What is thickening a dwelling (opdikken)?
Thickening — in Dutch opdikken — is enlarging a dwelling or housing block by moving the façade outward so that the dwelling becomes deeper. In practice this is often done by enclosing an existing balcony and adding it to the living room.
Thickening belongs to the toolkit of housing improvement, alongside topping up (adding a storey on the roof), amalgamating and subdividing. Where topping up goes upward, thickening goes outward. Both create more or larger dwellings within an existing block without demolition.
Why thicken?
- More generous dwellings — post-war gallery and stair-core blocks often have cramped living rooms; a few metres of extra depth make a real difference to how the flat works.
- Energy improvement in the same move — you are effectively building a new external envelope, so insulation, airtightness and new windows can all be done in one go.
- More sustainable than demolition — the structure, foundation and services are largely retained.
- A new elevation — the intervention is at the same time an architectural upgrade of a dated block.
Points to note
- Capacity and foundations. Extra floor area means extra weight. A structural engineer has to assess whether the existing structure and foundation can take it; this is often the deciding factor.
- Daylight. A deeper dwelling receives less daylight at the back. A larger opening in the façade compensates only in part.
- Regulations and consent. Increasing the building volume touches the building line, the zoning plan, and requirements for daylight, ventilation and fire safety. Expect to need planning permission.
- Occupied or vacant. Thickening can partly be carried out from outside, which limits disruption — but the moment the existing façade comes out is always disruptive.
- Junction with the existing floor. The level difference between the old balcony and the living room floor has to be resolved, including insulation and a junction free of cold bridging.
Related terms
- Roof extension
- Adaptable building
- Planning permission
- Zoning plan
- Cold bridge
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