The Low-Carbon House:
Developing an airtightness strategy

• A continuous airtightness barrier system is the combination of interconnected materials, flexible sealed joints and components of the building envelope that provides the airtightness of the building enclosure and the separateness of heated and unheated spaces.

• The airtightness barrier needs to be designed into the building envelope during the initial concept design stage.

In the design office

• Define an airtightness performance target.

• Use a performance specification.

• At an early stage of the design, define the line of the airtightness barrier. It can be useful to take a section and draw a continuous red line that passes through all the elements that separate heated and unheated spaces thus:

• It is useful at an early stage to identify critical details that will have a bearing on the airtightness barrier. Details should be thoroughly worked out at design stage and not ‘left-to-chance’ later on site.

• Tightly manage the design implementation by appointing an ‘airtightness barrier manager’. If the design team is inexperienced, it might also be prudent to appoint an independent adviser.

• Specify airtight components.

• Check interfaces between components and work packages to ensure the continuity of the air barrier.

On site

• Brief the construction team of the importance of airtightness.

• Clearly identify the location of the air barrier.

• Institute a regimen of inspection during construction, with particular regard to ensuring the air barrier is uncompromised by shoddy workmanship.

• Ensure that the air barrier is complete prior to covering up by other work and trades – failures found during testing can lead to expensive uncovering and remedial work.

• Ensure that air testing is scheduled in advance to achieve maximum benefit for purposes of remedial work.

RIBA Work Stage	Design Team Tasks
A Appraisal	Establish an airtightness performance target.
B Feasibility / Briefing	Note Microclimate Identify procedure for review and testing
C Outline proposals	Consider air tightness issues in relation to decisions about form of construction
D Detailed Proposals	Identify requirement of additional consultants / design by specialists
E Final Proposals	Ensure co-ordination between Design Team to ensure air tightness envelope & penetrations Detailed application of airtight materials, junctions, service penetrations
F Production Info	Select sub-contractors for specialist works (incl. testing) Careful specification of components, membranes, materials Emphasise methods for airtightness on documentation Emphasise responsibilities in specification for dealing with ‘loose ends’ between sub-contractor interfaces
G Tender Documentation	Define Contractors’ responsibilities for co-ordinating work sequences
H Tender Action	Ensure selected tenders include adequate airtightness procedures
J Mobilisation	Brief all involved in areas critical to air infiltration before work starts Preparation of samples, training, testing and QA procedures
K-L Site Works	Co-ordinate inspection with Building Control if required Ensure inspection of areas to be covered Ensure audits and testing schedule is adhered to Ensure design changes do not compromise airtightness performance
M Post Completion	Obtain feedback from concerning comfort and energy consumption Carry out remedial work as required at end of DLP.
Source: Design and Detailing for Airtightness, Chris Morgan, SEDA 2006