Powerdeck F on flat roofs: thermal performance and compatibility with roof waterproofing

A change in lambda alone is not enough, because a similar colour of the PIR core does not determine whether the surface is compatible with the chosen membrane. The solution should allow the choice of product to be based on the requirements of the specific roof assembly. As a starting point for comparing variants, record the type of facing, the adopted covering and the documentation of their mutual compatibility.

For Powerdeck F boards, the declared thermal conductivity lambda is 0.026 W/(m·K). It is on this value that the comparison of the thermal resistance of a layer of a given thickness must be based.

When comparing polyurethane boards, include the calculation of the Powerdeck F layer with the declared lambda of 0.026 W/(m·K). The thickness of Powerdeck F must be calculated with its own lambda of 0.026 W/(m·K), so that the comparison relates to the same thermal effect. The result must be read with caution, since quoting a lambda of 0.022 from another product would lead to an incorrect result for this board. The calculation is intended to help determine the thickness resulting from the parameters of Powerdeck F rather than from the general name PIR. In the energy summary, show the design resistance, the available layer height and the calculation of the full roof section, so that it is clear what exactly changed between the solutions.

At a given roof height, Powerdeck F must be calculated with its own lambda of 0.026. For an example of 100 mm, a simple d/λ gives approximately 3.85 m²K/W. This is not a result that can be improved by attributing to the board a parameter from another PIR variant. The advantage of the chosen product may lie in the suitability of its facing for a specific covering system. The comparison should therefore set the required thermal effect against the actual method of constructing the roof.

The Powerdeck F product data sheet specifies straight edges and a tongued-and-grooved variant. Whether a given format and thickness are available must be confirmed for the specific variant being ordered.

Check the straight-edge or tongued-and-grooved variant specified for the Powerdeck F version being ordered, because continuous polyurethane insulation also requires correct terminations. The side geometry of Powerdeck F must be agreed before determining the cutting plan and the number of boards ordered, because losses at the joints must be assessed together with the main insulation field. A good joint does not arise automatically, since a change of format or side profile affects offcuts and the actual surface coverage. The layout of elements should allow the delivery geometry to be agreed before the number of boards and the direction of successive rows are fixed. On the detail drawing, show the format as ordered, the method of bringing the elements together and the support at the end of the field; this record will make it easier to check the work later.

Powerdeck F can be combined with selected glued or self-adhesive membranes and with suitable fastening systems. The mere name of the adhesive – polyurethane or bituminous – does not by itself determine compatibility.

When assessing the durability of the thermal effect, include the bond with a bonded or self-adhesive membrane in a clearly defined material set. When bonding, the compatibility of the membrane and the bonding material with the mineralised glass fleece must be confirmed if the insulation is to perform under the conditions assumed in the design. Polyurethane foam does not replace protective layers: the general chemical name of the adhesive does not replace confirmation of the compatibility of the specific product. The intended safeguards should allow the bonding method to be selected together with surface preparation and installation conditions. Before covering up, assess the system instructions, the requirements for the substrate and the method of checking the bond before the details are covered, because later repair may require opening up the finished assembly.

For Powerdeck F, the declared compressive strength is CS(10/Y)120. Fire reaction class E is given for thicknesses from 40 mm, whereas B-s2,d0 relates to the specific end use.

The thickness limitation does not release you from checking other requirements, so analyse the CS120 declaration and the conditions of class E stated for Powerdeck F from 40 mm. The end-use classification must be linked to the actual substrate and fixing of Powerdeck F, even when the choice of board was mainly determined by its low lambda. A separate assessment is needed because a change of covering or fixing may go beyond the scope of the previously assessed assembly. Only a complete set of data will allow the requirements of the whole roof to be maintained when considering mechanics and behaviour in fire. Alongside the thermal results, state the board thickness, the complete layers and the documentation corresponding to the actual method of fixing them; this will ensure that the comparison does not omit the service conditions.

When purchasing Powerdeck F, both the board thickness and the joint detailing must be agreed. The quotation should cover substrate preparation, the required layers and the details.

Polyurethane board insulation should have a calculated effect and a defined scope of works; include the cost of substrate preparation and of connecting the insulation to the chosen waterproofing system. The quote should include substrate preparation and all materials needed to install the covering, so that the cost relates to a single, comparable result. The price of the material is only part of the decision, since a favourable board price does not automatically include priming, bonding and the making of flashings. The final summary should allow the expenditure leading to a finished, watertight covering with specified requirements to be compared. Ask for a schedule of the boards, bonding materials, substrate works and details around the perimeter of the covering, so that any additional charge has a stated technical justification.