Cladding systems don’t fail because of the timber. They fail because of the system and the choice of profile. The profile defines the way timber is used in the cladding system. Moreover, how the profile is used in a particular wall direction defines the exposure level of a wall. If a specific profile is selected to match a certain timber species for a specific wall direction, then wall exposure is not a problem. However, if the profile is not selected, then it is very possible customers will be complaining about the said wall within a very short period of five years. The same can be said for different combinations of profile and timber. Other than vertical boards, the most prevalent profile used in cladding systems is the feather edged, shiplap and open jointed, rainscreen profiles. Although vertical board cladding systems are not used solely for aesthetic reasons, the choice of cladding system is largely dependent on the way the system manages water flow. Feather edging is arguably the oldest systems and can be very effective if used properly. The feather edging boards are not only used in horizontal overlapping construction, but where timber is used in the old system, the top board is used to hide the joint between the boards and the bottom board is used to lap over the next board. The solution to how to leave a board to lap over the top board is to ensure a maximum of 25mm timber is used to lap over the top board and a maximum of 25mm of a capillary is used to lap.
Essentially, while interlocking joints are able to shift moisture outward, if not maintained, the joints and timber can shift to the point where moisture is allowed to seep in. Because Siberian larch handles moisture well and therefore timber gaps better, it is good choice for shiplap. Pine can vary greatly and cause timber gaps because of moisture content, but Siberian larch can avoid the gaps if moisture content is balanced. Open-Jointed Rainscreen Rainscreen System is basically a different system. Rainscreen is designed to be a inclined façade deflector with gaps between boards and a breather membrane concealed behind. It is balanced by the cavity behind the membrane and, if done right, should be the most durable of all three systems. It is a better option for timber because the boards aren’t sealed tightly so timber movement isn’t problematic. Concealed fixings are the most popular because they allow a seamless finish, but they also create rigidity at the fixing point so, if and when the timber does move, the gaps can’t shift and the timber will be distressed at the fixings.
In certain types of timber, especially in pressure-treated softwood, the timber is prone to expansion and can be observed to be weathered and appear to be damaged in some manner. This timber to some may look like it has been damaged over time and is due to movement with the expanding timber and timber splitting. Using stainless steel screws and pre-drilled clearance holes brackets which are face-fixed may be frowned upon in some circles, but it actually provides the timber with some comfort and flexibility. Also, a pre-drilled clearance hole provides lateral expansion of timber by lowering the ambient stress at the screw.
One Decision That Shapes Everything Else
Horizontal or vertical timber board placement is a decision that may denote the position of the drainage, maintenance access, and the fastening system. The vertical and horizontal timber boards allow for drainage between each board joint. The position of the gap and the proper detailing of the system are very important factors to consider. The position of the gap and drainage system load, when vertical timber boards are used, becomes almost the entire system behind the boards and is conditions that must be met. The trade off for the vertical timber boards is that gravity and drainage control of the system behind them are very important.
The position of each choice affects the others. This is why species and selection of timber is dependent on timber for system loads.