Convective currents can cause higher moisture in the roof. The warm, damp air rises, presses against the envelope and escapes through the leakages.
In winter, the vapour pressure gradient due to the cold dry air outside and the warm damp air inside causes diffusion from inside to outside.
Overlaps of vapour control layers can be sealed by means of special high-performance adhesives to ensure permanent airtightness and prevent building damage.
Air and windtight sealing technology
The airtight building envelope
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 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 serves to proof this.
To create the airtight building envelope in most cases 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 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 sd value of a vapour control layer is of importance. With a fixed sd value of 5 m SIGA- 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
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 sd 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 sd 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 perfectly tailored to your requirements. So you can easily avoid damage to your building!