Many of Florian Nagler’s buildings seem austere and rooted within the region, based on their traditional appeal. However, they possess global relevance, due to their aim of rethinking conventional processes of construction, given recent and intensifying challenges. It isn’t obvious at a first glance that they are built manifestos. Within his research projects at the TU München he and his team explore how to implement the topic of “building simply” within our construction industry. We spoke with him in February 2022 in his office in Munich’s Pasing quarter, where he, with the most simple means conceivable, transformed the basement of a renovated house from the 1930s into a meeting room.
Frank Kaltenbach: There are plenty of reasons why building simply is important. What role does money play?
Florian Nagler: We are obviously interested in the question on how we can build in a cost-efficient way. Our research project “Einfach Bauen” – “Building Simply” was, however, inspired by a different motivation. We understood that the projects that we realised five to ten years ago were dominated by technology. Architectural elements had not been employed often enough in order to meet the different requirements. The most important question to ask at the beginning of a construction project therefore is: What do we actually need? We should only build what we actually need. That will eventually also reduce costs.
How can a pragmatic topic such as “building simply” be researched scientifically?
Our basic research led to scientific insight on how to use as little technology as possible in order to reduce heating energy demands in winter and overheating hours in summer.
What does this exactly look like?
We deliberated on which proportions a room requires and which window sizes are ideal in order to avoid the need for exterior sun protection. The results of our computer simulations based on rooms with identical area, yet different proportions resulted in a 3 m wide, 6 m deep and 3.3 m tall room. Windows should neither be too big, nor too small. Not surprising, but now we have scientific evidence that supports our line of argumentation. Once the simulations led to an ideal room geometry, we became interested in the influence of different materials on building performance. In Bad Aibling, we built three houses that are geometrically identical, yet consist either of timber, brick or concrete. Further buildings featuring loam and hybrid construction types will follow. By measuring indoor temperatures and energy consumption, we will gain empirical insight that can be transferred to general building practice.
How do you intend to convince your architectural colleagues to switch to smaller, more sustainable window sizes? The glazed curtain wall facade remains the ideal of architecture since the days of Mies van der Rohe.
I believe we have to build good houses that follow other principles. A successful example can achieve a lot of things! Perhaps we can even develop a new architectural language based on contemporary challenges. I am convinced that our research houses in Bad Aibling allow us to explore an interesting path forward. All three houses were developed based on construction-related requirements. The first features exterior walls consisting of solid timber, the second insulating brick and the third monolithic non-reinforced lightweight concrete. If you want to avoid reinforcement in solid construction or industrially prefabricated and multi-layered building components, an arched window lintel makes perfect sense, from a construction-based point of view.
Arches as a feature of residential architecture are often considered a sentimentality. Nowadays they even appear in administrative buildings. What do you think about their current revival?
Different than such mostly formal features, our arches are motivated by construction-based requirements. In the concrete house, we turned this requirement into a design theme. In the brick house, the arches consist of four quartered standard bricks laid on top of simple timber formwork. The walls feature a consistent U value without any thermal bridges. The mason was able to build the entire house using one type of brick. The arches don’t result in additional costs. However, more complex windows became necessary.
Mies employed single glazing. Nowadays we need triple glazing. Is extensive material consumption a further argument against glazed curtain walls?
Material costs aren’t the only issue. Many architects reject advice from building physics experts and opt for large glazed surfaces. Then they are upset that building services engineers fill the building with equipment for heating, cooling and air conditioning. We need to liberate ourselves from the false ideal of complete transparency. After all, there are many alternatives. We need to think about how to create a comfortable indoor climate with architectural means. Placing a window within a wall has been an architectural theme for ages. I think it is still relevant today. Complete glazing is pretty much dead.
Are your experimental houses a type of competition where either timber, brick or concrete can become the most sustainable material?
There are neither winners, nor losers. The idea was to show that walls don’t have to comprise many different layers, but instead and ideally only one. In the case of multi-layered systems, every single layer addresses one challenge – structural engineering, insulation or vapour barrier. In sum, follow-up challenges arise, due to the separation of materials and complex connections. We experienced that building in single layers isn’t simple, even in the case of the experimental houses. For the timber house, we opted for 30 cm thick solid timber walls that feature milled slots to improve thermal insulation. Weather protection, however, demanded an additional layer of siding. For the brick house, the perforations of the 42.5 cm thick bricks are not infilled with insulation. Yet, we had to protect them against moisture and frost with an exterior and interior render layer. Only the insulating concrete really allowed us to build a single-layer wall.
Concrete is under scrutiny, due to its larger carbon footprint compared to timber or the global decline in sand resources. And you build these exceedingly thick walls. How is that sustainable?
We don’t consider insulating concrete a material for the future mass production of buildings. We included concrete in the study, because it constitutes a major share of construction today. It also demonstrates great potential for renovations and historic preservation. But even in these fields, building simply is important. Historic facades shouldn’t be wrapped in polystyrene panels, simply due to energy conservation initiatives. Insulating concrete did appeal to us as architects, true. It is so much fun to build with. Nobody really knows how a thick, non-reinforced insulating concrete wall behaves in terms of building physics, for instance, if it is wetted. We are monitoring this across a period of time spanning winter and summer. In order to maintain the required U value, the insulating concrete wall would have to be 67 cm thick. We compensated this with additional insulation on the ground floor slab and the topmost ceiling slab. We were able to reduce the wall thickness to 50 cm and create more residential area as a result. None of the sloped roofs of the three houses are insulated. Cold attic spaces have been tried and tested for centuries and actually save costs.
Wasteful use of material and funding could be attributed to the exterior timber walls in Bad Aibling as well.
Sure, I could have used less wood for a load bearing wall and saved construction costs. But the commonly used lightweight construction types comprise less thermal storage mass, which is extremely important for the thermal functionality of simple houses. Unfortunately, thermal storage mass plays no role whatsoever in regulations on minimum energy use for new and renovated buildings. This is why developments in recent years led to increasingly thick insulation layers. Even though plenty of research shows that we are far beyond what can be considered sensible in this regard. This is why we want to research alternatives within this pilot project.
How does building simply relate to life cycle costs?
Current information on construction costs does not indicate the long-term expenditure for using materials that are discarded 25 years from now as hazardous waste. This aspect needs to receive consideration, also when providing subsidies for construction. An exclusive focus on insulation thickness or energy demand is wrong. Our monitoring has shown that building simply is more robust when it comes to improper ventilation behaviour of residents. In the case of low energy houses with mechanical ventilation and without thermal storage mass, permanent ventilation through open windows in winter has a negative impact. It is not intended this way, but actually happens.
Your Dantebad residential building in Munich (see Detail 7/8.2017 p. 26ff.) didn’t afford you the same degree of freedom as the research buildings. How did you achieve above-average quality despite a tight budget?
Experience has taught us that insulated wall framing construction is typically the most cost-efficient timber construction type. It hardly gets less expensive than that. Therefore, we used it. We chose cross laminated timber for the load bearing walls, either as a single layer or, where fire protection required it, with cladding. We wanted to know how we can meet the stated requirements by building as simply as possible. The rough sawn timber siding with back ventilation is a conventional construction type. Certain elements ennoble the building: The filigree timber frames display the size of the facade elements and indicate the composition of the building. The battens have a construction-related purpose. They cover joints and protect them from the weather. The house constitutes a grand gesture, contoured by the calm demeanour of the facade and, most of all, the clarity of the circulation space, including deep recesses in front of apartment doors along the access balconies. Tight scheduling finally did something good. We only had 12 months for the project, from start to finish. The need to be quick meant that the recesses, a tiny bit of luxury for subsidized housing, were actually overlooked when looking for savings.
Will the follow-up building, Dante II, exploit any and all potential for increasing efficiency?
We assumed that the major share of our planning could be sourced from the first building. The team was nearly the same as for Dante I – client, contractors, planning consultants. It is also true that different points of view regarding structural timber protection and differing availability of materials led us to revisit each and every detail.
In timber construction in particular, a high degree of prefabrication serves to reduce costs and construction time. Why didn’t you make use of this in your houses in Puchheim (see p. 78ff.)?
We always optimise logistics in cooperation with the timber contractors. The timber contractor for the Dantebad houses owns large assembly lines and completely prefabricated the exterior wall elements. In Puchheim, we worked together with a small company. It was more cost efficient and less time consuming for them to build elements on site.
Average rents in Munich are currently at 20.82 euro/m². For the apartments that you are planning for the Creative Quarter near the city centre, your client promised the city to set a rent limit at 10 euro/m². Do you have to build even more cost-efficiently than ever before?
We always build as cost-efficiently as possible. But even in the field of affordable construction, all requirements must be met. For soundproofing, we limit ourselves to the minimum requirements, similar to all our other rental apartment projects. If it were privately owned apartments, this would be difficult. In the Creative Quarter, the client is not a municipal housing authority, but instead, a private developer who builds premium apartments. Only when we lower our expectations on comfort we will be able to reduce costs. To abolish all that is redundant unleashes potential for completely new architectural qualities.
