Under Approved Document F, new homes must have effective ventilation to remove moisture and pollutants, bring in fresh air and quickly clear poor-quality air when needed. As homes become more airtight and energy efficient, getting ventilation right becomes even more important. Mechanical systems such as continuous extract ventilation are likely to become more common, but they are not mandatory in every new home. The key requirement is that the chosen system delivers the ventilation performance required by the Building Regulations.
Key Takeaways
What Are the Legal Ventilation Requirements for Buildings & Homes?
It also explains how ventilation systems should be designed, installed, tested and commissioned so they work properly. Some work, especially fixed mechanical ventilation systems, may need Building Regulations approval. In certain cases, a registered competent person can self-certify the work; otherwise, building control approval may be needed. Checking this early can help avoid delays or certification problems later.
Are Extractor Fans Required in New Builds?
Room | Intermittent Extract | Continuous Boost |
|---|---|---|
Kitchen – cooker hood vents outside | 30 l/s | 13 l/s |
Kitchen – no external extract hood | 60 l/s | 13 l/s |
Utility room | 30 l/s | 8 l/s |
Bathroom | 15 l/s | 8 l/s |
WC | 6 l/s | 6 l/s |
Note
l/s means litres per second and measures the amount of air a ventilation system moves each second. For example, a bathroom fan operating at 15 l/s moves 15 litres of air per second. Put simply, the higher the l/s rate, the greater the airflow the ventilation system provides.
How Should You Ventilate a New Build?
Whatever system is chosen, it needs to be designed around the property. Natural ventilation and MEV will usually need properly sized trickle vents or other background ventilators, while MVHR normally should not. New homes also need purge ventilation, usually through openable windows or doors. The best approach is to plan ventilation early and make sure the system is properly installed, tested and commissioned.
What Should a New Build Ventilation Checklist Include?
Before a new-build home is signed off, make sure the ventilation system meets these key requirements:
Do You Need Two Doors Between a Kitchen & a Bathroom?
Under Approved Document G of the Building Regulations, a WC can be located directly next to a kitchen as long as the toilet room has suitable handwashing facilities and there is a door separating the WC from the kitchen or food-preparation area.
A simple way to remember the rule is:
WC + hand basin + one separating door = no two-door lobby needed
However, there is an important exception. If the WC is in a separate room without its own hand basin, the layout should allow you to pass the associated handwashing facilities before entering the kitchen. The kitchen or food-preparation area must still be separated by a door.
You also need to think about ventilation. Approved Document F deals with ventilation requirements for kitchens, bathrooms and WCs. So, although a two-door lobby is generally not required, the toilet must still have suitable ventilation.
What Does Ventilation Work Mean for Your Tax Bill?
A simple way to think about it is: does the property still do broadly the same job, or has the work given it something materially new or better? HMRC accepts, for example, that replacing old single glazing with modern double glazing can still count as a repair. Using the same principle, replacing a failed extractor fan with a broadly equivalent modern model will often be treated as a repair. By contrast, installing a completely new whole-property ventilation system, such as Mechanical Extract Ventilation (MEV) or Mechanical Ventilation with Heat Recovery (MVHR) where no comparable system existed before, is more likely to be a capital improvement.
Ventilation work | Likely treatment | Tax position |
|---|---|---|
Replace a failed bathroom fan with a modern equivalent | Repair | Usually deductible from rental profits |
Install a new whole-property ventilation system | Capital improvement | Normally no immediate deduction from rental profits |
The Key Point
Do not assume that every new item is automatically a capital improvement. HMRC looks at what the work actually achieves, and a larger refurbishment can sometimes include both deductible repairs and capital improvements.
What Do the New Ventilation Rules Mean for Landlords?
For existing rental properties, the new rules do not mean every landlord has to upgrade their ventilation. However, if you do pay for ventilation work, the tax treatment can make a difference. Replacing a failed extractor fan with a similar modern model will often be treated as a repair and may be deductible from rental profits. Installing a completely new or significantly improved ventilation system is more likely to be a capital improvement. If a project includes both repairs and improvements, ask the contractor to show the costs separately on the invoice.
Property Investors & Landlords Action Checklist
- Decide whether the work is a repair or capital improvement
- Ask for itemised invoices where the work includes both
- Keep commissioning and handover records for new-build properties
- Keep invoices and evidence for any capital improvement costs
- Non-resident landlords should apply the same basic repair-versus-improvement principles to their UK rental properties
Conclusion
If you are building, buying or carrying out relevant work, it makes sense to plan the ventilation early, use competent installers and keep the commissioning and handover records.
For landlords, there is also a tax question to get right: is the cost a deductible repair or a capital improvement?
If you are unsure how ventilation or wider refurbishment costs should be treated, UK Property Accountants can review the work and explain the Income Tax and Capital Gains Tax position based on your circumstances.
This article is for general information only and does not constitute tax advice. Building Regulations compliance should be confirmed with an appropriate building professional or building control body.
Frequently Asked Questions
In England, unauthorised development completed on or after 25 April 2024 can generally become immune from planning enforcement after 10 years if no action is taken. For some work completed before that date, the old four-year rule may still apply. This is a planning rule only and does not replace the need for Building Regulations approval.
There is no single ventilation rule for every flat roof. The right approach depends on how the roof is built, such as whether it is a warm or cold roof. In England, Approved Document C and BS 5250:2021 provide guidance on controlling moisture and reducing the risk of condensation.
The main standard is BS 5250:2021 – Management of moisture in buildings: Code of practice. It provides guidance on controlling moisture and condensation in roofs and other parts of a building.
There is no fixed legal list. What is included depends on the developer and the purchase contract. Items such as flooring, appliances, light fittings or landscaping may or may not be included, so buyers should check the specification carefully before exchanging contracts.
There is no universal “2-foot rule” for HVAC systems under UK Building Regulations. Required clearances depend on the equipment being installed, such as ventilation outlets, flues or air-conditioning units. Always check the relevant Approved Document or manufacturer’s instructions rather than relying on a general 600 mm rule.
- Statutory Residence Test (SRT) Explained for UK Tax Resident and Non-Resident - 14 October 2026
- Deed of Variation: IHT, CGT & SDLT on Inherited Property - 13 October 2026
- UK Budget 2026 and Iran War: What Landlords Need to Know - 12 October 2026
