Choosing custom-made windows and doors for your home means weighing up several technical factors, each of which can have a very different impact on everyday comfort. Frame thermal performance, glazing type, compatibility with existing ventilation: each criterion matters differently depending on the layout of your home. Understanding these differences helps you avoid an investment that is poorly suited to your needs.
Uw value and solar factor: the indicators that set windows and doors apart
Two technical values determine the actual performance of a custom-made window. The Uw thermal transmittance coefficient (expressed in W/m².K) measures how much heat passes through the frame and glazing as a whole: the lower the Uw value, the better the insulation. The solar factor (Sw) indicates the proportion of solar radiation transmitted indoors.
| Material | Indicative Uw value | Solar factor | Maintenance |
|---|---|---|---|
| PVC | Among the lowest | Varies depending on glazing | Very low |
| Aluminium (with a thermal break) | Slightly higher than PVC | Varies depending on glazing | Low |
| Wood | Naturally high-performing | Varies depending on glazing | Regular (stain, paint) |
| Wood-aluminium composite | Comparable to wood | Varies depending on glazing | Low on the outside, regular on the inside |
The table highlights a point that is often underestimated: the solar factor depends primarily on the glazing selected, not the frame material. A PVC frame fitted with solar-control double glazing and an aluminium frame with the same glazing will have a comparable Sw value.
A specialist workshop such as menuiserie-airaines.fr tailors these frame-and-glazing combinations to the requirements of each opening, helping you avoid paying for a level of performance your home does not need.
Window airtightness and ventilation: a balance not to be overlooked
Installing highly airtight new windows in an older home can create a problem that product catalogues rarely mention. By eliminating unwanted air leaks around old frames, natural ventilation in the home is sharply reduced. If there is no mechanical ventilation system (MVHR) or it is undersized, indoor humidity rises, encouraging condensation on the glass and mould in corners.
Before ordering custom-made windows and doors, checking the condition of the ventilation system is an essential technical step that should not be postponed. Self-regulating air inlets built into the top rails of windows help refresh the air, but they are no substitute for a properly functioning mechanical ventilation system.
- Check the extraction rate of the existing mechanical ventilation system (or confirm that there is none) before approving the window and door quote
- Plan for air inlets in the windows of dry rooms (living rooms, bedrooms) if the home uses assisted natural ventilation
- Make sure the window installer includes the air-inlet modules in the custom-made frame, as some models offer them as an optional extra
This is what distinguishes a well-designed replacement project from a simple frame swap. High-performance windows and doors in a poorly ventilated home can worsen indoor air quality rather than improve it.
Facade orientation and summer comfort: choose glazing to suit each opening
Not all the windows in a home receive the same amount of sunlight. A south-facing opening receives intense sunlight that is relatively high in the sky during summer, making it easier to block with a roof overhang or a sunshade. East- and west-facing facades, by contrast, catch the low sun in the morning and late afternoon, which is much harder to filter with a simple roof overhang.
Custom glazing should therefore be selected according to orientation. Enhanced solar-control glazing is well suited to west-facing openings, where summer overheating is most pronounced. On a north-facing facade, the same glazing would unnecessarily reduce natural light in winter.
External solar shading (shutters, awnings, adjustable external louvres) is still far more effective than internal blinds. An internal blind lets through heat that has already passed through the glazing, whereas external shading intercepts solar radiation before it reaches the glass.
PVC, aluminium or wood: which material for which custom-made windows and doors?
PVC dominates the residential market thanks to its balance of insulation and price. However, its rigidity limits the size of openings: beyond a certain width, the profiles become thicker and reduce the glazed area. For large sliding doors, aluminium offers slimmer frames with equivalent structural strength.
Wood retains natural thermal and acoustic properties that synthetic materials replicate by adding chambers or insulating foam. Regular maintenance (staining or painting every few years) remains the main drawback for homeowners looking for minimal upkeep.
- PVC: suitable for standard-sized windows, budget-friendly, with some of the best thermal insulation on the market
- Aluminium: ideal for large openings, custom colours and slim profiles
- Wood: preferred in heritage areas or when sound insulation is a priority
- Wood-aluminium composite: combines the thermal performance of wood on the inside with the durability of aluminium on the outside
The material alone does not determine the final quality. Construction, precise measurements and installation are just as important to performance as the choice between PVC and aluminium. Poorly installed custom-made windows and doors lose a significant proportion of their insulating capacity, whatever the material.
Replacing windows alone does not automatically improve an energy performance rating or dramatically reduce energy bills. ADEME considers this work a priority mainly when existing windows have single glazing and deteriorated frames. Combining window replacement with a ventilation check and glazing selected to suit each orientation is the approach most likely to deliver a measurable improvement in comfort.
