Jump to: navigation, search


1 General

RoofStar-accepted insulation overlay boards shall be installed over all plastic foam insulations (EPS, XEPS, Polyisocyanurate) on all adhered low slope roofing systems. When heat sensitive insulations (EPS,XEPS) are used with heat welded membrane seams an accepted overlay board must be installed. Fibreboard shall not be used with flame welded seams.

2 Layering

Insulation and overlay board joints are to be offset/staggered 300 mm (12") from adjacent layers and rows. The uppermost layer of [insulation or] overlay board directly below membranes shall have joints that are offset/staggered from adjacent layers and rows.

See also RoofStar Guarantee Standards for insulation layering in INSULATION

3 Material Selection

See Accepted Insulation Overlay boards for RoofStar Guaranteed roof systems.

4 Application

4.1 Mechanical Fastening

The design authority should research and establish the correct fastener, deck and roof assembly components in order to prevent the possibility of fastener corrosion. Contributing factors to fastener corrosion may include dissimilar metal contact, excessive building humidity, corrosive chemicals within components of the assembly, or corrosive elements provided within the building envelope etc.

All insulation types shall have a minimum compressive strength of 110 KPa (20 psi) when installed without a cover board under mechanically attached membranes.

Mechanical fastening to steel decks provides more effective wind uplift resistance and greater horizontal shear resistance than adhesives (thereby decreasing potential membrane splitting). Fastening patterns and rates that have proven to be successful are published in RoofStar Guarantee Standards and should be enforced as a minimum. In addition to insufficient fasteners, the type of fastener can prove critical. For example, failure may occur from nails with inadequate head size to pull through the roofing felts.

The correct fastener should be specified by the design authority for each component of a roof system.

The design authority should consult with the fastener manufacturer to determine the fastener's pullout strength in specific deck types to determine the number of fasteners required.

Wind uplift has been shown to be greater at the perimeters and therefore fastener requirements vary between field and perimeter areas. In addition, mechanical fastening may be required at the perimeter detail to restrain lateral movement of the membrane.

The upper layer or overlay in a multiple-layer insulation application does not require mechanical fastening.

Minimum fasteners for Overlay Board 1200 mm x 2400 mm (4' x 8')
Using Field Perimeter Corner
Screws and Plastic or Steel Stress Plates 8 12 15
Accepted Nails (Wood Deck Only) 12 16 18
Fastener layout patterns and other board dimensions See diagrams above

4.2 Adhering

When asphaltic membranes are adhered (using hot asphalt, cold adhesives, or when applied with a torch), at least one layer of overlay board is required over all types of insulation. The exception to this requirement is mineral wool insulation used in a single or multi-layered adhered or partially adhered insulation assembly, where the top surface of the uppermost insulation layer incorporates an impregnated bitumen surface to which an asphaltic membrane may be torch welded, mop-applied or cold-adhered.

Conventionally insulated roof assemblies are required to have a minimum 12.5mm (½") adhered approved RoofStar-accepted gypsum overlay board, and insulation boards with a minimum compressive strength of 20 psi, under the roof membrane for Extensive Vegetated Systems (less than 150 mm, 6" in depth). Intensive Vegetative Roof Assemblies in excess of 150 mm (6") or more in depth are not permitted over conventionally insulated roof systems.

Note the following restrictions and conditions, which apply to the above:

  • flame protection may be required where only one layer of insulation is specified.
  • where mineral wool insulation is mechanically fastened through the uppermost insulation layer, an adhered non-flammable cover board with a thickness of no less than 12.5 mm (1/2”) is mandatory, to prevent fastener penetration of the adhered membrane. A cover board is not required where only the bottom layer of a multi-layer mineral wool insulation assembly is mechanically fastened.

The following standards, principles and information also apply:

Heat Sensitive Insulation: On all heat sensitive insulation (polystyrene - both extruded and expanded), an overlay consisting of two layers of acceptable cover board (each with min. 3/16" thickness) is to be used when using hot-applied adhesive, when torch-welding or where the cover board is less than 1/2" in thickness on torch-applied assemblies. Overlay board thickness shall not exceed 50 mm (2”). Fibreboard shall not be used with flame-welded membrane seams.

A. Single layer system: When insulation is installed as a single layer, flame protection over the cover board is required. Install the insulation and cover board with the proprietary accepted adhesive. Seal over all board joints and wall transitions with membrane manufacturer's approved self-adhered membrane tape.
B. Two layer system: When using a hot-applied adhesive, back mop and flop first layer of overlay board, or use manufacturer's accepted proprietary adhesives per published directions, offsetting the joints from those of the insulation. Tape the joints before applying the second layer, offsetting the joints from both layers below.

As an alternative to the use of hot bitumen, the membrane manufacturer's proprietary insulation adhesives may be used to adhere accepted cover boards and insulation.

RoofStar-accepted mechanically attached asphalt core overlay boards [minimum thickness 4.5 mm (3/16") nominal] or insulation and insulation overlay boards specifically designed for torch applications, must be attached with nails with a minimum 25 mm (1") nominal head size placed a minimum of one nail per 0.093 m² (1 sq. ft.) or plates and screws placed a minimum of 0.186 m² (2 sq. ft.). Seal all board joints and wall transitions with membrane manufacturer’s approved self-adhered membrane or tapes.

4.3 Joint Taping

Acceptable materials for taping joints, of hot asphalt, and cold adhesive applied roof assemblies on overlay board, insulation, gypsum board, and primed plywood are minimum 150 mm (6") wide No.15 felt, 150 mm (6") wide Fibreglass roof tape, or 150 mm (6") wide sheathing (membrane breather-type to CAN / CGSB 51.32-M77). The only acceptable methods of hot asphalt installation are by back coating with asphalt, or laying with a back-coating machine expressly intended for the purpose.

For taping joints of asphalt core overlay boards, without poly film surfaces, manufacturers purpose made self-adhered modified bituminous tapes are acceptable for use with hot asphalt, torch welded and cold adhesive applied roof assemblies.