The basic calculation: area × kg/m²
A layer of 6 kg/m² on 1,000 m² adds a calculated 6,000 kg of additional mass to the roof. Two such layers add 12,000 kg. This calculation is suitable for early option selection and transport planning. It is not a structural approval.
The total additional load includes more than the board: separation layers, fixing, any additional ballast, PV substructure, modules and ballast belong in the balance. Installation pallets create temporarily very high local loads and need their own placement plan.
Assigning comparison values correctly
The DensDeck Prime data sheet gives approximately 5.9 kg/m² at 6.4 mm and 9.8 kg/m² at 12.7 mm. BarrierSheet gives 3 kg/m² at 2.5 mm with ±10 % tolerance. These are values for different products and functions, not equivalent protective performance. [1] [2]
The technical assessment lists thickness-dependent densities. For 15 mm and a nominal 800 kg/m³, for example, this gives 12 kg/m² as a calculated value before the tolerances stated there. A constant density across all board thicknesses would be the wrong assumption here. [3]
Same area load, different local effect
Whether a PV foot has a small or large contact area changes the pressure on membrane and insulation. A stiff cover board can support load distribution but does not replace an assessment of the entire contact and insulation layer. Long-term deformation can matter more than a short compression test.
With WEER on the roof waterproofing, board edges and joints are also considered. Substrate unevenness must not create unfavourable point bearings. What governs are the actual bearing conditions, not just the weight in the data sheet.
Wind restraint can change the lightweight solution
A light board is pleasant to transport, but that does not automatically make it wind-secure. Roof height, edge and corner zones, building surroundings and the chosen fixing determine the solution. Additional ballast required can partly cancel an original weight advantage.
The material options are therefore compared with their complete fixing concept. For an initial enquiry, a roof plan, building height, location, PV layout and details of the existing supporting structure are helpful.
What you can decide with the calculator
The calculator below multiplies the planned area by a freely selectable mass per unit area. The preset serves as material orientation. For your project, enter the data of the board actually offered and add the remaining loads separately.
For economics, a second look at cost per protected roof area is worthwhile: a light layer with elaborate fixing can perform differently from a heavier, quickly laid board. The structurally and economically best choice results from the overall package.
Worked example: added roof load
Example values from the data sheets cited
Only the added mass of the layer; account for the moisture basis of the selected value. Not a structural assessment; the structural engineer assesses capacity.
Use the areal mass of the specified product. Add PV, fixings, any ballast and temporary pallet loads before having the remaining structural capacity assessed.