It’s not uncommon to see louvres attached to the outside of a modern office building, hospital or hotel. They have become a popular addition to the design, often for very practical reasons; sometimes merely to enhance the appearance.
In crude terms, a louvre can be described as a sort of external venetian blind, the multiple blades allowing light into the building while shielding it from direct sunlight and uncontrolled solar gains.
But very often louvres are included as an afterthought; a forgotten product that must be sourced and installed quickly. Insufficient thought is given to the purpose of the system and what it should achieve. According to John Park-Davies, the choice of louvre system should reflect the design requirements and performance expectations.
Park-Davies, of course, has an axe to grind: he is managing director of Ikon Aluminium Systems, a Birmingham-based manufacturer of architectural aluminium building products for the façade market.
“Poor specification can lead to poor performance not just of the system but across the entire building, from rainwater ingress and restricted ventilation to wasted energy,” says Park-Davies. “Louvres can improve the energy efficiency of a building by increasing air flow and optimising natural ventilation but if they are incorrectly specified or located, behind a perforated panel for example, this can increase resistance to airflow and cause an increase in the power needed to circulate air around the building.”
Up until now, the design of louvre systems has hinged upon their ‘free area’, which is calculated by measuring the clear distance between the blades and multiplying it by the width of the louvre panel, or the height if the blades are arranged vertically.
But this method has its limitations, especially when additional requirements, such as improved weather protection, are factored-in, says Park-Davies. “Free area can be affected by bird and insect mesh, structural supports and most importantly, it doesn’t factor-in how air flows through the louvre,” he explains.
Factors such as the location and exposure of the louvres, site orientation, prevailing weather conditions and the potential of wind-driven rain should be balanced with the required airflow, acceptable pressure drop and level of water penetration, says Park-Davies. Only then should the building’s exterior design and the aesthetics of the louvres be considered.
Park-Davies says that pressure drop is a key factor in establishing the right louvre and is a credible alternative to free area. Pressure drop (expressed in Pascals) is the pressure difference between one side of a louvre and the other; it is the result of resistance to air flowing through the louvre. “An increased pressure drop can impact on the performance of ventilation equipment, forcing it to work harder to draw the air through,” says Park-Davies. “The result is often overheating inside the building.”
While aesthetics must be considered, Park-Davies insists that performance should never be compromised. “Louvres are often hidden behind more aesthetically pleasing features, such as perforated panels, but this can restrict air flow. By acknowledging louvres early in the specification process, they can be designed into the building envelope for optimum performance and work with the fabric of the building,” he says.
Having said that, louvres can be specified purely for aesthetic reasons. Screening louvres, for example, offer a neat solution for disguising rooftop plant such as air-conditioning units, where good airflow is essential but water penetration won’t cause too many problems.
Similarly, barrier louvres provide both functional and aesthetic benefits. Designed for installation where there is a risk of falls from height they are a practical yet attractive solution. “They are particularly popular on medium-rise buildings including hospitals and student accommodation,” says Park-Davies.
And, indeed, Ikon has recently completed just such a contract at The Cycle Works, a new purpose-built student accommodation block for Coventry University. Here, Worcestershire-based installer Campbell-Mason has installed 280 of Ikon’s IKL505 barrier louvres in the window apertures and stairwells.
The barrier louvre, sometimes called a grill, negates the need for windows and doors to have restrictor systems which are prone to tampering and breakages. They are a cost-effective, safety solution with security. “The barrier louvre limits the risk of falling or items being thrown out of windows from height onto the area or people below. It is essentially, a safety barrier,” says Park-Davies.
This article was first published in the October 2018 issue of The Construction Index magazine