Sainsbury's Home Insurance has found that a fifth of homeowners plan to take advantage of the new rules, with 1.3 million planning loft or roof conversions while 950,000 will build a rear extension.
The new rules aim to strike a balance between freeing homeowners to make improvements and limiting the size of an extension so that neighbours are protected.
The Government has launched a new interactive guide to help people establish whether they need to seek permission for a planned extension.
Other changes mean that people putting in driveways or parking areas of more than five square metres will be exempt from planning permission only if they use materials that allow water to soak through into the ground. This will reduce surface water run-off and help prevent flooding.
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