Building a two-storey extension is a project that will completely transform your home, inside and out. Adding additional living space downstairs and a goodsized new bedroom upstairs can save you having to leave a location you love in order to gain the square meterage you and your family need.

A double-storey design might be added to the side, rear or even the front of a home and can be visually pleasing from the exterior, as well as improving the layout and functionality inside the property, on both floors.

But before you get started, it’s vital to understand the challenges as well as the possibilities and benefits of building a two-storey extension. We spoke to several architects and property experts to get their views on the costs and permissions involved, as well as whether they think it’s worth all the upheaval and hassle.

Q.1 Is it worth the spend and upheaval?

a ‘Extensions are often added when families are in flux, if kids are growing up and need their own space, for another baby, even sometimes if older generations are moving in,’ says Pereen d’Avoine, founder of architects Russian For Fish. Compared to a standard extension, a two-storey design can make a huge difference to a home. ‘The extra storey provides double the floor space, and allows for far more flexibility in room arrangement,’ says Pereen. It can provide the opportunity to rework the layout in a way that suits the way you want to use your home in the future.

It is, of course, a major investment. Building a two-storey extension typically costs a little less than a single-storey version on a per square metre basis since the foundations and a roof are common to both, and what’s extra are walls and floors. ‘Normally, the second storey adds only about 50% of the cost of the first, making it a more efficient choice for expanding space,’ says Rachel Moors, managing director of home transformation experts Adamsons.