Since introducing the service almost 10 years ago, our surveyors at Peter Barry have valued hundreds of loft spaces on behalf of leaseholders, freeholders and sometimes both when there is a share of freehold or they get along. We have probably clocked up over a thousand party wall awards covering loft extensions and have noticed an increase in the desire of flat owners to extend onto roofs and create outside space, especially when that flat has non to begin with.
The process and methodology is very similar to that of the loft extension, but one that is worth its own blog given it’s subtle differences.
Whether you have the right to extend onto an adjacent roof will depend on the wording of your lease as it is very rare for the leaseholder to own such spaces and have the right to develop it without paying a premium to their freeholder.
If none is payable, it is only the freeholder’s costs for the license to alter that need to be covered.
Where a premium is payable, it will need to calculated on the basis of marriage value in a similar but often more straight forward fashion to that of a loft space.
Proposed Valuation minus
Existing Valuation minus
Build costs and professional fees equals
Profit: split 50/50
With a loft space valuation there is usually sales data for before and after but in reality there is rarely reliable data for flats with and without terrace extensions which means the Valuer will have to make a subjective uplift based on the existing value and their experience.
You should always consult an architect who will advise you on feasibility and planning permission. Creating a scheme that does not overlook neighbouring properties can be a challenge. The Party Wall Act will need to be considered if the terrace will be over the flat below.