How to Maximise a Building’s Potential Nett Lettable Floor Area:



  1. Introduction
  2. Improve Nett Lettable Floor to Gross Area Ratio
  3. Internal layout
  4. Structure
  5. Extensions and roof additions
  6. How we can help
  7. Further Reading


In the current economic climate, with many buildings standing empty and tenants moving to find cheaper rents, it is can be difficult to see how investing in a refurbishment can pay dividends.

However, increasing the competitiveness of your portfolio may be a very smart move. Increasing the efficiency, amenity, and resource use of a commercial building may stop existing tenants looking elsewhere and it may attract new tenants to the building.

The Spring 2013 Invbrief report by Gerald Eve, shows that total return of UK commercial property in the first quarter of 2013 stood at 1.1%, up from 0.8% in the previous quarter, and saw rental yields rising for the first time in two years in the central London office markets. The report goes on to say, “…a significant proportion of any future investment flow will continue to emanate from foreign investors. In fact, recent survey evidence has indicated that foreign investors now own over half of the office stock within the City of London”. This statistic highlights the appeal of London as a commercial centre, regardless of local pessimism. The report summarises that, “…investment flow will remain targeted towards the prime central London markets, although transaction levels may fall in 2013 reflecting the scarcity in the availability of prime quality stock”. This comment highlights the need for much of the existing building stock requiring investment.

To ensure that your existing commercial property appeals to new and existing tenants and investors, it is critical that potential is maximised, which is turn maximises the return. There are a number of key areas that can maximise a building’s potential and return:

Improve nett lettable floor area to gross ratio by rationalising cores and reducing ancillary spaces.

Replace older building services installations with modern, efficient systems, to reduce energy consumption and carbon emissions.

Improve the environment and well being for potential building occupants.

Upgrade existing facilities to meet current standards, i.e. to ensure access for all, provide DDA compliance, etc.

In this article we focus on ways to improve the nett lettable floor area, as this can often provide the biggest return when letting a building.


Improve Nett Lettable Floor to Gross Area Ratio

When looking to increase the nett lettable ratio of an existing building we first need to think about the constraints imposed by the existing building. These constraints may be a result of the design methods used when the building was constructed, the structural frame (whether steel or concrete), the floor-to-floor height, the column spacing, loading capacities or current layout restrictions.

Typical areas that can be addressed include the structure, external walls and roof, mechanical, electrical and IT systems, hazardous materials (asbestos, lead, etc.), security and a review of safety issues.


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Internal layout:

Most older buildings have unused space, either through badly designed circulation spaces or excessively designed service shafts. It is often assumed that the existing service shafts and cores (lifts, toilets and entrances) are difficult to change. In reality it is these areas that are usually upgraded when a building is refurbished, giving the perfect opportunity to alter the floor plate layout.

These areas are more often common parts within a building, and thus do not provide any specific rental returns. This raises the question of how to make these spaces, in particular lobbies, circulation and toilets, more efficient. The two main enhancements are:

Change the layout and access of the toilets to make them part of the floor demise and thereby part of the rental return. Although this can have a negative spatial effect as each floor then requires male, female and disabled toilets, which can take up more area that the existing arrangement.

Rationalising common areas to substantially reduce the physical area that lobbies, circulation and toilets take up, therefore releasing prime nett lettable area back to the floor demise.

Making the common parts of a building part of the tenants demise is not always a desired approach, but a thorough review of the existing core layout, along with some lateral thinking in terms of space planning, can reduce the physical area taken up, improve the usability of the spaces, while improving the accessibility to facilities under DDA.


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Structure :

When considering a refurbishment of the existing building thinking about maximising the current footprint may provide the best return, or rearrangement of tenant demises within a building will provide more flexible spaces, or spaces that can more easily be split into smaller units.

When dealing with existing buildings, the relocation of a core will most likely involve a structural alteration, not least with new riser locations for the services, or new lift shafts, but the advantages of the new layout will create spaces that are appealing to new tenants, while installing new DDA compliant lifts within an old building will provide the accessibility that is a requirement of the modern office building.

Older buildings in particular often have load-bearing walls within their footprint that, with current requirements for open plan office layouts, will not provide the flexibility that a potential tenant may require. It is usually advantageous to consider removing these structural elements. The removal of a structural spine wall for example is easier when carrying out a whole building refurbishment, although it is also feasible when doing it floor by floor, but the complexity of installation and disturbance to existing tenants is a more difficult task to manage.

Another structural alteration that is often feasible, although fairly costly, is the redistribution of floor levels, in particular when converting old warehouses or retail units where there is a tendency to have higher floor to ceiling heights on the lower floors and lower ones on the upper floors. This arrangement often leads to lower rental yields for the upper floors. By redistributing the floor levels to create an even floor to ceiling height not only benefits the upper floors in terms of rental yields, but also the lower floors by reducing the heating and ventilation requirements for spaces that are too high. This kind of conversion is generally considered when an existing building cannot be demolished due to planning legislation or a financial review deems that the costs associated would be cheaper than a new build construction.



Extensions and roof additions:

In addition to internal alterations there is always the option of adding extra floor area by extending either outwards or upwards. The recent changes in permitted development allow extensions to be built that increase existing the floor area by up to 25% without the need for Planning Permission, although other restrictions apply . Local authorities are usually fairly amenable to extensions in the right circumstance.

A new extension to a building could purely provide additional floor space, or it could be used to provide a new entrance, freeing up the existing internal space for lettable floor space. As space surrounding a building is not always available, adding a new storey to the top of the building is another solution. This will immediately increase the nett lettable floor area of your building by as much as the existing floor area immediately below, and is usually a relatively straightforward proposal.

The biggest hurdle to overcome with this type of extension is making sure the existing structure can accommodate the additional loadings that will be imposed upon it, although with a proactive structural engineer there is always some solution available.


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How we can help:

As can be seen there are a variety of ways to increase the nett lettable space of an existing building, although not all options are suitable for all buildings. At Harvey Wright Architects we can assess a building and providing economically viable solutions and carry out feasibility assessments before any long-term commitment is undertaken.


Further reading:

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