Having an extension built is a far greater undertaking than adding on a conservatory, but they involve similar planning.
When you’re designing the layout of the new space, consider how you will use the space when it’s finished and how that might change in the future.
Also, will have the extra room affect the way you use the rest of the house?
The reason you need the extra space will dictate whether you choose a single- or double-storey extension and its position on the site. If you can afford only one storey now but would like to build up later, make allowances at this stage with foundations and walls that can support the extra storey.
If the extension will include a kitchen, laundry, or bathroom, how easy will it be to connect into existing waste services, plumbing, and electrical supplies?
In a large extension, it may be more practical to install independent heating and hot water systems, rather than place an extra strain on the existing system.
Design the layout of your extension so that costs of providing new services are kept to a minimum.
An extension must function well, and it should look as if it has always been there.
Windows and Doors
If the existing style is not available ready-made, have matching window frames and doors (both external and internal) made by a local joinery.
Although you should be able to match the colour of bricks fairly closely, modern bricks may not be the same size as old bricks.
You may be able to find suitable secondhand bricks, but the cost could rule this out. If you are working with different sized bricks, avoid butting directly up to the existing brickwork. Even a slight recess will minimize the difference.
Slates and tiles can look conspicuously new for years. To achieve an instant weathered look, buy secondhand.
If this is not feasible, take old tiles from the least visible part of your roof and use those on the new extension. Put the new tiles in the less prominent position.
The pitch should match or be sympathetic to the existing slopes and angles of the roofline. A flat-roofed extension on a pitched roof house always looks like an afterthought.
If the location or your finances don’t allow for a proper pitched roof, raising the roof at an angle for four or five rows of tiles will soften the effect.
Alternatively, consider creating a roof terrace (take that decision early as it will affect construction).