January20 , 2022

    Extension: Find the best contractor for your project


    Extension: Find the best contractor for your project

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    Do you want to create extra space outdoors? But don’t you see moving? Then choose an extension. On this page you will find more information about the costs of an extension, the types and you can read more about the different parts of an extension.

    Construction prices

    An extension increases your living space and increases the value of your home. On average, an extension of 3 meters deep by 5 meters wide costs €16,000 to €25,000. The price strongly depends on the construction method. Do you opt for a prefab or custom construction? View the table for the average prices.

    Type of extensionCosts of prefab construction Costs of prefab construction
    Default€16,000 – €20,000€19,000 – €23,000
    Classic/Modern€18,000 – €22,000€21,000 – €25,000

    Extension or extension

    Construction and extension are terms that are often confused. When building an extension, a separate space is created, such as a garage or utility room. An extension provides an enlargement of an already existing space. The costs of an extension or extension are very similar.               

    Custom or Prefab

    Do you want to have the extension installed as soon as possible? Then choose a prefab construction. Do you want to personalize your extension? Then opt for a custom construction.

    Prefab construction

    Do you want as little disruption as possible from a renovation in and around your house? Then opt for a prefab extension. A prefab extension is quickly installed. It is built in a workshop or factory. This ensures that it is installed within 1 day. A prefab extension cannot be completely adapted to your wishes. However, there are many varieties available. Do you have specific wishes? Then opt for a custom construction.


    The custom construction and finishing of the extension is built at your home. Construction will take longer than installing a prefab extension. In addition, the price of a custom construction is higher. With a custom construction you know for sure that your construction wishes are fulfilled.

    Wooden extension

    A wooden extension is cheaper than a masonry extension. This is due to the light frame. The foundation and building construction need not be as strong. A wooden extension is also available as a prefab extension. Do you want a unique wooden extension that gives your home a rural look? Then opt for customization.

    Bay window

    Do you want to give your house more charm? Then choose a bay window. A bay window is a closed extension of a facade. Bay windows bring more light into the room by allowing the facade to protrude 1 to 1.5 meters outwards. Bay windows can be found at both the front and back of the house. Keep in mind that you need a permit to build a bay window at the front of the house. View the table for bay window prices and dimensions.

    Bay window widthBay window depthTotal average costs (including labor and VAT)
    3 meters1 meter€ 4,300
    3 meters1.5 meters€ 6.300
    4 meters1 meter€ 5,600
    4 meters1.5 meters€ 8,400
    5 meters1 meter€ 7,000
    5 meters1.5 meters€ 10,500

    The construction process of an extension

    This is probably the first and last time you will have an extension installed. You will therefore be faced with many choices. It is important to maintain an overview during the entire building process. Below you will find the step by step planning for the realization of your extension.

     Step 1 – Preparation

    Prepare yourself well for construction. Think and sketch what your extension will look like. Check with the municipality whether you are allowed to expand and what the rules are. Discuss with the neighbours what they think about the extension. They have the right to object.

    Think about how big your building needs to be. Do you want a prefab or custom construction? What material is the frame made of? And do you like having extra light in your extension? Then choose to have a skylight installed. Later in this article we will zoom in on various attachments.

    Step 2 – Architect

    Do you have specific wishes for your extension? Then hire an architect. You will receive a tailor-made design for your situation. Ask your architects for examples of extensions. That way you get new insights. Do you have any special wishes? Then the contractor will take the measurements.

    Step 3 – Request quotes

    Request quotes from various contractors. Compare quotes on price, call-out costs, quality marks, warranty, reviews and delivery time. You can save a lot of money by comparing quotes. Choose the contractor that suits you best.

    Step 4 – Permit

    Applying for a permit from your municipality can take up to 3 months. In some cases it is also necessary to apply for a demolition and environmental permit. Applying for a permit is not always necessary. Ask your municipality for the current rules. Later in this article we will zoom in further on permits.

    Step 5 – Financing

    Financing an extension with your own money is fine. Isn’t that so easy? Then see if it is possible to finance the construction by means of a mortgage. It is quite possible that you; can withdraw money from your current mortgage, take out a second mortgage or convert your mortgage. 

    Step 6 – Contract

    Is the financing in place? Then conclude a contract with your architect and contractor. It is important that agreements made are on paper. This way there are no misunderstandings during construction.

    Step 7 – Planning

    Your contractor will make a plan. It is important that you keep an eye on things. This way you are aware of any delays or problems.

    Step 8 – Build

    When designs have been made, permits have been received and agreements have been laid down in a contract, it is time for construction. The duration of construction differs per type of construction and contractor. Do you opt for a prefab extension? Then it is possible that construction will be completed within 7 days. A custom construction takes an average of 2 to 6 weeks.

    Step 9 – Delivery

    Carefully examine the extension upon completion. Check the entire construction together with the contractor. Have all the jobs listed in the quote been completed? Now is the time to make agreements with the contractor. If the extension is completely to your liking, it is time to enjoy your new living space.

    Types of construction
    Types of construction

    Types of construction

    Do you already know how you are going to expand your house? An extension provides more space in your living room or offers space for an extra large kitchen. Keep in mind that with a kitchen extension many pipes have to be moved. Do you want more light in your home? Then go for a glass conservatory .

    Placing an extension is a large project that can sometimes take several weeks. First of all, the foundation will be take placed. Then the specialist will break open the facade and build the new walls. The new facade finds its new place and the roof closes the construction. Read on for more information about different parts of an extension.


    A foundation ensures that walls do not crack and the extension does not sag. Based on the type of soil under your house a choice is made for the type of foundation. Does the soil consist of clay and peat? The weight of the extension will then rest on piles. Is your house on a sandy bottom? The foundation will then consist of concrete.

    The price of the foundation depends on the type of foundation and the size. On average, a foundation costs € 2,000 to € 4,000.

    Windows in your construction

    The most commonly used materials for frames are plastic, wood and aluminium. Plastic has a long lifespan of an average of 50 years. In addition, this type of frame is very maintenance -friendly. Hardwood frames last an average of 40 to 75 years. Softwood frames last an average of 15 to 25 years. Wooden frames require more maintenance, a new coat of paint is need every few years. Aluminium windows last an average of 40 years. The windows require little to no maintenance. View the table for differences between the frames.

    Plastic framesWooden window framesAluminium frames
    Value for money++++ ++
    Maintenance++ + +++
    Security (burglary-resistant)++ ++++++
    Style and color (the frame type has a versatile design)+ ++ +++
    Environmentally friendly++ +++ ++
    about 50 years
    -Hardwood frames: 40 – 75 years
    -Softwood frames 15 – 25 years
    about 40 years

    Glass for your extension

    Use good insulating glass in your extension to save on energy bills. Choose the popular HR++ glass for good insulation. This type of glass has the best price-quality ratio. HR+++ insulates even better, but has higher price per square meter. View the prices per type of glass per square meter and the annual cost savings.

    Type of glassAverage price per m2 incl. VAT and assemblyAnnual cost savings for a home with 20m2 of glass
    insulating glass€ 115€ 140
    HR+€ 125€ 220
    HR++€ 130€ 260
    HR+++€ 170€ 280

    Roofing for extension

    The most common roofing material on an extension is bitumen. This type of roofing costs an average of € 45 per square meter. The bitumen roofing lasts on average 20 years.

    Would you like a greener roofing? Then choose to cover your roof with mosses, succulents or ornamental grass. A green roof is easy to realize. Make sure that the substrate consists of EPDM or bitumen. In addition, the angle of inclination should not exceed 45 degrees.



    Do you like natural light in your home? Then choose to install a skylight. A dome provides a lot of light. An opening skylight also provides a lot of fresh air in your home. You have the choice to opt for insect screens and electric control with a folding dome. The electrical control makes it possible to open the dome at the push of a button. Opt for an anti-burglary grille so that crooks can’t get in as easily. View the table for dome prices.

    DescriptionAverage costs
    Standard Dome€100 to €200
    Ventilating dome€400 to €500
    Anti burglary grid€200
    insect screens€100 to €150
    Electrical control€300

    Extension options

    Would you like electricity in your extension? And do you want to get it right? The contractor will charge additional costs for this. View the table below for prices.

    OptionAverage price
    Central heating (incl. radiator)€1,000
    carpentry work€300

    Construction permit for extension

    Before you start designing, take a good look at the building regulations in your municipality. It is not always necessary to apply for a construction permit . In some situations you may build without a permit.

    Placing an extension at the back of your house is often exempt from permits. Provided that the extension is not deeper than 4 meters and higher than 5 meters. Use the permit check of the Ministry of Infrastructure and the Environment. An extension to the front or side of your home almost always requires a permit. Please note: always ask your municipality for the current rules. Rules may differ per municipality.

    Tip: Sometimes you need a permit for other activities. For example, you may need a permit to cut down a tree or build a driveway.

    In some cases you are obliged to report demolition work to your municipality. In cases of asbestos removal or more than 10 cubic meters of demolition waste, you must notify the municipality. The municipality may require a demolition permit. The municipality is obliged to do this on the basis of zoning plans or the Monuments Act. 

    Do you live close to water? Please contact the Water Board in your region. Even if you build without a permit, it is still possible that permission from the Water Board is require.

    Construction specialists
    Construction specialists

    Construction specialits for extension

    Designing and building an extension is a specialist job. Specialists will help you with this. Based on your wishes, a beautiful extension will be built that increases the living space.

    Quality marks specialists

    Do you want to be sure that you are dealing with good contractor? Contractors with this quality mark have at least 2 years of experiences and have been checked for quotation, delivery and creditworthiness. In addition, these specialists are in possession of the correct diploma and insurance. Did something go wrong during constructions? And can’t you agree with the contractor? We helps you to solve the problem. An independent body will look into the problem and provide advice.

    Construction tips

    • Building material – Building an extension costs an average of 25,000 kilos of building material. On average, the price of this material is €10,000. Do you want to save money? If it is possible to order material yourself, so you save a lot of money.
    • Contractos – Request different quotes from contractors. They calculate the costs for your construction. In addition to the price, you can also compare the call-out costs, quality marks, reviews, delivery time and guarantees.