Windows are the primary entry point for heat in residential rooms. South-facing exposures are particularly critical in summer: the high solar elevation angle at midday maximises thermal gains through the glazing. For vulnerable people — the elderly, infants, patients with chronic conditions — excessive heat in a bedroom poses a genuine health risk, made even harder to manage without air conditioning.
This concern affects a large share of France's housing stock: according to INSEE data (2020 census), approximately 74 to 75% of dwellings in metropolitan France have no air conditioning. The priority, therefore, is to reduce solar heat gains at the source — by treating the glazing.
Why South-Facing Rooms Are Most At Risk in Summer
In metropolitan France, the sun reaches its highest point in summer, with a solar elevation at the June solstice exceeding 65° in Paris and 70° in Marseille. This geometric configuration means that south-facing façades receive maximum solar radiation at midday — precisely during the hottest hours of the day.
Standard untreated clear double glazing has a g-value of approximately 0.62 to 0.70, meaning 62 to 70% of incident solar energy enters the room. In a south-facing bedroom with 2 m² of glazing, this represents a heat input of several hundred watts during a summer day — the equivalent of a high-output electric heater running continuously.
The thermal mass of the bedroom (walls, floor, furniture) absorbs this heat and releases it gradually, keeping temperatures elevated well after sunset — including during sleeping hours.
Solar Control Film: A Direct, Reversible Solution
A solar control film applied to the south-facing bedroom window significantly reduces the g-value of the glazing-plus-film assembly. For example, a film with a TSER (Total Solar Energy Rejected) of 60% reduces the g-value of a reference double-glazed unit from 0.80 to 0.40 (source: Solar 50 C technical data sheet, Solar Screen). That represents approximately a 50% reduction in solar heat gains compared to the same glazing without film.
Dynamic thermal simulations on comparable cases indicate reductions of several degrees in operative indoor temperature, depending on wall thermal inertia and the area of glazing concerned.
Specific Benefits for Tenants and Carers
Solar control film has characteristics particularly suited to the needs of vulnerable people and their carers:
No building work, no planning permission: the film is applied to the interior face of the existing glazing, with no modification to the window frame or façade. In the vast majority of cases, installation requires neither prior declaration nor landlord approval (check the specific clauses in the tenancy agreement).
Reversible: the film can be removed without leaving lasting marks on the glazing, distinguishing it from permanent solutions such as window replacement.
Lower unit cost than air conditioning: cost per square metre of glazing is significantly lower than the combined cost of an air conditioning unit, installation, and annual electricity consumption.
Transparent: high-VLT solar control films (Visible Light Transmission above 60%) do not substantially alter the room's brightness. The view to the outside is preserved — important for the psychological wellbeing of people with reduced mobility or receiving home care.
Additional Measures Without Installation
Solar control film fits within a broader summer heat management strategy, which also includes:
- External shutters or blinds if available: close during the day on exposed façades, open at night for ventilation.
- Night-time ventilation: air the bedroom between 22:00 and 07:00 when outdoor temperature drops below indoor temperature.
- Air humidification: a fan combined with a misting spray can improve thermal comfort without air conditioning.
For health precautions during heatwaves, consult the recommendations published by Santé Publique France.
To find the most suitable solar control films for a south-facing residential bedroom, explore the Solar Screen residential solar film range with full technical data and application guidance.
For a deeper look at summer comfort solutions for apartments without air conditioning, the Solar Screen article on the best solar film for a south-facing bay window covers the selection criteria by exposure type.