Applying a vapour barrier

Reduce energy costs and insulate your attic yourself!

As energy costs continue to rise rapidly, good insulation is becoming increasingly important. Since a huge amount of heat can be lost through the roof, it’s worth getting to work here first. We’ll show you how you can quickly and easily insulate your pitched roof yourself with rafter insulation.

This is what you’ll need:

The quantities given are for a roof area of 100 m2 (2 x 12.5 m x 4 m)

  • vapour barrier membrane (125 m2)
  • double-sided, airtight adhesive tape (2 rolls)
  • mineral wool (for 100 m2)
  • sharp insulation knife
  • sealing and sound insulation tape (2 rolls)
  • sealant adhesive (6 pieces)
  • plasterboards (2000 x 600 x 12.5 mm)
  • cordless screwdriver
  • screws (approx. 300 pcs)
  • electric tacker (e.g. NOVUS J-165 EAD)
  • staples (flat wire staples, 6 mm)
Materials for installing a vapour barrier membrane

And here's how it's done:

1. Measuring the rafters and selecting the insulation material. 
First, measure up the rafters. Then select the insulation material. Insulation rolls are made of mineral wool, wood fibres and other insulating materials; in our example, we’ve used mineral wool.

Installing a vapour barrier membrane with a tacker
Step 1: Measure the rafters.

2. Cutting the mineral wool to size. Cut the mineral wool to size with the insulation knife. The best way to do this is to place the mineral wool under a narrow piece of wood, as this will produce an excellent cutting edge. To make sure that the felt stays firmly in place, it should be cut to a width that is about 1 to 2 cm wider than the clear distance between the rafters.

Insulating a vapour barrier yourself
Step 2: Cut the insulation material to size.


Before starting work, find out about your local regulations and any grants or subsidies there might be.

3. Wedging the mineral wool in place. Now wedge the mineral wool between the rafters with the application of a little pressure. Make sure that the panels connect to form a tight joint.

Installing a vapour barrier membrane correctly
Step 3: Wedge the insulation material between the rafters.

4. Applying the sealing tape. Now attach the sealing tape to the rafters. This stops the membrane tearing when you tack it later, and prevents moisture transfer at the stapling points.

Installing a vapour barrier membrane correctly
Step 4: Attach the sealing tape to the rafters.

5. Applying the vapour barrier and stapling it in place. Now place the vapour barrier, which you have previously cut to size, over the insulation and fix it to the rafters using a tacker.

Please note: Always wear safety glasses and hearing protection when working with a NOVUS electric tacker.

Installing a vapour barrier membrane
Step 5: A NOVUS electric tacker makes light work of stapling the vapour barrier in place.

6. Sealing the cut edges with adhesive tape. Next, seal the overlaps in the vapour barrier with double-sided adhesive tape so that they are airtight.

Installing a vapour barrier – workshop
Step 6: Seal the cut edges with adhesive tape to make them airtight.

7. Bonding the wall connections. Now apply a layer of sealant adhesive approx. 8 mm thick to the wall, then glue the vapour barrier to it. Surplus membrane can be cut away.

Insulating an attic by installing a vapour barrier membrane
Step 7: Glue the vapour barrier to the adjacent walls.

8. Installing a plasterboard substructure. We recommend using plasterboard as the substructure for later cladding. Mount the substructure for the plasterboard transversely to the rafters and fastened with screws.

plasterboard sheets, attic, instructions
Step 8: Fasten a plasterboard substructure in place for cladding later.