Passive House or nZEB: what are you paying for?

Agree your home’s energy target and certification scope before getting quotes. Nearly zero energy building (nZEB) requirements apply to new Irish dwellings under Part L of the Building Regulations; Passive House certification is an additional, voluntary assessment.

Ask the designer what the extra assessment will prove, who will supply the evidence and what the price includes. An old headline upgrade cost or a good energy rating cannot answer those questions for your house.

How the assessments differ

The dwelling nZEB approach includes an energy performance coefficient (EPC, which compares your home’s calculated primary energy use with a reference home) of no more than 0.3, a carbon performance coefficient (CPC, the same comparison for carbon emissions) of no more than 0.35 and a renewable energy ratio of 20%. They are not the same as a heating bill: the coefficient is not a heating bill or a number of kilowatt-hours per square metre. See nZEB and Part L requirements for the wider compliance checks.

A2 was the typical Building Energy Rating (BER) expected under the dwelling standards introduced in November 2019. That does not make a particular BER band a complete compliance test. Ask your designer to explain the applicable Part L evidence for your project, rather than treating the rating as the whole specification.

Passive House uses its own criteria and the Passive House Planning Package (PHPP), an energy-modelling tool. Its certification process reviews the design calculation and supporting construction evidence, including airtightness and ventilation commissioning records. Arrange the scope early; certification can also be possible after completion if the criteria are met.

Keep the two evidence packages distinct. A favourable result in one calculation does not establish a pass in the other. Your BER certificate and building-control documents still have their own purpose.

Price your design, not a historic upgrade figure

Shane Colclough’s 2018 chapter examines a south-east Irish case study using costs dated 1 January 2017. The reported difference between building to the minimum regulations of the time and building to the Passive House standard was €131 excluding VAT (see the study for the unit it is measured in). Site purchase and design-team/professional fees were excluded.

The analysis identifies extra spending on fabric, airtightness, ventilation and windows, offset by savings in heating provision, the chimney and overheads. It predates the 2019 dwelling standards. It cannot establish today’s premium over nZEB, a certification fee, or a saving for your site.

Use the study as a reason to compare the complete design, including any avoided costs. Do not assume your heating system can be omitted: ask the services designer to size heating and hot water for the proposed house. See the cost to build guide for the wider budget.

What you are asking the team to deliver

The Passive House Institute’s five principles address insulation, windows, heat-recovery ventilation, thermal bridges and airtightness. Thermal bridges are places where heat escapes more readily, such as junctions between walls and floors.

The Institute’s certification has three classes: Classic is the base level, and Plus and Premium add requirements for renewable energy generation. Ask the certifier to identify the applicable criteria version and class in writing.

Turn that ambition into a responsibility schedule before accepting a quote:

• Who prepares and updates the energy model when the design changes?
• Who checks window, insulation and ventilation substitutions before ordering?
• Who draws the junctions and maintains continuity of the airtight layer?
• Who photographs concealed work and assembles the completion evidence?
• Who arranges tests, investigates failures and pays for remedial work and retesting?

A promise to use the principles is too vague to resolve a dispute about a missing detail or failed test.

A worked quote comparison

Imagine you have one tender described as “nZEB” and another as “Passive House ready”. Neither description tells you whether the two prices include the same work. This is an invented procurement example, not evidence of typical prices.

Make a comparison sheet with a row for the base construction, design/modelling, certification, windows, ventilation, heating and hot water, airtightness testing, commissioning, VAT and exclusions. Ask each bidder to fill every row or explicitly mark it excluded. Keep the house size, site assumptions and finish specification the same.

Then ask what happens if a chosen window is unavailable. Does the replacement need approval and a model update? Is that work included? A lower initial quote with those responsibilities omitted is difficult to compare with a complete scope.

Finally, record a budget allowance for unresolved items rather than treating a provisional sum as a fixed price. Your contingency should reflect the uncertainties still left in the design and tender.

Principles or certification?

You can commission a design using the principles without commissioning certification. State the measurable targets and evidence you want in the appointment and building contract. Avoid describing an uncertified design as certified, or assuming that a successful airtightness test establishes every criterion.

Certification adds a defined assessment process. Ask the certifier what they review, what the design team must supply and which site checks fall to others. It does not replace the builder’s responsibilities, Irish statutory compliance or your own professional appointments.

Keep design assumptions, approved substitutions, test results and commissioning records with the house documents. They are useful when investigating performance or planning later alterations, whichever route you choose.

Check the design, work and handover

Before planning

Ask the designer to show how the proposed form, glazing and orientation fit the energy ambition. If the preferred appearance changes the energy design, ask for the consequences before signing off the drawings. Record which choices are fixed and which still need investigation. Ask the designer to compare the consequences for this house: the preferred shape or construction method alone will not establish the lowest cost.

Before tender

Turn the chosen ambition into drawings, schedules and appointments that bidders can price. For example, a window schedule should be accompanied by a clear route for proposing and approving alternatives. Ask how the energy model, junction details and ventilation design will be kept consistent if a product changes. Keep an agreed revision record so the builder and assessor are working from the same information.

Before covering work

Use the team’s inspection and testing plan to check that the required evidence has actually been collected. Ask for a list of outstanding records and who will supply them. If a test fails, get a written investigation and repair proposal before assuming that a later test will solve the problem. Agree access, cost and programme consequences through the contract process.

At handover

Request a document index rather than a folder of unexplained files. It should identify the final calculations, installed products, test reports, commissioning information and operating instructions, together with any certification outcome. Ask the designer to explain unresolved differences between the tender specification and the completed house. Keep a written list of outstanding items, the person responsible for each and the agreed next step, so you can follow up without searching through separate emails.

These checkpoints also help with the decision to proceed without certification. You still need a clear account of what you paid for and what was demonstrated. If the budget changes, agree the revised target and evidence explicitly; leaving the original label on a reduced specification creates confusion for everyone involved.

Questions before committing

1. What standard, criteria version and certification class are we pricing?
2. What Irish regulatory assessment is included alongside it?
3. Which design decisions must be fixed before the tender is reliable?
4. When will we test airtightness while repairs are still accessible?
5. What does each fee cover, and who carries the cost of a failed test?
6. What maintenance and operating instructions will the ventilation and heating installers hand over?

Check any proposed funding separately in the Sustainable Energy Authority of Ireland grants guide. Keep project-specific lender and insurer requirements alongside your completion documents, rather than assuming an energy certificate answers every request.

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