This post is a follow-up to the WUFI simulation practice problem posted earlier to share the results of our simulation.
The first stage of the simulation is to create the component build-up within WUFI. Based on the description and the detail shown, the WUFI build-up of the original roof is as follows:
To simulate this build-up with the cellulose, the air space is replaced with cellulose as follows:
To assess the health of this build-up, the critical values to look at are the water content of the plywood and the humidity levels on the cold side of the insulation where the plywood may be trapping vapour. Rotting of the plywood becomes a concern if the water content is above 20%-M (%-M = mass percent = kg of water/kg of dry material). Humidity levels at the cold side of the insulation should stay below 80% to avoid mould growth within the roof. To determine if the interior moisture load makes a difference, the simulation was run with interior climate set to a “Normal Moisture Load” (typical of a living room or bedroom) and a “High Moisture Load” (typical of a shower room or kitchen).
Simulating the cellulose filled roof with a normal moisture load, gives the following water content at the inner and outer 1mm of the OSB board.