Surprisingly fire resistant
In the event of a fire, a log house will not burn like a timber frame house, but will in fact only char due to the sheer mass of the logs themselves. In direct comparison with steel, wood can cope much better in a fire.
The charcoal generated in the combustion process has a much lower thermal conductibility than the wood itself and forms a natural insulating layer during a fire. This protects the wood from becoming even hotter, while the load-bearing capacity is retained practically unimpaired. In contrast, steel loses most of its load-bearing capacity at temperatures as low as 500°C and has to be encased in other construction materials to achieve fire safety characteristics similar to those of wood.
We have been working intensively on the tightness of log houses for a long time. Tightness is very important not only in fire safety but also in terms of a house’s energy consumption.
In a fire test carried out by the VTT Technical Research Centre of Finland, a load-bearing Honka Fusion massive wood wall, 128 mm thick and made of non-settling logs, withstood a fire load for more than 90 minutes. The result clearly exceeded previous fire test results for log walls. In practice, this result means that a log house made of massive wood gives its inhabitants more time to escape a fire as its load-bearing structures can withstand the heat for a long time without collapsing.
The fire-resistance of the test wall was found to be as high as that of a normal, 40% thicker laminated log that had been tested previously. This was the first time that the laminated non-settling Honka Fusion log was tested. The test wall featured the new Honka Tech™ sealing solution as well as an innovative notch solution for log corners. In the test, the Honka Fusion wall structure achieved the REI 90 fire resistance class. REI 90 means that the structure can be used in demanding buildings where load-bearing wall structures must be tight, insulated against a rise in temperature and able to withstand a fire for 90 minutes.