An ecological house made of straw, wood, and clay—the serene Villa Koppar is a minimalist’s dream

The house is simple and minimalist. The backyard is a terrace accessible from the second floor.

Onni the dog lounges in the middle of the entryway floor, patiently waiting for his master. Mika Ilvonen often takes Onni to nearby forests or a local pond, while Laura Sundström prefers to head out with the dog on forest paths that cut across the fields.

The couple’s new home, Villa Koppar, is named after the nearby Kopparnäs recreation and nature conservation area. The house stands on a rocky slope in the middle of the idyllic Inkoo countryside. The windows offer a tranquil view over the fields.

That same tranquility is evident everywhere you look. Besides the large dining table, there are only a few other pieces of furniture in the upstairs living area.

The floors, walls, and ceiling are made of clay. The clay plastering was done by Riikka from Rouhis. The natural cement floor from Vihdin Betoni contains no cement but includes clay and stone; its carbon footprint is small compared to a traditional concrete floor. A three-sided glass-doored fireplace by Brunner divides the space.

The kitchen countertops are Dekton. The lightweight pendant light above the island is by Luceplan. The fireplace is manufactured by Brunner.

The walls, floor, and ceiling seem connected to each other—monolithic, as an architect might say.

“All the surfaces here are made of clay. The walls and ceiling have clay plastering, and the floor is natural cement. Natural cement is a new material that also contains clay. Clay binds impurities from the air and balances humidity,” Laura explains.

The floors blend seamlessly into the walls and up to the vaulted ceiling, which soars to a height of four and a half meters in the living room.

The ceiling rises to four and a half meters in the living room. Wall lamps by Flos provide indirect lighting via the ceiling. The sofa is from IKEA.

Not a single piece of molding or casing catches the eye. The simplicity has required skill and meticulous planning from the designers. In this style, there’s no room for errors, as there is no molding to cover them up.

From the outside, the house is as minimalist as it is inside. Paired with an outbuilding housing a garage, a separate office, and a guest room, the house is built at the foot of a rocky slope. Both buildings are clad with spruce panels treated with ecological Organowood, which gives the wood a silvery surface and makes it durable.

The ash dining table, made by a carpenter, was designed by Laura and her interior designer friend Tuuli Virtanen.

The oak-fronted kitchen was designed by Collaboratorio and ordered from Zacus. The faucet is by Tapwell, the stainless steel sink by Franke, and the handleless oven by Miele. Windows were ordered from Lasita.

The kitchen island is one meter wide and three meters long, with space for two bar stools at the end.

Laura and Mika’s house was completed in 2023, and when they moved in at the beginning of June, little Edith was born just four weeks later. But in the beginning, there was only the couple’s dream.

“We wanted the most ecological house possible. Building always consumes natural resources, but in our project, we aimed to minimize the environmental impact,” Laura says.

The carbon footprint of a house over its entire life cycle is determined at the design stage. The most decisive factors are the building material and the heating method. Laura and Mika chose geothermal heating.

They quickly realized that defining an ecological material is not straightforward.

“A good example is the currently popular wood fiber insulation, whose production from virgin natural material requires a lot of energy. We chose insulation made from recycled wood material, that is, paper,” Mika explains.

Laura Sundström and Mika Ilvonen wanted to build a sustainable and healthy modern house with as little environmental impact as possible. Mika holds their one-year-old daughter Edith.

Architect Kasper Järnefelt was initially involved in the house’s design. He has a ‘summer cottage’ made of straw and clay in his yard, which sparked the couple’s interest in the material.

“I fell in love with the look and feel of clay plastering,” Laura says.

The final design of the 150-square-meter house was created by Kristiina Kuusiluoma and Martino De Rossi of architecture studio Collaboratorio. In addition to their architecture studies, both have studied ecological building in Austria.

The house’s straw bale elements, reinforced with wooden frames, were clay-plastered from the inside. The strength of the structure is best seen in the window openings: the windows rising directly from the clay floor are set in half-meter-deep recesses.

Behind the wood-slat staircase railing is a corridor-like utility room, which leads to the backyard. The wooden stair treads are made of oak. The large steps are coated with Wall2floor decorative plaster by Novacolor. The natural cement in the floor includes clay from Kouvola, Finland.

The bedrooms are located downstairs, while the living areas, sauna, and bathroom are upstairs.

The washrooms are finished with plaster. The original plan was to finish them naturally with traditional Moroccan Tadelakt plaster, but the price per square meter would have been too high.

“Because of the baby and the dog, the wet room surfaces have to endure a lot, and Tadelakt would have required more maintenance than the plaster we chose,” Laura adds.

The washroom is compact but functional. The sauna benches showcase Laura’s father’s craftsmanship. The walls and floors of the wet areas are coated with Novacolor Wall2floor decorative plaster. The glass walls were supplied by Lasitehdas.

The vessel sink is by Svedbergs and the faucet by Tapwell. The oak vanity unit was ordered from Zacus. Walls and floors are coated with Novacolor Wall2floor decorative plaster.

The shower features a functional and beautiful shelf for toiletries.

“At the very beginning of the project, it became clear that building sustainably is more expensive than conventional modern construction,” Mika notes. “Additionally, our crystal ball didn’t show the sharp rise in interest rates and the war in Ukraine when we scoped the construction budget, and the budget was exceeded by a fifth.”

Fortunately, there’s another way to look at it. The expensive initial investment pays for itself through low operating costs and longevity. A satisfied family lives protected by straw walls.

“If this house were left here to deteriorate, eventually there wouldn’t be much left of it on the plot—perhaps just the concrete foundation, metal roof, and windows. I think that’s a wonderful thought,” Laura says.

From the living room and sauna, there’s access to the 70-square-meter terrace behind the house, which feels like a bridge between the building and the rock. Standing on the terrace of Villa Koppar, you’d like to believe that this is the future of building: in harmony with nature, not against it.

Onni is ready for a walk in the forest. The pine-framed front door was made by Lasita, like the windows of the house. To the left is the entrance to Edith’s room. The interior doorways reach all the way to the ceiling. The chest of drawers was supplied by Zacus based on the couple’s design. The rug is from IKEA.

The home’s minimalist aesthetic continues in the decor of the parents’ bedroom. The clay-plastering of the walls was done by Riikka from Rouhis. The bed is from a collection by Karup Design. Wall lamps are by Flos, linens from IKEA.

The straw bale structure of Villa Koppar in Inkoo is protected by spruce cladding treated with Organowood to be durable, eliminating the need for repainting. Behind the facade cladding is a four-centimeter ventilation gap. The steel roof’s paint coating is rapeseed oil–based.

The detached house in Inkoo has an area of 150 square meters.

How the eco-home was built from straw elements

On the rocky 0.7-hectare sloped plot stood a dilapidated building. After it had been demolished and groundwork finished, the foundation of the new house was made on a concrete slab, with footings cast on-site from blocks laid on a gravel bed.

“We used as little polyurethane as possible in the foundation. Inside the footings, we chose Foamit foam glass aggregate for insulation and as a capillary break,” Mika says.

They chose straw elements as the building material, which were clay-plastered from the inside.

“Straw itself isn’t a load-bearing structure, even though it’s highly compressed and therefore quite fire-resistant, among other things. The elements are reinforced with a wooden frame,” Laura and Mika explain.

The old buildings on the plot were demolished in January 2022. Groundwork was done in June of the same year, the foundation was ready in August, and the element delivery arrived in October. Interior work began in November 2022, and the house was completed in May of the following year.

The intermediate floor of the two-story house is supported by Posi-Joists, which combine wood and metal.

“The joists are handy because you can run all the building services quite freely between them,” Mika notes.

The partition walls were built from wooden frames and Fermacell fiber gypsum boards, which were finally clay-plastered.

The natural cement floor has a lively surface.

The upper floor’s structure includes about a seven-centimeter layer of natural cement. Under the casting, the couple-centimeter-thick plywood sheets have the pipes for the hydronic underfloor heating attached.

Natural cement is a new material, and pouring it on the second floor added an element of suspense.

“Natural cement required compaction with a concrete vibrator. We were anxious about whether the Posi-Joists would stay in place. But everything went well,” Mika recalls.

In the middle of the living room, a fireplace acts as a room divider and additional heat source. The intermediate floor is supported by Posi-Joists, on top of which are plywood sheets where the hydronic underfloor heating pipes were later installed.

The strength of the straw element house is best seen at the window openings. Windows rising directly from the clay floor are set in half-meter-deep recesses.

Windows that extend almost to the floor bring the scenery inside. The frames are partially embedded in the wall and floor structures. No molding can be seen in the house.

“If we were to build again someday, we’d allocate even more budget to the project and monitor expenses very closely from the start. Fortunately, we had great support. Laura’s father deserves special mention; he was on-site building every weekend for a year. Without him, we would never have met our project’s timeline,” Mika notes.