Convection is a form of heat transportation: Warm air rises due to the thermal lift, "presses" against the building envelope and escapes uncontrolled through leakages. To prevent heat loss in this way an air and windtight building envelope is essential.

According to Part L of the Building Regulation from July 2008 (IRL, UK),
§ 6 of the EnEV, SIA 180 and ÖNORM B 8110-2 buildings must be constructed permanently airtight. The blower-door test serves to proof this.

To create the airtight building envelope in most cases vapour control layers are applied to the warm side of the insulation; overlaps and penetrations are sealed without gaps and the joint to the masonry is made.

The airtight building envelope has, however, another important function: Large amounts of water vapour are produced in households by exhaled air, cooking, bathing. A family of four produces about 15 l of water per day in this way. Professionally sealed vapour control layers ensure that this moisture does not get unimpeded into the insulation, impairs its function and causes dangerous mould formation in the construction. Moreover, these layers prevent heat loss by convection due to which up to 40% of the heating energy go lost.

In this context the s_d value of a vapour control layer is of importance. With a fixed sd value of 5 m SIGA-Majpell for example is on the one hand particularly diffusible. On the other hand, however, it also protects the building against excessive moisture penetration in the construction phase, e.g. by fresh cast plaster floor or walls just plastered.

The windtight building envelope is created by the breathable membrane and permanently sealed facade membranes. Unlike airtight sealing, windtight finish of the building envelope is not required by law. It may, however, be required, e.g. by The Roofing Trade Regulations. When the envelope is not windtight, cold outside air can easily cool down the insulation. Furthermore snow, rain, insects and wood pests can enter the construction unhindered and damage it. For this reason, the building owner is well advised to ensure sealing of the windtight layer without gaps.

In most cases the s_d value of breathable membranes and facade membranes is lower than that of vapour control layers to ensure that the moisture does not collect underneath the membrane, but can diffuse through the material. The general rule here is: The s_d value inside is ten times higher than that outside.

Consistent planning and professional creation of the air and windtight building envelope when building a house or renovating pays off. Not every adhesive tape suits every application. Moreover a multitude of substrates require high-quality products which adhere reliably and permanently to every ground. SIGA offers a comprehensive system of products perfectly tailored to your requirements. So you can easily avoid damage to your building!