Interior finishing of a dormer

Plasterboard

On the inside of the dormer, plasterboards are almost always mounted on the wooden frame. Standard 12,5 mm plasterboards are sufficient for regular rooms. In wet rooms like a bathroom, moisture-resistant green boards or cement-bound boards are a wiser choice.

Important points of attention:

• Fasten with plasterboard screws into the wooden frame, never with nails.
• Tape and fill seams for a smooth transition.
• Pass-throughs for electrics are cut out in advance.
• The vapour control layer must not be damaged during installation.

Plastering and ceiling

Plastering is usually applied over the plasterboards for a smooth and sleek final surface. There are three variants:

• Wallpaper-ready plastering — only seams and screws are filled; for those who want to apply wallpaper or paint themselves.
• Paint-ready plastering — a thin finishing layer that can be painted directly.
• Smooth-finish plastering — extra smooth, suitable for those who do not want wallpaper and only want to paint.

The ceiling of a dormer is usually plastered as well. In some cases, an acoustic ceiling board or an MDF board is chosen as a visual element.

Window sills

The window sill is a prominent visual element. Materials vary widely:

• Painted MDF — sleek, affordable, available in any colour.
• Wood — warm and suits traditional interiors.
• Composite or natural stone — luxurious appearance, high durability.

Practically, a radiator or a convector is often placed under the window sill. When choosing the window sill, take into account the width of the radiator underneath and any heat dissipation.

Knee walls

On the sides of the dormer, where the pitched roof slopes inward, knee walls are often placed. A knee wall is a vertical partition that covers the sloping space behind it. This creates:

• A neatly finished flat surface instead of an unused sloping triangle.
• Storage space behind the knee wall, often accessible via a small hatch.
• Opportunities for sockets or built-in cabinets in the knee wall itself.

The standard height is often around 1,0 to 1,3 meters. Lower is possible, but a lot of space will be lost.

Electrics: sockets, switches, and lighting

During the rough construction phase, electrical conduits are laid in the wall or ceiling. At that point, it must be decided where everything goes — adding them later often means breaking things open again.

Standard equipment

• Two to four sockets around the window frame and on the side walls.
• Ceiling connection for lighting, possibly multiple.
• Switches next to the door or at the top of the stairs.
• Network or data cable for home offices.

Lighting

In a dormer with a low ceiling, indirect lighting often works better than a central ceiling light. Recessed spotlights in the ceiling or LED strips above the curtain rails create ambiance without glare.

Heating and cooling

An attic room in a dormer can be heated in various ways:

• Radiator under the window sill, connected to the existing central heating.
• Underfloor heating in the attic, often combined with a new floor.
• Electric infrared panels as simple supplementary heating.
• Split air conditioning for a combination of cooling and heating, especially interesting for avoiding overheating in the summer.

Which choice is most suitable depends on the usage and the existing heating system.

Air conditioning and sun shading

For dormers on south- or west-facing facades, sun shading is almost essential. An exterior screen or drop-arm awning keeps the solar heat outside — much more effectively than interior sun shading.

In addition, some residents opt for a split-unit air conditioner to keep the bedroom or home office comfortable. The outdoor unit is placed elsewhere on the house, and the indoor unit is mounted on the attic wall.

Trim work

Narrow trim slats or profiles are often placed around frames and corners to neatly cover seams. With a "paint-ready" finish level, this wood is painted directly; with a "structural shell" (casco) finish, the bare wood remains visible until the occupant paints it themselves.

Other finishes that fall under trim work include:

• Corner profiles where the wall and ceiling meet.
• Skirting boards at the floor-to-wall transition.
• Built-in access hatches to the storage space behind knee walls.

Painting

The painting gives the dormer its final look. Usually:

• Walls and ceiling are finished with wall paint or wallpaper.
• Wooden frames and trim are painted with opaque lacquer.
• Skirting boards and trim are often painted in the same colour as the frame.

A light colour makes a small dormer visually more spacious; a dark colour instead creates a cozy interior.

Common mistakes

• Too few sockets planned.
• No connection for a network or wired lighting.
• Forgetting the vapour control layer around electrical pass-throughs.
• Knee walls that are too low, resulting in lost space and little storage capacity.
• Incorrect combination of radiator and window sill, leading to heat accumulation.
• No ventilation opening in a knee wall, causing musty air in the storage space.
• Painting before the plaster is fully dry.

Frequently asked questions

Brief answers to frequently asked questions on this topic.

What is included in a complete interior finish?

Plasterboard, plastering, window sills, trim work around the frame, knee walls, electrics, and painting.

Am I allowed to install the electrics myself?

Technically yes, but for safety and insurance purposes, a certified electrician is recommended.

Which materials are suitable for an attic bathroom?

Moisture-resistant plasterboards or cement-bound boards, combined with good ventilation.

How many sockets do I need?

For a bedroom, at least three to four; for a home office, six or more, preferably partly next to the desk.

Is underfloor heating a good idea?

In an attic usually yes, provided the existing central heating system can handle it and the floor structure permits it.

What should I choose for an attic bathroom: heat recovery (WTW) or mechanical extraction?

Both are possible, but mechanical extraction with humidity-controlled operation is often the simplest solution in practice.

How do I keep the plasterwork free from cracks?

Use a crack-bridging corner profile at expansion joints and ensure the structure does not shift (the trimmer joist and frame must be sturdy).

Which colour should I choose for the window frame?

Often the same colour as the trim work and skirting boards — a calm base makes the space visually larger.

How deep is a knee wall typically?

Between 30 and 80 cm, depending on the roof pitch and the desired storage space.

Can I add more sockets later?

Yes, but that requires breaking open walls and repairing the plasterwork. Thorough planning beforehand is much cheaper.

Summary

Interior finishing makes the difference between a wind- and watertight dormer and a space that truly feels like part of the home. Plasterboards, plastering, window sills, knee walls, electrics, lighting, and heating together form the finishing package. With a structural shell (casco), the occupant handles these steps themselves; with turnkey delivery, everything is provided.

Conclusion

A well-finished interior feels natural — as if the dormer has always been there. That result is no accident: it comes from careful planning beforehand (what goes where?), neat execution during the finishing process, and a finish level that suits the occupant. Taking the time for this phase ensures years of enjoyment from a dormer that requires no further attention.