Mastering Moisture Control – The Key to Success

A feature of mass timber is the ability to utilise the exposed structural timber as the decorative surface. This feature saves the need for additional covers, making mass timber competitive. However, the issue is keeping the exposed structural timber looking great during the building process.

The main culprit here is water. Excessive moisture promotes mould or simply stains the finished surface. Therefore, managing the water during construction is the key to a successful outcome.

The first issue to help solve this is to have all involved in the design and construction of the mass timber building understand that moisture management is part of the plan. This concept also involves the client, who needs to understand there will be an expense to manage the moisture. In the long term, this expense will be less than any remedial action that may be required.

The other aspect is that all on the construction site need to own the moisture management plan. This simply is put, don’t allow water to pond on the structure. Therefore, immediate action to sweep the water away is required when it rains, and yes, it always rains on a mass timber building construction site.

To prevent this water from damaging the lower surface, all joints in the floor or column penetrating through the floor need sealing. This is commonly done with vapour-permeable tape. Care is also required to check that the tape has not been damaged during the course of construction. If it does get damaged, it needs to be repaired. Again, it becomes a practice on the construction site to provide a budget and have someone check.

Where greater protection of the finished surface is required, or there is an extended break in the construction program, consideration should be given to placing a vapour-permeable membrane across the entire floor.

Consideration is then required to expel the water when the water ponds, requiring the ponding water to be swept away. A standard solution is to utilise the service holes in the floor and create a floor drain using tape or a puddle flange. But simply transferring the water to the next floor without dealing with it is not the solution. The water needs to be collected and diverted away, generally to a lift shaft or service core. Below are images of a simple collection point and garden hose disposal system.