hi,
I have the next wall build up:
Plasterboard
38mm Service void, formed with battens
OSB3 as airtightness layer
300mm ‘I’ Beams filled with Warmcell insulation
16 mm Agepan DWD wind tight, exterior protection board.
40mm ventilated cavity (1mm moisture capacity-38mm no moisture capacity- 1mmm moisture capacity)
20mm timber cladding
would you recommend to add a rain source in this build up? if yes, where?
Should I carry out the water content limit procedure check for this wall build up (Guideline for assessing the risk of interstitial condensation runoff)?
Do I need take into account the drying of construction moisture (phase 1 + phase 2)? In the guideline (https://wufi.de/download/guideline/Guid ... 240716.pdf) it is a masonry wall but I have a lightweight timber frame construction. if not, what initial conditions do you recommend for the materials?
Best regards,
Rain source location
-
Alberto Morales
- WUFI User
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- Joined: Tue Mar 29, 2022 10:57 pm -1100
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Christian Bludau
- WUFI SupportTeam IBP
- Posts: 1297
- Joined: Tue Jul 04, 2006 10:08 pm -1100
- Location: IBP Holzkirchen, the home of WUFI
- Contact:
Re: Rain source location
Hi Alberto,
I would primarily use a rain source if there is a realistic possibility that rainwater could penetrate behind the DWD board, for example at window connections, penetrations, or other vulnerable details. Lightweight timber-frame constructions are often much less tolerant of rainwater intrusion than massive constructions. Therefore, ensuring a rain-tight design and proper execution of all weatherproofing details is particularly important. A rain source can be useful to assess the consequences of potential leakage and the robustness of the assembly.
The water content limit procedure described in the guideline is primarily intended to assess the risk of moisture accumulation and runoff within the construction. For a timber frame wall, it can be a useful additional check if significant interstitial condensation is predicted. However, in many cases the standard evaluation criteria (moisture content, relative humidity, mold growth risk, and long-term drying behavior) are the primary indicators. Whether the runoff assessment is necessary depends on the results of the initial simulation.
Regarding construction moisture, the situation is different from masonry constructions. The two-phase approach in the guideline mainly addresses wet construction materials that require a prolonged drying period. In a lightweight timber frame assembly, construction moisture is usually much lower unless the materials have been exposed to rain during construction or were installed with elevated moisture contents.
Regarding the initial conditions, for lightweight timber-frame constructions it is common practice to start with an initial climate of 20 °C and 80 % RH. This assumption represents a moderate level of construction moisture and has proven to be a practical starting point for hygrothermal assessments of timber-frame assemblies. Additional construction moisture usually does not need to be considered unless there is evidence that the materials were exposed to significant wetting during storage or construction. In such cases, a separate sensitivity analysis with elevated initial moisture contents may be appropriate.
Christian
I would primarily use a rain source if there is a realistic possibility that rainwater could penetrate behind the DWD board, for example at window connections, penetrations, or other vulnerable details. Lightweight timber-frame constructions are often much less tolerant of rainwater intrusion than massive constructions. Therefore, ensuring a rain-tight design and proper execution of all weatherproofing details is particularly important. A rain source can be useful to assess the consequences of potential leakage and the robustness of the assembly.
The water content limit procedure described in the guideline is primarily intended to assess the risk of moisture accumulation and runoff within the construction. For a timber frame wall, it can be a useful additional check if significant interstitial condensation is predicted. However, in many cases the standard evaluation criteria (moisture content, relative humidity, mold growth risk, and long-term drying behavior) are the primary indicators. Whether the runoff assessment is necessary depends on the results of the initial simulation.
Regarding construction moisture, the situation is different from masonry constructions. The two-phase approach in the guideline mainly addresses wet construction materials that require a prolonged drying period. In a lightweight timber frame assembly, construction moisture is usually much lower unless the materials have been exposed to rain during construction or were installed with elevated moisture contents.
Regarding the initial conditions, for lightweight timber-frame constructions it is common practice to start with an initial climate of 20 °C and 80 % RH. This assumption represents a moderate level of construction moisture and has proven to be a practical starting point for hygrothermal assessments of timber-frame assemblies. Additional construction moisture usually does not need to be considered unless there is evidence that the materials were exposed to significant wetting during storage or construction. In such cases, a separate sensitivity analysis with elevated initial moisture contents may be appropriate.
Christian
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Alberto Morales
- WUFI User
- Posts: 79
- Joined: Tue Mar 29, 2022 10:57 pm -1100
Re: Rain source location
thanks for the reply, but, is it correct to follow "Guideline for the Calculation and Evaluation of an ETICS with Wood Fibre Insulation" for the build-up assembly that I have?
Plasterboard
38mm Service void, formed with battens
OSB3 as airtightness layer
300mm ‘I’ Beams filled with Warmcell insulation
16 mm Agepan DWD wind tight, exterior protection board.
40mm ventilated cavity (1mm moisture capacity-38mm no moisture capacity- 1mmm moisture capacity)
20mm timber cladding
Plasterboard
38mm Service void, formed with battens
OSB3 as airtightness layer
300mm ‘I’ Beams filled with Warmcell insulation
16 mm Agepan DWD wind tight, exterior protection board.
40mm ventilated cavity (1mm moisture capacity-38mm no moisture capacity- 1mmm moisture capacity)
20mm timber cladding
- Capture.PNG (62.75 KiB) Viewed 79 times
x
-
Christian Bludau
- WUFI SupportTeam IBP
- Posts: 1297
- Joined: Tue Jul 04, 2006 10:08 pm -1100
- Location: IBP Holzkirchen, the home of WUFI
- Contact:
Re: Rain source location
I would be cautious about directly applying the "Guideline for the Calculation and Evaluation of an ETICS with Wood Fibre Insulation" to your assembly.
The guideline was developed specifically for ETICS systems with wood fibre insulation. Your wall build-up differs significantly, particularly because the cavity between the I-joists is filled with Warmcel (cellulose insulation). Cellulose has different moisture storage and moisture redistribution characteristics compared to wood fibre insulation, so the assessment criteria are not necessarily transferable.
That said, some of the general hygrothermal principles discussed in the guideline may still be useful. However, I would recommend evaluating the results in the context of the properties of cellulose insulation rather than relying solely on the acceptance criteria established for wood fibre ETICS systems.
The picture is from the pitched roof guideline an not related to your ETICS?
Christian
The guideline was developed specifically for ETICS systems with wood fibre insulation. Your wall build-up differs significantly, particularly because the cavity between the I-joists is filled with Warmcel (cellulose insulation). Cellulose has different moisture storage and moisture redistribution characteristics compared to wood fibre insulation, so the assessment criteria are not necessarily transferable.
That said, some of the general hygrothermal principles discussed in the guideline may still be useful. However, I would recommend evaluating the results in the context of the properties of cellulose insulation rather than relying solely on the acceptance criteria established for wood fibre ETICS systems.
The picture is from the pitched roof guideline an not related to your ETICS?
Christian