‘Build tight and ventilate right’: airtightness and joined-up thinking for joined-up building
28 July 2015
Author: Niall Crosson, BTech, MEngSc, MIEI, CEPHC, senior technical engineer, Ecological Building Systems
At an airtightness presentation at the Centre for Renewable Energy and Sustainable Technologies (CREST) pavilion in South West College in Enniskillen, Co Fermanagh, in late May the key focus was on why airtightness is now recognised as not only a means of delivering truly low energy buildings, but it is also a precursor for higher levels of build quality.
Buildings that achieve higher levels of airtightness tend to also be built and executed to a much higher quality level. It was highlighted that while airtightness is essential it must also be combined with an effective ventilation strategy, be it by passive or mechanical means.
At its most basic, airtightness aims to eliminate any unintended gaps or cracks in the external fabric of the building, while ventilation focuses on replacing the stale indoor air with fresh outdoor air to meet the occupant’s needs. The key is to ‘build tight and ventilate right’.
Buildings built with higher levels of airtightness actually tend to have extremely high levels of indoor air quality, when combined with an effective ventilation strategy. This has been scientifically proven in many low energy Passivhaus’s and low energy buildings. Ventilation systems have progressed considerably compared with the basic permeant vents that are predominant in many buildings presently.
Three other common categories of air leakage in buildings were highlighted at the CREST presentation:
- Service leaks (for example, pipes, cables);
- Structural leaks (for example, windows-wall junctions, floor to wall junctions);
- A combination of both (for example, a downlight on a ground floor sealing leading to air leakage through a floor joist into an external cavity wall).
Air leakage can lead to significantly increased energy costs, increased risk of interstitial condensation within building elements, higher levels of overheating in summer months and a significant reduction in the acoustic performance of the building fabric.
The presentation referenced German research which illustrated that a 1mm gap – and the ensuing air leakage in an airtightness and vapour control membrane – can reduce the thermal resistance of an insulation layer by 4.8 times.
The same research also highlighted that this same gap in an air barrier and vapour control layer can increase vapour transfer by 1,600 times. This clearly illustrates the critical importance for increased airtightness, not just from a thermal perspective but also for increased building durability and increased indoor air quality.
Following this, the presentation focused on an array of images illustrating common leakage points in Irish buildings, and how these can be detected and alleviated. Various means of attaining a durable airtightness layer in masonry and timber frame constructions was shown.
More demanding building regulations not only require an improvement in individual skills but require a change in attitude to working collectively with a focused, co-operative approach to achieve compliance with regulations. The illustration, right, presents an example of good site control and communication between trades on a Passivhaus, built by Shoalwater Timberframe.
Changes in building standards directly affect on-site practices collectively and again require a focused, co-operative approach to achieve compliance with regulations. This is particularly pertinent since the introduction of the Building Control Amendment Regulations and the need for greater oversight and quality control on site.
Following the presentation, Roman Szypura of Clioma House Ltd, who has many years of experience installing thermal insulation and airtightness systems in some of Ireland’s lowest energy buildings, delivered an airtightness installation masterclass.
The production of truly low energy buildings require diligent attention to detail and co-operation between all trades involved in the construction and renovation processes. All trades should view the house as a system, rather than the sum of its parts. Trades must work as a team. All works must be co-ordinated.
The current fractured approach to building must be changed to a systems-based approach to building, in a similar manner to Passivhaus building principles and the quality standards, which are often observed on low energy or Passivhaus projects in Ireland, the UK and Germany.
From the design stage, planning and simplifying details is essential. Having ‘toolbox talks’ at an early stage of the build process with key personnel who interact with the thermal envelope of the building is essential to minimise costly errors, conflict and poor building performance.
A range of training courses are also being developed by the government, such as the Qualibuild training programme (www.Qualibuild.ie).
Ecological Building Systems also provides a range of thermal insulation and airtightness training courses at its purpose-built Centre Of Knowledge, in Athboy, Co Meath. More details regarding this can be viewed on its website.
CREST/South West College is also offering a Passive House Tradesperson course, which will begin in September.
It is not only important to ensure appropriate materials and systems are utilised in low energy buildings, but to ensure they are detailed correctly at the design stage. Materials must also be installed accurately in conjunction with all other trades on site, and planned and co-ordinated from the outset to deliver truly low energy construction. As building regulations rapidly evolve and become more onerous, it is essential that the skills of trades develop in tandem with this.
Ecological Building Systems provides practical and technical training at its ‘Intelligent Airtightness and Better Building: Fabric First’ courses. Further details are available at: www.ecologicalbuildingsystems.com
Ecological Building Systems provides an RIAI accredited CPD presentation which carries 2 CPD credits. Details regarding the course are available on the RIAI site: http://www.riai.ie/cpd/network-courses/
Niall Crosson, senior technical engineer, can be contacted at 046-9432104