Ask a tradesman


How much for a second storey extension where there is already a loft conversion?

We have just bought a 4 bed detached house and one of the bedrooms is a loft conversion above the garage. We would like to extend over the garage and square off the second floor. This would create usable space of approx 22’ x 7’3 which would be divided into two rooms; one bedroom to the front and a family bathroom at the back. The existing bathroom would be converted to an ensuite to bedroom 1.

The garage was built approx 12 years ago though I think it’s only a single skin on the outside. It runs along the side of the house and there is a dining room at the back. I’m expecting that the foundations are in place as hopefully these are required for the loft conversion anyway. I’m also hoping that the floor structure is already in place for a full storey, though it'll need raising as it has been lowered because of the low pitch.

Can anyone give me a ballpark figure for this please to take it up to the point of carpeting and decorating. We have a number of projects we want to undertake but if it's the difference between being able to extend this year or next, we'll wait on the others.

We haven't applied for planning yet so ideas of the costs of doing so and timescales to get this underway would also be very helpful. We are in the Southampton area. Many thanks.

We would also consider adding dormer windows to the pitched roof if there will be a problem with planning.

1 Answer from a MyBuilder Extension Builder

Best Answer

Loft conversions have little structural weight impact, so the walls or foundations of the garage will not have been taken into account with Building Control, but the floor joists will have. But, floor joists are in any event extremely cheap and easy to get right. If the garage is 12 years old, it is very likely to have adequate foundations and walls to carry the weight of an extension above. Building Control may well require a test hole to check the foundations. There are usually no planning issues for an extension above a garage. Neighbours tend to object but in fact, this does not matter in regards to planning for this, only front and back second floor extensions matter. Dormer windows at the back usually have no planning issues, they sometimes do at the front. In terms of costs, quotes will span roughly 1K to 1.5K/m2 depending on many things including quality, location, whether this is to full finish (ie painted, electrics, everything) or just the main building work. Planning permission will take 2 months. Building Control approval takes a few days. It will take maybe a week to draw up the plans needed for planning approval, maybe 3 weeks for the plans needed for Building Control approval, although they can be done by the same surveyor. Hope this all helps.


Paul Albright


Answered 25th May 2015

Post your job to find high quality tradesmen and get free quotes

Can’t find an answer? Ask a new question

Question Categories