New build air conditioning
By Airva Editorial Team · Checked against published UK guidance · Updated
New builds get hot, and the reason is not poor construction. It is that a well-sealed, well-insulated, highly glazed house is very good at keeping heat in — which is exactly what you want in February and exactly what you do not want in July. If you are in a new home wondering why the upstairs is unbearable by four o'clock, the building is doing what it was designed to do.
What surprises most people is that the building regulations have addressed this since 2022, and that the regulation explicitly refuses to let a developer solve it with air conditioning.
Part O will not let cooling be the answer
Approved Document O sets standards for reducing overheating risk in new residential buildings in England. It has two requirements: limit unwanted solar gains, and provide adequate means of removing excess heat [1].
The critical part for anyone buying a new build is how it must be met. The requirement is to be satisfied using passive means as far as reasonably practicable. If mechanical cooling is installed, the developer must demonstrate to the building control body that all practicable passive means of limiting solar gains and removing excess heat have also been incorporated [1]. Guidance is explicit that passive measures are adopted first, before mechanical cooling [1].
In plain terms: a developer cannot skip the shading, the glazing specification and the ventilation strategy by fitting air conditioning instead. Cooling is permitted, but it does not buy compliance.
Two consequences follow:
- If your new build overheats, the passive design is where the problem lives. Air conditioning added afterwards treats the symptom. That is often the right practical decision for an owner, but it is worth knowing what you are compensating for.
- Very few UK developers fit air conditioning as standard, because Part O gives them no reason to and it adds cost. Most new builds are designed to pass on shading, orientation, glazing and ventilation alone.
Compliance is demonstrated either by a simplified method or by dynamic thermal modelling against CIBSE TM59, with a report provided to building control [1].
Ask before completion, not after
The cheapest air conditioning you will ever install in a new build is the one specified before the ceilings close. Once you have the keys, everything is a retrofit.
If you are still pre-completion, it is worth asking:
- Whether the developer offers cooling as an upgrade, and at what cost. Some do on larger house types.
- Whether they will allow a first-fit, with pipework and drains run before plastering even if the equipment comes later. This is by far the highest-value ask, and it costs a fraction of retrofitting.
- What the warranty position is. New build warranties sometimes constrain alterations in the early years, and drilling an external wall is an alteration. Check before you plan the work.
- Whether a management company or estate covenant restricts external units. This is common on newer estates and is entirely separate from planning permission. A covenant can prohibit what planning would allow.
That last one catches people. Planning permission and estate covenants are different systems with different enforcers, and satisfying one says nothing about the other.
Retrofitting after completion
A new build is, in engineering terms, one of the easier retrofits. Modern construction usually gives you:
- Straight, uncluttered cavity walls that core cleanly, without the surprises of lath, plaster and rubble fill you meet in older stock.
- A modern consumer unit with capacity for a dedicated circuit, so the £400–£700 electrical extra is less likely to apply.
- Predictable loft space for pipe routing on top floors.
- Level external ground for a condenser, without the access problems of a hillside terrace.
The complications are different in kind: estate covenants, close-set neighbouring properties that make condenser siting a courtesy question as well as a technical one, and shallow gardens where the only sensible position is near a boundary.
On that last point, the 2025 permitted development changes help. The old requirement to keep a unit at least a metre from the boundary was removed, so a condenser can now sit against a fence where the sound assessment allows it [2] — which on a modern plot is often the only place it can go. The volume limit also rose to 1.5 m³ for a house, and detached houses may have two units [2]. Our planning permission guide covers the full Class G checklist, including the condition that the system must not be used solely for cooling.
Which rooms, and why it is usually upstairs
New build overheating concentrates predictably:
| Room | Why it overheats | Priority |
|---|---|---|
| Top-floor bedrooms | Heat rises, roof gains, and often the largest glazing ratio | Highest — this is where sleep is lost |
| South and west-facing rooms | Afternoon and evening solar gain, at exactly the wrong time of day | High |
| Rooms over an integral garage | Poor separation and awkward thermal bridging | Moderate |
| Open-plan ground floor | Large glazing, bi-folds, and a lot of volume to condition | Moderate — expensive to cool well |
| North-facing rooms | Little direct gain | Low |
Most new build owners are best served by a two or three room multi-split covering bedrooms, rather than trying to condition the whole house. Our bedroom guide covers the sleep case specifically, and house too hot in summer works through the cheaper measures worth trying first.
Do the free things first
This is not a sales page, and the honest sequence matters. Before spending several thousand pounds:
- External shading on the south and west glazing does more than anything else, because it stops the heat before it enters.
- Night purge ventilation — opening up when the outside air is finally cooler — is what the Part O assessment probably assumed you would do.
- Check the trickle vents and any MVHR system are commissioned and working. A summer bypass on an MVHR unit is frequently found switched off or misconfigured in new homes.
If the house still overheats after those, fitted cooling is the right answer and you will have the evidence to justify it.
What it costs, and what it costs to run
A two or three room retrofit in a new build typically falls in the £2,800–£8,000 range depending on room count, with fewer of the access and electrical complications that push older properties higher. Our cost guide covers the detail.
Running cost is modest for cooling — a bedroom unit through a summer is a low tens of pounds at the current Great Britain average unit rate of 26.32p per kWh [3]. The running costs guide works it through, including the winter heating side, which in a well-insulated new build is genuinely efficient.
Frequently asked questions
Why is my new build so hot in summer? Because it is airtight and well insulated, usually with a high glazing ratio. It retains heat extremely well, which is a winter virtue and a summer problem.
Do new builds have to have air conditioning? No. Part O requires overheating to be addressed, but principally through passive means — limiting solar gains and removing excess heat — with mechanical cooling only where passive measures have already been adopted [1].
Can I add air conditioning to a new build? Yes, and new builds retrofit relatively easily. Check your warranty terms and any estate covenant before starting, as both can restrict external alterations independently of planning.
Will it void my new home warranty? It should not if the work is done competently by a certified installer and the warranty terms permit alterations, but read those terms first and keep the commissioning paperwork.
Do I need planning permission? For a house in England, usually not, provided the system is reversible and meets the Class G conditions [2]. Estate covenants are a separate matter and are not covered by planning permission.
Should the developer have prevented this? They had to demonstrate compliance with Part O. Compliance and comfort are not the same thing — particularly where the assessment assumed windows would be open and, in practice, they cannot be.
Get it scoped for your house type
Tell us the house type, which rooms overheat and whether you are pre or post-completion, and we will match you with one vetted installer who can advise on a first-fit or a retrofit: get an installer match.