A log house? With logs carved from solid wood sticking out in the corners? In another word, a cabin?
The images of log construction are strong – to the point of standing in the way of development in the industry. This is one of the things that has been discovered in the Modern log city project of the University of Oulu.
The project started last year with a preliminary report which looked at what consumers, authorities and the construction industry think about log construction. The responses showed that in addition to attitudes, also traditions and design set challenges.
”Log house constructors traditionally work with one-family houses. Construction companies that specialize in large works do not have knowhow in log house construction. And when there is little will for cooperation, log construction has no working market, and it can become expensive”, says professor of Architecture in the University of Oulu, Janne Pihlajaniemi.
To overcome the obstacles, we need new kinds of ways and links for cooperation. This is what the current design research phase of the project is aiming for.
”The intention is to show what modern log construction is capable of. We make examples out of larger log construction works and study what their architecture could be like – they cannot just be huge holiday cabins. And for one-family houses we are designing new models, which are suitable for an urban type of environment.”
What makes design easier is how log construction has developed in the last couple of decades. The old problem of the log wall settling as much as an inch per vertical metre has been overcome with modern lamella logs: the log is no longer solid wood carved from one trunk, but it is constructed by gluing together several pieces of wood. This construction method will enable the diversity of the log, and the absence of settling allows the use of large structures.
Another innovation is connected with corners. They no longer have to be so-called “long corners”, where the ends of logs continue beyond the notch. Instead, there are now available models with short corners, and even “city corners” which hide the notch. The latter raises the question whether a log house should nevertheless still look like a log house.
”That is one thing we will look into at the design stage. A new kind of log architecture has the technical prerequisites if any productional or aesthetic reason demands it”, says Pihlajaniemi.
Blocks of flats require massive log walls
In one-family houses, models resembling a cabin are already on their way out, and modern prefabricated log houses have become popular. Log has for a long time had a share of over ten percent in one-family house construction. In public and bigger buildings log is still completely marginal.
”The preliminary report asked building supervisors how suitable they think log is. Churches and school buildings were seen as the most suitable for log. Respondents saw challenges in blocks of flats and health care buildings.”
The town of Pudasjärvi has taken part in the project, and the town has commissioned a day-care center and a 10,000 square meter school center built from logs. The town of Haapavesi has a log-built day-care center as well. The non-settling log has made it possible to build a block of flats as well.
Finnish regulations allow the building of eight-floor houses in wood. Such buildings have already been constructed of plywood, which has some similarities with the lamella log. “It is possible to build even higher if we use functional fire design”, says Pihlajaniemi.
Log would have to be used in relatively larger amounts, as the tight soundproofing norms of blocks of flats require massive, double log walls. In fact, heat insulation regulations already require a 30 centimeter thickness of a log wall.
The extra costs from the massive size and the wood as material will be regained in the simplicity of the structure, and in how quickly the houses can be put together.
”A house with a wood frame has a plasterboard, a vaper barrier of plastic, insulators, windscreens, air gaps, and cladding. A log structure has nothing but wood, not even insulators.”
Simplicity is the strength of the log structure
Because log is ecological, heat insulation regulations are lenient with it: as wood binds carbon, it is allowed to lose more heat and thus produce more carbon emissions with heating. In light of the experience gained from Pudasjärvi, it is not cold inside a log building, and radiators will not glow red hot.
”Wood is a warm surface, and it gives a stronger sensation of warmth than concrete, for example. In addition, the insulation ability of a wall can be compensated by adding insulation in the roof. The roof can be of any kind”, says the professor.
Another thing that makes the walls seem warm is their impermeability, which in a modern log wall equals that of other construction types. Still, indoor air remains fresh, which is connected with how wood “breathes”, how it stores and gives out moisture.
”Users have given very positive feedback on indoor air. Simultaneously, soundproofing and acoustics have turned out to be excellent in day-care center use. Computationally they are not top-notch with log, and now we are trying to measure why.”
The reason could be the log surface: log walls are usually not lined, as simplicity is the strength of log construction. Because of that, the Modern log city project does not aim for quirkiness, but instead to improve the market share of log construction.
”Finland and especially Northern Finland has much more log house industry than other Nordic countries have. This is a potential export asset”, says Janne Pihlajaniemi.
Log construction in Helsinki and Rovaniemi
In May, the Modern log city project takes log construction to the center of Helsinki.
”There will be a pavilion between the Design museum and the Architectural museum. It is a four and a half meter high meeting place, where you can also take a look at the surroundings if you climb to the second floor”, says Janne Pihlajaniemi.
The pavilion is the idea of OUAS construction architecture students and university architecture students, and it is part of the project’s research planning stage. This stage also includes an architecture competition for students, seeking urban log house models.
The project will also expand to Lapland.
”In the following months we will start together with the city of Rovaniemi to look at how log could be used in regional construction works in addition to individual buildings. We will aim to create contacts with construction companies and the log house industry in the area of Metsäruusu.
The log pavilion in Kaartinkaupunki, Helsinki, will be opened 7 June. During summer, estimates and experiences of how log architecture works in the heart of a big city will be collected. (illustration of the log pavilion, Matti Lakkala, University of Oulu)
pictures: The town of Pudasjärvi is a forerunner of modern log construction. Among other things, the town has the biggest school campus made of log in the world.
Last updated: 2.6.2017