Widening or adding foundations costs roughly €250 to €600 per linear metre for a shallow strip foundation, and considerably more if piles are needed.
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Widening or adding foundations costs roughly €250 to €600 per linear metre for a shallow strip foundation, and considerably more if piles are needed. For an extension of 3 by 4 metres, that often comes to between €4,000 and €12,000 for the foundations alone. These are indications, price level 2026, including VAT. The soil, the depth and the structural engineer's advice determine the real price. So always ask for a tailored quote.
The most common reason is an extension: an extension, rear extension or conservatory needs its own foundations that connect properly to those of the house. Sometimes it is about strengthening, for example when an existing wall will carry more load from an extra storey or a new opening with a steel beam.
On one of our projects we opened up the rear wall of a detached house, propped it with steel props and poured reinforced foundations for the extension. You can see it in the house conversion with window and door frames.
The soil is the biggest factor. Around Zwolle it varies a lot: on the higher sandy ground a shallow foundation is often enough, while in the lower areas with clay and peat along the rivers piles are sometimes needed. A structural engineer decides, based on a soil survey, which solution is safe.
Depth, access for excavation and removal of soil also count. A narrow passage to the back garden often means digging by hand instead of with a mini digger.
What lies underground matters too. Old sewer pipes, cables or the remains of an earlier extension only appear once digging starts. A good quote therefore states which unforeseen items are and are not included, so you know where you stand.
First a structural engineer is brought in. They work out the loads and specify how wide and deep the foundations must be. Then we excavate, place the formwork and reinforcement, and the concrete is poured. Only when the concrete is strong enough does construction continue.
The connection to the existing house is important. In the first years, new foundations often settle slightly differently from old ones. The engineer specifies whether to tie the two together or keep them separate, so that no cracks appear in the wall later.
More background on foundations under an extension can be found in foundations under an extension. What the whole extension costs is covered in what an extension costs.
A foundation price is only reliable once the structural engineer has done their work. Shahiro first looks at your plan and the situation on site and arranges the next steps. That way you know in advance where you stand. The service itself is described under widening foundations. For the rest of the project, see house extensions.
Through our network of companies and self-employed tradespeople, we also arrange the excavation and the pouring. You keep one point of contact, from the first spade in the ground to the moment the walls are up.
For new or widened foundations, yes. The engineer determines the dimensions and reinforcement, and a permit application requires structural substantiation. Without that document, no contractor can give a responsible price.
That depends on the concrete and the weather. Building can often continue after about a week, but the engineer or supplier indicates when the concrete is strong enough. In frosty weather it takes longer.
Sometimes, but often not. A conservatory is light, while a brick or timber frame extension with an insulated roof is heavier. A structural engineer can assess whether the existing foundations are adequate or need widening.
Every job is different. After a no-obligation chat, and a visit on site where needed, you receive a quote tailored to you.
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