Architecture Feasibility Study

An architectural feasibility study investigates and evaluates the potential of a site or building. It is usually designed for the client or clients to inform them on the possibility of a site. It clearly sets out a brief history of the site, its overall condition and significance, as well as the constraints and opportunities. These are further detailed in the flowing sections:

Planning History



Cost / Value

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An architectural feasibility study investigates and evaluates the potential of a site or building.

Planning History

This research is normally done via a desktop study, looking at various websites / the local authority’s website.

The government usually issues The National Planning Policy Framework (NPPF) which sets out a framework for Local Authorities to base their Local Planning Policy.

Below is a list of key areas to consider when conducting this desktop research:

  • What local authority does the site belong to?
  • Have there been any planning application on the site previously? Approved, Rejected, in progress.
  • What does the Local Authority’s Local Plan Policy Map say about any restrictions on the site?
  • Are there any further restrictions to building / extending / demolition / alerting structures on the site?
Sometimes all this information cannot be found directly on the local authority’s website and further websites need to consulted:

Flood zone – Building in a flood zone can still be allowed, however, further research and a flood risk assessment may need to be completed. This will advise you on how high above the risk zone you can go will need to construct the ground floor and what type of accommodation is allowed on the ground floor.


Area designated for increased development – These sites will usually form part of a wider masterplan by the local authority, allowing for the densification of a site.


Brownfield site / Industrial site – This could mean possible contamination on site or that further research and soil investigations may need to be undertaken.


Listed buildings / Locally listed buildings / scheduled monuments on or near the site


Protected views


Article 2(3) land – areas such as a Conservation area, area of outstanding natural beauty (AONB), an area specified by the Secretary of State for the purposes of section 41(3) of the Wildlife and Countryside Act 1981 (enhancement and protection of the natural beauty and amenity of the countryside), the Broads, a National Park and World Heritage Sites.


Article 4 Directions – These are specific restrictions on areas designated by the local authority that may restrict permitted development rights, requiring planning permission instead.


Green Belt land – These areas can also be protected under Article 4 Directions or other local policy.


Other area designations Areas in or near open green areas such as parks, green belt, areas of outstanding natural beauty or agricultural and rural land may have development restrictions as well as industrial and commercial areas that may restrict the conversion to residential or other uses.


Noise map – It can sometimes be useful to look at any neighbouring sound which may restrict the design. Extrium [] provide a map of England showing nuisance sound from roads and rail. For airplane noise, specific neighbouring airport noise maps will have to be consulted, such as the Heathrow flight path noise tracker []


Other mapping – There can be a huge list of other relevant maps to consult when conducting a feasibility. This can include anything from future tunnel transport locations such as Crossrail 2 [], historic bomb droppings [] or how well connected a site is to public transport [].

Are there any significant neighbouring approved applications?


This is the typical research which is sometimes called site analysis. This part of the research may require an OS map or survey of the site. More details about this can be found via the following link: Context Survey Post on First In Architecture
This will help in understanding the physicality of a site; its size, slope, neighbours, trees and other key context.
If the site is surrounded by neighbouring properties, there are a number of key considerations to bear in mind at the early stage of massing:

Right to Light – This is an easement in British Law protecting the right of light to existing neighbouring windows. Below are some rules of thumb that are sometimes used in designing massing’s although the only way of knowing if a window is affected by right of light is for a specialist input where they use Waldram Diagrams and apply the accepted ‘50:50 rule’.


Daylight, Sunlight and Overshadowing – Here is it worth bearing in mind if any proposed massing will reduce the daylight and sunlight to neighbouring properties. Below are some rules of thumb used by designers and planners in ascertaining if further expert advice and studies are required.


25o rule

A building massing should be no higher that 25o from the centre of the ground floor window.

45o rule

If building adjacent to an existing window, you do not want to project the new massing more than 45o from the centre of adjacent windows.

Further information on both of these rules can be found here.

Many of the above rules can be broken with a BRE daylight and sunlight report showing that the interior daylighting is only minimally affected by the development.


Outlook – Many local authorities will also restrict new development within 12m of existing front or rear facades. This is mainly for second floor outlook and not ground floor. This is a rule of thumb, using daylight and sunlight studies or surrounding context can justify reducing this distance. A surveyor that conducts daylight and sunlight reports can be found on an online search engine [].


Party wall – Whilst it may not be very relevant at this stage of a project, a site with many boundaries and possible party wall issues may take longer to develop and should be flagged to the client as soon as possible. A party wall surveyor can be found using an online search engine [] or on the Faculty of Party Wall Surveyor’s register.


Existing Garden – When building within an existing garden, either as an extension, self-contained garden room or an independent unit, the local authority will normally limit development to 50% of the existing garden area. This does not mean that a new unit can be the full 50% of the garden, as the new unit will also require access, outlook and amenity space. For extensions and garden rooms, it is usually acceptable to build over up to 50% of the garden as long as all other permitted development / planning rules are being met.


This is an opportunity to look at possible orientation, height and size of proposed massing/s bearing in mind all previous information collected.

This is highly site specific and can be done in a number of ways.

By hand – Some people prefer to sketch over a site plan. This is especially great at the beginning and for a small project. However, if areas of buildings or spaces are key, it can sometimes be difficult to calculate these accurately whilst sketching.

2D CAD – This is a good method when areas are required and the proposal does not have a lot of storeys.

3D CAD – Many designers prefer to work in three-dimensions from the start. This is especially good if a project requires various building heights. Both Sketchup and other more detailed BIM software can be used for block massing.

Combination of the above – Another option is to use a mix of the above.


Some feasibilities will go into great detail, showing internal layouts whilst others may be a simple massing study.

Cost / Value

Sometimes simply called a feasibility, this may be something the client does not require. This can be split into two main sections, the cost of construction and the value of any area/buildings created.

Cost of construction – A way to calculate cost roughly at this stage is to multiply the built area with construction costs for similar proposals or basing the figure on previous project costs.
Value of area / buildings – A rule of thumb at this stage is to multiply the value of neighbouring similar floor space by the new floor area created.
– It is also worth bearing in mind any other costs such as consultants, designers, planning, Section 106 Agreement(s)  and possible Community Infrastructure Levy (CIL).


The way the above information is presented can vary greatly depending on the type of client. This can sometimes be in the form of a simple email and quick sketch, if they are an experienced client, or as a document to be presented to them, if they are a residential client. Not all of the points above will need to be covered, just those that are relevant to the specific site. The architecture feasibility study is usually the basis for a client to decide if a project is feasible or not. This could determine if they want to proceed with an extension or if they should even purchase land to build a project. It can also begin to form the basis to information presented at as a pre-application or information within a design and access statement for a planning application.


Written by Aida Rodriguez-Vega, architect and researcher. At the Detail Library, Aida keeps busy by carrying out technical research and drawing new details for the ever-growing library.