Design guidelines for pitched roofs

Air tightness

Upward directed heat losses are the greatest. Prevent air from flowing through the building envelope and causing negative effects on the structure by placing a vapour barrier on the inner side of the roof. In practice, an air infiltration barrier (e.g., plastic foil) provides sufficient air tightness. In most cases there is overpressure in the top of the building. In wintertime, when the temperature difference is higher, the pressure difference is also greater. To avoid moisture damage, seal all joints, conduits and connections. This is also very important when the building is old and you are adding additional insulation. Measure the air tightness of the building envelope with the standardized pressure test EN 13829. Subject the building to 50 Pa of overpressure and evaluate the air exchange rate of the building. The air exchange rate should not exceed 1 per hour.

The importance of ventilation

In pitched roofs, place a ventilation gap behind the roofing material. The gap removes excess moisture from the structure using air flow. The air flow in the gap normally rises upwards. Openings at the bottom of the ventilation gap allow air to enter the gap. In the gap the air warms, absorbs the moisture, and flows up until it is released through the openings at the ridge. Use the same principle when insulating a cold attic but instead create the ventilation with a wind diverter.

Fire protection

Roof structures need to offer protection against fire. When selecting insulation for roofs, consider two issues: how the material reacts in case of fire and to what extent it can resist it. Non-combustible Paroc stone wool has an exceptionally high melting temperature of over 1000 °C, providing longer protection for the surrounding structures.

Minimising cold bridges

Massive beams that run through the roof structure create cold bridges. Heat loss via cold bridges is much greater than via surrounding structural components. In addition, moisture condensation that occurs at cold bridges increases the accumulation of moisture in the roof structure. To minimise cold bridges, use fully-covering insulation layer and minimise the size and quantity of fasteners and other components that pass through the thermal insulation layer.

Sound insulation

As traffic noise and other low frequency sounds increase, requirements for effective sound insulation become stricter. You can significantly improve noise reduction with stone wool insulation in roof structures.