Watch out for covenants within your house deeds.

If you add a home extension that needed approval from a person or company mentioned on your house deeds as a covenant and you failed to obtain written approval or acceptance, then you may find it impossible to sell your property on to new owners in the future.

Many properties have conditions as covenants as to what you can install on the site.  These are usually installed by the original land owner or the developer and are meant to be reasonable restrictions to prevent you doing something undesirable to your property that may put off buyers of neighbouring properties for example.  Sometimes previous intermediate owners can add additional restrictive covenants into a properties deeds.  Examples could be additional access rights for a neighbouring property or perhaps a neighbour has connected a drain from an extension that needs to be maintained.

Many homeowners extending their homes never even check the deeds usually because the main deeds are not easily to hand by being with the bank or building society. Some solicitors may have taken copies within their files.  It really does pay to check the house deeds BEFORE extending your home. 

The restrictions of a covenant can be in the form of activities on the site.  A common one is to prevent the keeping of chickens or other livestock that was common place between the wars.  In the post war building boom this was now seen as an undesirable past time that could affect house sales on a housing estate.

Another more modern covenant is with regard to future development of a site.  If a previous home owner felt that their large garden or side area of land may have development potential in the future and didn't want to miss out on this opportunity during their lifetime then they would include for a new covenant within the house deeds.  This can, however, adversely affect a properties value & desirability.

When a restrictive covenant needs to be discharged or complied with , you will normally be required to apply to the person or their estate handling agent (usually chartered surveyors) in writing and pay their reasonable administrative costs.  Many homeowners see these costs as being punitive or unreasonable so it is not unusual to try and negotiate on their suggested fees.

I am told that the approval of a  restrictive covenant cannot be unreasonably withheld so often it really is just a matter of writing in requesting written approval & paying a fee.

Some home owners who have a restrictive covenant on their properties that require consent for the works proposed often hit a brick wall by being unable to locate the previous controlling person usually due to the age of the restriction and the people having passed on without a future estate. 

Provided the homeowner can prove that they made every reasonable attempt to comply with the covenant approval, then it is normally acceptable to carry on with the works without receiving formal written approval but you are advised to seek legal advice from a solicitor first.

Sometimes you will need to purchase an indemnity insurance to cover any adverse eventualities just in case.  This is often required simply to appease future purchasers or their lenders.

Therefore you need to check your house deeds that there are no relevant covenants that need to be discharged or complied with that would prevent or restrict you from building your home extension.