Bathroom Ventilation Installation in Ireland: Rules and Steps

Installer connecting a bathroom extractor fan

A good bathroom ventilation installation comes down to four decisions: a fan with enough extract rate, a short insulated duct to the outside, a timer or humidistat so it runs long enough, and a safe electrical connection. In Ireland, Part F of the Building Regulations sets the standard, and a renovation is the best moment to get all four right.

This guide explains what the rules ask for, how a fan is fitted, what to ask about electrics and cost, and how to fix a bathroom that keeps steaming up.

Planbbathrooms

Plan Ventilation Into Your Bathroom

Plan B Bathrooms combines expert design with photorealistic mockups to help you consider your bathroom renovation before installation begins.

Explore bathroom design

TL;DR

Part F expects a bathroom with a bath or shower to have an intermittent extract rate of at least 15 l/s, and a fan that vents outside.
Where there is no window or background vent, the fan needs an automatic 15-minute overrun.
Duct through a cold attic should be insulated and sloped towards the outlet, or condensation forms inside it.
A fan near a shower must have the right IP rating and RCD-protected wiring, so use a qualified electrician.
Most condensation problems are an undersized fan, a blocked duct or a fan that switches off too soon.

What Irish regulations require
Choosing the right fan
Where the fan goes and where the air goes
How a fan is fitted
Electrical safety: why to use an electrician
What does it cost?
Fixing condensation and a fan that does not work
Our perspective
Plan the fan into your bathroom project
FAQ
Sources

What Irish regulations require

The Part F Amendment Regulations 2019 (S.I. No. 263/2019) require adequate and effective ventilation that limits moisture, so condensation and mould do not develop. They also require provision to prevent excessive condensation in a roof void above an insulated ceiling. They apply to works and major renovations starting on or after 1 November 2019, subject to transitional arrangements.

The technical detail sits in TGD F 2019. The figures that matter for a bathroom:

Item	What TGD F 2019 says
Intermittent extract, bath or shower room	Minimum 15 l/s
Continuous central extract, boost rate	Minimum 8 l/s for a bathroom
No background vent and no openable window	Automatic 15-minute overrun after switch-off
Bathroom without a WC	Humidistat control acceptable instead of the overrun
Any automatic control	Must have a manual override

The SEAI Homeowner’s Guide to Ventilation says all wet rooms should have a mechanical extract fan. For homes getting wall insulation under the Better Energy Homes programme, SEAI’s ventilation guidance note sets a 15 L/s fan with no timer, or a waiver, as the minimum upgrade for a bathroom without an open flued appliance.

If your home relies on natural ventilation, an AIVC research paper notes the minimum total background vent area is 42,000 mm², with 7,000 mm² more for each extra 10 m² of floor area above the first 70 m². That is the whole-house picture, so a fan in the bathroom works together with trickle vents elsewhere.

Choosing the right fan

Airflow first

The 15 l/s figure is the floor, not the target. Wew points out that undersizing is a common cause of persistent condensation: a fan that cannot move enough air simply cannot clear the moisture a shower produces. Pick the extract rate for the room, not the cheapest box on the shelf. Large bathrooms, long duct runs and rooms with a walk-in shower or wet room all push you towards a stronger unit.

Axial or centrifugal

This choice depends on the duct. TGD F 2019 says axial fans are normally suited only to short through-the-wall runs. For bathrooms, an axial fan can be acceptable with flexible duct up to 1.5 m long and two 90° bends. A centrifugal fan can generally use flexible duct up to 6 m for 15 l/s with two 90° bends. If your fan sits in the middle of the ceiling and the outlet is on a gable wall, you almost certainly need centrifugal or inline.

Axial and centrifugal fan duct limits compared

Controls and noise

A fan that is loud gets switched off, and a fan that is switched off does nothing. Choose a quiet model, then choose the control that suits the household:

Overrun timer: keeps the fan running after the light goes off. Required where there is no vent or window.
Humidistat: switches on when humidity rises. TGD F accepts this for a bathroom without a WC.
Manual override: needed on any automatic control.

A timer set too short is a classic cause of damp ceilings. If your shower is long, ask for the longest overrun the unit allows.

Where the fan goes and where the air goes

Place the fan as close to the shower or bath as the electrical zones allow, so steam is caught before it spreads. Avoid putting it right next to the door, where it pulls air straight from the landing and leaves the far corner damp.

The air must leave the building. A fan that discharges into the attic soaks the roof timbers and insulation, which is exactly what Part F’s roof-void requirement is there to prevent.

Extractor duct discharging into attic insulation

Duct route and outlet

The Part F installation and commissioning guide states that:

duct through unheated areas and voids should be insulated with at least 25 mm of material with a thermal conductivity of 0.04 W/mK or less;
horizontal duct should slope away from the fan;
the free area of the external terminal should be at least 90% of the duct’s free area.

The reason is simple. An uninsulated duct crossing a cold loft is a cold pipe full of warm, wet air, so water forms inside it. Keep the run as short and straight as the roof allows, pull it taut, and give it a slight fall towards the outlet so any condensate drains out rather than back to the fan.

How a fan is fitted

This is the sequence a competent installer follows. It is here so you know what good work looks like, not as a prompt to take on the wiring yourself.

Check what is there. Is there a window, a trickle vent, an existing duct? That decides whether you need the overrun.
Choose the position and the exit. Ceiling or wall, and the shortest sensible route to an outside wall, soffit or roof terminal.
Cut the opening and fix the housing or back box securely.
Run insulated duct to the outlet, sloped and taut, with a grille or terminal of full free area on the outside.
Run the wiring from a suitable supply, with the switching and overrun arrangement the fan needs.
Fit the fan, seal around it, and check it spins freely.
Commission it. Check the airflow at the grille, that the timer overruns, and that the manual override works.

If the bathroom is being refurbished anyway, this all happens before tiling and plastering, when ceilings are open and cables are easy to route. Retrofitting later means opening finished surfaces.

Electrical safety: why to use an electrician

Bathrooms are split into electrical zones by distance from water. Wew notes that a fan over or near a shower needs an IP rating suited to its zone, and that this is a safety and compliance matter under IS 10101.

The detail is worth knowing when you talk to your installer:

In the UK wiring rules, the IET says a suitable 230 V fan may go in zones 1 and 2 if protected to at least IPX4. A fan on a lighting circuit in a windowless bathroom should have its own isolation, and a fan with an overrun needs a triple-pole isolator outside zones 0, 1 and 2.
EnviroVent says 30 mA RCD protection is needed for fans and cables entering the bathroom, and that low-voltage (SELV) fans add a margin of safety.
In Ireland, Hager’s IS 10101 guide says final circuits supplying luminaires in domestic premises need additional protection by an RCD of 30 mA or less, which matters when the fan shares a lighting circuit.
ESB Networks says a 30 mA RCD gives the highest level of protection in domestic installations.

The practical advice: have the connection made and tested by a registered electrician, and tell them the fan’s zone and IP rating before they start.

What does it cost?

Prices vary too much to quote one figure honestly. The main drivers are:

Replace or new: swapping a like-for-like fan is a small job. A first-time installation needs an opening, a duct and often new cable.
Duct length and route: a short run through an external wall is cheap. A long run across an attic to a roof terminal costs more in duct, insulation and time.
Fan type: a basic axial unit, a quieter centrifugal or inline fan, or a humidity-sensing model.
Access: a high ceiling above a bath, or a finished ceiling that must be opened and made good.
Electrical work: new switching, an overrun, or a spur from a protected circuit.

Get the quote in writing, with the fan model, the duct and terminal, and the electrical work itemised. We do not publish a price for ventilation on its own: it is part of the design, supply and fit scope of each bathroom, so it is priced with the rest of the room.

Fixing condensation and a fan that does not work

Steamed windows, black mould on the ceiling and peeling paint usually have one of five causes.

The fan is too small for the room or the duct run. Compare its rated extract against the 15 l/s minimum and the room’s size.
It switches off too soon. Lengthen the overrun, or fit one if there is none.
The duct is blocked, crushed or sagging. A slack flexible duct holds water and cuts airflow. Pull it straight and support it.
The duct is cold. Insulate it, as above, or condensation drips back through the fan.
The outlet is restricted. A clogged grille or a terminal with too little free area chokes the flow.

Two quick checks: hold a sheet of toilet paper to the grille, and it should cling firmly. Then listen for a rattle or grinding that suggests a worn motor or dust-clogged impeller. Dust build-up on the grille and impeller is common; with the power isolated at the consumer unit, a gentle clean often restores airflow. If the fan hums but does not spin, or trips the RCD, switch it off and call an electrician.

In a very damp room, also look at the rest of the bathroom. Closing the door during showers, drying towels elsewhere and wiping down glass all help, but they support a working fan rather than replace one.

Our perspective

We see ventilation treated as an afterthought on bathroom jobs, and it shows up a year later as mould on a new ceiling or tiles that will not stay clean. Ventilation should be designed with the layout, the shower position and the ceiling, not added at the end.

That is why we plan the fan, the duct route and the outlet during the design and survey stage, alongside the tiles and sanitaryware. Our studio team can show you the room in a photorealistic 3D mockup before work starts, so decisions about a ceiling, a bulkhead or a wet room are made on screen, not on site.

The same team looks after the project from survey to completion, which keeps ventilation, electrical connection and finishing in step. For wet rooms and accessible bathrooms, where more water is released in a smaller space, we think this early planning matters most.

David

Plan the fan into your bathroom project

If you are renovating a bathroom in Kildare or Dublin, we can include ventilation in the design, supply and fit, from the first onsite consultation to the finished room. See what we offer on our bathroom, kitchen and flooring services page.

Planbbathrooms

For a wider view of the process, our bathroom renovation checklist lists the decisions to make before work begins, and our guide to bathtub to shower conversion covers a change that often needs the fan and electrics reviewed.

FAQ

Does a bathroom fan have to vent outside?

Yes, the air should be carried outside the building. Part F aims to limit moisture and prevent condensation in the roof void, and discharging into an attic works against both. Use insulated duct through cold spaces and a terminal with enough free area.

Do I need an electrician to replace a bathroom fan?

We advise using a registered electrician. The fan’s zone, IP rating, RCD protection and any isolator all affect safety, and a bathroom is where mistakes carry the highest risk.

How long should the fan run after a shower?

TGD F 2019 requires an automatic 15-minute overrun where the bathroom has no background vent and no openable window. A humidistat is an accepted alternative for a bathroom without a WC. Any automatic control needs a manual override.

What extract rate does a bathroom need?

The minimum for a bathroom with a bath or shower is 15 l/s on an intermittent system, or an 8 l/s boost rate on a continuous central system. Larger rooms, longer ducts and wet rooms often justify more.