Permitted Development Rights have fast-tracked housing delivery, but often at the expense of thermal comfort and occupant wellbeing, says Andrew Nash from Nuaire, who warns that reforms and ventilation innovation are urgently needed.
Permitted Development Rights (PDR) emerged as a fast-track response to the UK’s housing crisis. From 2013, PDRs have allowed for change of use for buildings in commercial, business and service use to a dwelling, without the need for planning permission from the local planning authority (LPA). Nor are they subject to full Building Regulations.
By allowing commercial buildings to be repurposed as residential units in this way, they offer a speedy solution to increasing the housing stock. Between 2015/16 and 2022/23, 102,830 new homes were created in England through change of use PDRs, which is approximately 6% of the net additional homes delivered since 2015/16. Has PDR created more problems?
A 2020 study commissioned by the Government found that homes created through PDRs resulted in ‘worse quality residential environments’ than those that required LPA planning permission. By sidestepping the usual regulatory frameworks, PDR conversions often escape the rigorous checks designed to ensure homes are safe and comfortable. Critically, they are exempt from Part O of Building Regulations, which addresses overheating in residential dwellings and aims to protect the health and wellbeing of occupants by reducing the occurrence of high indoor temperatures. This exemption leaves thousands of homes at risk, specifically those transformed from office buildings with sealed facades and extensive glazing, architectural legacies that can work against thermal comfort.
A 2023 survey on PDR housing and health published by UCL showed that only 63% of respondents were able to keep comfortably cool during hot summer weather conditions.
The risk is growing
This year has been the driest January to June for England since 1976. Spring 2025 is the UK’s warmest and sunniest on record, with June the second warmest for the UK since records began in 1884.
The situation is worsening; the state of the UK Climate Report 2024 shows the UK is warming at a rate of approximately 0.25°C per decade.
These temperature extremes have serious implications. There were 2,985 heat-related deaths in 2022, the year that saw the highest recorded temperature in England, according to the UK Health Security Agency. This figure is the highest since recording began. Beyond the health risks, overheating affects mental wellbeing and economic productivity.
According to the Chartered Institution of Building Services Engineers (CIBSE), a predominantly mechanically ventilated home overheats when internal temperatures exceed 26°C for more than 3% of annual occupied hours.
No reliance on natural ventilation
The core challenge with PDR projects is that they often repurpose buildings designed for a completely different occupancy. Former offices were not built to house people 24/7. They typically feature large glazed facades, minimal external shading, and restricted natural ventilation. In densely built up urban heat islands, where many of these buildings are located, opening windows (if they can be opened that is) may not be an option due to noise, air pollution, or security risks. These environmental constraints effectively render passive ventilation strategies unworkable.
Part O prescribes maximum glazed areas on facades (depending on orientation), encourages the use of solar shading and glass with lower g-values to limit solar gains, whilst setting minimum openable window areas so that excess heat can be passively ventilated away. But in the case of PDR schemes, this requirement is not mandatory, leaving developers to comply only with the bare minimum ventilation requirements which are stipulated by Building Regulations Part F. The result is a proliferation of homes that are technically compliant, yet thermally dysfunctional.
A viable solution
Manufacturers work extensively with sustainability engineers carrying out dynamic thermal modelling simulations to assess overheating risk in new build developments. Elevated mechanical ventilation rates and Mechanical Ventilation with Heat Recovery (MVHR) with hybrid cooling must be trialled before a designer can consider resorting to air conditioning, and this approach really should be considered in PDR conversions, even if it’s not a requirement.
MVHR systems offer a practical and effective approach to meeting Part F and can also assist in improving thermal comfort. MVHR not only preconditions air and filters out pollutants but also provides summer bypass functions, which can be used in combination with elevated airflows to provide free cooling when external temperatures are favourable. These systems can help maintain acceptable indoor temperatures year round and are still regarded as passive means in Approved Document O.
Where window openings are limited and insufficient to naturally ventilate excess heat, standard MVHR systems may not suffice. Hybrid cooling units working in tandem with MVHR could assist in mitigating overheating, activating when indoor temperatures exceed a set threshold (typically 23°C). The potential effectiveness of such a system should be assessed through dynamic thermal modelling.
A call for reform
The urgent need to reform policy around overheating is becoming widely recognised. The House of Commons Environmental Audit Committee recommended expanding Building Regulations Part O to include refurbishments and material change of use.
The built environment community must confront the reality that current practices in PDR conversions are insufficient for the demands of a warming climate.
Andrew Nash is residential divisional manager at Nuaire