Design rules etched in wood
There are some precautions, however, one must take to ensure the material’s durability. General design rules that apply to all natatoriums must be followed when using wood, too. The area needs to be conditioned by a dehumidifier to avoid any condensation and to keep the space at a relative humidity (RH) of 50 to 60 per cent. Additionally, the building envelope needs a continuous and unbroken vapour retarder, on the warm side of the envelope dew point, to ensure the moisture does not travel through it and condense within the structure.
According to the Western Wood Products Association (WWPA), wood cannot become mouldy until its moisture content reaches or exceeds 20 per cent.
Wood Handbook, published by the United States Forest Service’s laboratory, states wood would never have moisture content that high unless RH is at least 90 per cent, at any temperature.
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), has set recommendations on air movement, humidity, and temperatures within pool and spa facilities. Local codes often use ASHRAE standards as their basis, but these must be checked when designing or renovating a space. That said, standard design principles for pools must be followed to ensure the wood does not decay. The designer should get information from the wood supplier regarding what RH level will ensure the wood remains pristine. Suppliers will most likely call for 50 per cent RH. Note: Although the wood will not become mouldy, it will expand and contract as it absorbs and releases moisture; therefore, the design must account for these changes.
Whether or not one is using exposed wood, one of the most important things a designer must keep in mind is the airflow pattern. The goal is to allow good air that comes out of the dehumidifier to flow uninterruptedly to where it needs to go—in this case, the ‘breathing zone’ where people are usually present, plus any special concern areas, such as walls or windows that are likely to get cold.
The overall airflow pattern needs to ensure there are no areas of stratification, where air is not as well-conditioned as in the rest of the room. One must also make sure the overall air within the space is churning and not stagnating. The air within the breathing zone should be turned over, simply for the purposes of occupant health and comfort. It is not necessary the airflow be directed at any (and all) wood present in a natatorium, but it is important no part of the room falls outside the design condition range. Condensation on wood is as unacceptable as moisture on a window or door.
The Desjardins Sports Complex in Rimouski, Que., is a good example of how wood can successfully be used in an indoor facility. Opened in 2019, this building is modern in every sense of the word. From its highly efficient dehumidification system to the homogenous blend of wood elements and glass curtain walls, the structure brings both high-end design and facilities under one roof. The air distribution design in the complex is well executed, too. The project engineer and general contractor, Stantec, integrated the ducts into the building’s cedar ceiling, with air nozzles projecting slightly from the surface to direct air into the breathing zone and along the windows.