Why does my conservatory become too hot to sit in, and can it be fixed?

Recently reviewed·Reviewed June 2026, next review December 2026

Conservatories are almost always built outside the thermal envelope of the house, which is why they can be twenty degrees warmer than the rooms next to them. The fix depends on how much you are willing to change. Roof treatment, internal shading and improved ventilation will rescue most conservatories. Without those, even powerful air conditioning is fighting a losing battle.

Editorial confidence: High confidence. Multiple regulator, government or academic sources agree.
Evidence status: Recently reviewed · reviewed June 2026 · next review December 2026
Monitoring: Every six months, plus whenever Approved Document O or CIBSE TM52 is updated.

Evidence drawn fromBuilding standards: Part O, CIBSE TM52Professional bodies: EST

You may not need to read the rest of this page

You probably already have enough to act if:

The conservatory reaches 30°C or more on sunny days
It has a polycarbonate or unshaded glass roof
It faces south or west

Open the cooling planner

This is probably the wrong page for you if:

The conservatory has been brought inside the thermal envelope
Your concern is winter cold rather than summer heat

Adaptive comfort limit (free-running rooms)

≈28°C

Source: CIBSE TM52 (Limits of thermal comfort) · CIBSE TM52 upper adaptive limit for free-running UK living spaces; conservatories routinely sit well above this.

Who this advice is for

Applies to

Conservatories built outside the main thermal envelope
South or west-facing conservatories
Polycarbonate, glass-roof and lean-to conservatories

Not intended for

Conservatories already converted into Building-Regs-compliant rooms
Garden rooms inside the thermal envelope
Diagnosing condensation rather than heat

What it usually looks like

These are the symptoms readers describe most often. None of them alone is diagnostic, but together they build a picture.

Room above 35°C on sunny days
Unbearable within an hour of sunrise
Adjoining room overheats whenever the door is open
Plants wilt despite watering

Most common in: Conservatory

Before you buy anything

Watch the house respond as you scroll.

These checks are listed in the order we would work through them. The illustration on the left changes with each one, so you can see what each check is actually addressing before deciding whether it is worth doing.

A glass roof and glass walls. There is no version of this room that is comfortable in August without intervention.

Look at the roof material

Polycarbonate and old glass roofs admit huge amounts of solar gain. A solid roof retrofit or reflective film transforms the room more than anything else.

Assess the orientation

A south or west facing conservatory will need much more aggressive intervention than a north facing one. Knowing this shapes every other decision.

Plan for cross ventilation

A single opening window leaves hot air with nowhere to go. Roof vents, side windows or a powered extract make a substantial difference.

Add external or in-roof blinds before internal blinds

External shading stops the heat before it enters. Internal blinds only catch it once it is already inside.

Decide whether the conservatory should be a year-round room

A genuinely habitable conservatory needs to be brought inside the thermal envelope, which is a building project. If the room is occasional, lighter measures may be enough.

Before you spend money

The cheapest answer is usually the one nobody sold you.

01
Measure the conservatory at 2pm on a sunny day
If it is sitting above 35°C, no fan will rescue it. Knowing the peak temperature tells you whether shading alone can fix it.
Free
02
Open both ends and a roof vent for an afternoon
Cross-flow ventilation is often the only thing standing between a usable room and an unusable one. If it works, the room may not need cooling kit at all.
Free
03
Check the roof type and glazing spec
A polycarbonate or single-glazed roof will overheat regardless of shading; replacement is the only honest fix and changes the rest of the conversation.
Free
04
Close the door to the rest of the house at midday
An open conservatory door turns the whole ground floor into a passive solar collector. Treating the conservatory as a separate room is often the first real saving.
Free

What we recommend, and why

Every recommendation explains why it comes first, the evidence behind it, how confident we are, and when it would not apply.

Treat the roof and external shading before any mechanical cooling

Why this comes first

The roof is the largest unshaded glazed surface in a conservatory and dominates solar gain. A solid-roof retrofit, reflective film or external blinds reduces heat input far more cheaply than running an air conditioner against it.

Evidence

Approved Document O treats shading of glazing as the primary overheating mitigation; EST conservatory guidance reaches the same conclusion for retrofit.

Part O · EST

Confidence

High confidence. Multiple independent sources agree on the direction and the order.

Exceptions

Listed or conservation properties restricting roof alterations

Next step

See the cooling planner

Add cross and stack ventilation second

Why this comes first

Most conservatories have a single openable window, which traps hot air with nowhere to go. Adding a high-level vent or roof opening lets warm air escape upward and replaces it with cooler air from the house side.

Evidence

CIBSE TM52 adaptive comfort relies on effective cross and stack ventilation; EST conservatory guidance lists it as the second step after shading.

CIBSE TM52 · EST

Confidence

Reasonable confidence.

Exceptions

Conservatories on noisy or polluted roads where ventilation is impractical

Next step

Open the home planner

The trade-offs

Every choice gives you something and asks for something back.

The choice

What you get

What you give up

External roof and side shading
You get
The largest single drop in solar gain, a usable room for most of summer and no running cost.
You give up
Visible change to the structure, planning conversation in some areas and £1,500-£5,000 depending on size.
Replace polycarbonate roof with insulated solid or warm-roof system
You get
A room that works year-round, lower heat loss in winter as well as lower gain in summer, and a building you can heat properly.
You give up
Building Regulations involvement, a five-figure cost in many cases and several weeks of disruption.
Air conditioning unit
You get
Guaranteed cooling on the worst days and the ability to keep the room usable in heatwaves.
You give up
An outdoor unit, ongoing running cost, F-Gas servicing and the awkward truth that you are cooling a room designed to collect heat.

Real homes that faced this

Publicly documented UK projects that ran into the same problem and reported what happened.

We did not run these projects. Each links back to the original publisher so you can read the figures in context and judge for yourself what carries over to your home.

How we'd approach this

Stop the heat at the roof; cool the room only if you must.

If this were our conservatory we would start by accepting what it is. A glass box on a south-facing wall is, by design, a solar collector. No amount of internal shading or fan capacity changes that. The honest first question is whether to stop the heat at the roof or convert the room into something else.

External shading is almost always the right next step, and a warm roof is almost always the right longer-term one. Internal blinds are a comfort placebo; they shade your eyes, not the room. We would rather live with one more hot summer and do this properly than spend money on the wrong layer of the problem.

We would treat air conditioning here as the answer of last resort, and only after shading. Cooling a room built to collect heat is an honest losing trade in the long run, and the running cost will tell you so every August.

Evidence behind this page

Every recommendation on this page is traceable to its source. Click a publication to read the original.

Building standards
Used because these are the codified design standards UK building services engineers work to; they are written by the profession for the profession.
- Building Regulations; Approved Document O (Overheating)
- CIBSE TM52 (Limits of thermal comfort)
Professional bodies
Used because these organisations publish independent consumer and technical guidance rather than product marketing.
- Energy Saving Trust

Products that may help

Only consider these once the checks above have been ruled out. A product fitted into the wrong cause is rarely satisfying.

House Summary

The cheapest answer to conservatory unusable in summer is usually the one that addresses the cause rather than the symptom. The list above is in the order we would work through it, because the checks at the top tend to rule out the most expensive mistakes further down.

Related decisions

Next Best Step

Air Conditioning; the UK guide

Take the next step