Utherm Roof BM: when the facing matters more than a single lambda value

Full selection requires more than reading the lambda, because the gas-permeable fleece must not be equated with an aluminium laminate. The selection should help assign the correct contact with the adjacent layer to each side of the board. Before comparing variants, show the description of the facings and the technology for making the connection to the covering on a single drawing.

The thermal conductivity value in the Roof BM technical data sheet depends on thickness. For thicknesses from 30 to 70 mm it is 0,027 W/(m·K), at 80 and 100 mm it is 0,026, and for 120–150 mm it is 0,024. An energy comparison should therefore account for the change from 0,026 W/(m·K) at 100 mm to 0,024 W/(m·K) at 120 mm.

The thermal calculation will be clear only if the parameters of each Roof BM thickness variant under consideration can be read separately. The difference in thickness requires correct interpretation, since the quotient d/λ must not use the lambda of another thickness range of this board. The calculation should allow thermal variants to be compared without transferring the best result to the whole family. As a basis for the decision, retain the declared R_D of 3.80 for 100 mm and 5.00 m²K/W for 120 mm, instead of comparing only the price per centimetre of material.

The board format is 1200 × 600 mm and its edges are straight. Before laying, the surface orientation must be confirmed and the requirements of the waterproofing system checked. The continuity of the polyurethane insulation must also be maintained where the arrangement of the straight edges of Roof BM boards in the 1200 × 600 mm format needs to be resolved.

When analysing continuity, it is worth planning offset joints and Roof BM cuts at roof elements. The fit must be assessed for the actual geometry, because a straight edge has no factory overlap that could be matched in the adjacent row. The installation plan should allow continuous contact between boards and correct termination of the layer at the edges. In the energy assessment, include the distribution of joints, the support of edge elements and the method of forming penetrations, because these places will remain after purchasing the board with the best lambda.

At the junction of insulation and covering, adhesion, cleanliness and dryness of the surface are what matter. Fixing must be checked for the central, edge and corner zones of the roof. To preserve the thermal improvement, the method of joining the covering to the bituminised surface of Roof BM must be verified.

When assessing the durability of the effect, the documentation for the first layer of covering above Roof BM should be checked. The actual construction of the connection is important, because the presence of bitumen in the facing does not constitute consent for arbitrary torch work. The layer build-up should allow compatible contact materials and the sequence of work to be selected for the actual roof. At acceptance before covering, it is worth comparing the type of adhesive or fixing and the surface preparation conditions with the adopted detail.

Roof BM has a declared compressive stress of at least 150 kPa at 10% deformation and a fire reaction class of F. These two pieces of information describe different properties. When limiting layer height, the CS stress of at least 150 kPa and the fire reaction F declared for Roof BM must be assessed in parallel.

Beyond selecting the lambda, the Roof BM test result must also be separated from the requirements of the complete roof covering. It is worth separating these requirements, because the compression value and the reaction class describe different phenomena and do not prove arbitrary load-bearing capacity. The collected data should allow loads and fire protection to be assessed within the appropriate scope. Alongside the thermal calculation, present the product data together with the support, fixing and system classification solution, so that the result relates to a usable solution.

The enquiry must specify Roof BM with its full designation, the thickness and the selected waterproofing. The note “PIR board” alone is not precise enough. When comparing cost and effect, include the Roof BM offer covering the correct bonding side and thickness variant.

Before calculating cost-effectiveness, it is worth linking the supply of Roof BM with the materials needed for a compatible covering. The cost-effectiveness calculation will be incomplete if it is omitted that the same PIR name does not mean interchangeable facings or an identical lambda. The selected variant should allow complete solutions to be compared once the required insulation level has been established. When assessing the surcharge, set the full board designation, a description of the contact layers and the scope of work at details against the benefit obtained in the finished building element.

A comparison of Roof BM 100 and 120 mm shows the importance of reading the correct range. The catalogue R_D is 3.80 and 5.00 m²K/W respectively. Both the thickness and the lambda change. Both variants should therefore not be calculated with one arbitrarily chosen value. In the energy assessment, the compatibility of the facing with the planned covering must be retained in parallel.