Concrete tips for a good façade

Aktuella Byggen # 6

When designing a facade or a window band, it can feel confusing. How should I read the reports from the daylight consultant and the energy consultant? And how are they affected by the report from the acoustics consultant? I've written a whole book outlining the options. And work a lot with the consultants who use building simulation to produce these reports. If you google my name, you can find my landing page and download the book free of charge. Here, in a more limited space, I want to share tips on how to achieve a good facade with happy residents and a low CO₂ footprint, in the construction phase as well as in the operation phase:
 

Start from daylight

The main tasks of the glass are to accomodate a view to the outside and to let in daylight. If you choose a glass with too little daylight penetration and perhaps low quality color reproduction, the damage is difficult to repair. A daylight analysis is expensive to revise and low quality of daylight cannot be improved by interior lighting. My proposal in the rest of the article is based on a light transmission of 63% in triple-glazed insulating windows, but it is possible to navigate to efficient solutions even with 67%. If you go for 70% or higher, you severely limit the possibility of reaching good solutions for thermal comfort and glare protection.
 

Control sound reduction early

Many buildings today are located in noisy places. With a single-skin facade, a sound reduction of Rw 51 dB can be achieved at best, above that double facades are required. But already from about 38 dB, the sound reduction can become cost-driving. And with higher noise reduction comes heavier constructions, which quickly increase the built-in CO₂ footprint. Different room types have different requirements for sound reduction. Meeting rooms often have high sound requirements and you should avoid placing that type of room against noise-prone facades, this can result in high requirements in the acoustician's report. As there are no rules for daylight and views in meeting rooms, it makes sense to place this type of room in the interior of the building.
 

Cell office to the north

A facade usually has a fixed relationship between wall surface and window surface. In a home, there are often 20% windows in the wall, in a facade 30-50% windows. The smaller the room that is behind the facade, the greater the requirements for ventilation, cooling and solar control. A single small room with large windows can have major consequences in the energy consultant's report. If you can put cell offices towards the north and avoid small rooms in corners where the energy comes in from two directions, you can significantly downsize these expensive HVAC systems.
 

"Best" solution glass

If you solve the problems I outlined here at the beginning, what is my best recipe for a facade for a low CO₂ footprint and good well-being? And what does it look like? The most advanced solar control glass are more expensive than other glass but offer several advantages that allow for cost-effective facade solutions. The development on the glass side has progressed rapidly. The best glasses on the market only let in energy in the form of visible light. Infrared heat accounts for more than 50% of the energy from the sun. When you block the infrared, you get a magical feeling of light without heat behind the glass. My favorite is a glass called COOL-LITE® XTREME 70/33, because it lets the most daylight through of the glass types that block the infrared energy.

"Best" solution solar control

The remaining energy from the sun can be effectively reduced with interior solar shading solutions. These have a hard time dealing with infrared heat, but the glass has already taken care of that. A good metallized fabric provides very good glare reduction, an improved u-value in the facade and at least a halving of the remaining solar energy that has entered through the glass. It does not have to contain PVC like external zip screens, operation and maintenance becomes easier and you do not need to install a separate solution for glare control.

So what does this facade solution look like? All modern glass for energy and solar protection has low reflection. It gives a good view to outside even at dusk. And it shows the interior, which is usually 50 times darker than the exterior (the Boverket wants us to keep 1% of the daylight indoors compared to outdoors). If you only have windows in one direction in a room, the glass is therefore perceived as dark from the outside. On the contrary, in corner rooms or where there is a glass ceiling, the glasses are perceived as very bright, they become the thin membrane you see in renderings. The Kasper Salin winner Merkurhuset in Gothenburg applies the specified facade solution. When the solar shading is activated, the glass looks slightly greener, because the roller blind highlights all three glasses in the insulating window. Without a curtain, the reflection gets stuck in the outer glass and the green tone disappears. The curtain diffuses the light, so no external glare occurs when they are active.
 

”Best" solution façade control

Now we have designed a solution that meets many requirements from consultants and certifications. In order to go from there to satisfied residents, the control of the solar shading is important. Motorization of solar control devices are important so that it does not get too hot inside. Behind an east-facing facade, there is no one to pull down the sunshade when the sun rises on a spring morning, and the energy that enters there stays in the house all day.

Today, the standard design is that the sun protection is activated and closed completely when more than 20,000 lux hits the facade. For a south-facing window, this can mean that the shader is completely closed 70% of the working time seen over the year. Building simulation has shown that with the correct control, the solar control curtains, thanks to the solar control glass, usually do not need to be completely closed more than a maximum of 20% of the time.
 

Additional measures for a lower built-in CO₂ footprint

Aluminum is still the very best material for keeping glass and facade protected from the elements without major maintenance. But carrying that system, wood begins to play an increasingly important role. With so-called add-on solutions, wood can replace aluminum in the structure that supports the facade on the inside. This can provide several benefits:

1. Low outside tempereatures do not convect through wood as it does through aluminum. The facade feels warmer on the inside and cold drafts are reduced.
2. Aluminum is hollow but wood is solid. This means better possibilities for noise reduction.
3. Wood has carelessly expressed no CO₂ footprint.

Wood requires a more careful evaluation than aluminum. You need to dimension the materials together, which is more demanding than designing a standard facade. And think about weather protection to avoid moisture problems during the construction phase.
Finally, alternatives for glass with a low CO₂ footprint are starting to appear. Saint-Gobain was first on the market with ORAÈ®, which is based on recycled glass. Today, 95% of all flat glass in Europe goes to landfill, which is a huge waste of resources. I want to close with a call to specify renovation and demolition in a way that puts an end to landfill. Here is a proposal for specification text:

Exterior glass (insulating glass) must primarily be inventoried for recycling into new flat glass, secondarily recycling with processing loss. Insulating glass cassettes intended for recycling into new flat glass must be dismantled whole and not crushed. Inventory of insulating glass intended for new flat glass should be carried out by a person with special expertise in glass.

Internal glass should primarily be inventoried for reuse.