Template:All Systems - INSULATION OVERLAY BOARD

1 General

RGC 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 Material Selection

See Accepted Materials for Insulation Overlay Boards.

3 Application

3.1 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.

3.2 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.

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 RGC 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

3.3 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. In addition, the following standards, principles and information apply:

Heat Sensitive Insulation: On all heat sensitive insulation (polystyrene, extruded, and expanded), an overlay consisting of two layers of acceptable cover board is to be used when using hot asphalt as an adhesive, or where the cover board is less than 1/2" in thickness on torch applied assemblies.

A. Two layer system: Back mop and flop first layer of overlay board (for hot asphalt adhered systems), or use manufacturers accepted proprietary adhesives per published directions, offsetting the joints from those of the insulation. Then tape joints and install second layer offsetting the joints from those of the insulation. Then tape joints and install second layer offsetting the joints from those of the layer below. Alternatively, the membrane manufacturer's proprietary insulation adhesives may be used to adhere accepted cover boards and insulation.

B. Single layer system: Flame protection over the cover board is required. Install the insulation and cover board with the proprietary accepted adhesive. Seal over all cover board joints and wall transitions with the membrane manufacturer's proprietary self-adhered membrane tape.

RGC 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 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.