A double storey extension is a great opportunity to maximise the value of building an extension to your home.
If you are planning on building a single storey extension the addition of an extra storey does not mean double the cost.
You only have to complete one set of foundations and one roof, which collectively account for about 30% of the total cost. The extra cost for an additional storey is the first floor structure, additional first floor walls and fit out.
Similarly, it won’t take twice as long to build. The construction programme will probably be 3-4 weeks longer than a single storey but more crucially it doesn’t mean twice as much mess!
The most common double storey extension takes advantage of the spare space left behind an attached garage and building over it. Re-modelling an open plan family kitchen extension can be easily combined with a new master bedroom and luxurious en-suite bathroom.
Depending on requirements it is often more difficult to successfully plan the interior layout of an extension than it first appears. The best designs integrate new rooms with old with a seamless transition and the whole house remains balanced.
In some instances though bad design can result in ‘rabbit runs’ between new areas and old where no consideration has been given for how spaces will be used and relate to the existing house.
If your home was built post war the existing garage structure and foundations are likely to be suitable for building off. However, the foundations will need to be exposed for inspection by building control to confirm this. If not it may be easier to knock the garage down and dig new foundations. Generally, it is a lot more time consuming and therefore costly to dig out and under pin existing foundations.
With most extensions careful consideration must be applied to the impact of the design on the original house both inside and out. With a double two storey extension this is especially critical.
Sometimes you can over extend a house consequently looking too big and squeezed in between neighbours. It is usually good practice to step new facades back from the original to provide definition and reduce the impact of an extension. In this instance the street scene will remain balanced.
In other situations a double storey extension can actually provide symmetry and balance compared to the original house. Stepping the extension back could be more detrimental.
In all cases though the proposed design is subjective and should be determined on individual merit.