Standard structural details
Logs are used mainly for wall construction. Floor and roof construction can be executed in the same way as in other forms of timber construction.
Standard structural details for solid logs are simple. It is important for the architect to specify the characteristics required of the wall, the shape of the logs and the joints, plus any possible surface treatment. The shape of the groove and the way it is sealed, plus the thickness of the logs are specified in accordance with the required characteristics.
In external walls, logs can be used as they are, or with additional insulation. The thicker the log, the better the technical properties associated with energy, fire and sound. The properties can be affected by the shape of the groove between the logs and the way it is sealed. Further information on the properties that can be achieved with logs of different shapes and thicknesses can be obtained from log manufacturers and from Building Information Sheet RT 82-11168.
In partitions, the important thing is that the height of the log and its vertical construction are the same as in the external walls, so that the sink or settlement will be the same. The sound insulation of a log partition can be improved by altering the shape and sealing of the groove and by using thicker logs. Logs can also be used for walls between apartments.
Besides properties associated with strength, special attention must be paid to ensuring that junctions are weather-tight. Preventing draughts is vital when trying to achieve high energy efficiency. Junctions must remain weather-tight despite changes of shape caused by sink or settlement. It is also important from the point of view of long-term durability that moisture is prevented from entering the construction.
Junctions with foundations
It is recommended that junctions with foundations are carried out using a soleplate. If a soleplate is used, it is easier to measure precise locations in the walls on top of the foundations. A layer of bitumen felt should then be used on top of the foundations to prevent moisture rising by capillary action. The soleplate must be properly fixed and sealed against the foundations. The joint between the bitumen felt and the soleplate can be sealed with adhesive sealant when fixing the soleplate, by squeezing a ribbon of sealant onto the underside. If necessary, a sheet-metal profile can be fixed to the soleplate to tidy up the joint by covering the top edge of the plinth rendering and the bitumen felt. A drip may also be required above the foundations in a log building, since the facade may not necessarily come above the plinth as it would in a board-clad elevation. The lowest course of logs is fixed to the soleplate by screwing though the logs. An EPDM seal is fixed under the lowest course of logs, so that it remains between two level surfaces. It is then a simple matter to install the lower joists of the suspended ground floor and fix them on top of the level soleplate.
Intermediate floor junction
It is recommended that, at intermediate floor junctions, the ends of the floor joists are supported in recesses cut in the log wall. The joists are installed in conjunction with the installation of the log frame and can be fixed by screwing into the top of the log-wall. In this way, the wall junctions will be tidy if the joists are to be left visible on the underside.
At the junction between the roof and the external wall, it is important to ensure that the junction allows movement of the roof joists as a result of sink or settlement. A gang-nail truss junction with the external wall is perfectly normal with other types of timber construction.
Door and window junctions
Because of the need to control sink or settlement, log-construction tends to have thick covering boards, or architraves, around doors and windows. Modern woodworking methods, however, allow logs to be shaped in such a way that doors and windows can also be fixed without external covering boards. It is recommended that a horizontal timber is used above the opening, to which the frame is fixed and sealed.