WUFI

Hi,

I'm looking at moisture accumulation in a wall constructed behind a curtain wall glazed panel. The wall assembly built in WUFI (from inside to out) is:

26mm plasteboard and plaster skim
0.5mm foil faced vapour control layer
150mm mineral wool in metal stud layer.
120mm unventilated cavity (without additional moisture capacity)
5mm unventilated cavity (without additional moisture capacity)
1mm unventilated cavity (without additional moisture capacity)
28mm double glazed unit (centre pane u-value @ 1.0 W/m2.K)

The climate data has been adjusted by -2oC & +5% RH to reflect 1 in 30 year condition, requested by the insurance company. Air infiltration is set to 3m3/m2 into the mineral wool layer.

I'm using the automatic time step control. The calculation has 0 convergence failures and Balance 1 & Balance 2 are relatively close, B1 = 0.06 , B2 = -0.03.

Plotting the RH throught the wall assembly, we have the results in the graph attached. This shows constant 100% RH in the 1mm cavity closest to the glazing unit, a range of 97-99% RH in the 5mm closest to the glazing unit and a range of 92-97% RH averaged across the whole 120mm cavity.

The outermost 13mm of mineral wool have RH in teh range of 87-97%, with no year on year moisture accumulation. The mid point of the mineral wool ranges from 65-92% RH. The water content in the 1mm cavity layer ranges annually from a low of 60g/m2 to 125g/m2 - both of which are high enough to induce water drips.

I'm interested in guidance on how to interpret the RH in the cavity positions and in the mineral wool. How much importance should I give to the cavity results compared those for the mineral wool?

Many thanks in advance.

Nick

To add to this question, removing the unvented cavity between the insulation and the glazing unit delivers much more stable results. Ie equilibrium is acheived within two years and the annual cycle of total water is regularly repeated.

Therefore, this raises the question of whether the unvented cavity, combined with impervious (to moisture) outer layers is messing with the equations.

regards

Nick