Ideal Design
The insulation is sealed on the outside by the roofing felt/sub-roof and on the inside by the airtight seal e. g. a vapor/vapour retarder or air barrier. The insulation is doubly protected against outside air by the roofing felt/sub-roof and against penetration of indoor air by the airtight seal.

Even Tiny Leaks can have Serious Consequences
Leaks often occur, however, when the materials for the airtight seal are being fitted.
These lead to:

• Increased heat loss, energy costs and CO₂ emissions
• Long-term structural damage
• Dry indoor air in winter
• Insufficient thermal protection in summer
• Reduced sound insulation