Ask the Experts Grand Designs Q&A: June '09

Date Published:

07/05/2009

Subsidence Scare

I’m concerned my house might have a subsidence problem as there are a number of cracks that are increasing in size. Should I get some expert structural advice? If so, where do I start and what should I expect to pay?

Stuart Tappin replies There can be a number of reasons why buildings crack and factors such as the type of foundation, ground conditions, ground water and nearby trees can all have an influence. For a house founded on clay, an area of local settlement can often be traced back to a leaking water pipe or drain. A structural engineer should be able to make an initial assessment of the possible causes and, generally, some investigations are required. These could include a trial pit to examine the foundations and verify the ground conditions and a CCTV survey of the below-ground drains to check for leaks.

The best place to find help is at the Institution of Structural Engineers website (istructe.org), where you can search for an engineer by region and area of expertise. For an initial visit and a letter report you can expect to pay around £250 to £400.

I’m thinking of converting my garage into extra living space. I’ve seen there are several specialist garage conversion companies out there, but would I be better off using an architect? And do I need planning permission?

Peter Caplehorn replies It will depend on how complex your situation is. For a simple, non-contentious change then a specialist company is probably better. It will work to a formula in much the same way that loft companies offer a packaged service. If you have a more complex situation, however, either concerning building regulations or planning, an architect will be able to help you through the process more efficiently. They also may be able to add some original ideas. In either case, look at the work they have previously done, seek direct recommendation and try to discuss how they worked with some of their previous clients.

In terms of consent, planning permission will probably not be required, but building regulations will. There is a change of use and technically you are losing one car-parking space. However, unless there are significant changes to the elevations, most planning authorities will not press these issues unless you are in a conservation area or have a listed home. Check before you start, and remember that if you wish to increase the hard standing/paving in the front garden this will require consent. Building regulations approval will also normally be required to ensure that the structure, weatherproofing and thermal standards are correct. Garages will have a lower floor than the house and this should be made up with the addition of insulation deck and floor finish.

Ensure that water from outside cannot track under the floor, which may require a damp-proof course and brick plinth across the existing threshold. The walls and ceiling (if part or all of the roof is outside) will need insulation to bring them up to the required thermal performance.

If you are adding a window or converting the door, the new glazing will need to be thermally efficient, safe and secure. If you have an internal door, this will be fire resisting and self-closing, so you may want to change this or use a lesser spec. And finally, wiring and heating can be installed in the insulation zone, so plan this early in the project.

This edition of Ask The Experts is taken from the June issue of Grand Designs magazine. If you would like to subscribe for as little as £9 then head here to find out more.