Page 35 - Build 153

damp-proo ng
insulation
insulation
Internally insulated basement
insulation
Externally insulated basement
insulation
Damp-proofing needs 50-year durability
Clearly specify the damp-proo ng system. Check that the speci ed system is suitable for the situ- ation and substrate and that the damp-proo ng membrane is su ciently durable. Under clause B2 Durability, the damp-proo ng must remain durable for not less than 50 years.
Options include:
● liquid-applied bituminous coatings — brushed,
rolled or sprayed on:
● epoxy
● bitumen emulsion
● polyurethane
● torch-on modi ed bitumen sheet
● self-adhesive modi ed or rubberised bitumen
or asphalt sheet with self-adhering laps
● trowel or spray-applied cementitious
(sometimes resin-modi ed) slurry.
Integrate the under-slab damp-proo ng with the wall damp-proo ng.
Get the thermal insulation right
Detail how the required level of thermal insulation will be achieved. Options are to:
● construct a 70 mm minimum wide framed wall
on the inside of the masonry wall (see Figure 1) ● install 50 mm minimum thickness polystyrene
over the wall before the installation of a base
sheet and the damp-proo ng.
There are a few guidelines when considering ther- mal insulation in basement walls (see Figure 2): ● Interior insulation is the most common and
least expensive but has the most moisture
problems.
● Exterior insulation is best from a physics
perspective. There are practical problems with protection, thermal bridging and insects that often make it impractical and
Insulation in middle of wall
Internally and externally insulated basement
Figure 2 Insulation options for a concrete or concrete masonry wall.
So what do we need to consider at the design stage and then on site?
Design considerations
If possible, provide a separation between the excavated bank and the basement wall. This will make it easier to keep the wall dry, and the wall can then be constructed using timber framing.
Always check the potential stability of the excavated bank.
Where the wall retains the soil:
● drainage must be provided behind the wall and
located below the level of an adjacent oor
● the wall must be damp-proofed
● the damp-proo ng must be integral with that
of the slab.
Build 153 — April/May 2016 — 33