Wood and clay: building materials with positive effects

Building and living are among the largest consumers of resources and energy worldwide. They cause a high proportion of our emissions. For a long time, planners and builders paid too little attention to the CO ₂ footprint of buildings. And far too often, building was done with energy-intensive materials and processes. There are solutions to build houses that have a positive impact on our environment and health.

The Berlin architect Eike Roswag-Klinge has been designing sustainable buildings for years, models for a more ecological future of construction. He explains how smart the combination of modern and traditional construction techniques can be.

The Berlin architect Eike Roswag-Klinge specializes in the construction of sustainable buildings.

Photo: Daniela Friebel

The house: You design buildings that differ significantly from others

Roswag-Klinge: We want to build healthy, climate-adapted buildings that focus on people. We are looking for construction techniques that come after the fossil era. This quickly leads to natural building materials.

Which materials do you focus on?

Wood and clay. Of course, the component that is in direct contact with the earth cannot be wood because it would rot.

But we work a lot with wood and clay. Clay is quite expensive, which is why we often replace it with gypsum fibreboard - then the respective component remains open to diffusion and moisture-active and controls the indoor climate. Wood fiber materials are also hygroscopic. We generally also keep the ceilings unclad so that they can also actively control the room air. The floor should be a waxed or oiled wooden floor and should not be sealed with a synthetic varnish that would seal off the pores. We can work up to seven floors with visible wooden surfaces everywhere and thus keep the house optimally climate-active. We have also developed a building system that can be classified as low tech.

What kind of system is this?

It is actually a further development of the classic half-timbered house. We are building a wooden stud frame with a highly insulated building envelope with clay plaster on the inside and maybe a wooden facade or other weather protection on the outside. These constructions should ideally be single-layered, i.e. not use complex layers or even composite materials. That works today with very good insulation values, even as a plus energy building. These houses are also highly airtight. But with natural materials they remain open to diffusion - without vapor barriers. In this way they create a healthy indoor climate. Wood and clay control the indoor climate in the optimal area, and so no mold can develop. In addition, no technical ventilation is required. A very healthy indoor climate is created by ventilating twice a day.

Slate on the outside, wood on the inside: the multi-family house on the small Wannsee was built almost exclusively from natural materials and shines with a low-energy standard. The extensively green roof and a solar thermal system also ensure sustainability. The building material wood makes it possible to dispense with technical ventilation.

Photo: iStock / Chinnapong Roswag Architects

Why are you against technical ventilation?

We have been looking for new engineering solutions in construction for decades. We had cheap energy, the oil made many things possible. We have completely glazed houses, and when it got too hot you cooled down. And in the cold it was heated properly. But actually, a well-designed building envelope can take on a large part of these tasks. Without energy expenditure. For example, if you use less glass. You also don't need full glazing to expose properly. Forty to sixty percent of the wall surface is sufficient as a window for a good light supply. In addition, the extensive technology has made houses complex and expensive. It would be good to reduce that a bit.

Why do we need technical ventilation at all?

Almost all conventional houses that have such ventilation also need them. They are airtight with vapor barriers, and mold would develop without a fan. However, the indoor air is very dry in winter due to the technical ventilation. The air humidity can drop to 20-30 percent, so the growth of viruses and bacteria increases massively. Studies show that around 30 percent more cases of illness occur in technically ventilated rooms than in naturally ventilated rooms.

What would be the ideal humidity for living?

That is between 40 and 60 percent. Houses made of natural building materials achieve this through their construction.

Are your healthy buildings competitive?

Quite. Our goal is to bring timber construction into social housing. The apartments there are often smaller, which means they have smaller air volumes. This requires good planning to be able to do without technical ventilation. We are currently in the process of designing such a house with five floors in Bremen. We will also accompany this with research to see how it works. In Berlin - as a client - we are in a competition for a similar house. But we probably cannot pay enough for the property. We would like to offer social housing on a quarter of the area there, but the Senate administration is demanding the prices of the free market for the land. This is not affordable because the price of the property now makes up almost a third of the cost per square meter of usable space.

The New Founding House in Berlin provides for a mix of affordable living and social business and is to be built entirely as a visible wooden structure.

Photo: Roswag Architects

What should a potential builder think about today?

I advise investing in a good building envelope first. An envelope has stood for many decades or sometimes centuries. With the house technology you can optimize the remaining deficits if necessary. But it is also about the type of building: From today's perspective, a detached single-family house is no longer sustainable, it consumes too much resources, both in construction and in operation. As a builder, you should ask yourself: What do I really need? I often hear that people want a “small house”. It is not uncommon for this house to have two hundred square meters. But this is no longer a small house.

A small house would be maybe eighty square meters, like Bruno Taut's houses in Berlin. They are one of the most sought-after apartments in the city today because they have a great quality in the floor plan. With a smart floor plan, you can save many square meters. And with it money and resources.

Is the development towards ecological building going fast enough?

Too few such buildings are still being built. Unfortunately, the benefits of building with natural materials have not yet reached many builders. When you think of your descendants, you should leave them with the resources of the future (and thus values) with natural building materials - instead of disposal costs for chemical composites.

Where can a builder get information?

First of all with a competent architect. Those who are primarily concerned with healthy living are in good hands with the Federal Environment Agency with their questions about materials.

From a sustainability perspective, what do you prefer: a new building or the renovation of existing buildings?

I would like to ban the designation of new building land. Urban sprawl is a major problem. We still need the unobstructed natural and open spaces of our landscape for future generations.

We have done too much overexploitation in the past with the construction of cities and traffic areas. The consolidation of existing settlements, the use of fallow land or an increase is therefore more sustainable.

Old houses should only be demolished if there are compelling reasons. There are a lot of resources in the old structures built. It is important to use these intelligently. That would help reduce our carbon footprint.