The "hot roof" type is made with bituminous or synthetic membranes, but the thermal insulation is always laid under the membrane. The advantage of this solution lies in the fact that is well known and has been widely used for a long time thus reducing any possible errors. The insulation is always protected by the waterproofing and its characteristics and performance are preserved at length without any washout effect. 

The type of insulation required in this type of application must have the following characteristics:
excellent insulation properties
good compressive strength
resistance to heat
resistance to solvents contained in bitumen

The most suitable product for this type of application is undoubtedly rigid expanded polyurethane. Please bear in mind that extruded polystyrene and expanded Styrofoam CANNOT RESIST to temperatures over 80°C that can be reached not only during laying, but also in operating conditions. Special attention is to be paid when laying these products in contact with artificial and bituminous membranes with a high content of plasticizers and solvents. Fiber products DO NOT HAVE adequate resistance to humidity to ensure constant performance over time. Fiber products DO NOT HAVE adequate compressive strength resistance to humidity to ensure constant thickness and resistance to treading over time. Expended polyurethane panels are the optimal solution for this type of application. POLIISO® SB is especially recommended for flat roofs under bituminous membrane and ensures best possible adherence to the waterproofing layer. 

The extrados of the slanting concrete slab (at least 1% gradient recommended) is to be cleaned by removing any cement clots that may alter the levelness of the laying surface and any differences in height are to be leveled. A hand of primer is to be applied as well in case of surface scrubbing. Once the slab is ready, a vapor barrier is laid to avoid that it can penetrate from the inside and to prevent the risk of condensate inside the insulating material. In applications with non-ballasted coating, the barrier must be glued to the covering. The vapor barrier must be resistant to the penetration of water vapor greater thanor at least equal to that of the waterproofing layer. The POLIISO® SB expanded polyurethane boards are then laid after the laying of the hot bitumen only on the surface of the single panel being laid (to avoid the cooling of the bitumen.  The recommended quantity of bitumen is 1.5-2 kg/m2). A separating layer and waterproofing bituminous membrane are applied on the polyurethane panels. The membrane is to be heated on the bitumen-coated glass fiber coating the panel, which quickly melts making the laying of the upper membrane much faster. A slated membrane with polyester fiber reinforcement is applied to finish. The slated membrane protects the coating, improves weather resistance and reduces the need for maintenance to a minimum. POLIISO® SB is easy to lay because it is lightweight and easy to handle: we recommend fitting the panels with staggered joints.

- Fast laying.
- Perfect adherence to membranes and coatings.
- Great stability and duration over time.
- Compressive strength and high thermal insulation.

The coating at sight is applied directly on the insulating layer either by total adherence, controlled semi-adherence or mechanical fastening and finished with self-protected membranes or reflecting protection applied subsequently. In some cases, thermal variations may cause lesions to the coating and affect bonding with the insulation and underlying layers.  Adherence between the coating, vapor barrier and insulation panel must always be greater than that between the panel and coating.

Warnings: If operating conditions are especially severe, diffusion layers are to be laid. They consist in thin perforated membranes that direct to the diffusers the water vapor from the inside or located below the coating during laying. It is fastened by points on top of and/or below the POLIISO® SB boards compensating the structural tensions or dilations due to thermal variations in the membranes.The installation of single or double diffusers to dispel the vapor that condensates on one or both sides of the insulation boards.

Compatible Products