Overheating Standards for New Homes in Scotland and Northern Ireland

Scotland and Northern Ireland do not have a Part O. England brought Part O of the Building Regulations into force on 15 June 2022, and Wales adopted Approved Document O in the 2022 edition, but the two devolved administrations north and west of that line have taken different routes to the same problem: how to stop new homes becoming uncomfortably, sometimes dangerously, hot in summer.

In Scotland, the answer has been folded into the energy standards rather than written as a standalone overheating rule. The Building (Scotland) Amendment Regulations 2022 introduced the need for an overheating risk assessment and mitigation measures as part of a package that also set a new energy target and revised minimum energy performance standards for building fabric and fixed building services¹. There is no direct requirement within schedule 5 of the Building (Scotland) Regulations 2004 for buildings to be designed and constructed to avoid the risks of overheating¹. The Scottish Government's own consultation on energy standards set out two proposed approaches to demonstrating compliance: a simple elemental approach, and dynamic thermal analysis¹.

Northern Ireland has gone further in the opposite direction: it has no dedicated overheating standard for new homes at all. Its building regulations discussion document of 2023 set out pre-consultation on next steps rather than a settled rule². The practical consequence is that a household buying a new build in Scotland or Northern Ireland has fewer overheating protections written into the regulations than one buying in England or Wales, and must rely more on design, orientation, shading and ventilation choices made by the developer.

What the Scottish regulations actually require

The Scottish position is best understood as an absence plus a partial substitute. The absence is a direct overheating standard. The substitute is the overheating risk assessment introduced by the 2022 Amendment Regulations, which applies to new buildings and new building work and sits alongside a new energy target, revised minimum energy performance standards for fabric and fixed services, and consequential changes to ventilation standards¹.

The consultation that preceded those regulations proposed that any new provision to assess and mitigate against the risk of summertime overheating should apply to all new dwellings, subject to the application of a set of trigger criteria¹. That is a broader scope than a single standard applied at building warrant stage, but it is also softer: it depends on assessment and mitigation rather than a pass or fail threshold written into schedule 5.

Two compliance routes were proposed. Approach A is a simple elemental approach; Approach B is dynamic thermal analysis¹. The distinction matters to a household because the two routes can produce different design responses. An elemental approach tends to produce prescriptive measures such as shading or opening sizes. Dynamic thermal analysis models the dwelling over a summer period and can allow a designer more freedom in exchange for more evidence.

The risk analysis behind the Scottish proposals assumed Category II buildings, meaning dwellings with a normal level of expectation of being occupied by vulnerable and fragile persons¹. A sample simulation established that the Glasgow weather file resulted in a higher overheating risk than the alternative tested¹. That is a reminder that overheating in Scotland is not a theoretical southern English problem: the modelling used Scottish weather data and found the west of Scotland file the more demanding of those tested.

The figures behind the Scottish approach

The headline number is uncomfortable. Research on 26 low energy new build homes in Scotland, built under 2007 or 2010 standards, found over half of homes exceeding the threshold temperature for more than half the year⁴. That is a small sample, and it is described as research rather than a national survey, but it points in the same direction as the wider UK evidence.

That wider evidence is starker still. The Climate Change Committee has estimated that the majority of existing UK homes fail the current standard used in the buildings regulations to limit overheating in new build homes⁵. A separate piece of official guidance states that a high proportion of existing homes fail to meet the new overheating standard for new homes⁸. Both statements concern the existing stock rather than new build, but they set the baseline against which any new standard is judged.

On energy performance, the UK cost-optimal report gives flats in Scotland at 2015 standards a flat primary energy figure of 71 kWh/m2/yr⁴. That is a fabric and services measure, not a comfort measure, but it shows the direction of travel in Scottish new build: tighter envelopes, which reduce winter heat loss and can, without care, make summer overheating worse.

The Scottish House Condition Survey provides the temperature definitions used in Scottish fuel poverty statistics. A standard heating regime is 21°C in the living room and 18°C in other rooms, for 9 hours a day during the week and 16 hours a day during the weekend⁹. An enhanced heating regime, for households with enhanced heating needs, is 23°C in the living room and 20°C in other rooms⁹. These are heating standards, not cooling standards, and they are the nearest thing Scottish official statistics offer to a comfort benchmark.

How Scotland, Northern Ireland, England and Wales compare

The four nations now sit in four different places on overheating.

Wales is the closest to England in structure. Approved Document O, 2022 edition, sets standards for reducing overheating risk in new residential buildings⁸. The Welsh regulations also impose an information duty: sufficient information about Part O provisions must be provided to the owner⁹. That duty is worth noting because it gives a Welsh buyer a paper trail that a Scottish or Northern Irish buyer may not receive.

Scotland's divergence is deliberate rather than accidental. The Scottish Government has implemented its heat policy using fully devolved building regulations, and the New Build Heat Standard was introduced on that basis¹⁰. Building standards are devolved, so the Scottish Parliament can set its own route without waiting for Westminster, and it has.

Northern Ireland's position is the least developed of the four. The 2023 discussion document and pre-consultation on next steps is a consultation stage document, not a standard². Until that process produces regulations, a new home in Northern Ireland is not assessed against a dedicated overheating standard in the way an English home is against Part O.

The New Build Heat Standard and what it covers

Scotland's most consequential recent building measure is not about overheating directly, but it shapes the services a new home can have, and therefore how it can be cooled. The New Build Heat Standard prohibits the use of heating and cooling systems, located within the curtilage of any new building, which produce more than a negligible level of greenhouse gas emissions at the point of combustion¹¹. It was introduced through standard 6.11, Heating and hot water, direct emission heating system, of schedule 5 of the Building (Scotland) Regulations 2004⁷.

Its scope is narrower than its name suggests. The standard extends only to the provision of space heating, cooling and hot water; any other processes which use or generate heat are out of scope¹¹. It applies to both new domestic and non-domestic buildings, as well as the conversion of existing buildings¹². The regulations were laid in the Scottish Parliament in the week commencing 5 June 2023¹¹, and the original regulations came into force in April 2024¹³.

For conversions, the heating systems standard requires that the building as converted shall meet the requirements of this standard in so far as is reasonably practicable, and in no case be worse than before the conversion, under regulation 12, schedule 6¹⁴. That is a practical limit rather than an absolute one, and it recognises that a conversion cannot always reach new build performance.

The minimum performance of space heating and hot water systems, heating appliances and controls in Scotland is set out in the Non-domestic Building Services Compliance Guide for Scotland, which replicates guidance published elsewhere in the UK and applies to new systems, replacement in whole or in part, and improvement work to existing systems¹⁴. The domestic handbook requires that every building must be designed and constructed so it can be heated and maintain heat at temperature levels that will not be a threat to the health of the occupants¹⁵. That is a winter health requirement, and it has no summer counterpart in the same standard.

What drives the Scottish and Northern Irish positions

Three forces sit behind the divergence.

The first is carbon. Heating homes, workplaces and other buildings is the third largest cause of greenhouse gas emissions in Scotland¹⁶, and heat in buildings accounts for approximately a fifth of Scotland's greenhouse gas emissions¹⁷. Heating in homes and buildings accounts for 30% of Scotland's total energy consumption¹⁸, and more than half of the heat consumed in Scotland is used in households¹⁹. A government focused on those numbers will regulate the heat source before it regulates summer comfort.

The second is fuel poverty and health. The Fuel Poverty (Enhanced Heating) (Scotland) Regulations 2020 define the standard and enhanced heating regimes that underpin Scottish fuel poverty statistics⁶. A household that cannot afford to heat to 21°C in winter is unlikely to be running cooling in summer, which changes the political weight of an overheating standard.

The third is the pace of legislation. The Heat in Buildings Bill is intended to give industry and homeowners the certainty they need to invest, boost heat network development and set a long-term direction of travel that is deliverable and affordable for households and businesses¹⁶. The Scottish Government has proposed a new Heat in Buildings Bill to require homeowners in Scotland to meet a minimum energy efficiency standard by 2033²⁰. The Bill would create powers to set minimum energy efficiency standards for owner occupier and non-domestic properties, and requirements for large non-domestic premises including powers to require public sector buildings to connect to district heating when available²¹.

The draft legislation has a short title: the Buildings (Heating and Energy Performance) and Heat Networks (Scotland) Act 2027²². Secondary legislation may be needed, for example to specify measures forming the minimum energy efficiency standard or exemptions from the Heat in Buildings Standard, subject to further consultation²³. The Scottish Government has also stated that it does not have all the powers to deliver zero emissions, and needs UK Government changes or more powers²⁴.

What the rules mean for a household

For a buyer, the practical position is this. In Scotland, a new home is assessed for overheating risk as part of the energy standards, with two possible compliance routes, but there is no schedule 5 requirement that says the building must not overheat¹. In Northern Ireland, there is no dedicated overheating standard at all, and the 2023 discussion document is a pre-consultation step². In England, Part O has applied since 15 June 2022³. In Wales, Approved Document O sets the standard and the owner must receive sufficient information about the Part O provisions⁸.

The Scottish heat rules that will bite hardest on households are the efficiency ones. The Heat in Buildings Bill would require owner occupied homes to meet a minimum energy efficiency standard by the end of 2033²⁵, equivalent to EPC C. The Heat in Buildings Standard has four triggers, two of which are worth stating plainly: at the end of a grace period which follows the completion of a property purchase, and at the end of 2033, when owner occupiers will need to have met the minimum energy efficiency standard²⁵. A third trigger is following notice from a local authority to a building owner in a Heat Network Zone that they are required to end their use of polluting heating²⁵. The Scottish Government has stated that the requirement would apply only after the Bill has been approved by the Scottish Parliament and further regulations consulted upon and implemented²³.

The Scottish Government has also proposed minimum energy efficiency standards for privately rented homes²⁶. The Heat in Buildings Bill would provide Scottish Ministers with the ability to require homes and non-domestic buildings to end their use of polluting heating in other circumstances, beyond the purchase of a property²³.

For a household thinking about cooling, the gap matters. A home built in Scotland or Northern Ireland without a Part O style assessment may have larger unshaded glazing, less cross ventilation or a layout that traps heat, and the buyer has no regulatory document to check. The remedies are the same ones that work anywhere: external shading, night ventilation and, where needed, mechanical cooling. The site's guide to passive cooling sets out the fabric first options, and external shading, shutters and awnings covers the measures that keep solar gain out before it enters.

What this means for energy independence

Overheating rules and energy independence pull in the same direction, but not automatically.

A home that is designed to stay cool without mechanical cooling uses less electricity in summer, which reduces draw on the grid at the moment of peak system stress. A home that is designed to stay warm with a heat pump and a well insulated envelope uses less gas, which reduces exposure to imported fuel. Scotland's building regulations are pushing hard on the second and only partly on the first.

The New Build Heat Standard is the clearest independence measure in the Scottish framework. By prohibiting heating and cooling systems within the curtilage of any new building that produce more than a negligible level of greenhouse gas emissions at the point of combustion¹¹, it removes the gas connection from the new build equation and shifts new homes onto electricity, typically a heat pump. The Scottish Government states that the standard helps ensure new buildings do not contribute to carbon emissions from heating Scotland's homes and buildings¹³. The dependence that remains is on the electricity grid and on a supplier, plus the manufacturer of the heat pump and any app or cloud service that controls it.

The overheating side is weaker. Because Scotland has no direct schedule 5 overheating requirement¹, a new Scottish home can be built to the energy standards and still overheat, as the research on 26 low energy homes suggests⁴. A household in that position has two routes to independence: passive measures that cost nothing to run, and mechanical cooling that adds to electricity demand. The site's home cooling pillar covers the full range, and cooling and energy independence deals with the trade-offs directly.

The wider Scottish framework adds a further dependence: the Scottish Government has stated that it does not have all the powers to deliver zero emissions, and needs UK Government changes or more powers²⁴. Building standards are devolved, which is why the New Build Heat Standard exists at all¹⁰, but the electricity market, grid connection and much of the funding landscape are not. A Scottish household's energy independence therefore depends on a mix of devolved building rules and reserved energy policy.

For Northern Ireland, the position is simpler and less favourable. With no dedicated overheating standard and a 2023 pre-consultation as the latest published step², a new home buyer has neither a Part O style assessment nor a Scottish style energy standard to point to. The independence question there is largely unanswered by regulation, and rests on the design choices of individual developers.