stone).