Extensions and loft conversions could add nearly a quarter to the value of homes

Meanwhile, there are warnings that misunderstandings over the new planning regulations changes could lead to thousands of illegal extensions

In an analysis of the value of improvements made to an average three-bedroom house, a report from Nationwide found:

* Creating an extra bathroom could add 6 per cent to the value

* Adding another double bedroom can raise the value by 12 per cent

* Building an extension or loft-conversion to create a double bedroom and en-suite bathroom could add 23 per cent to the value

* Increasing floor space by 10 per cent can add 5 per cent to the average value

Robert Gardner, Nationwide's Chief Economist, said: "With housing market demand still very weak, increasing numbers of homeowners may opt to improve rather than move. Our research assesses the factors that affect the value of homes, and the potential to add value. Having more useable space is generally thought to be consistent with better quality accommodation and people are prepared to pay for it."

However, the Society of Licensed Conveyancers (SLC) has warned that many home owners could find themselves in breach of building regulations, if they misinterpret the temporary relaxation around rules for domestic extensions.

Far from kick starting the economy, the SLC fears that a lack of clear communication about the obligations for homeowners wanting to extend their home could end up costing them thousands of pounds if they fail to secure the necessary building regulations approval.

John Clay, Chairman of the SLC said: "It is very important for home owners to understand that these recent changes do not simply allow you to press ahead with a planned extension if it falls within the new permitted dimensions. You are still required to secure building regulations approval. Failure to do so could result in the council later requesting that you take down your extension - a costly and easily avoidable scenario, if you ensure you secure the necessary permissions up front."