John HylandIf you were at the UK Passivhaus Conference 2014, you may have seen our John Hyland talking about the challenges faced from a contractor's point of view in achieving Passivhaus Standard on a retrofit project

It goes without saying that it is harder to achieve the required standards in a retrofit property than a newbuild, but which ever you are working on, there are certain things you need to have in place to ensure a successful project.

Here are some notes from John's presentation. 


Casey Airtightness Team
These projects can be difficult. The structures may be old and contain many voids that cannot be seen and are difficult to find.  Much of the work to ensure airtightness may have to be carried out 'blind' - drilling holes, pumping specialist foam into spaces you cannot see.  It involves lots of experimentation and multiple pressurised and de-pressurised air testing.

In a large block with multiple units, even if the units are all of the same house type and layout, you may find that each one is different to the last in terms of airtightness.  Measures that work in the first nine properties may be completely ineffective in the tenth, requiring new measures to be developed. Our experience has shown us that you need to take some very innovative approaches.  As this is a relatively new field, we have developed some new, ground breaking techniques.

And don't forget - it is much more difficult to carry out 'normal' works in airtight properties. For example, the usual drying time of wet trades can be multiplied almost exponentially when carried out in properties that are effectively airtight, and within which the mechanical ventilation and heating have not yet been commissioned.

So what do you need to have in place before you start? 


Passivhaus is a fairly new concept in this country and it is important that everyone working on the project 'gets' it. Ultimately it will lead to a better quality build!

  • It is critical that all the key personnel working on the project fully understand the concept of Passivhaus and the importance of airtightness.
  • There are several organisations that offer courses on Passivhaus: BRE, Passivhaus Trust, AECB, Green Building Store.
  • Airtightness testing training can be carried out by the testing engineer.
  • The site induction undertaken by all operatives should include the main principles of Passivhaus, and the care that needs to be taken to
           avoid creating voids or cavities and breaching membranes and tapes.
  • An Airtightness Champion should be nominated, and that person should be based on site.
  • Stress the need for site tidiness and order.
  • Manufacturers of the membranes and tapes etc and MVHR will usually come to site to do demonstrations. 


It is very easy at tender stage to underestimate the supervision and monitoring required during the installation of the Passivhaus elements.

  • Ensure that sufficient resources are made available to monitor the main aspects of the works - insulation, cold bridging details, airtightness
           and windtightness.
  • The completion of the test and inspection sheets and the photography of all the various phases is time consuming, but important.
  • Ensure that supervisors are covered during holidays and periods of illness by staff who have been suitably trained.
  • These are not normal levels of supervision, THESE ARE ENHANCED LEVELS OF SUPERVISION. 

Quality Control

There should be a detailed NBS specification covering all the Passivhaus elements. The requirements for samples, testing, possibly some Contractor Design Elements will all be detailed. All these items should be included in the Detailed Quality Plan for each element.

Early mock ups and samples should be provided, and the materials and workmanship approved by the Contract Administrator.

Test and Inspections Sheets should be bespoke for the project and cover all advice and instructions from manufacturers' literature.

Review quality on a regular basis with all interested parties and problems will be nipped in the bud. Specialist suppliers will provide instruction and demonstrations if asked. 

Installation of Tapes and Membranes etc

Building sites are dusty places and that can affect the adhesion of tapes. Also, if OSB 3 gets wet, the wood chip can flake slightly again making the tape harder to apply. Very cold surfaces can be a problem too.

Any surfaces to which tapes and membranes are to be applied should be cleaned properly - as if they are being prepped for painting.

  • Work areas should be clean, dry and clear of debris.
  • When applying, avoid creases and tears.
  • Use appropriate surface cleaners before applying tapes.
  • If in doubt, do samples and test.
  • Concentrate on the awkward areas such as junctions, changes of direction, changes of substrate.
  • Choose who is tasked with doing this work carefully!


Airtightness Testing

Choose your airtightness engineer carefully. A good one will work closely with your team to find and resolve any leak issues. We use Paul Jennings, Aldas

Resist the temptation to progress internal finishing works ahead of satisfactory test results. Once satisfactory results have been achieved, it is important that revisits by various trades do not disturb or damage the airtightness measures.

  • Choose your external specialist engineer early. This person will play a key role.
  • Choose experience and ability over price!
  • There should be at least three tests per unit: first when all membranes and seals are in place, but all areas are still accessible; second when all
           finishings are complete; final test is the acceptance test.
  • After all the tests, ensure that grommets and seals are not disturbed.



All members of the team need to work closely together and take joint responsibility for the success of the project.

  • The partnering approach is important.
  • Involve an experienced Contractor at an early stage.
  • If anything is unclear, ask. Never make assumptions.
  • The programme needs to include sufficient time for testing and re-testing.
  • Consider how you formulate any productivity incentives carefully. Eliminate the temptation to take shortcuts.
  • Aim for a better target than the minimum of 1 ACH.
  • At Design Stage, consider how air leakage routes though party walls can be sealed.