Template:Part 2 (Waterproofing Roofs - SBS)
Template:Part 2 (Waterproofing Roofs - SBS)
Refer to the Glossary for further definitions of key terms used in this Manual.
- Supporting deck ("deck")
- means the "structural surface to which the roofing or waterproofing system (including insulation) is applied" (ASTM D1079-18 Standard Terminology Relating to Roofing and Waterproofing).
- Deck overlay
- means a panel material secured to the supporting deck in order to render the deck surface continuous or suitable for the installation of roofing materials.
- means a structural or non-structural element in a building that vertically separates space. Walls may separate the outside environment from the interior conditioned space of a building, or they may separate one or more interior spaces from each other (adapted from ASTM E631-15 Standard Terminology of Building Constructions).
- Wall overlay
- means a panel material secured to the surface of a Wall, to render it suitable for the installation of roofing or wall cladding materials.
- The British Columbia Building Code, or the building code having jurisdiction, prevails in all cases except where it is exceeded by the RoofStar Guarantee Standards published in this Manual.
- Notwithstanding the RoofStar Guarantee Standards published in this Manual, the RoofStar Guarantee does not extend coverage to the supporting deck or to its securement, which is the responsibility of the Design Authority and the building contractor.
- Prior to the application of the roof system, the supporting deck and other surfaces receiving membranes must be smooth, straight, clean and free of
- dust and debris.
- objectionable surface treatments.
- release oils.
- If surface drying is required prior to roofing, use blown air to facilitate this.
- Walls, parapets, curbs, blocking and penetrations should be constructed or placed prior to the commencement of roofing work. This work is provided by other trades.
- The supporting deck structure should be dimensionally stable and capable of accommodating roof system component movement.
2 Roof Slope
- The RoofStar Guarantee Program classifies roofs according to their function – waterproofing or water-shedding. Within each classification, slope is defined as follows:
- Flat means a roof with a slope less than 1:6 (2” in 12”, or 9 degrees).
- Low Slope means a roof with a slope from 1:6 (2” in 12”, or 9 degrees) up to but less than 1:3 (4” in 12”, or 18 degrees).
- Common Slope means a roof with a slope 1:3 (4” in 12”, or 18 degrees) up to and including 1:1 (12” in 12”, or 45 degrees).
- Steep Slope means a roof with a slope greater than 1:1 (12” in 12”, or 45 degrees) up to and including 21:12 (21” in 12”, or 84 degrees).
- Extreme Slope means a roof with a slope greater than 21:12 (21” in 12”, or 84 degrees).
See Figure 2.1 for an illustrated guide to the above definitions.
- While good drainage is desirable but not always perfectly achievable, and waterproofing roof systems generally are not affected by standing water, each Project design should incorporate sufficient slope to move water off the roof surface. Sufficient slope is attained when (subject to conditions that permit evaporation) no standing water remains on the roof surface, after a reasonable interval following a rainfall. Local climate conditions may necessitate design slopes higher than the minimums published in this Manual. See 2.2.2 New Construction and 2.2.3 Replacement Roofing for minimum requirements.
- Roof slope can be achieved either by designing the roof structure with sloped decks, or by introducing slope with tapered board insulation.
- Deflection and settlement may interfere with roof drainage. Therefore, the Design Authority must take into consideration the anticipated deflection of the structure when designing the roof for proper drainage.
- Drainage is best achieved (in descending order of best practices) with
- four-way slope to drain.
- two-way slope to drain, in combination with crickets between drains.
- slope to a common valley, or with gutters.
- positive sloping valleys to drains (highly recommended).
- Curbs that span 1800 mm (6’) or more across the drainage plane should be designed with a cricket to divert water around the curb.
- Drain sumps, designed to isolate collected water for the drain, need not be sloped. The use of drain sumps is highly recommended. See also 220.127.116.11 (9) All Projects.
2.2 New Construction
- All new construction roofs that qualify for a RoofStar Guarantee must be designed and built with a slope of no less than 2% (1/4” in 12”), measured on the primary sloped planes of the roof.
- Single-ply SBS roof systems must be designed and built with a slope of no less than 6% (3/4" in 12"), measured on the primary sloped planes of the roof. Any roof areas with slopes less than 6% (3/4" in 12") require 2-ply membrane systems.
2.3 Replacement Roofing
- Replacement roof systems may qualify for a RoofStar Guarantee without correcting poor drainage, though the elimination of ponding (standing water) is strongly recommended.
- RoofStar 15-Year Guarantee: replacement roofs must
- be sloped at least 2% (1/4” in 12”), measured on the primary sloped planes of the roof, in order to qualify for a RoofStar 15-Year Guarantee.
- incorporate crickets at curbs and sleepers that impede drainage or are wider or longer than 1200 mm (48”).
- See also Part 7 INSULATION.
3 Supporting Deck Types
Steel roof decks are constructed of light gauge (usually 22, 20, or 18 gauge) cold-rolled steel sections (panels) that are usually galvanized. In cross-section the panels are ribbed, with the ribs usually spaced at 150 mm (6") O.C. The ribs provide the strength and rigidity of the panels. Steel decks are generally supported by open-web steel joist framing and are welded or mechanically-fastened to the framework.
For more information about steel decks, see Roof Decks in Division B: Essential Elements.
- Steel deck panels must be installed to provide a smooth uniform surface for roofing.
- A thermal barrier may be required to conform to building vode or fire insurance-rated assemblies, when the roof assembly is insulated (usually when the insulation is classified as combustible).
- Uninsulated systems require a deck overlay for the membrane. A RoofStar-accepted moisture resistant gypsum core deck overlay board may serve both as a thermal barrier and as a level surface. For more about this, see 5.3.2 Steel Decks.
Concrete roof decks to which a roofing system is applied include the following types:
- Pre-cast panels.
- Pre-stressed panels.
- Lightweight. Not all membrane assemblies are suitable for application on every type of concrete deck, and therefore the Design Authority is strongly urged to consider potential deck deflection when designing the assembly. For more information about concrete decks, see Roof Decks in Division B: Essential Elements.
- It is not permissible to adhere roof membranes to freshly poured concrete supporting deck structures, within the first 28 days after pouring, unless expressly instructed in writing by the Building Envelope Engineer. Adhered means adhered by means of an adhesive, hot bitumen or heat.
- Deck preparation by others:
- Remove all ridges and bumps, and repair cracks.
- Feather with grout all weld plates and elevation differences.
- Pre-cast decks joints should be “taped” or stripped-in with a membrane ply.
Wood is a common roof deck construction material that has been used for many years because of its economy, ease of fabrication, lighter construction, and ready availability. Acceptable wood roof decks may include (without limitation)
- wood board (dimensional lumber, ship-lapped planking, etc.).
- non-veneered wood decks (oriented strand board, waferboard, etc.).
- laminated timber.
For more information about wood decks, see Roof Decks under B. Essential Elements.
The following criteria apply to all types of wood decks:
- Notwithstanding minimum wood deck thickness requirements published in the Building Code having jurisdiction, when a roof must be designed to resist Specified Wind Loads, plywood or non-veneered panels (such as O.S.B. or wafer board) used as a roof deck must be at least 12.7 mm (1/2”) thick, unless exceeded by the deck thickness specified in a Tested Assembly (often 19 mm (3/4”), an Assembly with Proven Past Performance, or a roof assembly with custom-engineered securement .
- Wood decks shall be secured to other supporting structural elements of the building in keeping with the published requirements of the Building Code having jurisdiction .
- Differential edge movements or deflection exceeding 1/360 of the span must be prevented by any of the following options:
- construct the deck with tongue-and-groove plywood, and support the non-grooved edges with joists or solid blocking.
- support butt joints with solid blocking under non-supported edges.
- All wood decks must be affixed to the supporting framing or structure with corrosion-resistant
- wood screws.
- spiral nails.
- ring shank nails.
The structural suitability of the fastener is the responsibility of the Design Authority.
- All wood decks with knots or cracks must
- have metal affixed over them before the deck can be accepted for roofing (this work should be done by others).
- be overlaid with a layer of knot-free plywood at least 12.7 mm (1/2”) thick.
- All types of wood decks should be roofed promptly after installation.
- When a plywood deck is intended to support a Protected Membrane Roof System and a vegetated roof system, the plywood should be marine-grade T&G material at least 19 mm (3/4”) thick, depending up on the anticipated live and dead loads of the roof systems. The Design Authority is responsible to calculate these loads and design suitable approaches to mitigate deflection.
- All mass timber or wood board decks must be covered with a properly secured, suitable overlay to protect membranes from wood sap or deck surface irregularities and protruding fasteners. Plywood and non-veneered panel decks are exempted from this requirement .
- Plywood roof decks consist of exterior type plywood mechanically fastened to the roof framing. The plywood panels should conform to CSA 0121, “Douglas Fir Plywood”, CSA 0151, “Canadian Softwood Plywood”, or CSA 0153, “Poplar Plywood”, following requirements published in the Building Code having jurisdiction.
- Plywood roof sheathing should be installed in a staggered pattern with the surface grain at right angles to the roof framing.
3.3.2 Laminated Timber
Laminated timber decks are typically comprised of crossing layers of dimensional solid wood material, laminated to form a thick, dimensionally stable slab strong enough to support significant structural loads.
3.3.3 Non-veneered Panels
See Part 9 FIELD MEMBRANES for application standards and limitations.
3.3.4 Wood Boards
- Wood board decks include tongue-and-groove, ship-lapped, or splined boards or planks. These typically range in thickness from 19 mm to 89 mm (nominal 1" to 4").
- Wood board decks may also include Mill decks, also called Nail-Laminated Timber decks. These are constructed with a single layer of dimensional boards (dimensions can vary), placed on edge and spiked together to form a “mill deck”. The thickness of the boards is determined by the anticipated loads and spacing of roof joists or trusses (consult the local or provincial Building Code having jurisdiction).
- Wood board decks should be of sound seasoned lumber, properly secured to the supporting structure.
4 Expansion Joints
See Construction Details and 10.3.6 Expansion and Control Joints for membrane application.
Roof expansion joints, or movement joints, are designed to safely absorb thermal expansion and contraction of materials, or to absorb vibration. They also allow for movement caused by settlement and earthquakes.
- Structural expansion joints should be considered wherever
- the type of deck changes.
- additions connect to existing buildings.
- separate wings of a building join (e.g. “L” or “T” configurations).
- interior heating conditions change.
- differential movement may occur (e.g. parapet detail where the deck is not supported by the wall).
- The location of expansion joints must be clearly indicated on the drawings, drawn in detail, and included in the specifications.
- The construction of structural expansion joints is the responsibility of others and must be in place before the Contractor accepts the deck for roofing.
- Expansion joints constructed as a raised divider must have a sloped top surface and must extend in height above the Finished Waterproofing System no less than 200 mm (8"). The minimum height of the Expansion Joint may be reduced to 100 mm (4") if the primary roof membrane flashing is fully supported and sealed over the top.
5 Control Joints
See the relevant Construction Details and 10.3.6 Expansion and Control Joints for membrane application.
Control joints (sometimes referred to as roof dividers) are site-built but relatively uncommon for roofs with flexible membranes. They are designed to help control thermal expansion and contraction stresses in the roof system where no structural expansion joint has been provided in the building design. Control joints may be present on older roofs with built-up roof systems, and will have to be taken into consideration by the Design Authority; in some cases, control joints may be eliminated for replacement roofing. Still, control joints may be employed by the Design Authority to control expansion and contraction of any materials in the roof system, or for dividing existing roof areas for phased replacement roofing.
- The Design Authority is responsible to determine the need for roof dividers and control joints and is responsible for their design. The use of roof dividers and control joints should be evaluated on a product performance basis.
- When roof dividers are specified and detailed, they should divide the roof into approximately equal, regular-shaped areas. Ideally, roof dividers should be located at the high points of the roof, with drainage away from the divider on both sides, but drainage must not be impeded by the roof divider.
- The location of roof dividers must be clearly indicated on the drawings, drawn in detail, and included in the specifications. Specifications should clearly indicate responsibility for their construction.
- When roof dividers are already present (during replacement roofing), the dividers must extend at least 100 mm (4”) in height above the Finished Waterproofing System.
- Wall surfaces must be clean, dry and smooth, suitable for the application of roof system materials. When the wall surface is unsuitable to receive waterproofing materials, it must be resurfaced with an RoofStar-accepted wall overlay. See Part 5 DECK and WALL OVERLAYS for material and application standards.
- Sheathing, defined as a rigid panel material secured directly onto framing, is considered a wall surface for the purpose of this Standard.
- Wall surfaces receiving waterproofing materials must extend vertically beyond the maximum height of waterproofing materials but in any event must be installed at least 200 mm (8”) high, above the finished roof surface. For suitable wall surface materials, see 2.6.2 below.
- Walls and roofs commonly intersect in two ways:
- Directly, where the wall structurally connects to the roof structure, so that both move together.
- Indirectly, where the roof structure and the wall structure are independent of each other, so that the movement of one does not affect the other. These locations require an expansion joint.
- The Design Authority must ensure a continuous connection between the roof system from field to perimeter, in order to control or inhibit the movement of water, air and vapour.
- Wood or steel-stud walls must be sheathed with a material suitable for securing metal flashings.
- For concrete walls, refer to 2.3.2 Concrete above.
- Concrete surfaces must comply with the requirements set out in 2.3.2. When concrete surfaces do not comply, concrete walls may be sheathed with any one of the following:
- 15.9 mm (5/8”) thick treated plywood.
- fibre-mat reinforced cement boards with a minimum thickness of 9.5 mm (⅜").
- Both materials must also conform to ASTM C1325-04.
- For framed walls, the following sheathing material are acceptable:
- moisture resistant gypsum core boards specifically designed to receive roof membranes, with a minimum thickness of 12 mm (1/2”). These panel may be installed horizontally or vertically.
- fibre-mat reinforced cement boards with a minimum thickness of 9.5 mm (⅜").
- Plywood with a minimum thickness of 12 mm (1/2”).
7 Electrical Cables and Boxes
Electrical cables (including conduit) or boxes installed inside, on top of, or beneath a roof assembly may expose roofing workers to electrical shock, and may inhibit the installation of some roof systems designed to resist wind uplift. Furthermore, electrical cables on, in or under the roof assembly expose the building and the public to both shock and fire. Hidden electrical wiring and boxed junctions can be extremely difficult to document before work begins, and while some technologies are purportedly accurate in identifying energized circuits before they are damaged, false readings make these technologies less than reliable. During replacement roofing, avoiding damage to electrical circuits from cutters and fasteners is sometimes next to impossible. It is therefore desirable to design buildings with realistic separations between electrical wiring and boxes, and roof assemblies.
For more about this topic, see the reprinted Safety Bulletin issued by the BC Safety Authority, republished in the November 10, 2015 Technical Update.
Currently, neither the Canadian Electrical Code, Part I nor the British Columbia Electrical Code explicitly prohibit, nor explicitly permit, the installation electrical cables and boxes anywhere in close proximity to a roof assembly. The Design Authority therefore has the latitude to write restrictions concerning the location of electrical installations, and consequently eliminate shock and fire hazards. To do so, apply the following standards when preparing Project specifications to qualify for a RoofStar Guarantee.
7.1 New Construction
- Electrical cables, raceways or boxes shall not be installed within a roof assembly (Figure 2.7.1-1).
- Electrical cables, raceways or boxes shall not be installed on the underside of a roof assembly, unless
- the supporting deck structure equals or exceeds 76 mm (3”) in thickness (Figure 2.7.1-2), or
- the cables, raceways or boxes are installed and supported so there is a separation of not less than 38 mm measured between the underside of the roof assembly and the electrical installation (Figure 2.7.1-3).
- Notwithstanding either (1) and (2), cables or raceways shall be permitted to pass through a roof assembly for connection to electrical equipment installed on the roof, provided that the passage through the roof is a part of the roof assembly design.
- Electrical cables installed above the roof assembly should be elevated to permit proper support, roof maintenance and future replacement roofing (Figure 2.7.1-4).
7.2 Replacement Roofing
- If existing electrical cables or boxes do not conform to the standards in 2.7.1 New Construction, the Design Authority must consider the attachment of the roof system above the electrical system, and the requirements set out in Part 3 SECURING the ROOF ASSEMBLY.
- The Design Authority should
- specify protection of existing electrical cables and boxes (a 5 mm (3/16”) steel plate may be used to minimize the possibility of fastener penetration and cutter damage, but it should be understood that protection plates may interfere with mechanical fasteners used to secure the roof system against wind uplift, even for future replacement roofing).
- provide the building owner with detailed as-built drawings that accurately map the location of electrical cables and boxes.