How to guarantee good airtightness and wind tightness:

Good airtightness on a roof or wall can be achieved by ensuring a “Synergie” between design and execution and by trying to ensure that there are two airtight layers present:

• Internal Airtight Layer (for example a Vapour control layer)
• External windtight layer (for example a highly breathable membrane)

The weak points are not large surfaces but all the interruptions and openings in the roof or wall. The rule of thumb is that if you were to go around the design of the house with a pencil, every time you lift the pencil is a potential air leakage point, such as conduits, waste and soil pipes and ducts, pipes for solar systems, window and door frames. The key is to totally seal these air leakage points:

• Vapour control layers, barriers and breathable membranes should be sealed at their joints using Multi Tape
• Large pipes, conduits and roof windows should be sealed on the outside using butyl tapes, such as Coll Flexi, to the breathable membranes and to the vapour control layer on the inside using Multi Tape
• The internal walls of timberframe houses should be sealed at their joints with acrylic adhesive tape Multi Tape, butyl tape or sealants in cartridge containers
• Door and window frames should be sealed with elastic expanding foam, and sealing tape around their perimeters where they meet the wall or subframe. You can choose Synergie Duo Variable Easy, with full waterproof adhesive, where the tape is to plastered on smooth blockwork or choose FI-D Window tape where the blockwork is rough and you need to adhere the tape to the substrate with acrylic adhesive, Synergie AK adhesive. Both tapes, once fully adhered, can be plastered over.

Airtightness Test.

Under building regulations in Ireland and the UK the emphasis is set on achieving reasonable standards of airtightness, and it is compulsory to subject samples of newly built houses to an airtightness test. The current standard regarding the airtightness of a building is EN ISO 9972:2015. This standard does not specify a limit regarding airtightness but simply describes the measurement of airtightness. This standard distinguishes between two different tests – the preliminary test and the final test. The preliminary test’s purpose is quality control of the installed airtight layer and should be carried out immediately after the airtight system has been installed. This will help pinpoint if any improvements are required or if unintended damage has occurred to the airtight layer. The final test has to be carried out when the house is finished and ready to be moved in to. The method described in the standard is the Blower Door test in which a fan pressurizes and depressurizes the building envelope. The fan (mounted into the frame of an exterior window or door) is used to take a series of measurements which result in a regression curve which describes the air loss of the building envelope under varying pressure differential.