MVHR and Building Regulations in Ireland: TGD Part F, NZEB and What New Builds Must Meet

Since 2021, every new dwelling in Ireland has had to meet the Nearly Zero Energy Building (NZEB) standard under the EU’s Energy Performance of Buildings Directive. That means airtightness levels have risen sharply — and airtightness has direct consequences for ventilation. Build a home tight enough to hit NZEB targets, and you’ve also created a home that legally requires a proper mechanical ventilation strategy to remain healthy to live in.

This guide walks through what Technical Guidance Document (TGD) F actually requires, how it interacts with NZEB and Part L, and what “compliant” really means once you get past the design stage and into commissioning and sign-off.

Building regulations are amended periodically. This guide reflects guidance current as of mid-2026; always confirm the latest position at gov.ie or with your Building Control Authority before finalising a design.

TGD Part F: the governing document

Technical Guidance Document F – Ventilation (2019) sets out how to meet requirement F1 of the Second Schedule to the Building Regulations: adequate provision for ventilation of people in buildings, and protection of the building fabric from excess moisture. It covers minimum ventilation rates, system types, and — critically — installation and commissioning.

TGD F recognises several compliant approaches for dwellings, including:

• Natural ventilation with background ventilators and intermittent extract fans
• Passive stack ventilation (PSV)
• Continuous Mechanical Extract Ventilation (MEV)
• Demand-controlled ventilation (DCV)
• Continuous mechanical supply and extract with heat recovery (MVHR)

Which of these is actually viable depends heavily on how airtight the building is — and that’s where NZEB changes the picture.

Airtightness is what decides your system

TGD F ties system choice to the dwelling’s design air permeability, measured in m³/(h·m²) at 50 Pa. To meet Part L for an NZEB new build, airtightness needs to be 5 m³/(h·m²) @ 50 Pa or lower. Within that range:

• Below 3 m³/(h·m²) @ 50 Pa — natural ventilation and background ventilators can’t reliably deliver adequate air exchange, so continuous mechanical ventilation (MEV or MVHR) is effectively required to satisfy F1.
• Between 3 and 5 m³/(h·m²) @ 50 Pa — natural ventilation may still be viable but typically needs enhanced background ventilator provision.
• Above 5 m³/(h·m²) @ 50 Pa — doesn’t meet Part L for an NZEB new build, so this band doesn’t apply to standard new construction; standard natural ventilation approaches are more likely to be sufficient where it does apply (e.g. non-NZEB works).

In other words: the tighter you build to meet Part L and NZEB targets, the more Part F effectively pushes you toward mechanical ventilation. This is the “build tight, ventilate right” principle that underpins the whole regulatory logic — you can’t legally chase one target (airtightness for energy performance) without addressing the other (ventilation for air quality).

Why MVHR makes sense for NZEB homes

At NZEB airtightness levels, mechanical ventilation is effectively required to satisfy Part F — but the system also needs to work alongside Part L (energy performance). MVHR recovers heat from outgoing air before it’s lost, so it satisfies the ventilation requirement while supporting the fabric and heating performance you’ve spent the rest of the build achieving. Demand-controlled ventilation (DCV), a separate Aereco system based on humidity and presence sensing, is worth considering as an alternative route in projects where it suits the design better.

Minimum extract and boost rates

TGD F sets minimum extract rates for wet rooms (kitchens, utility rooms, bathrooms, sanitary accommodation) and minimum boost rates for MEV and MVHR systems, set out in the document’s reference tables. Design airflows should be calculated room by room against these tables rather than estimated — undersized ductwork or an undersized unit is one of the most common reasons a system fails commissioning later.

TGD F also requires provision for air transfer between rooms — for example, a 10 mm gap under internal doors — so that supply air can actually reach extract points rather than being trapped in individual rooms.

Commissioning and validation: where compliance is actually proven

This is the part of the process that gets skipped most often, and it’s where legal compliance actually gets demonstrated — not at the design stage, but on site.

The Department’s supporting guidance, Installation and Commissioning of Ventilation Systems for Dwellings – Achieving Compliance with Part F 2019, sets out what’s expected:

• Systems must be balanced and commissioned, with results recorded on a commissioning sheet
• Measurement should follow I.S. EN 14134:2019 (performance testing and installation checks of residential ventilation systems)
• On many projects, an independent Ventilation Validation is also required, carried out by a validator registered under the NSAI Ventilation Validation Registration Scheme
• Validators check the as-installed system against the design airflows — a premium MVHR unit with a weak design or poor commissioning can still fail to meet minimum rates in practice

For BCAR (Building Control (Amendment) Regulations) purposes, this documentation feeds directly into the Statutory Certificate of Compliance. Without commissioning records and, where required, third-party validation, a design that looks compliant on paper may not hold up under Building Control scrutiny.

Grant-funded retrofit projects: an extra layer Where MVHR or MEV is being installed as part of an SEAI grant-funded retrofit (typically under the One Stop Shop deep retrofit route), the SEAI Domestic Technical Standards and Specifications document sets additional requirements on top of TGD F, covering installation standard and specification for MEV and MVHR systems. If you’re pairing ventilation with a heat pump upgrade — increasingly the standard combination for Irish retrofits — both measures need to be assessed and signed off together to protect grant eligibility

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A practical compliance checklist

Before finalising a ventilation design against TGD Part F:

• Confirmed design air permeability target and which ventilation strategy it triggers
• Calculated room-by-room extract and boost rates against TGD F tables (not estimated)
• Confirmed door undercuts/transfer paths are specified for air transfer between rooms
• Checked interaction between the chosen system and Part L / NZEB energy performance targets
• Identified the index terminal and confirmed duct routing keeps resistance low
• Arranged commissioning and, where required, independent NSAI validation
• Confirmed documentation requirements for BCAR sign-off
• If grant-funded, checked the installation against SEAI’s Domestic Technical Standards and Specifications

Where Aereco fits in Aereco’s MVHR systems use Aldes units — Passive House certified — combined with a manifold air distribution design built to optimise unit efficiency and comfort. Aereco is also the developer of demand-controlled ventilation (DCV), a separate system based on humidity and presence sensing, which is available as an alternative or complementary approach depending on the project. Between the two, we can advise on the strategy best suited to hitting TGD F’s airflow targets for your specific build. We provide free ventilation design and advice for Irish new-build and retrofit projects, including support with TGD F compliance documentation and BCAR-ready certification. Talk to our technical team about your project

FAQs

Is MVHR mandatory for new builds in Ireland?

Not by name — TGD F recognises several compliant systems. But at the airtightness levels required for NZEB (typically below 3 m³/(h·m²) @ 50 Pa), mechanical ventilation becomes effectively necessary.

What’s the difference between commissioning and validation?

Commissioning is the balancing and testing work carried out by the installer on site. Validation is an independent check, carried out by a third party registered under the NSAI Ventilation Validation Registration Scheme, confirming the installed system meets TGD F’s minimum requirements.

Does an SEAI grant change the ventilation requirements?

TGD Part F still applies regardless of funding source, but SEAI grant-funded retrofit projects must also meet the SEAI Domestic Technical Standards and Specifications, which can add further detail on installation standard.