How far you may build differs per district and sometimes per street, and in a city on wooden piles the foundation has a say too. So before anything is designed, find out what is allowed at your address.
Three ways to add space
In Dutch you will see three words. An uitbouw or aanbouw is an extension on the ground floor, usually at the back to make a larger kitchen or living room. A dakopbouw is a roof extension: an extra storey or a raised roof on top of the house. A dakkapel is a dormer: a box-shaped window structure in a sloping roof that adds headroom and light to an attic.
Which one suits you depends on your garden, your roof and the rules for your street. A dormer is the smallest intervention; a roof extension adds the most space but also the most weight.
Rear extension: how deep can you build?
Nationally, a rear extension can be permit-free for the spatial part if it meets strict conditions. It must stand on the ground in the back garden, more than 1 m from public space, be no higher than 5 m and have no roof terrace or balcony. It is never permit-free on or next to a listed building, and in a national protected cityscape only at the back.
Amsterdam adds its own layer. In the West district an extension can go up to 2.5 m from the rear façade, not visible from the street, up to 5 m high, with at most half of the back garden built on and 60 litres of water storage per m². In Zuid a similar 2.5 m rule applies, but only in Plan Zuid and not in the part in De Pijp. In the city centre, the design code caps an extension at 3.00 m deep and 4.00 m high.
Because the rules differ this much, we never promise that an extension is permit-free. Run the Vergunningcheck on the Omgevingsloket for your address before a drawing is made.
Roof extension (dakopbouw)
A roof extension always needs a permit check, because it is not on the national list of permit-free building work; unlike a dormer, it is not permit-free on the technical side. In Amsterdam the design code usually follows a trendsetter: an earlier approved roof extension on the same block becomes the example to follow.
The Oost district has its own rules: a roof extension only on a flat roof, not visible from the front, at most half the size of the largest floor below and without a roof terrace on top. Betondorp, the Groene Staart and buildings the City rates as order 1 or order 2 are excluded. In an apartment building the roof is usually shared property, so you need your VvE's consent first.
Before a storey goes on top, a structural engineer checks whether the walls and foundation can carry it. For a house on wooden piles that includes a foundation investigation. That check comes before the design.
Dormer (dakkapel)
A dormer on the rear roof can be permit-free if it meets every condition. It needs a flat roof, a maximum height of 1.75 m, a bottom edge between 0.5 m and 1 m above the eaves, a top more than 0.5 m below the ridge, and sides more than 0.5 m from the edges of the roof.
At the front it is a different story. In the city centre, the 19th-century ring, the 1920s-1940s belt and the garden villages, Amsterdam's design code allows one dormer per home, only on a roof pitch of at least 30°, at most 30% of the roof width and in the city centre at most 2.00 m wide. Listed buildings always need a permit.
Daylight and your neighbour's view
A deeper living room is a darker living room, and Dutch building rules set a floor under that. The Besluit bouwwerken leefomgeving requires a minimum daylight area per habitable room; the exact figure sits in the table belonging to article 4.147 and depends on the room. Not every window counts the same: obstructions on your neighbour's plot are left out, and where your plot borders a road, water or public green space, the calculation runs to the middle of it.
Run that calculation before anything is drawn, because it can decide the depth of your extension or push you towards a roof light. When the sum falls just short, an extra roof window is usually cheaper than losing half a metre of floor.
Civil law adds a second limit that has nothing to do with the permit. Within two metres of the boundary you may not have a window, balcony or similar structure that looks out over your neighbour's land, unless they agree to it. A fixed, non-transparent window is allowed there. That is why the side wall of an extension is often closed or fitted with frosted glass.
Foundations, prefab and the build itself
A new extension settles differently from an old house on wooden piles. A structural engineer decides what foundation the extension needs and how it connects to the existing house, and the state of the house itself is checked first, so the new part is not tied to a foundation that needs repair.
Prefab is fast on site but needs a crane and a reachable garden. Many Amsterdam back gardens can only be reached through the house; then a traditional build is often the only practical choice.
The extension is closed up before the rear wall comes out, so your home is open for as short a time as possible. Your extension comes with a guarantee; the quote sets out the period and terms.