for use with ICF systems
8. Typical construction details
8.1 Ground level
8.1.1 Basements
8.1.2 Service opening
Habitable space
Alternative or additional hydrophylic strip or crystallization coating
Ground level
Waterproof membrane
Service within penetration may also need to be sealed Basement wall
Figure 8.1 Provision of services through an ICF.
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Damp-proofi ng of the vertical ICF walls against rising damp can be provided by a variety of methods, dependent on the type of ICF system in use. The conventional masonry method of satisfying the building regulations is to install a horizontal DPC, and this can be done with ICF using a liquid DPC. However, if a block system is being used, care will be required to avoid physical damage or concrete spillage spoiling the fi t of the castellation. Duct tape secured along the tops of the formwork faces is an effective protection during the pour. One method uses a solvent-free liquid DPC, applied across the surface of the castellated block abutting the slab, and dressed down to the underside of the slab (see Figure 8.2). If the upturned edge of the slab DPM is pressed fi rmly onto the vertical surface of the DPC while it is still tacky, and before casting the slab, this will increase the effectiveness and minimise the risk of capillary action. The concrete used below-ground is the same specifi cation as the above-ground work. This method does, however, require the pour to be interrupted at DPC height, to allow the concrete to set and the liquid DPC applied across the core.
8.1.3 Ground-fl oor wall junctions
150min
Ground level
Slab dpm Solvent free liquid dpc across
castellations and core
Figure 8.2 Application of liquid dpc to ICF interlocking
block system.
Clearly, the use of rigid or semi-rigid plastic PVC types of DPC requires the castellations to be cut off and the upper walls effectively restarted from a smooth base.
More conveniently, if the concrete core is specifi ed as a water-resistant concrete and this concrete is continued to at least 150mm above the external fi nished ground level, this may adequately resist rising damp in the core. The water-resisting core is itself the DPC. Any wall DPC detail must, however, be considered in conjunction with the internal ground-fl oor detail. The use of water-resisting concrete in this way is common in the USA and other countries where ICF is extensively uised.
A cost-effective method when water-resistant concrete is intended as the DPC, suitable for ICF square-edged boards or plank systems, or when castellations are to be fi lled, is to bring up the slab DPM against the inner plank face, dress it over the top and turn it down into the cavity. This creates a long path length which, taken in conjunction with the hydrophobic nature of the polystyrene formwork, effectively eliminates the possibility of capillary action between slab and wall. This method maintains the recommended continuity between wall DPC and slab DPM (see Figure 8.3). A variation on this method is to dress the slab DPM up the face of the wall, and fi x it to the wall above DPC level with duct tape.
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Suspended ground fl oors do not have the complications of an under-slab DPM. However, the same precautions regarding the installation of a dpc against rising damp need to be considered (Figure 8.4), although the possibility of capillary action, when using a non-ground bearing slab, may be disregarded.
When expensive brick or stone cladding is to be used and the foundations are deep, some systems offer a corbel. These are useful and cost-effective because they reduce the need for wasteful under-building below ground level (see Figure 8.5).
The last three paragraphs make reference to the use of concrete with the addition of a water-proofi ng admixture used to control rising damp. This method may be considered as a DPC in certain ground conditions. The exception is where account needs to be taken of radon or other gases, where it will be necessary to provide a specifi c continuous gas membrane, which will also act as the DPC.
The provision of a DPC is to control water rising by capillary action and it will also generally control ingress of water-vapour, when of a membrane form. A water resisting concrete may not control water-vapour to the same extent as a membrane, however due to the presence of the insulation the wall, the inside temperature will typically be higher above ground than below, which will tend to make water vapour move downwards rather than upwards.
DPM
Waterproof concrete to a minimum depth of 150mm above ground level
GL 150mmmin
DPM wrapped into H-Rail Insulation (added later)
Screed (added later)
Cast in-situ ground bearing slab
DPM / Radon barrier
Sand blinding
Compacted stone fill Existing
ground
Selected fill
Figure 8.3 Positioning of DPM membrane on a water-resisting concrete wall dpc.
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bearing Precast concrete suspended
floor system
Void
150 min
Stainless steel ties
External masonry cladding
Ground level
Corbel unit
Reinforcement (as required)
Above left Figure 8.4 Example of DPC in a wall supporting a
suspended slab.
Above right Figure 8.5 Example of a proprietary corbel.
If a proprietary corbel is not available, an alternative is to use a galvanised pressed steel lintel or shelf angle (see Figure 8.6). Alternatively, the insulation may be removed after concreting and the angle then fi xed to the core.
Block cut out to allow core to extend to rear face of lintel.
Alternatively, the insulation may be removed
Lintel or shelf angle fixed direct into extended concrete core See Chapter 7
Figure 8.6 Alternative steel bracket support system to
an outer masonry skin.
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Tile hanging and weatherboarding can be provided by screw fi xing the battens to the fl at ends of the system ties, as shown in Figure 8.7.