A listed townhouse in Wassenaar received an entirely new basement level. We provided the design, structural calculation and building permit. The deep clay soil required a sheet-pile construction with a watertight concrete slab.
Illustrative blueprint view · existing situation, permit sketch, 3D impression and the delivered result.
The townhouse in Wassenaar is a national listed building. Every structural intervention requires an extensive permit procedure, including an advisory opinion from the Cultural Heritage Agency. The Wassenaar subsoil consists of heavy clay with a high groundwater level. A conventional basement approach with lightly shuttered walls was not applicable here: groundwater would have flooded the excavation immediately.
We designed a sheet pile screen around the excavation with a watertight cast concrete base. The structure was fully calculated, including the earth-retaining forces and the anchoring to the existing foundation. The construction drawings were tailored to the building permit application and the heritage advisory process. We coordinated the design in advance with the municipality and the Cultural Heritage Agency (RCE), which allowed the procedure to proceed smoothly.
The basement level provides 38 m² of dry living space, fitted out as a home cinema and storage room. The permit was granted within 12 weeks. The listed building has remained undamaged: all details at the existing foundation and retaining walls have been carefully documented. The contractor could start immediately with the complete drawings.
Key project details
What we delivered
A permit-ready drawing for a basement conversion starts at Tekenpunt from €595. The exact price depends on the scope and complexity; you receive a fixed price upfront with no additional billing. Request a no-obligation quote.
That depends on the type of intervention and the rules of the municipality of Wassenaar. We check the aesthetic review policy and the zoning plan in advance, so you know where you stand and your plan typically passes the review in one go.
We deliver the construction drawing within 0-3 weeks, or 0-2 weeks on an urgent basis. The permit procedure itself takes eight weeks for a standard application (Environment Act).
Whether you live in Wassenaar, Den Haag or anywhere else in the Netherlands: we handle design, structural engineering and permits from A to Z. Since 2016, 800+ projects. A no-obligation quote within 1 business day.