The full document of the regulation it can be found at:

https://www.gov.uk/government/publications/overheating-approved-document-o

The key elements affecting shading are

O1 Overheating mitigation

(1) Reasonable provision must be made in respect of a dwelling, institution or any other building containing one or more rooms for residential purposes, other than a room in a hotel (“residences”) to—

(a) limit unwanted solar gains in summer; and not just in summer low angle sun on east and west has a greater solar intensity and can be an issue mid-season.

(b) provide an adequate means to remove heat from the indoor environment.

(2) In meeting the obligations in paragraph (1)—

(a) account must be taken of the safety of any occupant, and their reasonable enjoyment of the residence; and

(b) mechanical cooling may only be used where insufficient heat is capable of being removed from the indoor environment without it.

0.16 Solar gains in winter can reduce the amount of space heating required to be delivered by the heating system. Reducing summer overheating by limiting glazing areas will impact winter solar gains and therefore increase the need for space heating.

Dynamic blinds and shutters can be retracted to enable beneficial winter gains

1.9 Residential buildings in the high risk location should, in addition to following the maximum glazing areas in Table 1.1 and Table 1.2, provide shading for glazed areas between compass points north-east and north-west via the south. Shading should be provided by one of the following means.

a. External shutters with means of ventilation.

b. Glazing with a maximum g-value of 0.4 and a minimum light transmittance of 0.7.

c. Overhangs with 50 degrees altitude cut-off on due south-facing façades only.

Option b with a g-value of 0.40 will be unlikely to reduce the solar gain sufficiently without the addition of external shading

Option c confirms that brise soleil are not appropriate for east and west elevations and require an unrealistic projection to be effective on south

Acceptable strategies for reducing overheating risk

Limiting solar gains

2.7 Solar gains in summer should be limited by any of the following means.

a. Fixed shading devices, comprising any of the following. Fixed relates to fixed to the building see 2.8

i. Shutters.

ii. External blinds.

iii. Overhangs.

iv. Awnings.

b. Glazing design, involving any of the following solutions. i. Size.

ii. Orientation.

iii. g-value.

iv. Depth of the window reveal.

c. Building design – for example, the placement of balconies.

d. Shading provided by adjacent permanent buildings, structures or landscaping.

2.8 Although internal blinds and curtains provide some reduction in solar gains, they should not be taken into account when considering whether requirement O1 has been met.

That does not mean that internal blinds should not be used. The reason for their exclusion is that they are not fixed permanently to the structure so could be exchanged by the occupier for a less effective blind after construction. External blinds, shutters and awnings and internal shutters are in scope as they are unlikely to be changed by the occupier and of course their performance in rejecting solar gain is more effective

The over-riding requirement is that all recommended passive means must be considered before mechanical cooling as follows:-

2.11 The building should be constructed to meet requirement O1 using passive means as far as reasonably practicable. It should be demonstrated to the building control body that all practicable passive means of limiting unwanted solar gains and removing excess heat have been used first before adopting mechanical cooling. Any mechanical cooling (air-conditioning) is expected to be used only where requirement O1 cannot be met using openings. Any method to reduce overheating risk in residential buildings must comply

How does shading save cooling energy? - Dynamic shading Vs air-con

The main energy consumption in the UK is not from cars or from planes. 40% of our energy use is for buildings mainly for heating and cooling. Efficient use of sunscreening can reduce that amount considerably.

The 2021 report by leading EU consultancy Guidehouse highlights link and use the graph the potential savings that shading offers to reduce the increasing energy costs required for air-con. Compared to the “business as usual” if the preferred solution of dynamic solar shading was implemented compared to buildings requiring air-con for cooling with their projection the savings in operational energy costs in Europe by 2050 would be a massive €14.6 billion every year.

The Shade Specifier project developed by our Trade Association, BBSA, shows that efficient solar shading can reduce consumption by over 15% where air conditioning is used and up to 10% in domestic buildings. Even a saving of just 5% would reduce total UK energy consumption by 2%. If we could achieve that it would contribute significantly to the Government’s energy use targets.

This is not just an issue that can be solved by incorporating into new buildings. It is estimated that in Europe we replace little more than 1% of our housing stock annually and less than 2% of our commercial buildings so it would take nearly 100 years unless we attend to existing buildings.

What is sustainable shading? The windows are the weak point in energy efficient building design. They can gain too much energy in summer and lose too much in winter.

Shading is a sustainable solution that can control that solar gain in summer, be raised to maximise it and lowered to reduce heat loss in winter.

A study by the Austrian Association, BVST, link to pdf showed that an external Venetian blind will save around 8.5 tonnes of CO2 over its life cycle - and creates only 150 kg of CO2 from production to disposal!

This means that it saves nearly 60 times its CO2 emissions footprint over a 20-year life! The lifecycle for most is a lot longer than that.

These enormous savings come from three elements:

Firstly, in summer the Venetian blind reduces the solar heat very effectively, so that mechanical cooling (with correspondingly high CO2 emissions) is not necessary, as well as complying with the construction technology for housing regulations.

Secondly, in cold weather during the day it is raised and allows in the sun's warming rays into the interior, and during the night in the closed position, reduces heat losses. In a zero-energy building that reduces its heating cost by 20% or more.

And thirdly with this sunscreen it enables the maximum use of natural daylight can be harvested as a free energy light source - that can, for example, reduce the power required for lighting in offices and schools by up to 80%!

The report clearly demonstrates the importance of shading in sustainable building design. There can be few other building elements that can match this performance.

Studies are continuing on other types of blinds and shutters but are likely to be similar for other external products and a multiple of the energy used in their lifecycle for internal shading.

Our Techtonic PV Rooflight system is even more energy efficient as its PV collector produces the minimal power needed to operate it, a true Negative energy solution.

This a design concept that is not just for housing but also for commercial buildings. The objective is to create a building that creates the energy it needs and uses virtually no external energy. That demands passive sustainable solutions.

However, several post-occupancy studies of these high performance buildings report high temperatures when shading has been overlooked as the most frequent problem. So why is that and how do you solve it?

As the cheapest energy is the energy that you do not need, the design maximises the insulation and seals it to prevent heat loss.

To minimise the energy need for heating, the system utilises free energy from the sun on bright winter days. That is done by having large areas of south facing glazing designed with low U values that allow the gain in and then trap it inside the building.

That is fine in winter but in summer the glass still acts as a heat collector and without shading overheating is inevitable and not just in summer, on bright winter days the design can be so efficient it can overheat then as well.

Shading has to be external and dynamic to adapt to the weather conditions.

External as solar gain has to be intercepted before it reaches the glass and moveable so that it will allow the heat gain when it is needed and prevent it when it is not. For internal comfort the Gtot value needs to be a minimum of 0.15 and preferably better than 0.10. (Gtot is the measure of the solar gain of the shading and glazing system combined.)

We attach links to more information on the principals of shading including a video from our trade association BBSA. Link or preferably add BBSA solar heat reduction in domestic buildings

Add photos of Carrowbrook, Kent, Highbury barn, hastoe with names and link to Trojan External venetian blinds.

This is a case study in Bayham Street, Camden, London. The building was an old factory that had been converted into apartments.

On completion it was obvious that they were over-heating. The developer could not decide whether to sell or let it so while he decided there was an opportunity to test different shading systems.

With the assistance of students from London South Bank University our BBSA researcher was able to test in 4 identical apartments to compare an un-shaded apartment with different types of shading in the other 3 over a period from August to October. The building had been re-furbished without shading as the consultants, the local authority and the building modelling all said it would not overheat despite the recommendations of the developers preferred shading supplier.

Video run the Bayham video

Slide repeat image of the Bayham Building

Note that the study was mostly in September not the height of summer yet the temperatures and light levels were unbearable.

This is a published scientific paper and has become the study referred to in other scientific papers and reports. That includes the Climate Change Committee recommendation to Government before COP26 that overheating was one of 8 essential mitigation measures and that dynamic external shading is a solution.

Glass is the source of natural daylight and biophilic design bringing the outside in. Appropriate glass for heat retention is essential so low-e double glazing is essential.

Large areas of glass that are beneficial. Realistically we do not want the solution to overheating to be smaller windows as that means smaller blinds. The regulation states clearly reducing summer overheating by limiting glazing areas will impact winter solar gains and therefore increase the need for space heating.

2.07 Glazing is fixed so the positive is that unlike shading that can be moved by the user it always performs as predicted. That is the U-and G values are known so in building design the outcome can be calculated. Whereas on a bright sunny day the user might not operate the blinds.

2.27 Except

2.50 Slide Cibse 24 the concept that a user will sit in front of a window and not operate the blind if it gets hot is clearly illogical but that can be the assumption of regulators. In some ways the assumption is right as, whilst the blind will almost certainly be operated to prevent heat gain, it might not be raised to improve light levels when the sun is clouded over.

3.14 Slide KP A That is then the reason that shading should be automated to quash that assertion.

3.26 Slide 121 With static glazing solutions you do not have the option of dynamically adjusting the glazing depending on the time of year, day or season.

Solar protective glazing which improves the g-value and stops solar gain entering in summer months also reduces the solar gain entering in winter. Which means that more heating energy is needed to heat those buildings in winter months.

3.50 Solar protective glazing has a coating which is applied to the 2nd glazed pane. – the one closest to the outside.

4.53 Slide with values To maximise the G- value performance there have to be compromises. A low-e double glazed unit will have a G-value of 0.59 that is it rejects just 41% of the gain so less than a medium performing internal blind with single glazing . It will have a U-value of 1.6 compared to single glazing which is 5.7. Whilst we would not recommend it and put it into context that low U value figure could be achieved with single glazing and our best performing shading.

5.28 Slide repeat previous with % overlay, Crucially though the lower the G-value with special glasses beyond the 0.40 value in Building Regulation Part O the bigger the problems for health and well-being and daylight. The best performance cannot get much lower than 0.22 that is 78% rejection but to do that the glass distorts the spectrum and that affects colour rendering, health and well being..

5.50 Slide KP B Whatever the U and G values they will always be improved with shading.

6.04 Slide previous on op temp There is also the issue that when the eyes can see the sun the brain tells you that it is hotter. That is the operative temperature and is the measure of thermal comfort as it is the temperature that you feel and is usually 4-5⁰ higher than if a blind or shutter was in place.

Take text and two lines under it from the psychological effects

When most designers and building modellers consider shading they assume that the biggest problem is in the middle of summer when the sun is at its highest. Surely that must be right it is when we go on holiday to sit out in the sun.

Except that when designing a building it is not and to show you why let us look at the next four graphs.

2.48 Mod 5 Slide 43 north. It can be seen that: North exposed façades, receive the lowest level of solar irradiance. As you would expect it is only at the beginning of the morning and late in the evening in summer add arrows at peak 0600 and 1800 that the sun that makes a difference when only a small amount of solar radiation hits the vertical surface at other times it is reflected sunlight from other buildings or objects

3.12 Slide 42 south Explain Graph text in SLEB page 15

So on this graph we have the South elevation and it more clearly shows a measurement of the amount of solar irradiance up the side and the hours of the day along the bottom. On the South it shows peak at midday in July add arrow . South exposed façades receive solar radiation almost throughout the day. That is why it is necessary to maximise the glazed surfaces on this orientation to optimize the solar gain that could enter the building add

words maximise in winter in winter add arrow to red line and essential to protect the façades in summer add arrow to blue line with shading devices add words control in summer to avoid overheating. Because of the low altitude of the sun, it can be seen that the add following words irradiance is higher in winter than in summer.

4.01 So earlier we showed that in the UK the earth receives up to 1300 watts per square metre horizontally on the ground and here you can see in winter (the blue line) we actually receive as much as around half of that. These measurements were taken at a specific latitude 50 degrees north as the latitude will alter the amount of solar irradiance received.

5.04 Slide 44 east

East and west orientated façades show a symmetric pattern: the east surface will receive the largest part of the radiation before noon, 5.14 Slide 45 west whereas the west surface receives it in the afternoon.

5.18 Bring East and west on to one slide It can be seen that the irradiance is at a maximum when it is composed of the direct part of the radiation. After noon for the east façade and before noon for the west façade, the radiation is mainly composed of the diffuse part coming from the sky. That is the reason why it is lower.

5.43 Slide 46 And here they are all together, South, East, North and West the significance though is that the intensity is actually higher on the east and west than on the South.

5.56 That then clearly shows that lower angle sun is more problematic and the importance of protection from early morning sun on the East that could for example overheat an office building or home office before the staff arrive for work.

6.15 This then shows clearly why shading needs to be dynamic and why because low angle sun is the biggest problem fixed shading does not work.

The G value is the measure for rejecting heat gains in the same way that the U value is the measure for retaining heat.

For an accurate assessment of the performance of a glazing system the figure to use is Gtot, that is the figure for the glazing with shading. The position of the shading, that is internal external or mid pane, will affect the Gtot figure as will the type of glass, that is single, double, low e or special surfaces.

It is defined as the measure of the total energy transmission of the glazing in combination with the blind when exposed to solar radiation.

It demonstrates clearly how effective and essential shading is for energy calculations.

It is difficult to achieve a G value of better than 0.27 for glazing alone and a glazing system can be A+ rated for energy performance with a G value of more than 0.27. Whereas even with single glazing that on its own would have a G value of 0.87 an external blind in the shading position can achieve 3 times more heat rejection at 0.09 than the most high performing glass and a closed blind almost 10 times more effective at 0.03.

Shading will always improve the G Value of a glazing system. Need illustrations

Validated Gtot values for some Hallmark products can be found on the ES-SO database. www.es-so-database.com

Shading is the insulation of the transparent parts.

Solar gain refers to the increase in temperature in a space, object or structure that results from solar radiation. Sunlight is made up from ultraviolet, visible and infrared wavelengths.

Nanometers (nm) are the units used to measure the suns wavelength. The shortest, Ultra Violet, are 250-380 nm. Visible rays (light) are short wave 380 -780 nm. Infra red are long wave, 780 -2500 nm (also known as heat.)

Objects that are struck by sunlight absorb the short wave radiation (light) and then it is re-radiated as longer infrared wavelengths (heat).

This affects the glazing because when the rays have passed through glass, the glass is more transparent to the shorter wavelengths and opaque to long wave. So the longer infrared wavelength will not pass back through the glass heating up the room causing solar gain.

Similarly where the radiation is absorbed by the internal shading system some is transmitted back into the room and some is trapped between the blind and glass. Unless it is vented with an air flow (from mechanical ventilation or an open window) it will heat the blind which will become a radiator.

An external shading system is the most effective in reducing solar gain as it is converted into long wave heat when it hits the blind. Most that is transmitted through or absorbed by the blind will then not pass through the glass and is trapped as hot air between blind and glass. As hot air rises it is then dissipated above the blind by natural convection (It rises and draws cooler air up between blind and glass.)

A report from the World Green Building Council (link) identifies that benefits of views outside are also closely connected with the provision of daylight.

Ideally views should be aesthetically pleasing, and there is good evidence that shows the benefits to occupants are particularly strong if the view features nature. This is an example of ‘biophilia’, a phrase that describes a relationship between nature and humans, which suggests that because humans are intrinsically “of nature” we need contact with the natural environment to sustain our health and wellbeing.

Biophilic design will grow in importance with greater realisation of the impact of today’s working environment as urbanisation continues apace and we risk becoming further divorced from nature in our day to day lives. The benefits on physical and mental health are becoming increasingly well understood, with a significant body of evidence supporting this view. With the increase in home working design of that working environment has become more relevant.

The window is our view on the world and shading that controls the energy of the sun whilst maintaining that connection to nature is crucial to a comfortable productive working environment. Our Hemera Markisollette link is an option

Saving on energy costs is important but the higher cost in any business is its employees. That can be as high as 90% of the total so a 1% saving on that cost will have far more impact on the bottom line than a 10% saving in energy costs.

The World Green Council Report link highlights the issues and benefits that can accrue from staff comfort, well being and health. Many are obvious if you take the time to think about it not least that an indoor working environment has only been developed over the last century. The natural environment for humans is outside and many of the issues of health and well being are connected to our need to be part of the outside world.

Health and sickness are just a part of the picture the report also shows how improvements to staff comfort can be rewarded with really significant gains in productivity and performance as shown on the chart taken from the report.

The windows in a building are the connection to the outside and the power of the sun and nature to activate our body clocks. We need the sun and the light and heat that it gives us but it needs to be controlled. Too little and we become lethargic and unproductive, too much and we cannot work productively.

As heat loss in winter has a greater cost than removing heat gain in summer the rating system has been designed to encourage the development of the best glass for retaining heat that is to have a low U value.

In that respect it has been really successful in encouraging the development of glazing systems (the complete window not just the glass) that has significantly improved the performance. If you consider that U values for single glazing are 5.7 and for first generation double glazing 2.9 we are now getting figures of 0.8 and even down to 0.6 may be possible.

The requirements introduced in the latest version of Part L of the Building Regulations will bring that down to 1.4 and 1.2 by 2024 with progression to triple glazing.

So what is the problem with that?

In fact the additional benefit of a triple glazed system will probably not regain the additional cost in energy saving throughout its lifecycle, 50% more glass does not mean 50% better it is nearer to 5%. If fitted to standard spacing frame it actually has a worse performance than a good double unit as to be effective it has to have a deeper, heavier and more expensive frame.

Taking glass to extreme levels of heat retention will inevitably lead to overheating not just in the summer but on sunny winter days.

There are more triple glazed windows in Scandinavia where the winters are far colder than in UK yet they have more external than internal shading even though their summers are cooler.

Heat retention depends on air gaps created by the layers and the additional layer of a blind or shutter will have the same effect as each layer of glass. A low permeability blind such as the Ebony or Hemera 103R or a VR130 shutter links with good performing double glazing will match the performance far more cost effectively and will have the added benefit that the blind can be adjusted and it can be raised on sunny winter days to gain from the free solar energy.

Low-e glass is designed to keep solar gain out so cannot do that.

LIGHT CONTROL – maximising the use of daylight

The energy issue is relatively simple. Energy, as daylight provided by the sun, is free energy providing that controlling it does not cost more than it saves in artificial lighting.

Working in artificial light causes lethargy and irritation which affects productivity and wellbeing.

Natural daylight has an uplifting effect; sunlight creates vitamins in the body and suppresses the development of melanin, a natural occurring hormone, generated by the body, which is produced to tell you when it is time to sleep.

The passing of time throughout the day, linked to light levels and stimulation through the eye, trigger the production of this hormone. When the eye sees sunlight melanin is suppressed. Good natural light also supports health through various other mechanisms including regulating sleeping rhythms.

So daylight has the potential to provide the necessary light levels for a productive, stimulating environment, while reducing reliance on electric lighting.

Blinds such as the Lumax light shelf blind link will provide the ability to control and maximise the daylight whilst enabling the user to adjust the shading for their visual comfort.

A comfortable environment leads to a productive workforce. Cost savings in efficient operation will be achieved in a building designed for staff comfort.

The human body adapts itself to its surroundings maintaining constant internal temperature by thermal regulation. In the cold, muscular activity will be required to release internal warmth or wrapping up in layers of clothing will conserve body warmth. In hot temperatures movement is reduced so conserving stored energy. Any excess calories are eliminated by sweating (which evaporates in the heat) or by moisture in exhaled breath.

Thus thermal comfort basically relies on heat exchange and hygrometrics between the body and the environment. To avoid the need for the body to expend energy in this way correct temperature, an ideal level of humidity and a light air movement are necessary for thermal comfort and efficient working conditions. Whilst sunscreening will have the most significant effect natural ventilation is also important. As an example a temperature of 30°C with a breeze moving at a rate of 1m per second would feel the same as 26°C if the air was still.

Clearly this should not be taken to extremes!

Productivity in an office will drop 1% for every degree above the comfort threshold of 26 °C. Effective shading that maintains this comfort level will thus have a significant impact on the highest cost item in any office – the performance of the employees.

Sunscreening that allows air circulation combined with natural ventilation can significantly improve the thermal comfort of the user and is healthier than a sealed air-conditioned environment.

Ventilation and shading and shading are complimentary and their effect should be considered together for effective design.

Computer simulation programmes have now advanced so that it is now possible to predict the operational cost of a building before construction commences. Using a simulation programme enables the designer or services engineer to predict the energy savings that can be achieved with effective shading.

With a culture in the UK of assuming that shading is a decorative feature the extent of those savings is not widely appreciated. They can be substantial.

The problem is many programmes do not correctly calculate shading and where they do it is not to current standards. This has been highlighted by two studies comparing modelling programmes assessment of overheating on our case study building. They showed a massive difference of 18°C between the measured temperature and the model that indicated that the building would not overheat but at a measured operative temperature of 47°C it certainly did.

Many of the leading modelling programmes were originally designed to promote the use of air-conditioning. Many of those programmes are “Black Box”, that is you cannot adjust the parameters and internal algorithms and completely ignore the benefit of shading. The issue is detailed in the ES-SO Campaign for Accurate Simulation of Shading link

Slide 161 & C just take the RH image and the ESBO light logo To demonstrate accurate performance of materials we have the ES-SDA data base link and the ES-SBO modelling tool

Slide 161 & D take just the ESBO image and the two logos ESBO is a simulation tool where shading is considered in a correct way.

This system that does model to standards BS EN ISO52022/3 and BS EN ISO 15099 is from the Swedish company EQUA. They have a free to access simple to use programme called ESBO. That stands for Early Stage Building Optimisation and has been created so that a designer can test ideas without needing to create a complete building model. For us it is an easy to use tool to recommend that can be used to quickly demonstrate the benefits of specific types of blinds and shutters and has a library of manufacturers fabrics and materials.

It you are uncertain whether your preferred model is accurate test it against the ESBO tool.

At Hallmark we believe that energy saving is not a matter of green credentials or saving the planet although that may well be the result. It is common sense economics, for as energy costs rise, any effective means of reducing cooling costs should be assessed.

We hope that we have highlighted some of the issues for you to consider. It is our belief that efficient shading should be used to complement rather than dominate design.

However our ideal solution is clearly not appropriate to all design and whilst natural ventilation may be appropriate for some buildings we believe that the main function of shading should be to reduce cooling loads, rather than replacing air-conditioning. With glass we believe that sensible shading solutions can enhance rather than reduce the glazing. The latest amendments to the building regulations do not mean the end of the fully glazed building if shading is incorporated in façade design.

In the UK we have a cultural issue, we do not believe that the sun is a problem – the market for external screening is far larger in cooler Scandinavia than here – but clearly that will begin to change.

Finally do not forget the requirements of the user and also their need to understand the reasons for the shading system and its benefits. Systems will only work if used as designed.

Holistic design of glazing, shading, lighting, ventilation and controls is essential.