Template:Part 12 (Waterproofing Roofs - SBS)

1 Protected and Modified Protected Membrane Roof Assemblies

This Part pertains to the design and installation of roofs that are designed and constructed as Protected Membrane Roof Systems or Modified Protected Membrane Systems; in these systems, gravel ballast or pavers are used to secure the system materials against wind uplift and floatation in water. For roofs designed with accessible coverings, refer to Part 14 THE ROOF as a PLATFORM: Coverings, Living Spaces and Structures.

1.1 Design

1. Only fully adhered membranes are permitted for application on a Protected Membrane Roof System.
2. When a roof is designed as a Protected Membrane Roof System or as a Modified Protected Membrane System, it must be secured in keeping with the design standards and ballast weight requirements in Part 3 SECURING the ROOF ASSEMBLY. In addition, the roof must be designed to incorporate
   1. gravel ballast guards around drains
   2. a drainage layer beneath XPS insulation.
   3. filter fabric installed over XPS insulation, in order to
      1. contain the insulation and thereby prevent ‘insulation stacking’ (displacement) when insulation boards become buoyant in water.
      2. prevent fines from settling at the membrane level and filling the voids between insulation board joints.
3. Where membranes installed on vertical surfaces may be damaged from foot traffic or shifting coverings, they must be protected as, for example, with base metal flashings.
4. Every Protected Membrane Roof System or Modified Protected Membrane System designed with gravel ballast must conform to the securement requirements set out in 3.3.2 Ballasted Roof Assemblies and specify ballast conforming to the minimum requirements shown in the table below.

Table 12.1 RGC Ballast Guide

XPS Insulation Thickness	Stone Ballast Required Weight	Ballast Depth (approximate)
Up to 50 mm (2")	60 Kg/M2 (12 lb./sf)	40 mm (1 ¾")
75 mm (3")	8r Kg/M2 (17 lb./sf)	60 mm (2 ¼")
100 mm (4")	108 Kg/M2 (22 lb./sf)	75 mm (3")
125 mm (5")	132 Kg/M2 (27 lb./sf)	90 mm (3 ½")
150 mm (6")	156 Kg/M2 (32 lb./sf)	105 mm (4 ¼")
175 mm (7")	180 Kg/M2 (37 lb./sf)	125 mm (5")
200 mm (8")	204 Kg/M2 (42 lb./sf)	140 mm (5 ½")

1.2 Materials

See also 3.2.2 Gravel Ballast in Part 3 SECURING the ROOF ASSEMBLY.

1. Membranes must conform to the material requirements set out in 9.2.1 Composition, Thickness and Selection.
2. Insulation must be Type IV XPS, and must be supplied by the Contractor. Refer to 7.2 Materials.
3. Drainage mats and filter fabrics must conform to the standards set out for overburdens in 14.2.4 Components for Vegetated Systems and Other Roof Coverings.
4. Pavers that are partially supported (i.e. with pedestals) should be capable of resisting anticipated loads (consider, for example, hydraulically pressed concrete pavers).
5. Pedestals
   1. should be adjustable, when a level surface is required.
   2. must be proprietary (purpose-made) and include an integral spacer rib measuring at least a 3mm (⅛”), to uniformly separate pavers.
6. Gravel ballast used to secure a Protected Membrane Roof System or Modified Protected Membrane System must be clean, washed, round or crushed stone, falling within the following gradations:
   1. 35 mm (1 ½") - 100 % Passing
   2. 25 mm (1") 70 - 100 % Passing
   3. 20 mm (¾") 5 - 20 % Passing
   4. 12.7 mm (½") 0 - 6 % Passing
   5. 5 mm (3/16") 0 - 2 % Passing


Any variance to the above must be accepted by the owner or the owner's representative and be confirmed in writing.

1.3 Application

1.3.1 General

1. All components of a Protected Membrane Roof System or Modified Protected Membrane System, including the gravel or paver ballast, must be supplied and installed by the Contractor. Where a Vegetated Roof System (VRS) is used as ballast, the VRS may be installed by others but
   1. the work must be coordinated with the Contractor.
   2. the VRS installed immediately upon completion of the Contractor’s work, to ensure the roof system is held in place.


See also 12.1.3.5 Filter Fabric and 14.1.2.2 Roof Coverings.

1.3.2 Membranes

1. 1) Membranes, membrane flashing and insulation must be installed in keeping with the requirements found elsewhere in this Standard.
2. No UV-sensitive membrane may be left exposed to UV radiation and must be fully protected by a granulated cap membrane, metal flashing or overburden.
3. 3) The second ply in a Protected Membrane Roof System may be a base membrane that is acceptable to the membrane manufacturer for that application, and must meet the membrane requirements in 9.2.1 Composition, Thickness and Selection for puncture resistance and thickness.
4. All membrane flashing must be carried up the vertical surface at least 200mm (8”) higher than the top of the ballast.
5. Before any roof covering, structure or equipment is installed, roof membranes must be
   1. inspected.
   2. scanned for leaks when an integrity scan is specified.
   3. free of deficiencies.

1.3.3 Insulation

1. Insulation must be installed by the Contractor.

1.3.4 Drainage and Penetrations

1. A drainage mat must be installed below the XPS insulation. A second drainage layer may be installed above the insulation but is at the discretion of the Design Authority.
2. Specialized proprietary drainage products must be acceptable to the membrane manufacturer.
3. Ballast guards must be installed around all roof drains. See 11.2.2 Roof Drains & Scuppers.
4. For drains and penetrations, refer to the standards in Part 11 DRAINS and PENETRATIONS.

1.3.5 Filter Fabric

1. Fabric filter mats must be
   1. installed loose-laid (un-bonded) over the insulation and below any type of ballast or roof covering.
   2. overlapped at all edges a minimum of 300mm (12").
   3. at least 2.5 m x 2.5 m (8’ x 8’) in size.
   4. slit to fit over roof penetrations, and cut out around roof drains and other openings.
2. Filter fabric must extend up perimeter edges and curbs, and placed loose (unattached) under metal counter flashings or wall finishes. See also 13.3.4 (6) concerning linear metal flashings.

1.3.6 Gravel and Paver Ballast

1. Gravel or pavers used as ballast on a Protected Membrane Roof System constitute part of the roof system and therefore each kind of ballast must
   1. conform to the minimum requirements set out in Part 3 SECURING the ROOF ASSEMBLY.
   2. be evenly distributed or installed over the insulation, drainage layer and filter fabric assembly.
   3. be supplied and installed by the Contractor, not by another trade.
2. Pavers and unit-type masonry, such as brick or stone, must be supported by
   1. proprietary (purpose-made) pedestals with at least a 3mm (⅛”) integral spacer ribs for uniform spacing of pavers.
   2. a proprietary drainage layer overlaid with a filter fabric mat.
   3. a drainage layer of loose aggregate (such as pea gravel) measuring at least 25 mm (1") in depth, installed over a filter fabric.
3. Pedestals or a drainage layer must permit at least 12.7 mm (½″) of vertical separation between the paver and the underlying substrate, to provide airflow for drying surfaces and assist in leveling. Pedestals should not impede the flow of water or air, and should uniformly distribute the dead load of pavers, and other unit masonry products, as well as predicted live loads.

2 Built-in Membrane Gutters

2.1 Design

1. When a built in membrane gutter adjoins a RoofStar-guaranteed water-shedding system, the gutter waterproofing must be constructed by the Contractor to be included by the RoofStar Guarantee. Built-in membrane gutters that drain a roof not covered by a RoofStar Guarantee are not eligible for a RoofStar Guarantee.
2. Conventionally Insulated Systems that drain into a built-in gutter must, at the gutter edge, abut solid blocking that provides
   1. a stop for the insulation assembly.
   2. a solid substrate for the securement of flashings and membranes.
3. The Design Authority is responsible to design the gutter for its anticipated capacity, with consideration given to
   1. rainfall and snow load calculations for the building location.
   2. drain type, size and flow rate.
   3. size and placement of the overflow drain.


For rainfall and snow load capacities, refer to the British Columbia Building Code, Div. B, Appendix C, Table C-2 which lists various types of loads, including rain and snow loads, for specific reference locations throughout the province.

4. Only fully-adhered membranes or acceptable metal gutter liners may be used in built-in gutters.
5. When a waterproofing system transitions to a water-shedding system by way of a common built-in gutter, the gutter membrane must be carried up the water-shedding system slope (when measured vertically from the maximum water level)
   1. at least 150 mm (6”), or
   2. at least 300 mm (12”) in regions with typical heavy snow.
6. New gutters shall be designed with a minimum width of 300 mm (12”) and a depth not exceeding the gutter’s width. At least 100 mm (4") clearance on the horizontal plane is required between any gutter wall and the
   1. the edge of the drain bowl for spun drains.
   2. the edge of the drain leader for flat spun or welded drains.


Cast drains must be installed according to the requirements set out in 11.3.2 Roof Drains.

7. To qualify for a RoofStar Guarantee, existing gutters should be redesigned if their capacity is undersized, but they must nevertheless incorporate an overflow drain in keeping with the standards in this Part. Where the primary drain in an existing gutter is undersized for the capacity of the gutter, the primary drain must be replaced with a properly sized drain.
8. An overflow drain must be located at least
   1. 100 mm (4”) above the primary gutter drain.
   2. 25 mm (1”) below any mechanical fasteners used to secure the adjoining roof system.
9. For transitions between the built-in gutter and water-shedding systems, refer to Part 10 PERIMETERS and WALLS in any of the water-shedding systems standards.

2.2 Materials

NOTE: These material standards are applicable to membrane gutters for all waterproofing system membrane roofs; hence, references to various membrane types.

1. Only 2-ply modified bituminous membranes or reinforced PMMA are acceptable for this application:
   1. 2-ply bituminous membranes must meet the minimum thickness requirements in 9.2.1 Composition, Thickness and Selection.
   2. Reinforced PMMA liquid membrane systems approved for field use, applied on an accepted SBS-modified base membrane.
2. A metal gutter liner may be fabricated from
   1. copper sheet material, incorporating soldered seams.
   2. stainless steel, incorporating welded seams.


See 13.2.1 Sheet Metal Grade and Gauge for gauge requirements. See also Application below.

2.3 Application

1. All gutter membranes must be installed according to the membrane manufacturer’s published instructions.
2. Gutter membranes must be
   1. installed perpendicular to the gutter length.
   2. carried up an adjoining water-shedding systems (measured vertically from the maximum water level)
      1. at least 150 mm (6”), or
      2. at least 300 mm (12”) in regions with typical heavy snow.
   3. lapped under and sealed to the adjoining membranes at least 150 mm (6”).
   4. installed in keeping with application requirements in this Standard.
3. Gutter membranes must be mechanically secured at their terminations, both on the outside of the gutter edge and on the field:
   1. Fasteners securing the membrane on the field must be placed at least 150 mm (6”) above the maximum water level.
   2. Securement fastener spacing shall be no more than 300 mm (12”) O.C.
4. Gutter drains and overflows must be installed in keeping with the Design requirements outlined in Design above. Drain flanges that are bent to accommodate the side walls of the gutter must be mechanically fastened to the gutter wall before membrane application. Refer to the requirements for roof drains in any of the Standards for waterproofing systems.
5. A metal gutter liner
   1. fabricated from copper sheet material must incorporate soldered seams.
   2. fabricated from stainless steel must incorporate welded seams.
   3. must be installed
      1. over an adhered single ply membrane no less than 2.3 mm (bituminous membranes) or 60 mils (non-bituminous membranes).
      2. with a slip sheet between the membrane and the metal liner to prevent damage to the membrane caused by the liner at its joints.
6. When an adjoining water-shedding system is insulated (typically ASM only), the transition from gutter to the water-shedding system may require the use of tapered insulation incorporating a drainage plane between layers of tapered insulation. See Construction Detail ASM 12.1.2 Built-in Gutter Assembly for an illustrated example.