Code of Good Practice

The Waterproofing and Roofing Association Cape (WARAC) has been proactive and adopted the proposed amendments to the SANS 10400-L: The National Building Regulations – Part L: Roofs as submitted to the South African Bureau of Standards (SABS) for inclusion in their revised building regulations.

NOTE: The structural design of concrete slabs, screeds to falls and the truss design; or wind influence; or thermal performance of the structure; or calculations of storm water catchment areas or outlet, gutter and downpipe sizes, is not covered in this regulation.

1. DRAINAGE AND WATERPROOFING OF FLAT ROOFS

1.1 Drainage:

1.1.1 Flat roofs shall have a fall towards outlets or gutters (or both) of not less than 1:50. (SABS 021) However, aminimum fall of 1:80 would be acceptable, provided there are no interruptions to the flow of water to outlets or gutters.

The falls on concrete roofs can be formed by casting the concrete slab to the required falls. However, sand/cement triangular screeds will have to be laid at the lower points of the concrete slab to shed storm water to the outlets. Where the gutters are fixed at the lower points of the falls of the concrete slab then no screeds would be required.

Where concrete slabs are cast “flat” the correct falls can be formed by laying a standard sand/cement screed or a suitable lightweight screed. When laying a screed in the rainy season, especially in winter rainfall areas, it is recommended to add a polymer modifier to screed mix as per the resin manufacturer’s specification.

Standard 20mm thick sand/cement screeds must be laid on top of all lightweight screeds to receive waterproofing. (Lightweight screeds can be too porous and friable for good adhesion of some waterproofing systems).

Pre-cast panels and pre-cast roof structures must be securely jointed to prevent any subsequent movement of the concrete elements. (This is to prevent the possibility of screeds on top of the pre-cast roof structures cracking.)

Note: There can be adhesion problems where certain exposed waterproofing systems are laid directly onto dense substrates, such asconcrete surfaces. The reason for delamination of certain waterproofing systems is that such dense substrates are notable to dissipate any minimal amounts of retained moisture vapour. (A less dense sand/cement screed will allow for dissipation of any minimal retained moisture vapour.)

1.1.2 The falls and cross falls to timber flat roofs must be created in therafter design.

1.1.3 The number and diameter of outlets, and the size of the gutters and number and size of down pipes,must be correctly calculated based on the total catchment areas of the roofs in question. Refer to the relevant SANS code of practice.

The minimum size of outlets and down pipes must be not be less than 75mm in diameter on small roofs and balconies etc. and should be 100mm in diameter on larger areas.

Where the outlets are not the standard “coned” fullbore outlet type, the pipe must be flanged to allow the waterproofing to be dressed onto a flat surface, not into a round hole.

Outlets must be set flush with the concrete or recessed into the timber decking to prevent ponding around the outlets.

The position of all outlets must be at least 200mm away from upstands, parapet walls and well away from expansion joints.

1.1.4 Drips shall be provided beneath all concrete roof overhangs.

1.2 Waterproofing:

1.2.1 All concrete or screeded surfaces to be waterproofed must be sound, smooth and even in a wood floated finish to the correct falls and cross falls and with no undulations and without any protrusions or contaminants. Concrete and screeded surfaces must not be highly polished, e.g. power floated.

1.2.2 All concrete and screeded surfaces must dry before applying any waterproofing system. Concrete must not contain more than 7% moisture by weight. Sand/cement or lightweight screeds must not contain more than 10% moisture by weight.

1.2.3 There should be no penetrations through flat roofs. However, where penetrations through flat roofs are required, such penetrations must not be flexible and must be kept to a minimum.

Any necessary penetrations, including outlets, must be kept at least 200mm away from all vertical surfaces, e.g. upstand beams, walls etc.

Plumbing pipes, electrical conduits, air conditioning pipes etc. must not be in clusters. Any lagged pipes, such as air conditioning pipes must be placed in a “U” shaped sleeve with the lagged pipes and sleeve protruding downwards.

The waterproofing membrane dressed around protruding pipes should be mechanically clamped (e.g. with a hose clamp) around the pipes and then counter flashed over the mechanical clamp.

1.2.4 The correct steps in concrete slabs, pre-cast concrete structures, or in timber decking, between the internal and external areas must be formed. The height of the step will be relevant to the distance of the outlets or gutters from thresholds and walls etc. to allow for screeds to falls, the waterproofing systems, and on trafficable areas the screed and tile or sand and brick paving finishes etc.

1.2.5 Expansion joints on flat roofs must not go across the falls. The expansion joints should be at high points.

Kerb upstands should be installed on either side of the expansion joints to raise the joint out of the “water table”.

Expansion joints along building lines must have upstands and be capped with a mechanical flashing. Waterproofing systems should not be used in this situation.

1.2.6 Unless a specific waterproofing system does not require them, sand/cement coves with radii of 45mm must be installed at all internal corners of horizontal and vertical surfaces or 38mm timber fillets fixed at all junctions of horizontal and vertical surfaces on timber decks, to be waterproofed.

1.2.7 All external corners/edges where the waterproofing is to be dressed over must be suitably rounded.

1.2.8 The height of all damp-proof courses (DPC’s), whether straight in solid walls or stepped as in cavity walls, must be at the level of the top of all waterproofing turn-ups. (They must not be below the turn-up).

1.2.9 It is recommended in regions of extreme weather conditions (e.g. coastal regions) where DPC’s interface with waterproofing systems on flat roofs, balconies, terraces and parking decks etc. that the membrane used as the DPC should be the same type as the main waterproofing system and overlapped and bonded onto the main waterproofing turn-ups.

(Creating a continuous damp-proof course and waterproofing system.)

The height of the DPC’s, whether straight or stepped will be relevant to the distance of the outlets or gutters from thresholds and walls etc. to allow for screeds to falls, the waterproofing systems, and on trafficable areas the extra screed and tile or sand and brick paving finishes etc.

1.2.10 Waterproofing turn-upsagainst solid brick walls, or solid plastered brick walls, or if not linked to the stepped DPC’s in cavity walls must be counter flashed with the same membrane and cut intothe walls to a depth of at least 40mm. This is to prevent delamination due to moisture penetration into the walls above the waterproofing system.

1.2.11 Where the waterproofing turn-ups are against a concrete wall a “Z” galvanized metal or aluminium or copper etc. counter flashing should be mechanically fixed and sealed to the concrete wall to cover the waterproofing turn-up. This is to prevent delamination due to moisture penetration into the walls above the waterproofing system.

1.2.12 The waterproofing must be taken underneath and up the back of all door thresholds. There must be no fixings of the frames through the horizontal waterproofing.

1.2.13 The waterproofing system shall be taken to the outside edge of all perimeter upstands, parapet walls, etc., and preferably turned down the outside face of the structure by 50mm.

1.2.14 Where other structures, such as planter boxes, water features, brick benches etc., are to be constructed on balconies, terraces and parking decks etc., the roof deck areas must be totally waterproofed first. The structures can then be constructed on top of the waterproofed areas. Where structures are to be built against solidwalls, or cavity walls, the waterproofing system must be taken above the finished heights of such structures, terminated and interfacing with the straight or stepped DPC’s as detailed in items 4.3.2.7, 4.3.2.8 and 4.3.2.9 above.

1.2.15 The waterproofing system shall be installed by competent qualified waterproofing applicators and strictly in accordance with the manufacturer’s instructions and to good practice terminating details, such that the roof must be left in a watertight condition.

1.2.16 The same waterproofing principles apply to internal areas requiring waterproofing, e.g. plant rooms, bathrooms and showers etc.

1.2.17 Any warranties/guarantees issued on the waterproofing materials and workmanship/application are only for a maximum period of 10 (ten) years. Such warranties/guarantees are subject to the industries standard terms, conditions and maintenance requirements. Any waterproofing systems in covered situations do not carry guarantees.

1.3 Below ground tanking/waterproofing:

1.3.1 All concrete, brick or plastered vertical surfaces to be tanked/waterproofed must be sound, smooth and even (plastered surfaces to be in a wood floated finish) and with no undulations and without any protrusions or contaminants. Concrete and plastered surfaces must not be highly polished. Brick surface must besmooth and all brick joints flush.

1.3.2 All concrete, plastered and brick surfaces must be dry before applying any tanking/waterproofing system. Concrete must not contain more than 7% moisture by weight. Sand/cement plasterwork and brickwork must not contain more than 10% moisture by weight.

1.3.3 There should be no penetrations through the walls. However, where penetrations are required, such penetrations must not be flexible and must be kept to a minimum.

1.3.4 Any protruding pipes through the walls should be flanged to allow the tanking/waterproofing to be dressed onto a flat surface as well as around the pipes. The tanking/waterproofing membrane dressed around protruding pipes should be mechanically clamped (e.g. with a hose clamp) around the pipes and then counter flashed over the mechanical clamp.

1.3.5 Unless a specific tanking/waterproofing system does not require a cove, sand/cement coves with radii of 45mm must be installed at all junctions of horizontal and vertical surfaces.

1.3.6 All external corners/edges where the tanking/waterproofing is to be dressed over must be suitably rounded.

1.3.7 Where any tanking/waterproofing system terminates horizontally at the tops of the walls, or vertically against  the sides of the walls, even in a raking situation, a counter flashing of the same material must be cut into the walls to a depth of at least 40mm and bonded/sealed onto tanking waterproofing membrane. This is to prevent delamination due to moisture penetration into the walls aboveor on the side of the waterproofing system. Where the wall above is a cavity or solid wall the tanking/waterproofing system can be linked to the stepped or straight DPC’s in the walls.

1.3.8 Where the walls are concrete a “Z” galvanized metal or aluminium or copper etc. counter flashing should be mechanically fixed and sealed to the concrete wall to cover the tanking/waterproofing. This is to prevent delamination due to moisture penetration into the walls above the waterproofing system.

1.3.9 The tanking/waterproofing system must be dressed onto sound, smooth, even and dry concrete foundations and with no undulations and without any protrusions or contaminants, and dressed down the outside face of the foundations.

1.3.10 All tanking/waterproofing must be protected with either a brick skin, hardboard or a composite drainage board system before back filling.

1.3.11 No warranties/guarantees are issued on below ground tanking/waterproofing materials or workmanship/application.