airtightness

In the “Exemplary Buildings” program of the Brussels Capital Region, building owners and designers are challenged to realise building projects of both high architectural quality and superior environmental performance. After a project competition phase in which the Exemplary Buildings are selected, winning projects are supported by grants and expert guidance throughout further design development and construction. Building envelope airtightness is an important aspect during the follow-up, given its influence on the net energy demand.

The airtightness just after the end of a building phase is assumed to be relevant criteria for high energy performance. Testing on site the initial performance of the airtightness via the blower door test has become nowadays a common practice. This test is generally realized at the end of the construction works. What about the influence of ageing on the airtightness? Many questions exist on the durability of this initial performance.

When one intends to evaluate buildings energy efficiency their airtightness is a fundamental parameter. Airtightness is linked to undesirable and uncontrolled ventilation and, therefore, should be minimized. Quantitative characterization of expected leaks of common building elements would be useful for practitioners that intend to improve building enclosures for airtightness optimization. The most well accepted experimental procedure to evaluate in-situ buildings’ airtightness is the fan pressurization method, typically making use of a “blower door” device.

Air tightness is essential to building energy performance, which has been acknowledged for a long time. It plays a significant role in improving building energy efficiency by minimising the heating/cooling loss incurred during unwanted air movement through the building envelope, consequently reducing the building’s energy demand and cutting down carbon emission in the building sector.

For the coming energy-efficient buildings, the guarantee of energy performance becomes a major challenge. It is therefore crucial to implement accurate and reliable measurements, in order to ensure this performance. The in-force French EP-regulation RT2012 already imposes compulsory justification of envelope airtightness. Moreover, the Effinergie+ label requires ventilation systems control and ductwork airleakage performance. These requirements, ventilation controls for IAQ concern and regulatory compulsory controls of buildings need reliable diagnostic protocols.

With the increasing need for higher energy efficiency in buildings, airtightness and ventilation systems choice become major performance issues in well insulated buildings. Buildings energy requirements lead to adapt ventilation strategies in order to reduce energy losses through mechanical balanced or extract ventilation. With the new French thermal regulation, the use of energy-efficient ventilation systems is implicitly required; low air infiltration is explicitly required in residential buildings through minimum airtightness levels.

During the construction of a multi-family residential building the developer decided that the building must comply with the airtightness requirements for passive houses. Based on inspection work and preliminary testing, the original design was revised. The execution of the new air barrier system was supervised. Selected flats were repeatedly tested during the construction process. The whole building was tested once before the completion of the construction. After the completion of the building, all the flats, the whole building and the staircase were tested again.

The improvement of air tightness in existing residential buildings could be triggered from the desire for better indoor comfort conditions and the expected reduction of cost for space heating. While the improvement of comfort sensation could not be easily understood from the building owner, the reduction of cost for space heating is much easier.

Laboratory measurements have been performed to investigate the airtightness of clamped joints in the wind- and vapour layers. Air leakage was measured immediately after mounting with moisture content of the wooden members at approximately 17 weight %, and after drying down to approx. 7 weight %. It was found that screws as fasteners provided better airtightness than nails. Center distance of 600 mm resulted in general higher air leakages than shorter center distances like 300 mm or 150 mm.

This paper analyses approaches for setting airtightness requirements whether in voluntary or regulatory schemes. We have classified approaches for upper limits into two major types: default values and minimum requirement. Lessons learnt from existing schemes where minimum requirements have been enforced show that the scheme to justify a given airtightness level is one fundamental ingredient in terms of market impact.