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The changing face of window design and specification

Jon Palethorpe looks at current trends and latest technical advancements for high-performance school windows

Posted by Stephanie Broad | August 18, 2015 | Outdoors

In the UK, Building Regulations are imposing ever more stringent targets with the aim of achieving zero carbon performance in non-domestic buildings by 2019.  As a result, schools are having to become more informed about the need for energy efficiency to minimise the demand for mechanical heating, ventilation and cooling, with the aim of reducing running costs and future-proofing their buildings 

The façade of any building is one of the most important factors in determining energy efficiency and window systems are therefore a critical part of the specification process.  Effective fenestration design has to achieve the balance between aesthetics, thermal and weather performance, natural ventilation, acoustics, safety, security and cost – and the challenge is that these factors often work against each other. 

Technal Soleal window

Exceeding building regulations to further improve thermal performance

We are seeing much greater demand for levels of thermal performance that exceed current Building Regulations. These require Uw values for the glass and frame of 2.2W/m2K but values of 1.5 or as low as 1.2 W/m2K can be achieved. These performance levels exceed the requirements but for a relatively small additional cost, the school will benefit from a much more thermally-efficient solution to help reduce future running costs over the life of the building. 

The thermal performance of window systems can be enhanced with the use of:

  • Increased thermal breaks
  • New materials for thermal strips
  • Increased module depths
  • Larger glazed unit sizes – 24mm was the standard but this has been increased to 28mm and up to 52mm is now common
  • Additional insulating gaskets
  • Profile engineering

These features should now be available as standard for high performance aluminium window systems. 

Forest Park School

Safety and security considerations 

It is essential that window designs enable safe and authorised access for operation of the window systems, proper management of the building and implementation of safety and security procedures. 

For example, in a primary or secondary school it is critical for children’s wellbeing that the window type, configuration, fittings including restraints, and location are all considered to avoid falling out, entrapment, collision, and slamming shut. Additionally, platforms – such as desks positioned near windows, which could be used to gain access to the window or opening, should be taken into account. 

Consideration should be given to levels of security, the test performance of the window system, and any enhancements required.

Also, consider how the window systems interface with the building management system – and how they integrate with the building’s ventilation strategy. Will windows be opened manually for natural ventilation or will this be automated? Either way, operation needs to be controlled, safely and securely. 

The façade of any building is one of the most important factors in determining energy efficiency

Developments in natural ventilation 

There have been technical advancements in trickle ventilation to allow fresh air to circulate when the window is closed but with no passage area for sound. This is a useful feature where classrooms are adjacent to busy roads. The vents can be fitted into the window system or can be installed independently above the window. 

Casement windows can also now incorporate hinges for wider opening up to 90 degrees rather than the previous standard 50 degrees but specifiers should be aware of the safety implications of wider openings which can be a hazard for children. Parallel opening options to optimise airflow can be a better option for education applications. 

Chilton Trinity

How to minimise solar gain 

Solar gain can be an issue with windows. As well as curtain walling and reducing it is increasingly a requirement, particularly for schools. Staff and students need the benefit of natural ventilation and high levels of natural light to help maintain comfortable learning environments and fresh air has been proven to contribute to concentration levels, but highly glazed buildings are vulnerable to heat gain.

Weather performance issues 

Air tightness is becoming even more critical in building design and very low levels of air or heat loss are now being demanded, well in excess of Building Regulations.

It is also more common now for specifiers to request an EPDM perimeter seal between the structure of the building and the window system. This can make a considerable difference to reducing heat loss and improving the overall building performance. 

For water tightness, it is vital that schools and local authorities check that only well-trained glazing fabricators and installers are contracted to ensure correct manufacture of the system and accurate fitting on site – whether for new build or refurbishment projects.

Window and door sizes 

Increasing mullion and transom sizes will allow building designers to achieve larger spans and greater vision areas for maximising natural light and striking aesthetics. The most advanced aluminium window systems will have less visible aluminium for further visual appeal. 

Occupier comfort and usability is also an issue with larger windows or doors. Specifiers are demanding ever-bigger doors but do need to balance aesthetics with ease of operation. A three-metre high door, for example, will be too heavy for children to open in a school environment. 

Pegasus Academy

Enhancing aesthetics 

Technical advancements in window design have included the increased use of concealed drainage and fittings such as hinges, restrictors and closers for an improved finish. Concealed fittings are less likely to be vandalised and can also be supplied for open-in windows and tilt/turn configurations. 

Balancing specification considerations for effective design 

Finally, there are multiple considerations that affect window and glazing specification – including size limitations, comfort, running costs, location and orientation of the building, ventilation requirements, safety and security, solar gain, acoustics, maintenance, finish, cost, compliance with disability legislation, Building Regulations, environmental impact, life cycle costing and recyclability. 

John Palethorpe is Commercial Director at glazing systems specialist, Technal    

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