CBS Renovation · house extensions in het Gooi
Single-storey and two-storey extensions as one project: from survey and drawings through foundation, roof and glazing to heating, finishing and the garden.
An extension usually starts with a ground floor that no longer fits the way you live. A single-storey rear extension can make room for a proper kitchen-diner, or a living room extension can push the room out towards the garden, with glass doors onto the terrace. Go up two storeys and the extension adds rooms upstairs as well.
Adding an extension to a house touches almost every part of the building work: foundation, brickwork or timber frame, roof, glazing, heating, electrics, plastering, floors and often the garden afterwards. We run it all as one project. You have one contact person from the survey to handover, and one itemised quotation for the whole extension instead of a separate offer from each trade.
Further down are three extensions we have built in Hilversum and Bussum, with what we did on each.
Extension built, kitchen enlarged, 3000 × 6090 mm skylight – see the project
Our projects
Each of these houses called for a different extension. The cards list what we did; the full story and the photos are on each project page.
Hilversum · 1955 house · 2024
Bussum · 1920 house
Hilversum · 1922 house · 2022
An extension is a small building set against an existing one: the work starts in the ground and ends back inside the house. These are the parts we carry out, roughly in the order they come up.
Every extension starts with a visit to your house. We look at where the extension will stand, the structure it will be joined to, the documents you already have and the technical options for what you have in mind. From that visit we draw up a plan of the work and an itemised quotation, with each part of the extension priced on its own line.
Whether a permit is needed depends on the house and on what you want to build, and we find that out before any work starts. Where a permit is needed, we prepare the drawings and file the application. For Meentweg 62 in Bussum, a 1920 house in a protected townscape, we prepared the architectural drawings, the structural calculations and the construction drawings, and filed the permit application.
The extension gets a foundation of its own, and the facade of the existing house is reinforced where needed. The walls are built in brick or as a timber frame, with the insulation going in as they rise. At Meentweg 62 the walls were insulated with PIR panels; in the 1955 house in Hilversum we also insulated the crawl space under the floor.
More about masonry
The roof is built up from its structure, insulation and covering, and the glazing is planned together with it. In the 1955 house we installed a skylight of 3000 × 6090 mm and made-to-measure French doors to the garden. At Eikbosserweg 210 the glazing turns the corner, with clerestory windows and a timber fascia, and at Meentweg 62 folding doors open onto the terrace.
More about insulation
A room with a lot of glass has little wall left for radiators, so underfloor heating is often the better fit. In the 1955 house in Hilversum we laid underfloor heating with automatic controls and renewed the electrics and the meter cupboard. At Meentweg 62 a heat pump with underfloor heating replaced a gas boiler from 2004. Cables and pipes go in before the walls are closed.
More about underfloor heating
An extension only feels like part of the house when the old and new rooms run into one another. We open up the rear wall, support it over the opening and finish the join with floors, plaster and paint. In the 1955 house in Hilversum the wall between kitchen and living room came out as well; at Eikbosserweg 210 we plastered the walls and laid new wooden floors.
More about flooring
An extension takes up part of the garden and changes the way you step outside, so the garden is often the last stage of the project. We lay the terrace outside the new doors and, if you wish, rework the rest of the garden. At Meentweg 62 in Bussum our work ran from the first drawings through to planting the garden.
More about garden design
Tell us what you want to tackle. After a survey at the property you receive an itemised quotation.
+31 34 679 40 57
Costs
What a house extension costs depends on where it is built, how complex the design is and which materials go into the structure and the finish. A straightforward single-storey extension stays closest to the starting price. Large areas of glass, a second storey, a complicated foundation or expensive finishes push the figure up.
A price per square metre is a starting point, not a quotation. After the survey you receive a written quotation for your house, with every part of the work on its own line: foundation, walls, roof and glazing, installations, finishing and, if you want it, the garden. You can then see where the money goes and what changes when you adjust the plan.
How we work
Six steps take an extension from the first visit to handover.
Step 1
We visit your house to see where the extension can go and how it will join the existing structure, and we talk through the technical options with you.
Step 2
You receive a plan of the work and a quotation with each part on its own line, so you can weigh up the choices before anything is fixed.
Step 3
Not every extension needs a permit. Where one is needed, we prepare the drawings and file the application, as we did for Meentweg 62 in Bussum.
Step 4
Building and finishing materials are ordered and delivered to the site. If you would rather choose and order some of them yourself, you can.
Step 5
We lay the foundation, reinforce the facade, put up and insulate the walls in timber frame or brick, and build the roof before heating and electrics go in. We report on progress as the work goes on.
Step 6
Your contact person stays the same until the extension is handed over, and the work we have carried out comes with our guarantee.
How we run every project, from the first visit to the handover, is described on our page about the working process.
From the survey to handover you deal with one person, and we plan the foundation, the walls, the glazing, the installations and the finishing so that each follows on from the one before.
After the survey you receive one quotation for the whole extension, with every part of the work on a separate line.
Our team counts 75 engineers and tradespeople and works six days a week. The structural work, the installations and the finishing of your extension are in experienced hands.
We give a guarantee on the work we carry out, on the extension itself and on what we do in the existing house.
Our roots go back to 1995, and more than half of our work comes from previous clients and the people they send our way.
Our office is in Breukelen, at Merwedeweg 5b, and we work across het Gooi and in the adjoining part of the province of Utrecht. The three extensions on this page are in Hilversum and Bussum. Wherever your house is, the project starts the same way: with a survey at the house, followed by an itemised quotation.
That depends on your house and on the extension you have in mind. The Dutch permit is called an omgevingsvergunning. We check whether one is needed before any work starts. Where a permit is needed, we prepare the drawings and file the application, so the paperwork stays within the same project and with the same contact person.
A house extension starts at around €600 per cubic metre, including materials and VAT. Measured per square metre of floor space, it starts from roughly €1,500. A simple single-storey extension stays closest to those figures; large areas of glass, a second storey, a complicated foundation or expensive finishes raise them. After a survey at your house you receive a written, itemised quotation.
With neighbours on both sides, a terraced house is almost always extended at the back, into the garden. The existing rear wall is then opened up, so the new room joins the house. Whether a permit is needed depends on the house and on the extension. During the survey we look at the rear wall, the space in the garden and how materials can reach the back of the house, and tell you what your house allows.
Yes, where the extension needs them. For Meentweg 62 in Bussum, a 1920 house in a protected townscape, we prepared the architectural drawings, the structural calculations and the construction drawings, and filed the building permit application. We ran that project from the first drawings through to planting the garden.
Yes. Meentweg 62 in Bussum is one half of a semi-detached pair from 1920, in a protected townscape. The house was first stripped out completely, and then we built a two-storey extension turn-key. The walls were insulated with PIR panels and the roof separately. A second storey gives you extra rooms upstairs on the same footprint and raises the price per square metre, which the itemised quotation shows.
Underfloor heating is a common choice, because a room with large glass doors has little wall left for radiators. In the 1955 house in Hilversum we laid underfloor heating with automatic controls and insulated the crawl space. At Meentweg 62 in Bussum the underfloor heating runs on a heat pump. Which system suits your extension depends on how the rest of the house is heated, and we look at that during the survey.
Our office is in Breukelen, at Merwedeweg 5b. We work across het Gooi, in towns such as Hilversum, Bussum, Naarden, Huizen, Blaricum, Laren and Eemnes, and in the adjoining part of the province of Utrecht, including Soest and Utrecht. Our team is at work six days a week, and every extension starts with a survey at your house.
No-obligation quote
After a survey at the property you receive an itemised quotation. One point of contact, from survey to handover.
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