How to Design an Extension House

Updated July 20, 2017

The most common type of extension house is the two-story side extension, but there are many more to choose from. There are many issues to consider when building extensions, but the moment you decide to build one, its design should be a major consideration.

Because the extension will affect neighbours, most municipal governments will not allow an extension of more than the ground-floor level.

Brainstorm and discuss with an architect, a builder and other affected parties, all aspects of the building. Where should the extension be? How big should it be? What functionality do we want? Even if you do the construction yourself, professional advice is still important.

Make the first sketches and draw the rooms you want to build. Consider such things as plumbing for the bathroom and/or the kitchen, electricity for the whole extension, gas pipes for heating and cooking.

Locate the windows in places that bring the most amount of sunlight in, but privacy should also be considered in the design layout.

Check whether the extension will affect the load-bearing walls in the original house. Choose the materials carefully, considering the original house and other things such as cost.

Decide on the style for the interior of the extension.
Make the final designs and hand them over to the building team. This means the designs should be done in such a way that the contractors should be able to follow every detail.


Finding a qualified architect is the best option because a trained architect can add vision and give professional insight. When building an extension, it is important look at the whole house, including the gardens, the relationship with the neighbours and the surroundings and not just the extension. Architects have been trained to have an expert understanding of such relationships. When an extension is on an old building, one should look for the key traits of the original design and should try to incorporate the two. However, with some creativity, it is possible to blend different designs, such as glass on timber-framed houses. In the design of an extension house, the materials should be properly chosen and it should be such that in case there is need for repairs later on, the material can be readily found. Cost is a factor. Security should also be considered.


Read the local bylaws with regard to extensions in your area. Consult the professionals, even if you will do the actual building yourself.

Things You'll Need

  • Architectural tools and resources such as drawing papers and implements
  • Sample materials
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