It is not correct to market the property as a 4 bed, if the 4th bedroom did not conform to building regulations at the time that it was converted.
'A Certificate of Lawful Existing Use or Development (CLEUD) is a certificate that is legally granted by a Local Planning Authority to retrospectively legalise a previously unauthorised development. Or to confirm development was carried out inline with an approved permission.'
This means that the planning authorities cannot required the building to be returned to it's previous state. What I do not know is what impact this has on the buildings insurance for the house.
What you need to ascertain is whether the construction was done in line with the regulations and approval was simply not sought at the time or whether the construction was not done correctly, and then.. how you feel about this.
from www.planningportal.co.uk/info/200130/common_projects/36/loft_conversion/3.
The regulations will be applied to ensure, for example:
- the structural strength of the new floor is sufficient
- the stability of the structure (including the existing roof) is not endangered
- safe escape from fire
- safely designed stairs to the new floor
- reasonable sound insulation between the conversion and the rooms below.
If the floor, roof stability, stairs and fire safety aspects are not sufficient, what is your attitude to the risk that in inherent in that. What are the potential costs associated with rectifying the work (usually similar to the costs of redoing the work from scratch if none of the usual remediation works were carried out.. could be significant if the roof space is not of adequate height). It may be that the existing structure is adequate, what I don't know is whether it is possible to determine that without significant work and damage.
Is the house priced as a 4 bed? Is there room to negotiate? When was the work done? Are there any records regarding the alterations?
Remember: There are plenty of old properties with bedrooms in the loft, steep stair cases and roofs that are supported by thin beams. What you need to consider is if you are prepared to pay the price you have agreed for a property that is not as described.
It is a really tough decision and the 'worst case scenario' (off the house collapsing and the repair costs not being covered by insurance) is very very remote. What is much more likely is that you will be faced with a similar problem when you come to sell, unless you choose to have the conversion redone or you market it as a 3 bed with extra space.