Redesign with existing foundation - ideas

Good day!

New to this forum, I immediately have an extensive request for the community. We (wife + small child) recently bought a 980 sqm south-facing plot with an existing wooden shed and equipment hut. After last year mainly renovating and clearing out the house itself (wooden construction, built around 1900), the shed can be described as a nice summer retreat. While the electrical wiring (including high voltage) and sewer connection have been "renewed," the house has no heating except for an electric heater. It cannot currently be lived in all year round. I can attach photos of the condition of the house if needed.

For our future together in the countryside, the retreat should of course be upgraded and become our main residence. We have already had initial plans and cross-sections (by architects) drawn up to get a rough cost overview. That means 160 sqm living space with a low-energy house (timber frame construction) and partial use of the existing foundation (strip foundation). The first offers ranged from 160,000 to 320,000 euros, depending on the level of finishing. Without going into the details of the offers now, we do not want to build in this price range at first and rather plan to only slightly extend the existing foundation and then put up a nice timber frame (block) house. According to the structural engineer, the existing strip foundation (wall thickness about 30 cm) should be equipped with side braces and a base slab so that there is no weight-related obstacle to a timber frame house. Additionally, we want to add another part to the existing foundation to expand the current floor area from 40 sqm to about 60 sqm. My question to the experts in the group: Is such a foundation extension generally advisable and technically feasible? We have a partially cellar space in the old foundation which will remain. There could later be a wine cellar. The existing foundation is old but dry. Note: Inside, I completely exposed the wooden floorboards last year (they were covered with carpet) and sanded them. Nothing rotten or damp.

For the planned foundation extension, it will be necessary to demolish the old house and expose the foundation. When extending the foundation, does one need to set a complete or supplementary strip foundation, or are there perhaps alternatives? I know that such questions are not always easy to solve for "non-technicians" — if additional information is needed, I can of course provide it. I would be interested in general solution approaches that do not require the destruction of the entire existing structure.

Many thanks in advance for any opinions and help!

Best regards Thomas

Hello Thomas,

For the planned foundation extension, it will be necessary to demolish the old house and expose the foundation. When extending the foundation, does one have to set a complete or supplementary strip foundation, or are there perhaps alternatives? I know that such questions are not always easy to solve for "non-technicians" – if additional information is necessary, I can of course provide it. I am interested in principal solutions that do not require the destruction of the entire existing structure.

Whatever answers you expect or may receive here in the HBF: do not rely on the accuracy of the information under any circumstances!

You have rightly commissioned an architect – if he hasn’t told you yet, he certainly will – for your own safety, invest more money and commission a soil surveyor first and then a structural engineer. Based on the results of the soil survey, the structural engineer will tell you exactly how the extension is possible and – if yes – how it should be executed.

Kind regards