When covering over old roofs with incompatible insulation or plywood decks, slipsheets are used to improve fire resistance, to cushion and protect membrane from any abrasive materials, and separate incompatible materials.
Different types of slipsheets include polymath protection mat which comes in 3 oz or 6 oz polyester mat. Fire resistant slipsheets are available in versashield 1 s or 2 s. When using a polymath protection layer or a fiberglass fire resistant slipsheets as separator sheets. Loose lay separator sheets with 6″ minimum overlaps at sides and ends.
Most roofing systems need insulation or a coverboard to improve insulating value of the roof system, improve the fire resistance, and to provide a smooth surface for the membranes insulation. Types of insulation that may be used are polyisocyanurate, polystyrene insulation, extruded polystyrene in 15 psi and expanded polystyrene in 15 psi, perlite, high density uncoated wood, fiber board, and fibrous glass.
Types of coverboards that may be used are gypsum board, densdeck, fanfold, wood fiber board, and perlite. Common mistakes occur when installing EPS/XPS. When installing the membrane in very hot weather, do not forget to install without a coverboard if the maximum roof membrane temperature is expected to reach 165 F or more. When installing PVC over the EPS/XPS install a coverboard or acceptable slipsheet between the PVC and the insulation.
If fleece backed PVC is used, the fleece separates the PVC and EPS/XPS and a coverboard or a slipsheet is not needed Also, PVC and polystyrene insulations are incompatible in direct contact. The EPS/XPS will extract plasticizers in direct contact with PVC. Insulation coverboards may be secured with mechanical fasteners, with hot asphalt, and with foam adhesives. For all attachments methods, make certain to choose the correct board, make sure to butt the edges together so there is no more than ¼” gap between the adjoining boards. This will reduce energy loss. Cut the insulation to fit around all penetrations with no gap greater than ½” to minimize energy loss
Do not use scraps of insulation or coverboard smaller than 2″ x 2″. Minimizing the number of joints will improve the performance of the insulation. Stagger multiple layers of the insulation at least 6″ so the joints do not align. This will also reduce energy loss at the joints. Support the edges properly assuring that they are properly supported to reduce potential damage to the insulation. Replace wet, warped, buckled, or damaged insulation or coverboard.