When do you need an extension drawing?
An extension lengthens an existing space of your home, such as the kitchen or living room, with a connecting volume at the rear. For virtually every extension, a construction drawing is needed: either to apply for the environmental permit, or to give the contractor an accurate guide for the execution. The drawing shows how the new space relates to the existing home, which materials are used and how the roof connects to the existing roof.
Common situations where an extension drawing is needed:
- A continued kitchen or living room at the rear of the home.
- An extension with a flat roof and a large sliding door towards the garden.
- Enlarging a too-small eat-in kitchen in a terraced house or 1930s home.
- An extension in which the existing facade is broken through for an open connection.
What does an extension construction drawing include?
A complete extension drawing consists of floor plans of the existing and new situation, facade views of the relevant sides, one or more cross-sections and a site plan. The floor plans show the continuous lines from the existing space to the extension, including the position of frames, doors and any structural adjustments such as an opening.
The facade views show the extension from the rear, with materials, colour and the position of the sliding door or French doors. A cross-section shows the height of the extension, the roof build-up and how the extension connects to the existing facade. On the site plan are the plot boundaries, distances to the neighbours and a north arrow.
Permits and permit-free building
An extension at the rear of the home can be carried out permit-free if it falls within strict conditions of depth, height and distance to the property boundary, as laid down in the Buildings (Living Environment) Decree. The maximum depth depends on the size of the rear garden and the existing main building. For extensions that exceed these rules, or for extensions on the front or side facade, an environmental permit is needed.
Even if the extension is permit-free, it is often assessed whether the structure complies with the Building Decree: insulation, fire safety and daylight access. A professional drawing helps to make this demonstrable and gives the contractor a guide to build the extension in accordance with the rules.
What does an extension construction drawing cost?
An extension construction drawing is available from €400 including VAT. The final price depends on the size of the extension, the complexity and the extent to which we can build on existing drawings. An extension with a simple rectangular floor plan and flat roof can be drawn faster than an extension with a bend in the facade, a pitched roof or an opening in the existing load-bearing wall.
For an extension with an opening in a load-bearing wall, a structural calculation is often involved. This is not part of the standard drawing, but we can put you in touch with a structural engineer who connects to this.
Common pitfalls with an extension
The most common mistake with an extension is underestimating the rules around the rear-garden area. Not every part of the garden counts as rear garden, and so not every extension is automatically permit-free. The height of the extension is also often underestimated: a flat roof does not automatically have to be at 3 metres and the surface area of outbuildings on the plot counts towards the maximum permitted building.
In addition, many people opt for extra wishes at the end of the process, such as a larger sliding door or a glass skylight. These choices have consequences for the structure and the building physics. By making these decisions before the drawing, you avoid revision rounds and extra costs later in the process.
