Why Perimeter Insulation?
A substantial amount of heat is lost through an un-insulated slab, resulting in cold, uncomfortable floors.
Even if the foundation wall is insulated vertically under the slab (Figure 3), significant heat is still lost from the slab edge that is closest to the cold outside air.
Where and How to Install Perimeter Insulation
The insulation can be applied outside (Figure 4) or inside (Figure 5) the foundation wall to a depth of not less than 300 mm.
Exterior applications require a metal flashing or durable finish for protection.
The insulation can also be placed vertically along the foundation wall (Figure 5) or horizontally under the slab (Figure 6).
Perimeter slab insulation can give termites access, so be sure to provide a termite shield (Figure 7). Some jurisdictions do not allow external insulation because the foundation must be visible for termite inspection.
Perimeter slab insulation protection against moisture and termites
One option is to install the insulation inside the foundation wall and provide a protective membrane (termite shield) between the sill plate and foundation (Figure 6).
Under Floor / Slab Insulation
Typical methods of installation for EPS ﬂoor insulation for concrete ground ﬂoors are shown in Figure 6.
The concrete ﬂoor over which the EPS boards are to be laid should be left as long as possible to maximize drying out of moisture. The ﬂoor surface should be smooth and ﬂat to within 5 mm when measured with a 3 metre straight edge, e.g. when concrete is laid on site it should be in accordance with SANS 10109-1 Concrete ﬂoors Part 1: Bases to concrete ﬂoors.
Irregularities (up to 10 mm) may be levelled with mortar.
The EPS boards can also be used on a beam and block suspended concrete ﬂoor. The surface of the ﬂoor should be smooth and ﬂat to within 5 mm when measured with a 3 metre straight edge. Irregularities greater than this must be removed.
Where the EPS boards are used over ground-supported concrete ﬂoor slabs they should incorporate a suitable damp-proof membrane, in accordance with SANS 10021, to resist moisture from the ground. If a liquid type damp-proof membrane is applied to the slabs, it should be of a type compatible with expanded polystyrene and be allowed to dry out fully before laying the EPS boards.
Where the EPS boards are used on hard-core bases underground-supported concrete slabs, the hard-core must be blinded before application of the EPS boards. Where a screed or concrete slab is laid over the EPS boards, vertical up stands of insulation should be provided and be of sufficient depth to fully separate the screed or slab from the wall.
During construction, the EPS boards and overlays must be protected from damage by moisture from sources such as water spillage, plaster droppings and traffic. Before laying EPS boards above a slab, care should be taken to ensure sufficient time for the dissipation of constructional moisture.
Exposed or semi-exposed intermediate timber ﬂoors
Before installing the EPS boards, the ﬂoor should be inspected thoroughly for possible defects and its condition should meet the recommendations of SANS 10109 Part 2.
The surface of the ﬂoor should be smooth and ﬂat to within 5 mm when measured with a 3 metre straight-edge.
The EPS boards are cut to size, as necessary, and laid with closely butted, taped joints.
Cement-based screed overlay
Perimeter edge pieces are cut and placed around the edges. A properly compacted screed of at least 65 mm is laid. The relevant clauses of SANS 10109 Part 2 will apply.
Before laying the EPS boards, preservative treated battens are positioned at doorways and to support partitions. Adequate time should be allowed for CCA based preservatives to become fxed, and for the solvents from solvent-based preservatives to evaporate.
Where EPS boards are laid on a dpm, a vapour check consisting of 0.25 mm (250 micron) polyethylene sheet is laid between the EPS boards and the chipboard. The polyethylene sheet has 150 mm overlaps taped at the joints and is turned up 100 mm at the walls.
The selection of chipboard/particle board must be in accordance with SANS 50312. An expansion gap between the chipboard and the perimeter walls should be provided at the rate of 2 mm per metre run or a minimum of 10 mm, whichever is the greater.
Where there are long, uninterrupted lengths of ﬂoor, e.g. corridors, proprietary expansion joints should be installed at intervals on the basis of a 2 mm gap per metre run of chipboard. Before the chipboard panels are interlocked, either a PVA or mastic adhesive is applied to the joint.
Once the chipboard is laid, temporary wedges are inserted between the walls and the ﬂoor to maintain tight joints until the adhesive has set.
To prevent cold-bridging suitable compressible fller, e.g. pieces of expanded polystyrene, should be fitted around the perimeter of the ﬂoor between the chipboard and the walls when the wedges are removed and before the skirting boards are affixed.
Where there is a likelihood of regular water spillage, e.g. in rooms such as kitchens, bathrooms, shower and utility rooms, additional chipboard protection should be considered, for example a continuous ﬂexible vinyl sheet ﬂooring with welded joints and cove skirtings.
Cement-based screed overlay
Perimeter edge pieces are cut and placed around the edges and taped at joints.
The concrete slab is laid to the required thickness
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