Window frames and glass in dormers

uPVC window frames

uPVC window frames are the most frequently chosen variant in dormers. They are low-maintenance, well-insulated, and available in many colours. For most terraced houses, uPVC frames are more than sufficient. With high-quality profiles, U-values are around 1,1–1,3 W/m²K.

Wooden window frames

Wooden window frames have a warm appearance and connect well with older homes or monuments. The downside: they require periodic painting. Species such as meranti, accoya, or oak are common.

Aluminium window frames

Aluminium window frames are slim, strong, and modern. The insulation value is excellent with thermally broken profiles. However, they are usually more expensive than uPVC or wood. Often chosen in architectural projects where the profile deliberately needs to be thin.

Fixed window, casement window, tilt-and-turn window

Fixed window

No ventilation, only daylight and a view. Cheaper and with the highest insulation value due to the lack of moving parts.

Casement window

Can be opened for ventilation. Classic, but nowadays less common than tilt-and-turn.

Tilt-and-turn window

Combines turning (fully open) and tilting (ajar). The tilt position provides continuous ventilation without having to open the window entirely.

Combinations

A combination often works best in a dormer: one tilt-and-turn window in the middle or on the side, with fixed parts for the rest.

HR++ glass

HR++ glass is double glazing with a low-emissivity coating and noble gas filling. Standard for most new builds and renovations. U-value around 1,1 W/m²K. Good price-quality ratio.

Triple glazing

Triple glazing is triple-pane glass, with a U-value around 0,5–0,7 W/m²K. Insulates better, but weighs about 50% more. The frame and connection must be able to handle this weight. Especially interesting for large glass surfaces or if there is noise nuisance.

Safety glass and fall-through protection

Safety glass

Toughened or laminated glass that is less likely to produce sharp shards when broken. Recommended in places where people could fall against the glass.

Fall-through-safe glass

Mandatory when the parapet height is lower than a certain measurement and someone could fall outward through the glass. A professional determines this based on the actual dimensions.

Ventilation setting and grilles

A tilt-and-turn window with a ventilation setting or a ventilation grille in the upper part of the frame enables the necessary continuous ventilation. With high-quality profiles, this can be done without significant draught issues.

Maintenance

• uPVC window frames: occasional cleaning, no painting.
• Wooden window frames: painting every five to ten years.
• Aluminium window frames: virtually no maintenance.
• Fittings: lubricate moving parts annually with suitable oil.
• Seals: check for hardening over time and replace if necessary.

Choice based on the room's use

• Bedroom: tilt-and-turn window with good sound insulation.
• Study: combination of a fixed window plus a tilt-and-turn for fresh air.
• Bathroom: as much fixed glass or frosted glass as possible, with separate ventilation.
• Playroom: fall-through-safe glass naturally.

Profiles, fittings and connection

A window frame only performs properly when the profile and the connection to the structure are also right. Three technical points that are often only briefly described in quotes:

• Number of chambers in the profile. A five-chamber profile insulates noticeably better than a three-chamber one at the same depth.
• Reinforcement profiles. Broad uPVC frames have a steel core in the mullions; without this core, wide tilt-and-turn windows will sag after a few years.
• Connection to the wall. A frame finished only with PU foam and sealant will eventually create leaks and thermal bridges. It should sit on a compriband or EPDM strip, with airtight taping on the inside and vapour-permeable taping on the outside.

Always ask for the structural connection details on a drawing with every quote. A supplier who cannot deliver these often doesn't know them either.

Fittings and operation

The fittings (hinges, locks, mushroom cams) determine how long a window will continue to operate smoothly. Important points:

• Burglar resistance according to SKG: one star is domestic burglar-resistant, two stars is standard for new builds, three stars for increased risk.
• Multi-point locking with mushroom cams locks the window at multiple points simultaneously — a serious barrier for burglary via a dormer.
• Concealed fittings: hinges built into the frame, no visible steel on the outside.
• Operating height. A tilt-and-turn window in a dormer with a high parapet must also be operable by shorter residents — an operating rod or electric motor is often a wise choice.

Colour, flashing and detailing

Aesthetics are not a secondary issue for a dormer that makes the entire upper floor visible from the street. Points where regret most commonly arises in practice:

• Dark colours (anthracite, matter black) look modern but heat up more; usually acceptable with triple glazing and a good frame, risky with standard profiles.
• Glazing bars inside the glass (Wiener Sprossen) match well with 1930s homes; they can be disruptive in modern architecture.
• A slim profile provides more glass surface and daylight, but insulates slightly less than a wide profile with the same Uw-value.
• The detail between the window frame and the fascia board determines the street view; ask for a drawing of the transition before you sign.

You choose a window frame for at least thirty years. Twenty extra minutes spent on this detail often saves thousands of euros in later corrections.

Frequently asked questions

Brief answers to frequently asked questions on this topic.

What is the best material for a dormer window frame?

For most terraced houses, uPVC is an excellent choice: low-maintenance and well-insulated.

Is triple glazing always better?

In terms of building physics, yes, but the heavier weight requires a suitable frame and connection.

When is fall-through-safe glass mandatory?

With a low parapet height where someone could fall through the glass. A professional assesses this per situation.

What is a Uw-value?

The combined heat transfer coefficient of the frame and glass together.

How long do wooden window frames last?

With regular maintenance, easily thirty years or more.

What can I do about noise nuisance?

Glass with asymmetrical pane thicknesses, good sealing, and possibly triple glazing help significantly.

Is a tilt-and-turn window standard?

Increasingly so, especially in modern dormers.

Which colour should I choose?

Often tailored to the facade's appearance. Dark colours are popular but heat up faster.

What are window panes or glazing bars?

Profiles on or inside the glass that create the appearance of multiple smaller panes.

Can I replace my glass later?

Yes, glass can be replaced in existing frames, provided the frame can accommodate the new glass thickness.

Summary

The window frame and glass largely determine the appearance and performance of a dormer. uPVC, wood, and aluminium are the main choices; HR++ and triple glazing are the standard glazing options. Safety and fall-through-safe glass come into play in specific situations. The best combination depends on use, colour, noise load, and the connection to the rest of the home.

Conclusion

Invest in good window frames and good glass. A dormer with perfect insulation but a mediocre frame performs worse than a dormer with average insulation and a top-quality frame. Request quotes that explicitly mention profiles, U-values, and glass choices, so you are comparing apples to apples.