Airtightness and ventilation in Ireland

Last reviewed: October 2026

Reduce uncontrolled leakage, keep planned ventilation

Airtightness describes how well the building limits unintended air movement through gaps in its envelope. Uncontrolled leakage can carry heat away and create draughts. Planned ventilation supplies fresh air and removes moisture and pollutants. Treating these as one design problem helps avoid improving warmth while leaving the home without an adequate air supply.

Insulation slows heat transfer through the roof, walls and floor; airtightness deals with air passing through gaps. One does not prove the other. Ask the retrofit designer where the intended air barrier lies and how its junctions will be coordinated with the selected work.

Background, extract and mechanical ventilation

Background ventilation provides the continuing fresh-air supply, through an appropriate natural or mechanical system. Extract ventilation removes moist air from wet rooms. Opening windows for short periods is useful for purge ventilation, but is not evidence that the planned background or extract arrangements are adequate.

Mechanical options include extract systems and balanced systems with heat recovery. Selection depends on the building, intended airtightness, duct routes, commissioning, maintenance and the occupants’ needs. A heat-recovery label alone does not establish performance in your home.

SEAI’s SEAI homeowner’s guide to ventilation explains these functions and the separate permanent air supply required for open-flued appliances. Do not seal or obstruct ventilation openings or combustion-air supplies to address a draught. Have their purpose and any proposed replacement assessed by a competent professional.

Coordinate windows, doors, walls and roof work

• Windows and external doors: replacement changes leakage and can alter existing ventilation. Ask how vents, extract systems, opening details and appliance air supplies will be maintained.
• External and internal wall insulation: agree details at windows, floors, ceilings and services; internal systems also need a construction-specific moisture strategy.
• Ceiling-level attic insulation and rafter insulation: the thermal boundary differs. Roof-space ventilation and room ventilation serve different purposes; one must not be substituted for the other.

Moisture and condensation need investigation

Water vapour from everyday activities can condense on colder surfaces or within unsuitable construction details. Leaks, damp, cold junctions and inadequate ventilation can overlap. A survey should distinguish the causes before work conceals them. Persistent mould or condensation calls for assessment, not a promise that new insulation will resolve every problem.

Discuss air paths, material compatibility, vapour control, thermal bridges and drying with the designer. These decisions are especially important in older or traditional construction and when several fabric measures are combined.

Heat-pump readiness and SEAI support

A heat pump needs a heat-loss assessment and heating design appropriate to the finished home. Reduced leakage can be part of that plan, but a BER grade or an airtightness measure alone does not prove suitability. Ventilation remains necessary.

SEAI’s OSS schedule lists mechanical ventilation support of €1,500 and airtightness support of €1,000 within qualifying assessed packages. These are not standalone Individual Grants to add automatically to a calculator estimate. DanannIQ does not currently offer these as separately priced selectable projects; their scope and support must be confirmed with the provider. See SEAI One Stop Shop: eligibility, services and grant schedule and the grants overview.

What to ask before you proceed

Ask who designs and tests the ventilation, what is included in commissioning, how performance is verified, and what maintenance is required. Review SEAI’s SEAI Domestic Technical Standards and Specifications with the registered contractor. Include necessary related work in the quote, then use the calculator or BER planner to organise the supported project scope.

Official sources

Official grant information checked on 7 October 2026. Follow the measure-specific rules and your grant offer; announcements may precede detailed implementation guidance.

• SEAI homeowner’s guide to ventilation
• SEAI Domestic Technical Standards and Specifications
• SEAI windows and doors
• SEAI homeowner’s guide to wall insulation
• SEAI homeowner’s guide to attic and rafter insulation
• SEAI One Stop Shop: eligibility, services and grant schedule

Read our Methodology & data sources or view all guides for the assumptions behind DanannIQ estimates.