New roles for glass in renovation construction?
Architects and structural engineers agree: natural light is very important for people’s well-being. Even large glass surfaces do not need to be avoided, because with good planning and careful implementation they can be energy-efficient and even producing electricity.
Architect Asko Takala from Kirsti Sivén & Asko Takala Arkkitehdit Oy states that he is an omnivore when it comes to building materials, but wood and glass are particularly pleasant. He also appreciates simple massive structures, simpler construction in general and the design of buildings that serve a good everyday life.
Takala states that windows and other glass structures have two tasks: bringing light into the interior and opening up the views to the outside. Sometimes both come true, sometimes only one.
Takala names a Finnish architect, designer and academician Juha Leiviskä as the master implementer of both. Leiviskä received the Danish Daylight Award in 2020. The award is intended to support daylight research and the use of daylight in architecture. According to the jury, Leiviskä’s light is an oblique light that both hits vertical surfaces directly and is reflected, resulting in layers of light. Leiviskä’s light not only illuminates but is born and lives in the space. The Myyrmäki church in Vantaa in Finland, completed in 1984 and currently under renovation, is a good example of this.
– In the church hall you can see light but no windows, and in the other rooms of the church, the windows open up views of the adjacent park, Takala states.
As much natural light as possible
Light and views also guide Asko Takala’s own architecture.
– Importing light is easy, creating a view is more difficult.
– If there are no views of the environment to show, then we try to bring as much natural light into the interior as possible within the limits of the fire regulations. It is important for mental health to be exposed to natural light as much as possible, preferably according to the daily cycle, Takala states.
According to Takala, the conversion of attics and old industrial buildings into residential use offers an opportunity for creative solutions for transporting natural light deep inside.
– If the facade cannot be touched, the light must be taken from above. On the other hand, views are important in attic construction; I believe that these solutions will certainly develop in the future.
Takala considers many residential buildings from the 1960s and 1970s to be good examples of thoughtful transportation of natural light. Back then the doors of wet rooms could have frosted glass and there could be a window over the door of the stairwell. Today, there is no place for such a window, when building technology takes up the spaces of the lower ceiling.
When balconies were started to be glazed, there were many different glazing versions available at first. As the requirements for building efficiency increase, the selection has shrunk.
According to Asko Takala, more attention should be paid to the role of the balcony: does the balcony shade or open views, what role does the balcony play on the facade?
– It is quite common that our balconies are bulky, poorly designed glass boxes, Takala states.
Big windows have their reasons
At this year’s housing fair in the city of Loviisa there was a lot of talk about the large windows of detached houses. For some they were the best possible openness, for others they were impossible aquariums.
– Before judging the floor-to-ceiling windows of premium properties, you should sit on a stool, because from there you can better see the role of windows. Big windows open up possibilities, says Asko Takala and reminds that in nursing homes you should also be able to see out from the bed.
According to Takala, the wall-sized glass surfaces have come to Finland from Holland and Denmark, where there is compact and low construction. The large uncurtained windows of the residential buildings reflect the Calvinist principle: we have nothing to hide at home.
– The large glass surfaces on the facades of office buildings also symbolically depict openness, even though the buildings are actually very controlled.
Asko Takala considers the large glass surfaces of facades to be technically sustainable solutions, even in extreme weather phenomena brought about by climate change, because technology related to glass is developing all the time.
– However, an architecturally high-quality facade requires more than just glass, because the open-close rhythm of the wall is important, Takala states.
Glass as a load-bearing structure
Sweco Finland Oy’s structural engineering expert, Master of Science in Engineering Andreas Limnell has been dealing with facade materials and building physics since the beginning of his career. Engineering expertise accumulates with projects.
Large glass facades have been built in Finland for a long time, but it was only in 2019 that the first official dimensioning standard SFS EN 16612 was published for calculating the transverse load resistance of building glass. The standard contains a calculation method for determining the transverse load resistance of glass elements used as infill elements that are continuously supported on their sides. Transverse loads include, among others, wind and snow loads, the self-weight of the inclined glass and pressure fluctuations in the space between the insulating glass elements.
Limnell states that the strength resistance of glass is not as well predictable as the strength resistance of other materials. Glass is fragile, but can be strengthened by lamination. There are also different laminations, and the engineering must take into account the special features of each product, for example in terms of humidity, temperature and load resistance, and recognize the combined effects.
– The challenge of glass is that its compressive strength is higher than that of steel, but its bending strength is low. When there are 20 pieces of glass being cut, the breaking point has a large scale: one can break at 20 kilos and some at 100 kilos.
– Glass is sensitive to mistakes and micro-cracks appear on the edges when cutting, which can expand quickly. Refining the edges eliminates these risks. In addition, the durability of the glass is weakened by treatments applied to its surface, such as a print or sandblasted glass surface. All these must be taken into account in the calculations, Andreas Limnell states.
Since 2014, Andreas Limnell has been involved in the structural engineering of shopping center REDI and the surrounding residential and office towers in Kalasatama in Helsinki. The first residential tower block Majakka was completed in 2019: 35 floors, 134 meters high. A huge number of superimposed load-bearing glass structures, which must be rigid, compact and yet also flexible.
The facade of Majakka is built from one-story high aluminium-framed elements that rest on the floor level. All elements of the facade, also other than the windows, have a glass surface. The back side of the element has a steel casing, thermal insulation and plasterboard.
The glass elements on the facade of Majakka have been repaired for a couple of years. According to the main contractor SRV, there have been quality defects in the glass of the facade elements, which is why the thermal expansion in the facade structure has caused the glass to crack.
New tasks for glass
The large amount of energy needed in the manufacture of glass and the concern about overheating of the interior would give reason to assume that the role of glass in sustainable development construction will decrease.
However, reducing the size of the windows is not necessary and perhaps not even sensible.
– If the facade has a lot of walls and few windows, it is very heat resistant and requires less heating and cooling, but more lighting to make people feel well, Andreas Limnell states.
The norm requires the U-value for thermal transmittance of the window to be no more than one, but you can do better. With energy-efficient glass and frames, the U-value of the window is much less than one. In addition to that, the solar radiation coming through the large light opening can be prevented, for example, with a sun protection film that does not take too much of the transparency of the glass.
– There has been a big leap forward in the properties of glass in the last five years, Limnell states.
In addition to light and views, windows and other glass structures are starting a new task in collecting solar energy. Light-transmitting solar cell glasses on facades have become commonplace alongside roof panels, either installed in a window or elsewhere.
The cell layer that collects solar energy is a very thin, light-transmitting film that is laminated between two glass sheets. From a structural designer’s point of view, solar cell glass works exactly the same as laminated glass, as long as the cables running in the aluminium profile are taken into account.
Architect Asko Takala has been designing an almost zero-energy and an energy hybrid rental house in Sompasaari in Helsinki. The facility, which will be completed in 2024, will produce electrical energy with solar panels on the roof and solar glass on the facade.
New uses for glass can also be found in increasing real estate development projects.
– Glass and interior windows could play a big role in the use of the old building stock and changes in the way it is used. Glass could enable the current building stock to be preserved in active use, says Asko Takala.
He thinks that the number of glass facades may decrease with the decrease in new construction. Instead of facades, glass could be used more indoors and in window solutions for attic construction. New places for glass could also be found in intermediate floors and lofts. In all these cases, glass deliveries would be more customized than at present.
Andres Limnell expects more standardization for glass construction in the future. He states that the slanting rains that come with climate change have already been well taken into account. There are recommended rain resistance values for glass systems, and in high-rise construction the tightness of the glass facade has been thoroughly tested.
– More consideration should be given to the warming climate and the effect of air humidity on construction. We are used to the fact that most of the humidity is inside. When the air humidity outside is higher, the moisture moves inside. If this is a long period, moisture can accumulate on the wrong side of the vapor barrier. And it can change a lot in ventilation engineering as well, says Andreas Limnell.
Text and photos by AHTIPA/Jaana Ahti-Virtanen
Translation by Google Translator, edited by Jaana Ahti-Virtanen
The article was originally published in Finnish in issue 4/2023 of magazine Projektiuutiset.