Refurbishing existing buildings has particular cost implications.

As with all refurbishment schemes, a big obstacle to overcome in residential refurbishment/conversion is to actually understand how the existing building works.

This is further complicated in residential refurbishments as there are more interfaces and tolerances to manage than in an office refurbishment, for example.

It is easy to underestimate the difficulty of making a new residential layout work in an existing building.

A successful scheme needs a careful balance between minimising expensive structural alterations and achieving optimum unit sizes and layouts to maximise value.

Achieving the most appropriate unit sizes and an efficient net-to-gross ratio is a particular challenge.

The choice of material needs to be carefully considered. Expensive stone and joinery, and even plaster, can sit uncomfortably on retained walls that are out of alignment.

An early decision has to be made whether to respect the existing building lines or to spend more money by lining and levelling walls, ceilings and floors.

Undertaking the necessary surveys is essential.

Developers must also consider how to achieve Part E (acoustic), Part L (energy) and Part M requirements in the development.

Achieving the current sound reduction requirements in an existing building can be difficult. Retained floors, often timber or hollow clay floors, and existing walls create the challenge of achieving suitable acoustic properties without affecting the all-important floor-to-ceiling height or impacting on the net area of flats.

Installing services within existing buildings is a huge challenge. Invariably the buildings were not originally designed to accept comfort cooling or other IT, data and security services. Co-ordination can lead to significant cost and time delays.

All residential developers look to differentiate their product and offer a wide choice of unit mix and size. With refurbishment schemes, repetition in layouts can be difficult.

Careful attention needs to be made to the bathroom and kitchen layout and dimensions.

Finally, residential schemes require a greater level of resources from the contractor and trade contractor in managing the workflow and numerous subcontractors involved, in order to achieve the required level of quality and completions.

The biggest impact of all this is on preliminaries where we have seen spending in the 10%-15% range for new-build developments, rising to as much as 25% on refurbishment projects.