Loft conversion with ridge raising — what is possible?

When is your loft a 'habitable space'?

The Bbl (Dutch Building Decree) distinguishes between habitable space (where you structurally stay: bedroom, living room, study) and circulation or storage space (hallway, stairs, cupboard).

For a habitable space, the minimum requirements are:

• Floor area: at least 5 m² per room.
• Headroom: at least 2.1 metres over a minimum width of 1.5 metres (usually not a problem after a ridge raising).
• Daylight: minimum 10% of the floor area as window area (provided it faces open outdoor space).
• Ventilation: minimum 6.5 dm³/s per person (to be achieved via a window + mechanical ventilation).
• Fire and escape route: escape route via stairs within the required time to a safe place.

If you deviate from this, the space will formally be listed as a 'storage loft' in the WOZ (property valuation) — which means your gained m² will not count.

Bedroom or children's room

Most common application. Points of attention:

• Minimum 8–10 m² for a single bedroom, 12–14 m² for two people.
• Daylight via skylight or dormer — Velux or a dormer of 1.5–3 metres wide.
• Sound insulation for the floor (rock wool between joists + floating screed) keeps noise away from the bedroom below.
• Cupboards integrated into low sections — lost space becomes storage.
• Heating: extra radiator or underfloor heating. Sometimes recirculation of existing central heating.

For children's rooms: think ahead (10+ years of stay). Sufficient sockets, internet cable, space for a desk and bed.

Second bathroom in the loft

A second bathroom is nice but structurally the most complex option:

• Water pipes and drainage must go vertically down through existing floors. Check beforehand if this is feasible.
• Drainage for shower / toilet requires sufficient fall (1–2 cm/m) — sometimes a macerator system is needed (Sanibroyeur).
• Heavier ventilation: mechanical extraction with direct exhaust to the outside. Otherwise, you will get moisture and mould.
• Central heating boiler or heat pump sometimes too light — check if a second shower can supply hot water simultaneously.
• Waterproof floor with sealing tape + tiles.
• Count on € 10,000 – € 18,000 extra on top of the ridge raising itself.

Study or hobby room

Often the easiest and cheapest application:

• No extra water pipes or drainage.
• Daylight via skylight or small dormer.
• Internet: run cables beforehand (wired is faster and more stable than Wi-Fi through joists).
• Extra socket group advisable — laptop, monitors, lamp, printer.
• Acoustics: Timber frame construction (HSB) and insulation wool are naturally acoustic-friendly. Provide acoustic panels for video calls if necessary.

An average study in the loft is ready for € 1,500 – € 3,500 extra on top of the ridge raising.

Smart layout — three principles

1. The staircase is decisive. The place where your stairs end up determines the layout. Plan the stairs where you lose the least habitable space (often above the existing stairs). 2. Low corners have a function. Beds, cupboards, or desks fit under the sloping parts — do not waste them. 3. Concentrate water on one side. Bathroom, washbasin, and possible toilet together above the existing soil pipe — saves considerably on installation costs.

Make a layout drawing including furniture before the renovation. Many people only discover during construction that their bed does not fit due to a roof pitch.

Frequently asked questions

Short, honest answers to frequently asked questions.

Does my new loft count towards the WOZ?

Only if it is formally a habitable space (Bbl: headroom, daylight, ventilation). Request a revaluation after the renovation — the extra m² work to your advantage when selling.

Can I make two bedrooms in one loft?

Often yes, provided you have a width of ≥ 6 metres. Every room ≥ 5 m² (Bbl) and its own daylight. A light cove or transom window makes layout easier.

May my loft be used as a rentable studio?

Only with a separate front door, private sanitary facilities, and an independent meter cupboard. In most municipalities, planning permission for property subdivision is also required. Ask the municipality explicitly.

What if I do not have a second staircase?

An escape route via the existing stairs is usually acceptable, provided the fire resistance (60 minutes) is in order. The fire brigade recommends smoke alarms on every level.

How do I arrange daylight in a children's room?

Two Velux skylights of 78×118 cm already provide over 1.8 m² of glass — for a room of 12 m², that is 15%, well above the Bbl requirement.

What does floor insulation do for sound?

A layer of rock wool between the joists plus a floating screed (10 mm rubber foil + chipboard) reduces impact sound by 15–25 dB. An audible advantage compared to a direct floor.

Is a sauna or bath possible?

Yes, but count on extra structural calculations (weight of the bath) and a heavier central heating/heat pump. Discuss in advance with the contractor and structural engineer.

Summary

With a ridge raising, you open the door to a bedroom, children's room, study, or bathroom in the loft. The freedom is great, provided you meet the Bbl requirements for daylight, ventilation, and headroom. A study is the cheapest (€ 1,500–3,500 extra), a bathroom the most expensive (€ 10,000–18,000). Plan the stairs, water, and daylight in advance — then you will truly get the most out of your new floor.