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ASSESSMENT CRITERIA
ACTMAP 1 PART 1: INTRODUCTION
SCOPE
This general ACTMAP covers the assessment of manufactured flexible sheets, or in situ liquid-applied, continuous membranes used in roof waterproofing systems. It is a guide to the assessment of roof waterproofing products for which no SABS standard specifications exist and which would, therefore, not be adequately covered by SABS 021, Waterproofing of buildings.
The requirements, test methods and criteria relate to waterproofing that consists of single layer systems or multi-layer systems. They apply to roof coverings for use on:
- inaccessible roofs including façade projections, balcony roofs, etc (inaccessible except for maintenance
- accessible roofs (pedestrian traffic only).
Generally these systems are suitable for roofs with a minimum fall of 1 in 60.
The ACTMAP does not attempt to assess the whole roof but in assessing any waterproofing products, account has to be taken of those elements of the roof structure (ie the support and the protection) that may affect the performance of the waterproofing system. (See Appendix 1 and Appendix 2).
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Supplementary ACTMAPs applicable to specific ‘families’ of waterproofing materials will be prepared when necessary. These specific ACTMAPs will indicate which of the tests, requirements and criteria in the general ACTMAP are applicable to the family of materials concerned. They will also specify the particular identification characteristics and durability requirements of the materials used in the system, including any additional test methods and criteria that are necessary.
TERMINOLOGY
Waterproofing system
A waterproofing system consists of all the essential materials, components and accessories that are essential to providing a waterproof barrier to the roof structure; it includes the necessary detailing for internal and external angles, upstands, verges, gutters, gullies, rainwater outlets, expansion joints, pipes and other protrusions through the roof, etc.
Substrate
The layer situated immediately below the waterproofing system.
Roof
For purposes of this ACTMAP the roof is defined as consisting of the structural elements and all intermediate elements up to the surface that is exposed to the weather. The various elements that may be used in a roof are given below. In any particular roof one or more of the elements may be omitted, the minimum specification being a structural deck and a waterproofing system.
Elements of roof waterproofing
Anti-perforation layer: a layer between the waterproofing and the protection; its function is to minimize the effect of mechanical loads.
Isolation layer (including underlays): a layer of material laid between the roof elements to prevent adhesion between the elements and allow differential movement, and/or to prevent physical or chemical interaction between the various elements.
Protection: one or more layers applied or placed on the upper surface of the waterproofing system. The protection may have an aesthetic requirement but its main function is to protect the waterproofing system from the effects of solar radiation or mechanical effects such as wear or wind uplift.
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Sloping layer: a layer of varying thickness to provide the finished roof with a slope which ensures free drainage of water.
Surfacing screed: screed use to produce a smooth, level or sloping on an element, and/or give it the mechanical properties required for the application of the next layer. A surfacing screed is distinct from a screed (sloping layer) which is applied to create drainage falls on the support.
Thermal insulation: a layer or layers of lightweight material to provide thermal insulation to the roof.
Vapour barrier: a vapour-resistant layer or membrane used to restrict migration of water vapour to the upper layers.
Structural deck (support): part of the roof designed to take both dead and imposed loads, constructed in accordance with the relevant codes of practice referred to in the National Building Regulations.
National Building Regulations and Building Standards Act, 1977 published in Government Notices R1081 and R1726 (Government Gazettes No 11333 dated 10 June 1988 and No 11474 dated 26 August 1988) and in any subsequent amendments or revisions.
Weathertight layer: one or more layers of waterproofing material applied over the roof area designed to prevent water entering the roof structure of a building.
Venting or equalising layer: continuous air layer located under the roofing system or under the water vapour barrier to equalise the water vapour pressure. This layer may or may not be vented to the outside.
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Classification
Classification according to build-up of waterproof layer
Single layer systems: the waterproof layer is laid as a single sheet, or applied in situ as a continuous membrane. The joints usually consist of an overlay at the edges of the sheet. The joints may be formed on site or in the factory.
Multi-layer systems (based on manufactured flexible sheets): two or more sheets are laid on site consecutively to make up the waterproof layer. The sheets may be fully or patch-bonded to one another and laid so that the joints are staggered between the different layers. The system may be:
- a homogenous system consisting of two or more layers of the same material although the thickness, type of reinforcement and surface finish of the individual sheets may be different;
- a mixed system where two or more layers of dissimilar materials (eg bitumen/polymer sheet and traditional bituminous felts) are used.
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Classification according to the accessibility of the roof
Non-accessible roofs: domed, curved or sloping roofs on which it is difficult to walk without special equipment.
Limited access roofs: maintenance traffic only; maintenance of equipment housed on the roof requiring frequent access is excluded from this category.
Access roofs: pedestrian traffic.
Roofs for special purposes: roofs or parts of roofs accessible for frequent maintenance of equipment houses on the roof such as lifts and ventilation equipment.
Classification according to the slope of the roof
Class I: allows for free drainage of water and the possible use of heavy protection.
Class II: allows for free drainage of water but does not allow the use of heavy protection.
Class III: special laying techniques are required because of the slope.
Classification according to the method of fixing the waterproofing to its support (systems based on flexible sheets)
fully bonded
partially bonded
mechanically fixed
bonded and mechanically fixed
loose laid
loose laid and ballasted.
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APPENDIX 1: Note on the supports to the waterproofing
The support of the waterproofing has an important influence on the behaviour of the waterproofing apart from its function of ensuring the general level of the roof.
The following characteristics of the support affect the behaviour of the waterproofing:
the internal cohesive strength (in relation to the effects of wind uplift)
the reaction of the roof assembly to fire when the source of fire is external to the roof covering
movements of the support as a result of changes in temperature or humidity, and mechanical vibrations (such as air conditioning plant, etc). Distinction is made between:
- irreversible movements (drying shrinkage and/or deformations which may produce cracking of the support)
- reversible movements caused by variations of temperature and/or moisture content at the surface of the supports
the resistance to loads (static loads and impacts)
the compatibility between the support, surface material and the waterproof covering.
The use of traditional multi-layer bituminous felts, mastic asphalt and sheet metal roof coverings on special supports is covered by SABS 021, Waterproofing of buildings. The code considers the properties of the support in relation to the roof slope, the accessibility of the roof and the method of fixing the waterproofing to the support.
Where a specified support covered by SABS 021 is to be used with a waterproofing system, such support will be referred to in the Agrément certificate.
Where novel forms of support are to be used with waterproofing systems, the conditions of use will be explicitly defined in the certificate.
APPENDIX 2: Nomenclature of protection used on waterproof coverings
Type of protection
No protection
Factory-applied protection (to flexible sheets)
- mineral finish
- metallic finish
- organic finish
Site-applied protection
- paint
- sheet
- loose or slab protection may be:
- light: a layer of gravel or chippings 10 – 20 mm thick
- medium: a layer of gravel or chippings 20 – 40 mm thick or fibre-cement tiles
- heavy: a layer of gravel or chippings more than 40 mm thick, concrete slabs, hollow blocks, clay tiles or paving bricks, etc.
Methods of application on site
Bonded to the waterproof layer
Laid loose on the waterproof layer with or without anti-perforation layer
Separated from the waterproof layer by an air space (slabs on supports).
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