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Want to know how to prepare for the implementation of The Future Homes Standard in 2025? Access our latest webinar recording and slides containing all you need to know. Take me there!
8 Minute Read • Part L/Section 6

Which ventilation system is best?

Part L/Section 6
Part L/Section 6

Which ventilation system is best?


In this series of articles, we aim to answer some of your questions about the upcoming changes to Approved Documents L and F, SAP methodology and the Future Homes Standard.

Current proposals suggest these regulations will be coming into force in England from October 2020. Contact us with your own questions about the regulation changes, or to discuss our training seminars and workshops.


Which ventilation system is best?

This all depends on how the house is designed and how well it will be constructed. Changes to Building Regulations next year make it clearer about which systems aren’t suitable.

How our homes should be ventilated is covered by AD F in English Building Regulations. This ensures we have fresh air, that pollutants are quickly removed and helps to avoid mould growth.

The current Approved Document lists four types of common approaches to ventilation:

System 1 uses intermittent extraction fans in bathrooms and kitchens, and trickle vents above windows. This system has gone unchanged for years and is still a common way of ventilating a new home.

System 2 is Passive Stack – stale air from wet rooms is removed from the dwelling using the chimney effect.

System 3 is split into continuous whole house ventilation (wet rooms are connected to a single extract system) and decentralised (similar to intermittent fans, except they run constantly at a much lower rate.)

System 4 is continuous supply and extract. This includes whole house heat recovery systems.

As part of the Future Homes Standard, AD F will be changing to give better clarity to developers about which ventilation system to use.

Firstly, guidance on System 2 could be removed completely, as Passive Stack is unpopular in the UK.

Choosing between the remaining three depends on whether your house is ‘highly airtight’ or not. Under the proposed regulations, this is defined as a dwelling designed to reach an air test of 5 or lower, and achieves an actual result of 3 or lower.

If you have a highly airtight home, you should use Systems 3 or 4 only. Intermittent extraction fans won’t provide enough air flow by themselves.

If you don’t have a highly airtight home you should use Systems 1 or 4 only, but remember the efficiency of System 4 ventilation drops off with a higher air permeability, and this can impact fuel bill costs as well as SAP compliance.

A final point to consider is if you are building in an area of poor air quality. Under the proposed changes to AD F you will be expected to install an advanced ventilation system that can only be sufficiently met using System 4. See our article about this.


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Delayed Scottish building regs are now live


New energy performance targets in Wales


Transitional Arrangements (Wales)


GLA Energy and Cooling Hierarchy: 2022 Changes



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