Testing Daylight and Sunlight in Masterplanning

“The code is more like guidelines than actual rules’  Captain Barbossa

Thus Captain Barbossa enlightens the confused Elizabeth Swann on the difficulties of interpreting the Pirate Code. When is a guideline a rule, and when is it a guideline, and what does it mean when it is treated by some as a rule and treated as a guideline by others. BRE Daylight guidelines are treated by some people like the Pirate Code, to be taken as rules in some cases, and as guidelines by others? Taking one approach or the other can have a significant impact on the design of masterplan, sometime with negative consequences for the urban design.

Most of, if not all of, the recommendations offered in the BRE Publication ‘Site Layout Planning for Daylight and Sunlight: A guide to good practice’ are guidelines and should not be strictly applied. The introduction to the documents even states “The advice given here is not mandatory and the guide should not be seen as an instrument of planning policy: its aim is to help and not constrain the designer. Although it gives numerical guidelines, these should be interpreted flexibly since natural lighting is only one of many factors in site layout design. In special circumstances the developer of planning authority may wish to use different target values. For example, in a historic city centre, or in an area with modern high rise buildings, a higher degree of obstruction may be unavoidable if new developments are to match the height and proportions of existing buildings“.

Yet, in many cases, authorities and even the BRE itself, make these guidelines into rules or targets for planning policy and sustainability appraisals.

In more specific instances, the BRE guidelines also state that ‘In a mews in a historic city centre …a VSC(Vertical Sky Component) of 18% could be used as a target for development in that street if new development is to match the existing layout’. This statement highlights the contrast between homes designed to match the character of historic environments by meeting a threshold value of 18% of Vertical Sky Component, compared to the ‘normal’ recommended threshold of 27% of Vertical Sky Component. This highlights the idea that different daylighting thresholds are appropriate for different types of urban neighbourhood.

In the Code for Sustainable Homes the BRE sets a level of 2% of Average Daylight Factor for kitchens, and 1.5% for living rooms and home offices. The guidance recommends a minimum of 1% for bedrooms. Credit scores are awarded in the Code for homes that meet these guidelines. While there is an acceptance that different rooms could have different light levels, there is no allowance made for differences in design that could mean that some homes may not meet the target at all.

Many local authorities use the BRE guidelines as de facto planning policy, and use them to argue against development that reduces the daylight or sunlight for other existing properties and residents. Unhelpfully, Rights to Light, a legal right to light, is a separate matter and dealt with in a parallel process, sometimes involving the courts. This is usually an issue when new development affects the daylight of an existing building by overshadowing it.

When designing large-scale developments, covering a new urban quarter, current practice guides the designer towards layouts that are partially reminiscent of historical urban quarters containing streets and squares.  It is entirely consistent with the design of modern urban masterplans that there will be areas of high density living and areas of low density living that have different characters, amenity, outlook, density, and property values. Daylight is part of the character of a building and the homes within it. It is part of the character of a street. In London, there is a world of difference between the character of the houses in a Victorian terrace, suburban Barnet, and mansion blocks in Kensington. Each have their own character and value.  Designing homes, streets and squares to all meet a particular daylight threshold may not help to produce an enjoyable and varied urban environment that reflects the variety available in most cities. I think that the BRE guidelines should be treated as guidelines and strict daylighting thresholds should rarely be applied across large scale masterplans.

Some countries apply this type of guidance very strictly, Russia and China particularly enshrine daylight into national regulation. The result is often poor quality urban design resulting in all new buildings facing South and ignoring traditional street layouts. It may deliver the appropriate hours of sunlight on a particular date in March but the impact can be very detrimental to the quality of life in cities.

I think that it is very difficult, if not impossible, to design a high density urban environment without having some units at street level with low daylight amenity, as well as many units at high level that have much higher levels of daylight than guidelines would suggest. Large glazed areas may give apartments a stunning view, but high levels of daylight almost always translate into high levels of solar gains and overheating.

It is important that streets are overlooked at all times by windows and have front doors coming from them at regular intervals. This means that homes on east-west streets will always have facades with a northern aspect and will have low levels of sunlight on that facade. Where streets are aiming for an urban character and are 4-6 stories high on both sides, it is inevitable that the units on the ground floors will have low daylight levels. This does not prevent those units from being attractive and useful. Central London has many basements which are fully occupied and enjoyed by residents and which undoubtedly have low levels of daylight. Their proximity to services and jobs is deemed to be of higher importance by their residents than daylight levels.

The Mayors Standard for Dual-Aspect Homes

London homes are designed to meet the Mayors Standard. This includes Standard 5.2.1 which states that “Developments should avoid single aspect dwellings that are north facing, exposed to noise levels above which significant adverse effects on health and quality of life occur, or contain three or more bedrooms”. The guidance adds “A home with opening windows on at least two sides has many inherent benefits, including better daylight, a greater chance of direct sunlight for longer periods, natural cross ventilation, mitigating pollution, offering a choice of views…..”.

Following this guidance means that even in situations where some elevations of buildings have poor access to daylight or sunlight, the likelihood is that homes within the plan can be designed to gain daylight and sunlight from another elevation, either from a side street or from a courtyard. The detailed design can prioritise the design of single aspect dwellings in areas where there is good daylight/sunlight availability to ensure that every unit has rooms that provide the best level of light available.

External Spaces & Courtyards

BRE guidance would suggest applying a single guideline for external amenity spaces, but the actual use of them may be very different, and may be in different character areas of any masterplan, external spaces should be designed to have different characters. For example, ground floor courtyards may become a first floor podium depending on the parking requirements, making it difficult to test the design at an early stage. Do you test the worst case or the best case, even though the worst case in daylight terms is the best case in urban design terms, as a courtyard on the ground will be a better used space than a courtyard on an upper level. If there are taller building should the roofs be designed as amenity spaces? High level roofs have very good levels of daylight/sunlight amenity, but they can never replace a ground level external space as the best possible common space.

Where courtyards are to be used for doorstep play, sunlight analysis can be used to show where there are places within each courtyard that have good light levels where play equipment can be located. It makes sense to put play spots in a sunny location, even if that location isn’t sunny for long periods.

Public Open Spaces

Daylight for Public spaces is even more difficult to deal with. Does it matter whether an urban square is well lit or not? When most of the activity in the space is transient and the space is largely serving the needs of people moving through the area from outside, it is arguable that the amount of light in the space is largely irrelevant. If the space is not to be used for people to sit, or play, then it is difficult to argue for a particular threshold of light or sunshine. This is not to say that sunlight or sunshine is not going to add enjoyment and character to the space, but that setting a particular threshold value of sunshine or daylight is not a valid approach. If the landscape designer wants to plant the space with trees, then the amount of light available is also a consideration for the types of planting that will thrive there.

Overheating

As the UK climate changes and average annual temperatures continue to rise, the danger of overheating due to solar gains will increase. High levels of daylight will also mean high levels of solar gains, which brings with it the risk of overheating. Currently there are no overheating tests that are required to be carried out by regulations that are sufficiently robust to deal with this problem. Overheating can be mitigated by a number of measures, including external shading, ventilation and occupant management. The people at most risk of heat stress are the older and younger parts of the resident group and particular care should be taken to protect older residents from overheating. There are some advantages to older people being in units at low levels of buildings with lower daylight and sunlight levels as these will be cooler in hot summers than units at high levels.

Summary.

Applying a single standard of daylight amenity to something as complex as an urban masterplan is not advisable. Different external spaces and streets have different requirements, and different buildings can and should have varying characters to make an interesting city. Daylight and sunlight are very important aspects of that character and should be appraised from the beginning of the design. The design team and planning officers should be aware of the impact of their decisions on the daylight available from the earliest part of the process but not rely solely on numbers to guide their decisions. Quality matters as much as quantity, but is much more difficult to appraise.

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2 thoughts on “Testing Daylight and Sunlight in Masterplanning

  1. This article is entirely misconceived. The point of the BRE guidelines is that they give decision makers a framework for understanding the daylight conditions of the development.

    If you go under them daylight will be poor, achieve them and you will have a good level of daylight. The reason why many authorities use the guidelines is that they want to achieve good levels of daylight on new developments and protect the amenities of existing residents.

    You often hear people say that it is OK to have lower levels of daylight in densely built urban areas. It isn’t an either or, there are plenty of high density developments which have been built to achieve good levels of daylight.

    That is the purpose of the passage you cite – the guides tell you how to achieve well lit homes. I very much doubt you would like to live in a poorly lit one!

    • I disagree pretty fundamentally. Any city around the world, good and bad, will have places where there is less daylight than others. Sometimes, particularly on warm days, this is a relief. My point is that this is OK in the grand scheme of things, and that applying blanket rules is a bad idea. Some people work a lot, and spend very little time at home, and don’t care how much daylight they get. Others live a lot at home and it matters a great deal to them. We should accept this in masterplanning and allow ourselves to occasionally have units which don’t meet BRE guidelines. In my experience it is pretty impossible to design a high density urban quarter without some failures of these guidelines, and I don’t believe that these guidelines were conceived with high density urban quarters in mind.

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