To preserve the character of a barn in Kressbronn once used for farming and treat the architectural heritage of the location with due consideration and respect, Steimle Architects from Stuttgart made as few, gentle changes to the building as possible, and only after careful thought. Great care was taken to reuse the delicate construction of the far-overhanging roof and barn floor level and adjust them for future use. The concrete foundation that forms the base of the ground floor, manufactured by Bohner Bau from Tettnang, is made entirely of insulating concrete.
The quality of your “library in Kressbronn” project rests on more than just the great teamwork between you two as architect and contractor. What made up and shaped it?
Thomas Steimle: Of course, as planners we already had a clear impression of the desired quality and effect of the concrete component as early as the design process. Here in particular, the Bohner company proved very cooperative, goal-oriented and active in achieving the desired result. The processing of the insulating concrete was particularly challenging as it is a brand new material and one that most construction companies are not yet familiar with. This called for close collaboration. What’s more, we were able to support the Bohner company with our experience from a previously completed project using insulating concrete and we could make contact with appropriate advisory contacts. The openness to set foot into as yet unknown territory and work together in a constructive way to solve the tricky details was critical for good collaboration.
Michael Bohner: The steps between the planning and execution in this project were exemplary. Above all, one decisive factor was achieving the best possible quality instead of – as is often the case – keeping building costs down and working to tight timelines. Our collaboration was definitely shaped by the regular and thorough construction discussions where we were able to talk about a lot of the details and find solutions, even before construction began.
Had you worked together before? How did your cooperation on this project come about?
Thomas Steimle: Before now, there hadn’t actually been any chance to work together. The Bohner company qualified regularly in the tendering process for the exterior construction work trade and was therefore able to implement the shell of our planned construction work. Looking back, we’re glad that the services of such a demanding exterior construction were awarded to a highly qualified, local construction company.
Michael Bohner: No, we had never worked together before. As a regional, locally-based building construction company, we took part in a public tendering by the Kressbronn commune and ended up receiving the bid for this project.
Can you share a little anecdote from your time together on the Kressbronn project?
Thomas Steimle: The first time we sampled the exterior concrete walls for the base level, we were met with a gloomy mood by the builders and Bohner company. You could see the disappointment in the resulting appearance of the initially smoothed concrete surface in their faces. But as architects, our eyes lit up at the result. The crude-looking concrete surface with its yellowy shimmer obviously wasn’t a good fit for the Kressbronn library project, but for us it was the perfect sample for a different project we were working on – the reconstruction of the town hall in Remchingen.
Mr. Steimle, what expectations do you usually have for a design idea or a detail when you approach a contractor?
Thomas Steimle: Generally, by the time a contractor is involved, our planning is already well underway so that the desired result is clearly defined by the planning and tender. Of course, it means a lot to us that we are able to share our expectations of the execution with the contractor this way so that they are understandable and the contractor can have a clear image of the desired end result with the planning and additional coordination meetings.
Which characteristics are important to you in a contractor for working on your project?
Thomas Steimle: Mutual respect is the first priority. Looking beyond one’s own trade for the project in its entirety plays an important role in a smooth execution of a construction task. Openness to new things and accepting unconventional tasks as a challenge can stimulate cooperation and positively contribute to success.
How far into the design and planning process would you say there are no limits to what is doable or feasible for an architectural idea, such as with predefined standard products?
Thomas Steimle: During the design and planning process, the limits of what is doable are always being reassessed. Making decisions on the implementation of architectural ideas depends on a number of factors. Most of the time the architectural ideal is competing with the economic factors. Therefore the goal should always be to see the limits you find as an impetus to create great architecture.
Mr. Bohner, at what point in the planning are you normally brought in to consult on a project, and what would be the ideal scenario for you?
Michael Bohner: Because the library was a public construction project, the contract was also tendered and awarded accordingly by the commune. There’s not much wriggle room between the contract being awarded and the start of construction, so unfortunately contractors are often consulted very late.
What characteristics do you value most in architects and in collaboration with them?
Michael Bohner: For the implementation and coordination of the many trades involved to go smoothly, open and transparent communication on equal terms is essential. Any ambiguity should be cleared up personally and directly. Other important parameters for collaboration are patience, decisiveness and a building schedule that’s realistic in terms of the demands of construction.
How does the library building in Kressbronn respond to current energetic, constructive or creative trends?
Thomas Steimle: Because it has the feature of being an historic barn conversion, the library in Kressbronn am Bodensee doesn’t have to follow any current trends. This makes the building unusual, its construction integrated with the pre-existing. Its character was simply updated.
How were resources and the topic of recycling dealt with in this project?
Thomas Steimle: The existing wooden construction of the barn floor level and truss were deconstructed, mapped, adjusted for future use and re-erected with the new concrete base. The wooden slat facade is made from local woods. The woods and the monolithic, mineral building material of the insulating concrete guarantee that deconstruction will be easy and recycling will be uncomplicated.
Which construction task stood out and what specific solution did you find for it?
Michael Bohner: One task in particular was definitely processing of the insulating concrete and manufacturing the window sills, which were sometimes more than 7.00 meter long. After sampling several models, in the end the solution was to form and concrete all of the outer walls in two parts. Initially, work was only carried out up to the sill height. In a second operation, the rising walls were then completed up to the level support.
Thomas Steimle: As the customer, it was very important to the commune of Kressbronn am Bodensee that the character of this historic barn was preserved, thereby keeping its history alive while strengthening its presence in the center of the commune. For this purpose, a special slat structure was developed from existing, incomplete wooden paneling. The slats are rotated differently on their vertical axis, producing a different incidence of light on the library level.
How did the project change from the initial design to the fully completed construction?
Thomas Steimle: Originally, the plan was to obtain the base largely from rough masonry and concrete. At the start of construction it quickly became apparent that this material was weaker than expected and had to be replaced with the massive insulating concrete base. This was beneficial for the entire project and beyond, which is reflected in the numerous prizes and publications since.
What were the special features of construction on site?
Michael Bohner: When the earthwork and development works began, the library was a construction site without any remarkable features. But during the foundation works, when we had formed and concreted the first insulating concrete sample wall it became clear that there were still a few adjustments to make. The second sample wall which had a modified concrete mix and corresponding concreting had a satisfactory result, but it wasn’t quite secure enough to be used for the entire building. So, we formed a third sample wall and this finally produced a result that could be transferred to construction and, crucially, lead to an impressive uniformity in the visible concrete surfaces.
Thank you for the interview, Mr. Steimle and Mr. Bohner.
This interview was conducted by: Thomas Geuder, World-Architects.com.