Case 1

Good Practices

Design

It is essential for the designer to have an understanding of the effect of joint movement in order to select specifications which eliminate the risk of movement being transmitted to the waterproofing covering.

To prevent potential construction and maintenance issues, consider good design practices such as allowing proper flow paths to suitable discharge points, specifying a suitable waterproofing membrane, and using the necessary movement joints. Properly detail all openings, penetrations, upturns and corners to ensure watertightness in accordance with BS EN 1107-2, BS EN 12039, BS EN 12730, SS 637 (formerly CP 82) or equivalent.

Provide waterproofing (materials and details) to prevent water leakage through external joints in accordance with BS EN 15037-5, BS EN 13693, BS EN 12730, BS EN 13369, SS 677 or equivalent. To avoid the risk of movement being transferred to the waterproofing membrane, detail expansion joints in accordance with BS 093. Refer to the code of practice for structural use of concrete in accordance with SS EN 1992-1-1, SS EN 1992-1-2, CP 65-1 or equivalent for RC roof design. For precast roof slab design, refer to the guidelines in accordance with BS EN 15037-5, BS EN 13693, BS EN 13369, CP 81 or equivalent.

Ensure positive drainage in all low-slope roofs. Design roof gutter in accordance with the performance requirements set by BS EN 12056-3, SS 525 or equivalent. Roofing components should follow the allowable thermal stresses under temperature variations.

When preformed sheet waterproofing is specified, ensure proper lapping with min. 75 mm end-to-end and min. 50 mm side-toside. Waterproofing membrane when reaching parapet wall should turn up at
least 300 mm upwards. At congested or difficult areas for the application of preformed sheet waterproofing, e.g., near penetrations and vertical services and shafts/walls, a combination use of liquidapplied sheet waterproofing as well as integral waterproofing should be considered.

Design flat roofs made of reinforced concrete with an adequate fall to prevent ponding and maintain minimum pitch variation over the entire roof to avoid water ponding at the perimeter and water leakage through the roof slab/parapet wall junction in accordance with BS 6229, BS 8218, SS 637 (formerly CP 82) or equivalent. Ensure positive drainage in all low-slope roofs. Do not obstruct joints of areas prone to water, ice and freeze/thaw damage.

Construction

Use low-permeability concrete for roof structure construction. Mix concrete appropriately (maintain specified water-cement ratio) and ensure proper curing to prevent excessive evaporation, which can lead to defects.

Consider storing aggregates under shade in accordance with SS EN 1992-1-1, SS EN 1992-1-2, CP 65-1 or equivalent. Waterproofing and drainage should be coordinated to form an integrated waterproofing system. Maintain construction quality control to ensure proper curing of concrete prior to membrane application.

Ensure consistency of construction quality in terms of installation of fixtures and fittings, proper dressing of pipe penetrations, and good lapping and adhesion of the waterproofing membrane to the base with no mortar stains. Check for any signs of leakage during construction. The sealant material used should be tolerant of climatic variations on-site and be able to accommodate high movement if necessary. Joint sealing slots need to be cleaned (i.e., remove all dust). Proper installation of a backer rod is necessary to
avoid sealant adhering to the base of the slot. Tightly pack joint filler to a slot.

Consider providing an upturn at expansion joints (with metal capping). Expansion joints should be properly constructed in accordance with BS 6093.

Laying waterproofing membranes on a roof requires skill, experience and patience. The moisture content of the substrate must be monitored to ensure proper adhesion. Conduct proper surface preparation. Special attentions must be paid to locations with openings, penetrations, upturns, corners and vertical services and shafts/walls. When mixing adhesives, ensure the manufacturer’s instruction is strictly followed. Where preformed sheet waterproofing is specified, ensure proper lapping for both end-to-end
and side-to-side as well as an upturn tucked into a parapet wall according to the specification.

Ensure quality waterproofing by maintaining adequate and correct fall directions and angles to gutters in accordance with BS EN 12056-3, BS 8490, BS 8000-0 or equivalent. The waterproofing and drainage should be coordinated to form an integrated waterproofing system.

Carry out visual inspections and ensure that all gutters are tested for ponding upon construction in accordance with BS EN 12056-3, BS 8000-0, SS 525 or equivalent.

Materials

Water cement ratio in the concrete is a important parameter to keep concrete free from defects. To prevent excessive evaporation during concreting on hot weathers, curing should begin as soon as possible. Water should be fogged or sprayed for 12 hours before using other curing methods.A white, heat reflective membrane or polyethylene may be applied later.

The curing period should also be extended seven days or longer during hot weather. Also, to prevent ealy slump loss and rapid settling during hot weather concrete casting, temperature of the concrete mix can be kept low by using cooled water to mix the concrete.

The aggregates should also be kept in a shady place before use and kept moist by sprinkling water on it. Placing equipment should be shaded or cover with a wet burlap to keep the temperature low. the rate of water evaporation is rapid, especially for slabs.

Sealant should be tolerant of climatic variations and have high movement accommodation. An elastomeric sealant would be suitable for movement. Correct sealant should be used to reduce sealant deterioration:

1. Metal – metal = urethane, polysulfide, acrylic
2. Metal – concrete = urethane, polysulfide, acrylic, silicone
3. Metal – glass = silicon, urethane, polysulfide
4. Concrete – concrete = urethane, polysulfide, polyurethane