Six clauses you should add to your Passive House construction contract

15 February 2021 by Jason Quinn

Consider homeowners who want their new home to be a certified Passive House. Certification provides independent reassurance about the quality of the build. (Further, independent third-party certifications like Passive House increase the resale value of buildings overseas and we can expect that will happen in New Zealand too.)

If they don’t get what they paid for, who should be responsible? More importantly, how can clients avoid ending up in this situation?


The most immediately obvious option is to specify in the construction contract that the building has to be a certified Passive House. In my view this is not reasonable—not unless it is a full design and build contract with a single integrated team.

Otherwise, I don’t recommend or approve of this option. The client is asking the construction team to take full responsibility for the outcome but if the problem lies in the design of the building, it’s not their fault and they can’t fix it. (On the other hand, the design team can’t guarantee airtightness, although they can make it easy or stupidly hard by their design choices.)

I believe the correct solution is to require the designers to get pre-construction approval—ideally before getting the Building Consent but certainly before starting construction. This is the first and arguably most critical phase of the Passive House certification process. Second, ensure that the design team and construction team are integrated during construction by establishing ‘hold points’, where the construction team checks in with the Passive House professional and can’t continue with construction until approval is received.

Not involving the design team in the construction phase is a false economy if you care about the quality of the result. I’ve seen examples where saving a little bit of money by not involving the Passive House professional in the build cost a very great deal more in rework, delays and worst, missing certification.

Pre-construction review and design stage approval are both very thorough reviews so allow some time. Each review cycle takes about two weeks and typically competent design teams usually go through each review twice. If the design uses a new window manufacturer (or even a new window profile with an existing manufacturer), or other components that are new to the design team and potentially the certifier, this can add time as well.

The process goes most smoothly when the Passive House professional is experienced (they’ve received certification for previous projects) and they are well organised. A two-week time frame assumes a competent and complete set of information is submitted at the outset.

The pre-construction approval letter from the certifier will contain a very short list of open items (risks), which the design team needs to address at the final review submission stage. If that risk list is tiny, the building will be built per the drawings and information in PHPP (the modelling software) provided for the pre-construction review.

Now it’s up to the construction team. And with this groundwork established, it is appropriate and recommended to include some conditions in the contract to guide the builders in the right direction. Builders (other than experienced Passive House builders) are used to varying construction significantly on site. They’ll substitute materials, add additional timber, change window glass specifications … this is completely normal practice and they see nothing wrong with it. (The specification (hundreds of pages of small print) generally forms a part of the construction contract document, but I don’t recommend relying on that too heavily.)

Sometimes variations happen because of delays in getting materials, but it might also be because a switch will save the builders money or increase their rebate from a supplier. The client and designer aren’t necessarily even told. It’s not documented because, in the opinion of the builder, the variations don’t affect weather tightness or structural stability, the two main foci of the Building Code.

This undocumented variation is one thing you absolutely want to prevent, but it’s just one of six additions to the contract recommended by me (and other Passive House professionals I have discussed this with). Here goes.

  1. Specify a pre-construction building staging meeting between the design and construction team. Work through the intended construction sequence along with air control install, ventilation ductwork install, air tightness testing and ventilation commissioning. The materials should be marked directly on the drawings already, but if not, the design team needs to mark them up now.

  2. Require a design team representative to have oversight of construction. For a single-family home, this could be a weekly phone call between the builder (whoever’s on charge on-site, not back at the office) and the architect or designer. The purpose is to make certain that no changes are being made to the building that would impact its performance.

    On a big project, I recommend appointing a clerk of works who is on-site regularly (every few days through to once a fortnight, depending on the construction phase). The clerk of works needs to be familiar with airtightness and Passive House. Happily people with this expertise are now available in Auckland and Christchurch. A clerk of works could be involved on a smaller project, although that would be unusual and the builder is bound to argue it’s unnecessary.

  3. Require the construction team to perform an airtightness test at the pre-lining stage. The contract could define a penalty if that test doesn’t meet the standard (and/or a bonus if it exceeds the standard). If there is a problem at this stage, it is possible to determine if it’s a fault of the design or the construction but identifying that will take additional testing. I’d suggest a large enough financial penalty to make the design team focus clearly on air tightness[1].

  4. Require photographs that provide sufficient evidence of the process of construction. The Passive House certifier will review all these as part of the final review. A photographic log of the thermal and air control layers is required, as well as important installation details that are important. If the design team and construction team are new and uncertain about what to photograph, the certifiers can, on request, mark up a set of drawings during the pre-construction certification review that shows what is required. (Please request this before the review starts).

    Otherwise, the Passive House professional on the project should create a proposed list which will be checked at the pre-construction review stage. As a certifier, I prefer photographs with captions in a .docx or .pdf file. And we much prefer 25 clear photos than a folder containing 400 random photographs of everything imaginable.

  5. Require final airtightness testing and ventilation commissioning. I recommend including an agreed-on penalty here also. I recall one case where the final airtightness result was significantly higher than the pre-lining air tightness test. It’s likely someone penetrated the air control layers and it wasn’t noted or repaired. Ventilation commissioning just shouldn’t fail. Provided a modern, semi-rigid Passive House-certified ductwork system is installed, it’s just a matter of work to get it balanced properly (unless the design was flawed).

  6. And lastly, prohibit any substitutions or variations that aren’t specifically approved in writing by the Passive House professional on the team[2]. A single unwitting variation in materials can result in a project failing certification.

So that’s it: make the construction team responsible for construction and leave everything else to be shouldered by the design team, as it should be.

I’m very interested to hear ideas and comments on this issue from other Passive House professionals, whether designers, architects, consultants and tradespersons.

NB: Glenn Murdoch from THECA  Architecture has written a contract section in MasterSpec style which can be downloaded here. It covers most of what has been detailed above but doesn’t include an agreed penalty value. If you use MasterSpec or SmartSpec contracts, please ask these companies to get something like this into their system.

[1] I strongly recommend builders appoint an on-site airtightness champion on-site, even on the smallest projects.This is someone who’s on-site everyday. They brief sub-contractors on where the air control layer is and the importance of keeping it intact. Penetrations must be kept to the absolute minimum and appropriately air-tighted. Accidental punctures must be immediately reported.

One process that seems to work well here and overseas is to flag any penetrations right away with red spray paint. Once the airtightness champion approves the repair, he or she records this with blue spray paint. Provide an air control layer repair kit on-site so any penetrations (scheduled or otherwise) can be immediately made good.


[2]The timber fraction in the walls is an item that often gets past both the design and construction teams. Pre-nail frame manufacturers are used to putting heaps of timber in—even when it’s not needed and even after they’ve been asked nicely not to because additional timber means less insulation and a lower performance wall). The construction team needs to ensure that the pre-nail manufacturer works with the design team to minimise timber or allow significant timber fractions to ensure the PH requirement is realised. The pre-nail manufacturers can provide nice drawings so the timber fraction of the walls can be calculated but it can take persistence to obtain them.