Why are more homes in the UK reporting damp and how can architects help?

Back in February (2025), the government confirmed the timelines for the implementation of Awaab’s Law. Part of the Social Housing (Regulation) Act, the law is named after two-year-old Awaab Ishak, who died following a respiratory condition caused by mould in his social housing home despite the Ishak family reporting the issue to the landlord.

The law will come into effect in October and will target social landlords, requiring them to address damp and mould hazards within fixed timescales.

While Awaab’s Law seeks to improve only a specific area of the built environment, it draws attention to the importance of understanding causes of excessive levels of damp and mould, and provides an opportunity for architects to discuss ways to mitigate these problems in the design process.

After all, statistics show that mould and damp real problems in this country.

In 2021, Shelter said that damp and mould affects 26% of rented homes in the UK. Subsequently, the English Housing Survey 2022-23 found that 3.5 million households (14%) in England lived in a home that failed to meet the Decent Homes Standard, 2.1 million households (9%) lived in a home with at least one Category 1 hazard, and 1.0 million households (4%) lived in a home with damp.

So why is this happening and how can architects help when seeking to improve existing buildings?

Why are houses getting damper?

There are lots of factors combining to exacerbate problems of damp, says Claire Humphreys, co-founder of Bristol-based Shu Architects, which specialises in conversion projects including historic buildings.

Living habits have changed over recent decades: family members might now have multiple showers during the week or even in a single day, people often dry clothes on radiators instead of an external washing line, and kitchens are seeing rising moisture levels from dishwashers, washing machines, microwaves and the appliance du jour, the air fryer. And yet, kitchen ventilation is generally reliant on the switching on of the cooker hood.

Crucially, since Covid the UK has also seen an increase of people working from home, which means more boiling water in kettles to produce more cups of tea every day, and more production of moisture generally.

These lifestyle changes have also coincided with the rise of draught proofing.

“Homes are generating moisture in places where it can’t possibly get out, but it has to go somewhere,” Claire says. “What happens is that it travels around the house, usually working its way upwards, and then condenses in the coldest area it can find.”

In recent years, the focus has been on heat retention through insulation and airtightness, often overlooking the need for some form of controlled ventilation that will allow inevitable moisture to escape. Controlled ventilation tends to be treated as an afterthought if at all.

Builders and contractors are another part of the problem, she argues, often giving ventilation no proper consideration even on high end and heritage building projects. For instance, Claire says she has seen a very expensive kitchen provider telling the owner of a listed building that they need nothing more than a recirculating fan on a cooker hood for the ventilation of the new kitchen. The issue here is that often recirculating fans only buffer moisture and remove smells, and for them to truly be beneficial they need to provide active forms of ventilation that removes moist air from a space.

What can architects do to help damp and mould?

In an ideal world, Claire would always specify a mechanical ventilation with heat recovery (MVHR) system, but they can be bulky, require a lot of pipework and are often not practical for an existing building. But she will generally recommend continuous extract fans and trickle vents, unless she is faced with heritage windows that even when draft-proofed will be leaky enough to serve as trickle vents. (Shu draught-proofs older windows.)

There is a widespread fear among homeowners that trickle vents are responsible for excessive heat loss, but Claire counters that there is a huge difference between controlled ventilation and uncontrolled runaway ventilation.

“Quite often what we will do on the conversion of an existing building is to plan it so that we can run a centralised continuous extract fan, and we may do this even at the planning stage, particularly if it is a heritage building,” She says. “So, we’ll have multiple inputs, such as the spider vents that everyone does a version of these days, with all of the ventilation coming to that central point.”

“It will run on background trickle rate and then as soon as the humidistat senses a higher humidity level it will go into boost mode.”

She continues: “This way, you only have a single outlet that avoids an elevation being peppered with outlets, which is particularly important if you are in a sensitive area. The fan can be placed in a remote area so you don’t really hear it.”

What are misconceptions around MVHR units?

Her colleague, Part 2 architectural apprentice, Gemma Llewellyn, who already shares Claire’s frustration with the lack attention given to ventilation systems, says the key lesson she has learned is that ventilation decisions should be taken early on. She is well aware that ventilation is not the most exciting aspect of a project for most young designers, but if decisions are left too late there may be no space for a MVHR unit, or no ceiling depth that can accommodate ductwork, and effective ventilation will be quietly forgotten about. The siting of the unit is also important, not only for noise considerations, but also as an opportunity to limit ducting and arrange an optimum ducting layout.

She adds that it is frequently forgotten that low-humidity ambient air is cheaper to heat than moist air and is a big factor in achieving thermal comfort.

There are new compact MVHR solutions being developed all the time that are well worth more attention from architects, particularly on retrofit projects. There are now single room MVHR units, units that will sit within the thickness of a wall, and smart mini-units that talk to each other from different rooms to coordinate their efforts.

Gemma says it is a misconception that MVHR is always expensive to run - systems have become way more efficient than they were 10 years ago. She cites a project Shu has worked on where a the MVHR unit for the whole house has the energy draw of a single, old-style light bulb.

She has also learned that no retrofit or conversion project should have to overlook potential ventilation problems, however airtight the building might be: “No house should have to be damp – there is always a way around it.”

Thanks to Claire Humphreys, co-founder, and Gemma Llewellyn, Part 2 Architectural Apprentice, Shu Architects.

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RIBA Core curriculum topic: Sustainable architecture.

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