How it is calculated
The required thickness is divided by the thickness of one board to get the number of layers. The area is multiplied by the layers and a reserve and divided by the board area. Boards are rounded up to whole packs. Board sizes and pack counts follow the country you choose and can be changed to match the label. For external wall insulation the calculator also adds adhesive, fixings and mesh.
Layers = required thickness ÷ board thickness, rounded upBoards = area × layers × (1 + reserve) ÷ (board length × width)Packs = boards ÷ boards per packExample
A 50 m² frame wall with 100 mm of mineral wool from 1200 × 600 × 50 mm boards needs two layers: 146 boards with a 5 % reserve, which is 19 packs of 8 boards (5.76 m² per pack). The insulation volume is 5 m³.
Tips from practice
- Cut boards for a frame 10–20 mm wider than the gap between studs so they hold by friction without gaps.
- Stagger the joints of the second layer over the first so heat cannot escape through them.
- Put a vapour control layer on the warm side of wool in a frame and a breathable membrane outside.
Questions and answers
How many boards are in a pack of mineral wool?
A pack usually holds 0.25–0.35 m³, for example 8 boards of 1200 × 600 × 50 mm or 4 boards 100 mm thick. The exact number is on the label and can be entered in the settings.
How thick should wall insulation be?
It depends on the climate and the wall. New homes in central Europe usually have 150–200 mm, Nordic countries 200–250 mm.
How many fixings do I need for external wall insulation?
Usually 5–6 per square metre for EPS and 6–8 for mineral wool, more at the corners. The calculator uses 6 and 8.
Found a mistake in a formula? Write to contact@planicalc.com