Large increase in Water content

[Alberto Morales]

Hi,

I have the next build-up with water repellent and foil faced PIR in both sides modelled as vapor retarder (sd=1500).

is it right?

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Evaluating the WC in the PIR I have observed irregular, non-periodic changes in the total water content what makes me think that something can be wrong in the results. any thoughts about this change in trend?

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However there are no larger differences in balances as it can also be recognized in part by the total
water content curve above

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Best regards and thanks in advance

[Daniel]

Dear Alberto,

you're right, that does not look very good.

The steep vertical increases in water content are obviously not correct. However, in the total balances these problem remain unvisible - this may be because the issue is simply a slightly incorrect distribution of moisture within the building component, which is not apparent either in the total water content or in the surface moisture fluxes.

In any case, you can assume that no moisture accumulation will occur between two layers with an sd value of 1500 m. And ss the total error ist only 0,01 kg or 10 g (0,1 kg/m³ * 0,1 m³) over 10 years, the influence on the neighbour materials remains completely negligable.

In other words, to sum up: You can perform a normal evaluation.

best regards
Daniel

[Alberto Morales]

thanks Daniel once again.

two more question:

1- Could the "Assessing the Risk of Interstitial Condensation Runoff" guideline be applied for a foil face PIR insulation which is between an unventilated cavity and concrete?

2- could be used these formulas:

µ* = 0.09 · Rmet / (3.5 · Dx*) = 0.026 · Rmet / Dx*
lambda* = Dx* / Rnon-met

for the case we have unventilated air layer facing in one side with a brick and the other side with a face foil aluminum PIR insulation, which value should we take? the one from the column Rmet to calculate µ* and lambda*?

[Christian Bludau]

Hi Alberto,
regarding your questions:
1) yes, the condensation in air layers part
2) yes, the Rmet values - these should always be used if there is at least one metallic surface connected to the air gap
Christian

[Alberto Morales]

thanks, but how can we evaluate the risk of interstitial condensation in a wall which includes face aluminum foil PIR as none of the guidelines include steps to follow for cases with this type of close-cell insulation?.

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as the difference in water content over 10 years is around 25g (above ± 10 - 20 g/year) in the PIR, I have some concerns.

Any thoughts?