13
5.3.8
The cavity should be sealed where the opening
has been cut. We recommend filling fully across the
cavity with Rockwool or equivalent to at least
100mm above and each side of the recess opening.
Fill at the bottom of the opening to the level of the
hearth/fireplace floor. It may be simplest to back fill
the cavity with the insulation material and then cut
through the insulation to the size of the flue box
hole.
An alternative to rockwool
above
the opening is to
seal across the top of the cavity with superlux board
or equivalent. The board should slope downwards to
the back so that any moisture will be channelled to
the outside.
See figure 8c.
Figure 8c Cavity sealing
