Template:All Systems - MEMBRANES SBS

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Template:All Systems - MEMBRANES SBS

1 General

While the roof is being applied, all membrane openings at eaves, walls, vents, etc. must be sealed to prevent moisture from entering roofing or between plies of stripping.

NOTE: Fully nailed base sheet and torched cap sheet is considered a single-ply for Guarantee purposes.

Both the base sheet and cap sheet in 2-Ply modified bituminous systems must be of modified bitumen materials using the same polymer. For example, if the cap sheet is an SBS modified bitumen sheet, then the base sheet must be an SBS modified bitumen sheet. Oxidized asphalt sheets will be considered as underlay only and must not be counted as one of two plies.

Both the base sheet and cap sheet must be installed in a parallel direction (not at 90° to each other).

For the application of 2-ply ungranulated membranes; both the cap sheet and base sheet are to be applied separately. Shingle fashion application (i.e., 50% lap) is not acceptable except where membrane back nailing is required.

All modified bitumen base stripping terminating on vertical surfaces must be mechanically fastened.

1.1 Slope Limitations

Only factory cap sheets are to be used on slopes exceeding 1:24 (1/2" in 12"). Manufacturers published instructions as to application methods, materials, and slope limitations are to be followed. On slopes less than 1:24 (1/2" in 12"), double pour, modified double pour or alternate modified double pour and gravel surfacing may be used.

1.2 Membrane Lap Preparation

  • Manufacturer's printed instructions for overlaps are to be followed.
  • Granules are to be embedded prior to forming laps on all torch applied modified bituminous cap sheets.
  • Membrane end lap corners must be cut on a bias (clipped or trimmed on an angle) prior to forming laps on all torch applied modified bituminous membrane roof systems.

2 Material Selection

See Accepted SBS Membranes for RoofStar Guaranteed roof systems. See also Section 3 for special requirements concerning Membrane Roof Systems.

Not all membranes are ideal or even acceptable for every type of application. Below is a table that outlines the new minimum thickness and puncture resistance requirements for SBS-modified bituminous membranes, based on what type of assembly they will be used in (effective for projects bid after March 1, 2018):

SBS-modified Bituminous Membranes: Type, Reinforcement, Thickness and Accepted Applications
All thicknesses shown are in mm; Puncture Resistance measured in Newtons (N)
2-Ply SBS Modified Roof Membranes:
Field & Membrane Flashing

Membrane Application Method
SBS Cap Sheet
Single-Ply SBS
Cap Sheet for
Membrane Type, Reinforcement & Grade Mechanically



Base Sheet (fibreglass) - Grade 3 2.3 2.2 2.3 2.3 n/a n/a n/a n/a 3.0 n/a
Base Sheet (polyester) - Grade 3 2.5 2.2 2.5 2.5 3.5 400 n/a n/a 3.0 n/a
Base Sheet (composite) - Grade 3 2.3 2.2 2.3 2.3 3.5 400 n/a n/a 3.0 n/a
Film Cap Sheet (fibreglass) - Grade 2 n/a 3.3 3.3 4.0 n/a n/a n/a n/a n/a n/a
Film Cap Sheet (polyester) - Grade 2 n/a 3.5 3.5 4.0 4.0 400 4.0 400 3.0 400
Film Cap Sheet (composite) - Grade 2 n/a 3.3 3.3 4.0 4.0 400 4.0 400 3.0 400
Granular Cap Sheet (fibreglass) - Grade 1 n/a 3.3 3.3 4.0 n/a n/a n/a n/a n/a n/a
Granular Cap Sheet (polyester) - Grade 1 n/a 3.5 3.5 4.0 4.0 400 4.0 400 3.0 400
Granular Cap Sheet (composite) - Grade 1 n/a 3.3 3.3 4.0 4.0 400 4.0 400 3.0 400

3 Application

3.1 Cold Weather

In cold weather regions, membrane selection must conform to the membrane manufacturer’s recommendations for January in service design temperature.

3.2 Single-Ply Modified Bituminous Membranes

Membranes used for a single ply modified bituminous membrane system adhered or mechanically fastened shall be a minimum thickness of 3.5 mm on the selvage edge, with a minimum 150 g / meters squared polyester or equal strength polyester-fibreglass combination reinforcement.

Torch applied membrane applications require a deck separation sheet of a minimum 40-lb asphalt coated glass base sheet or torchable overlay board. Direct torch application to wood surfaces is not permitted.

A minimum slope 1:15 (¾" in 12") is required. Any roof areas less than 1:15 (¾" in 12") require 2 ply membrane assemblies.At roof slope transitions locations where slopes of less than 1:15 (¾" in 12") meet steeper slopes a two ply membrane assembly must be carried 900 mm (36") beyond the lower sloped roof transition point.

Membrane gussets must be installed to all inside and outside corners.

Modified Bituminous Base Sheet pre-stripping ply required at all perimeters, upstands and penetrations. Direct torch application to wood surfaces is not permitted.

Cap sheet stripping is required and must extend 150 mm (6") horizontally and 200 mm (8") vertically from the base of all upstands.

All stripping terminating on vertical surfaces must be mechanically fastened.

3.3 Mechanically Attached

On all adhered flexible membrane roof slopes that exceed 1:24 (½" in 12"), the manufacturer's published instructions are to be followed regarding mechanical fastening and/or back nailing of sheets, and the size and direction of sheet application to the direction of roof slope.

When applicable, all mechanically fastened flexible membrane systems installed under RoofStar guarantee shall conform to the CSA A123.21 Standard test method (latest edition) for the dynamic wind uplift resistance of mechanically attached membrane roofing systems.

Mechanically Attached Base Sheet

Cover wood surfaces with a minimum 40-lb asphalt coated fibreglass base sheet conforming to CAN / CSA – A123.16 – M88 (R1996), Type II or manufacturers’ accepted base sheets of equal or greater weight and reinforcement. Attachment of base sheets shall be a minimum of one nail, with a minimum 25mm (1") nominal head size, per 0.093 m2 (1 sq. ft.), or one plate and screw per 0.186 m2 (2 sq. ft). Lap base sheet end laps minimum 150 mm (6"), mechanically fix laps at 100 mm (4") o/c and seal all corner details with membrane manufacturers’ approved self adhered SBS membrane or tape. Wood surfaces must be “dry mop” dry, no pooling or standing water permitted. Metal base flashing is required on all vertical surfaces, walls, curbs, etc., that are 200 mm (8") or greater in height above the finished roof surface, when the mechanically attached base sheet method is used.

3.4 Cold-Applied and Self-Adhered Membranes

When the base sheet and cap sheet membrane assemblies are self-adhered or applied using a cold adhesive, the cap sheet membrane must be installed on a clean, dry base. Therefore, barring extreme circumstances, and to comply with the manufacturer’s requirements, the base and cap sheets must be installed and completed together on the same work day. This standard does not apply where torch-applied cap membranes will be bonded to a self-adhering base membrane. Specifications and manufacturers’ written application instructions must be strictly followed. Phased installation of membranes is not permitted.

RoofStar-accepted self-adhered membranes must be installed over wood surfaces to manufacturers’ product installation specifications. Self-adhered membranes must not be installed on contaminated wood surfaces. A minimum 9.5 mm (⅜") nominal thick plywood sheeting (overlay) must be installed over all contaminated wood surface (eg. asphalt) to receive self-adhered membranes. Metal wall base flashing is optional with these application methods.

Self-adhesive membranes must only be installed when ambient temperature meets or exceeds the manufacturer’s printed product installation temperatures. All self-adhesive field membranes must be fully rolled with a manufacturer’s accepted roller that is a minimum 34.2 kg (75 lbs.) or greater and provides an evenly dispersed weight. All flashing (stripping) membrane must be hand rolled with a membrane manufacturer’s accepted roller.

The RoofStar Guarantee Program accepts cold adhesive applied membranes installed over wood surfaces to manufacturers’ product installation specifications.

4 Protected and Modified Protected Membranes

NOTE: See more information on Protected and Modified Protected Roof Systems in Section B: Essential Elements.

4.1 General

In a Protected Membrane Roof Assembly (PMRA) the membrane functions solely as the waterproofing agent (the requirement for a vapour retarder is eliminated) and the properties of the insulation become more critical. Extruded expanded polystyrene (conforming to CAN / CGSB-51.20-M87, Type 4) is the only commercially produced roof insulation suitable for a PMRA, providing properties such as water resistance (i.e. resistance to water absorption, moisture transfer, and capillary action), resistance to freeze-thaw cycling, and high compressive strength.

A Modified Protected Membrane Roof Assembly (MPMRA) is similar to a PMRA except that a layer of insulation is installed underneath the membrane as well as on top. This may offer cost savings as only the top layer of insulation requires ballast and the bottom layer (mechanically-fastened or adhered) need not be extruded expanded polystyrene and may be tapered to provide slope. The membrane must be located such that the dew point temperature (for the inside air) occurs above the membrane. As a general rule, two-thirds or more of the total thermal resistance (RSI or R value) should be above the membrane, but in all cases the design authority should perform the required psychrometric calculations before designing a roof system.

4.2 Roof Decks and Drainage

All roof decks should have proper drainage of the membrane. The RoofStar Guarantee Program recommends the deck have a minimum slope of 1:50 (¼" in 12") towards the roof drains. If, however, an existing roof allows ponding, the insulation is to be applied loose with a permeable fabric over the insulation.

Roof drains are to be located at the low points in the roof. Stone ballast must be prevented from entering drains and gutters. Perforated collars and paving stones are common methods used.

4.3 Membranes

Membrane flashings to be extended well above the expected high water level. Refer to the Perimeter Flashing: Membranes section in these Standards for details.

Materials used in the roof assembly must be listed as accepted in the Accepted Materials section of this Manual and conform to applicable material standards CGSB, ULL, CSA, etc.

The roof system must be designed to meet applicable building codes. This may require that 12.7 mm (½") thick gypsum board with siliconzied core and fibreglass facers or equivalent be installed on steel decks. Concrete decks do not require a separate barrier.

4.4 Insulation & Filter Mats

Insulation, which is bonded or mopped directly to the roof membrane, is not acceptable.

On all protected and modified protected membrane roofing projects, a filter mat of approved material is to be properly installed between gravel ballast and insulation. The filter mat is required under pre-cast pavers that are used as ballast or walkways.

Filter mats specified must meet the insulation / membrane manufacturer's specifications.

The use of fabric filter mat allows for the use of less ballast. This is achieved by using water permeable fabric between the loose laid insulation boards and the stone ballast. The effect of the fabric is to prevent the displacement of individual boards in case of flotation. The fabric will also prevent fines in the stone ballast from entering the board joints. The fabric must be water permeable and have proven long term weather resistance. It should be strong enough to withstand traffic abuse and prevent displacement of the boards under flotation conditions. The fabric is applied unbonded over the installed insulation. Overlap all edges a minimum of 300mm (12"). If a small piece of fabric is to be used, its dimension shall be at least 2.5 m x 2.5 m (8’ x 8’). Slit fabric to fit over roof penetrations, cut out around roof drains and other openings. Extend fabric up roof perimeter cants and roof protrusions and place it loose under the metal counter flashings.

4.5 Ballast

The building structure must be designed to support the weight of the ballast or surface treatment and other superimposed loads on the roof.

Concrete ballast, poured-in-place concrete or concrete topping as ballast or traffic topping is not permitted on RoofStar-guaranteed roofs. Only ballast, which permits easy or reasonable access to the membrane, is acceptable.

Acceptable ballast includes: properly sized gravel, concrete pavers, concrete-topped insulation, etc.

Gravel Ballast: Protected Membrane and Ballasted Membrane Roof Assemblies (EPDM, TPO, PVC, etc.) shall use clean, washed, round or crushed stone, falling within the following gradations:
35 mm (1 ½") - 100 % Passing 25 mm (1") 70 - 100 % Passing 20 mm (¾") 5 - 20 % Passing 12.5 mm (½") 0 - 6 % Passing 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.
Pedestals: Installation of proprietary (purpose-made) pedestals, with integral spacer ribs for uniform spacing of pavers, or an accepted drainage layer designed to provide vertical separation between pre-cast pavers and substrate or other underlying materials, is mandatory. The use of proprietary drainage boards or pea gravel with filter fabric to provide drainage for unit masonry products (bricks, stone, etc.), is required.

Proprietary (purpose-made) pedestals must have a 3mm (⅛”) integral spacer ribs for uniform spacing between pavers that provide a minimum 12.5 mm (½″) of vertical separation layer for airflow and leveling. The choice of pedestal or drainage layer type is the responsibility of the design authority. Pedestals / drainage layers provide airflow for drying surfaces and assist in leveling. They 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.

Ballast Requirements for PMRA's
Extruded Polystyrene Insulation Thickness Required Weight of Stone Ballast Approximate Depth of Ballast
Standard Measurements
Up to 2" 12 lb./ sq. ft 1 ¾"
3" 17 lb./ sq. ft 2 ¼"
4" 22 lb./ sq. ft 3"
5" 27 lb./ sq. ft 3 ½"
6" 32 lb./ sq. ft 4 ¼"
7" 37 lb./ sq. ft 5"
8" 42 lb./ sq. ft 5 ½"
Metric Measurements
Up to 50 mm 60 kg / m2 40 mm
75 mm 84 kg / m2 60 mm
100 mm 108 kg / m2 75 mm
125 mm 132 kg / m2 90 mm
150 mm 156 kg / m2 105 mm
175 mm 180 kg / m2 125 mm
200 mm 204 kg / m2 140 mm

For an engineered design approach, consult the DOW Chemical TECH SOLUTIONS 508.2 Ballast Design Guide for PMRA roof systems. The resource is provided for reference purposes only.

Resistance to Wind Loads

Roof corners subject to high winds or gusts may scour the stone ballast. Parapets and / or paving slabs can be used where necessary to prevent scouring. In the case of a lightweight PMR roof, with insulation loose applied over the membrane and covered with 50 kg / m2 (10 lb. / sq. ft.) of ballast, external pressures due to wind are mostly applied to the membrane.

The membrane will withstand the National Building Code (Canada) calculated pressure if it is properly attached to the deck. In the case of a loose applied membrane it is important to prevent any air infiltration underneath the membrane. Indeed, when air infiltration is restricted, any movement of the membrane will create a vacuum which will neutralize the uplift forces and keep the membrane on the deck.

Tunnel tests done at the National Research Council Canada show that the suction applied to the insulation boards is much lower than the calculated pressure applied to the membrane because of the rapid pressure equalization between the top and the bottom surfaces of the boards. This reduced pressure is insufficient to uplift insulation covered with 50 kg / m2 (10 lb. / sq. ft.) of ballast.