The design of a single-storey extension is the most important decision that you make when planning and costing your extension project, whether you’re building a conservatory, or extending your kitchen. The design will dictate cost and appearance, so it is worthwhile making sure that you are happy with the design, that it is cost-effective, and that it can increase the value of your property once it is finished. There are several decisions that must be made as part of the planning, to help create the space you want, and to create an extension that blends seamlessly into your existing house.

Decide On The Footprint

The footprint of a single-storey extension is usually determined by the space required within the property, but it will also be defined by factors like the proximity of neighbouring boundaries, the positions of any existing windows, and how the footprint is oriented towards light, views, and your garden.

Planning constraints will also be a factor you must take into account. Many smaller single-storey extensions will fall within the criteria for permitted development, and so may not need a planning application. Always check to make sure this is the case for your plans before you start, however, to avoid trouble later on.

At this stage, you must consider the roof design, especially the height of the ridge and how this will impact on existing windows on the first floor. Make these decisions early, so you can design them into the footprint of the space and create something that fits well into the space that you have available.

Choose The Roof

A smaller extension can usually be covered by a mono or duo pitched roof, but the spans that can be achieved with these are quite limited. A roof with a very low pitch might be an option, but this may not work aesthetically and could cause problems when trying to get planning permission.

In this case, there are only a few design options that will work well. You could choose a contemporary flat-roofed box, usually featuring a lot of glass, an orangery-style extension, or a traditional conservatory. Another option is a parapet roof. This roof design has an area of pitched roof around the eaves, which conceals a flat roof over the extensions, and gives the appearance of a pitched roof.

Spend some time looking into the different options so you can make the best decision.

Choose Doors and Windows

There aren’t many constraints on where you position your doors and windows in single-storey extensions unless you want to choose places that impact directly on neighbouring boundaries. Choose the size, style, and position of your doors and windows based on the architectural style of your extension. Don’t ignore the option to bring in lots of light from above, such as with roof lights.

Maximise The Opening From The Existing House

The wider and taller the opening is that links your existing house to your new extension, the more the two spaces will feel like one room.

Any new opening will need to be spanned by joists, which are usually made of steel, which will support the walls and the floor above. The size of the joist and its supports must be calculated by a structural engineer. The smaller and less visible these elements, the more seamless the flow between the old and the new parts of the building will be. In most cases, it is possible to completely conceal the joins within the ceiling void, especially if you are only removing a partition wall that isn’t load-bearing.

Create A Continuous Ceiling Level

The height of the ceiling between the new and old spaces should ideally be kept the same. If they are different, then the higher ceiling can often be brought down by adding new battens and plaster-boarding over the top.

Flooring At The Same Level

When you are setting out the floor levels for your extension, you should work backwards from the finished level of the floor in the existing property to make sure that the two will be identical once they are linked together. When you’re remodelling, rather than extending, any differences in the floor level be corrected by building up, often by using a quick-settling silicon floor screed. If you can’t easily get the same floor level, then it is better to create a full step. A small difference can easily become a trip hazard, so create a step.

Use Finishes To Match The Existing House

Old and new parts of the building can be linked seamlessly by using the same flooring material throughout the two spaces. This principle also applies to any architectural dealing, such as windows, doors, skirting, architraves and coving, and the same decor, such as colour schemes, flooring, curtains, and furniture.

In some extensions, you may want to create an extension that looks seamless, so choose the same (or as close as you can get) windows and other details of the rest of the house. In some cases, you may want the extension to stand out, for example, if you are trying to add a very contemporary extension to a more traditional house, then choose details that contrast, such as large panes of glass instead of a more classic window style.

The materials you use should match or complement the existing house too. If you want contrast, choose something that complements the original building, but will stand out against it, such as smooth white walls against older brick.

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