The short answer
Many conservatories with polycarbonate or standard glass roofs become uncomfortably hot in summer because direct solar gain through the glazing raises the internal temperature rapidly. The problem is worst with south- or west-facing conservatories and polycarbonate roofs. Solar-control glass, good ventilation and external blinds all help significantly. See conservatory roof options and are conservatories cold in winter for the full thermal picture.
Overheating is the most common complaint about conservatories in the UK, and it is a genuine and well-understood problem rather than an inherent flaw in the concept. A south-facing conservatory with a polycarbonate or old glass roof can reach temperatures of 40–50°C on a hot summer day — well beyond comfortable. The physics are straightforward: glass and polycarbonate transmit short-wave solar radiation easily, but once that energy is absorbed by the surfaces inside the conservatory it re-radiates as long-wave heat, which glass traps. This is the greenhouse effect. The practical response is to reduce solar gain, increase heat dissipation, and where necessary provide shading.
Summer overheating at a glance
- Main cause Solar gain through roof glazing
- Worst orientation South- and west-facing conservatories
- Worst roof type Polycarbonate or uncoated glass
- Best fix at build Solar-control glass roof
- Retrofit option External blinds or roof film
- Best long-term fix Solid roof conversion or well-specified glass
Why conservatories overheat
The physics of conservatory overheating are simple. Solar radiation — the direct energy of sunlight — passes through glass and polycarbonate relatively freely, warming the surfaces and air inside. Those surfaces then re-emit the energy as longer-wave infrared heat, which does not pass back through glass as easily. The result is a rapid and substantial temperature rise on sunny days. The problem is compounded when the glazing covers a large proportion of the roof, as in a conservatory, because the solar energy collected per unit of floor area is high. A polycarbonate roof is particularly bad because it has a high solar heat gain coefficient and poor insulation value, so the conservatory heats up fast and the small amount of insulation value in the material provides no buffer.
Solar-control glass — the most effective solution
Modern solar-control glass uses a metallic coating applied to the glass surface to reflect a portion of the incoming solar energy before it enters the conservatory, while still transmitting natural light. A good solar-control glass can reduce solar heat gain by 30–60 % compared with standard double-glazed units, which makes an enormous difference to peak summer temperatures. The performance is measured by the Solar Heat Gain Coefficient (SHGC): a lower value means less heat admitted. When specifying a new conservatory or replacing a roof, ask installers for the SHGC of the glass they are proposing — values below 0.3 represent good solar control. Self-cleaning coatings on the outer surface are an additional benefit that reduces maintenance.
| Roof type | Solar control | Summer heat | Noise |
|---|---|---|---|
| Polycarbonate | Poor | Very hot | Loud in rain |
| Standard glass | Moderate | Hot | Quieter |
| Solar-control glass | Good | Warm | Quieter |
| Solid tiled roof | Excellent | Comfortable | Excellent |
Ventilation — essential for all conservatories
No matter how good the glass specification, a conservatory that cannot ventilate will still overheat. The general rule of thumb from the Glass & Glazing Federation is that ventilation should represent at least 5 % of the floor area — a combination of roof ventilation (roof windows or vents in the ridge) and low-level ventilation (opening windows or doors at ground level). Natural cross-ventilation through low-level openings and roof vents is the most effective passive cooling mechanism in a conservatory. Roof vents in the ridge or the rear slope of a lean-to roof are particularly effective because hot air rises to the apex and can escape directly. If the conservatory was built without adequate roof ventilation, retro-fitting roof vents is one of the most cost-effective upgrades available.
Blinds — practical but limited
Conservatory blinds — particularly external roof blinds or pleated internal roof blinds — can reduce solar gain meaningfully and are often the most practical retrofit solution for an existing conservatory. External blinds are more effective than internal ones because they intercept the solar radiation before it enters the glazing and heats the air inside. Internal blinds still allow the glass to heat up, which then radiates back into the room. Bespoke roof blinds are expensive (£200–£500 per blind panel is common) and require periodic maintenance, but for a conservatory in otherwise good condition they represent a significant comfort improvement at lower cost than a roof replacement. Avoid cheap adhesive window films on the interior of the glass — some can void glass warranties and cause thermal stress cracking.
The longer-term view: a solid roof conversion
If summer overheating is severe and the conservatory is important to the household, the most effective long-term solution is a solid tiled roof conversion. A solid roof eliminates solar gain through the roof entirely, dramatically reduces summer temperatures and typically makes the space comfortable year-round. It also greatly reduces noise in rain. The cost is typically £7,000–£15,000 for a medium conservatory — see conservatory roof replacement cost — and it changes the structure’s legal classification, so check building regulations requirements. This is general information, not a technical specification; consult a qualified conservatory installer to assess your specific structure.
Want a conservatory that works year-round?
Getting quotes from installers who can specify solar-control glass, roof ventilation and blinds — or a roof replacement — lets you understand the options and costs for your conservatory.
Frequently asked questions
Why does my conservatory get so hot?
Solar radiation passes through the glass or polycarbonate roof and heats the air and surfaces inside. The glass then traps the re-radiated heat. Poor or no ventilation makes it worse. Solar-control glass, roof vents and blinds all help reduce peak temperatures.
What is the best glass for a hot conservatory?
Solar-control glass with a low Solar Heat Gain Coefficient (SHGC) is the most effective glazing solution. Look for SHGC values below 0.3 for good solar control. Self-cleaning coatings also help reduce maintenance.
Do conservatory blinds help with heat?
Yes, particularly external roof blinds, which intercept solar energy before it enters the glass. Internal blinds are less effective but still help. Blinds are a practical retrofit option for an existing conservatory with an old polycarbonate or plain glass roof.
Should I replace my conservatory roof to stop overheating?
A solid tiled roof conversion is the most effective solution and also reduces rain noise significantly. Solar-control glass is a good intermediate step. Get a quote for both options and compare against the cost and how you use the space.
Sources & further reading
- Glass & Glazing Federation — conservatory ventilation guidance, 5 % floor area rule and solar-control glazing standards
- FENSA — glazing energy performance standards and solar heat gain coefficient guidance
- GOV.UK — Building Regulations Approved Document L, conservatory thermal performance and exemption conditions
- LABC — Local Authority Building Control guidance on solid roof conversions and building regulations
This is general information about conservatories and orangeries in the UK, not planning, structural, legal or financial advice. Costs are typical illustrations only and are not quotes for any specific project; actual prices vary with size, site conditions and your chosen installer.