Research article

The moisture distribution in wall-to-floor thermal bridges and its influence on mould growth

Authors
  • Yucong Xue orcid logo (College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China)
  • Yifan Fan (College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China)
  • Jiang Lu (School of Civil Engineering and Architecture, Zhejiang University of Science and Technology, Hangzhou, China)
  • Jian Ge (College of Civil Engineering and Architecture, Zhejiang University, Hangzhou, China)

This is version 1 of this article, the published version can be found at: https://doi.org/10.14324/111.444/ucloe.000042

Abstract

Moisture in building envelopes increases the energy consumption of buildings and induces mould growth, which may be amplified within the area of thermal bridges due to their different hygrothermal properties and complex structures. In this study, we aimed to (1) reveal the moisture distribution in the typical thermal bridge (i.e., wall-to-floor thermal bridge, WFTB) and its surrounding area and (2) investigate the mould growth in a building envelope that includes both a WFTB and the main part of a wall, in a humid and hot summer/cold winter region of China (Hangzhou City). The transient numerical simulations which lasted for 5 years were performed to model the moisture distribution. Simulated results indicate that the moisture distribution presents significant seasonal and spatial differences due to the WFTB. The areas where moisture accumulates have a higher risk of mould growth. The thermal insulation layer laid on the exterior surface of a WFTB can reduce the overall humidity while uneven moisture distribution may promote mould growth and water vapour condensation.

Keywords: coupled heat and moisture transfer, wall-to-floor thermal bridge, moisture distribution, mould growth

Rights: © 2022 The Authors.

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Published on
27 Oct 2022
Peer Reviewed

 Open peer review from Hector Altamirano

Review

Review information

DOI:: 10.14293/S2199-1006.1.SOR-ARCH.A4ZEST.v1.RHYYKU
License:
This work has been published open access under Creative Commons Attribution License CC BY 4.0 , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com .

ScienceOpen disciplines: Architecture
Keywords: Mould growth , Built environment , Coupled heat and moisture transfer , Moisture distribution , Wall-to-floor thermal bridge

Review text

Many thanks for answering and addressing my previous comments.

However, I still have a few that I would appreciate if you could address.

  • Regarding comment 2 on germination and development of mould, I would suggest re-writing the sentence: Further, mould growth is not limited to the indoor surface; it can easily germinate and expand inside building envelopes, especially where high levels of humidity are likely to occur. You can still use the same references.
  • Regarding comment 17, yes, mould may grow at the interface between two elements; however, only if nutrients are available (apart from appropriate moisture levels and temperature within a defined range). In this case, it is unlikely mould will grow inside a block of concrete and an autoclaved aerated concrete wall. Please review.
  • Regarding comment 19, the explanation is still not satisfactory. There is too much information in one diagram. Explain the diagrams in detail (e.g., arrows, dashed horizontal lines, etc.) and how you analysed the data in the graphs.


Note:
This review refers to round of peer review and may pertain to an earlier version of the document.

 Open peer review from Spyros Efthymiopoulos

Review

Review information

DOI:: 10.14293/S2199-1006.1.SOR-ARCH.AVHA9V.v1.RKOVRO
License:
This work has been published open access under Creative Commons Attribution License CC BY 4.0 , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com .

ScienceOpen disciplines: Architecture
Keywords: Mould growth , Built environment , Coupled heat and moisture transfer , Moisture distribution , Wall-to-floor thermal bridge

Review text

General remarks :

Very interesting article. However, the information and messages the authors want to convey are unclear on several occasions. Proofreading might help to communicate the messages more effectively.

37-39 Could you please rephrase this sentence?

41 This part could be changed: Further, Mould/ indoor surface

41-43 Could you please rephrase this sentence?

44 negative effects … is ( are )more apparent

45-47 Could you please rephrase / Also not entirely true (Can provide a few references but it might be a little impolite

(Ilomets, S., Kalamees, T. Evaluation of the criticality of thermal bridges. J Build Rehabil 1, 11 (2016). https://doi.org/10.1007/s41024-016-0005-6

Sedlbauer, K. (2001) Prediction of Mould Fungus Formation on the Surface of and inside Building Components. Ph.D. Dissertation, Stuttgart University, Stuttgart)

50-51 occupies the largest area?

51-52 This a little unclear could you please rephrase?

80-81 Could you please rephrase

82-83 bring out the moisture flow, Eq (7) are used… could you please rephrase

246 Figure 7 The y-axis of this figure is a bit unclear. Could you please explain a little bit more what information does this figure wants to convey?

246-256 I believe it is very difficult for fungi to grow inside such a construction even if the temperature and relative humidity conditions are favourable for growth. Two major reasons for this are 1 st ) there are no air-gaps between the elements of the construction so it is very unlikely that fungal spores could have been stored and would be able to flourish inside the material and  2 nd ) the materials used are concrete, expanded polystyrene and  autoclaved aerated concrete and cement mortar so the availability of nutrients is debatable.

248-252 Could you please rephrase?

260 The moisture affects the fungal growth. Seasons have an effect on fungal growth because of the changes in temperature and RH.

260-268 These statements might be true for the case examined in the context of this study but they cannot be generalized. The direction of the moisture transfer relies on the internal and external conditions and in different climatic conditions the opposite direction might be the norm.

263-264 Could you please explain this a little more

280-282 Please rephrase

294 Please rephrase

309-310 These conclusions can be drawn only for the cases examined in the context of this paper. Please avoid generalizing these conclusions.

321-322 The 4 and 5 conclusions are debatable. As mentioned earlier it is very unlikely that mould could grow inside the building construction. Therefore, the seasonal effect on the temperature and RH conditions within the construction cannot be used to assess whether the conditions become favourable for mould growth during different seasons.

329-330 Please rephrase.



Note:
This review refers to round of peer review and may pertain to an earlier version of the document.

 Open peer review from Hector Altamirano

Review

Review information

DOI:: 10.14293/S2199-1006.1.SOR-ARCH.A1FBCA.v1.RYKWOU
License:
This work has been published open access under Creative Commons Attribution License CC BY 4.0 , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Conditions, terms of use and publishing policy can be found at www.scienceopen.com .

ScienceOpen disciplines: Architecture
Keywords: Mould growth , Built environment , Coupled heat and moisture transfer , Moisture distribution , Wall-to-floor thermal bridge

Review text

Specific comments are below:

  • This document needs proofreading
  • There are a number of sentences where more information is needed  (e.g., line number 16, where was moisture distribution modelled?
  • In line 42, the author referred to condensation for the germination and development of mould, however, mould only develop under high levels of humidity and not condensation.
  • Also, in line 42, the authors indicate that mould could grow inside building envelopes. Please provide a few examples of where inside the envelope, mould could grow.
  • It is not clear why the software COMSOL was used.
  • More details should be provided regarding the weather climate used in the modelling presented in Figure 2. You refer to a climate zone in China.
  • Fig 2a should be uninsulated, while 2b insulated. Please amend.
  • You also refer in section 2. 3.1 to an existing Atlas; what exactly is this?
  • In section 2.3.2 please provide more information on how data was collected from a residential building in Hangzhou.
  • Figure 3 explains how radiation intensity and moisture load were used in the study.
  • In figure 3, please use lines to express temperature and relative humidity. The use of dots makes it extremely difficult to read and understand the environmental conditions in both graphs.
  • Correct the text in lines 181 and 182; it should read Figure 4a and 4b.
  • Explain what each of the values in Table 3 refers to. But also how they were used to assess the risk of mould growth. Did you consider time in the evaluation?
  • Please explain the concepts used in the analysis, moisture sink and moisture shadow. This is very unclear in the document.
  • Please add some explanation in Fig 5, so what do the colours represent; red=cold and blue=warm?
  • Are you presenting in Fig 5 the results for the uninsulated or insulated detail?
  • Why is it important to calculate the area for each moisture sink and moisture shadow? Please explain, in more detail, how they were generated and how they can be used.
  • Please enlarge Fig 6. The moisture shadows and most of the information you are trying to describe in the text is unreadable.
  • In line 242, you refer to the germination of mould spores inside the building envelope; are you referring to the space between the insulation and concrete?
  • Regarding mould assessment, did you use the info in the isopleth to define transient conditions? The isopleths were created based on steady-state conditions.
  • Please better explain figure 7; it is unclear what exactly you are showing and where in the diagram and wall detail you have assessed mould growth. Also still very unclear how the risk of mould growth was calculated. What do the red arrows and red area represent?
  • Mould need time to germinate and grow. So, the conditions of RH and Temperature presented in the isopleths (Fig.4) need to be constantly occurring for the time there indicated for mould to germinate and grow. Under transient conditions, mould will take much longer or don't react to those conditions. Please explain and discuss.
  • Regarding your discussion, please expand the discussion on the urban heat island effect and how the phenomenon found could be affected in winter.
  • Explain further the role of solar radiation and wind-driven rain and their impact on the results obtained. This was not at all assessed in the paper. You need to consider that in practice, external wall insulation won't be just insulation on the external pane of the wall. Other materials will be installed and
  • Explain in more detail the white dew and cold dew concepts


Note:
This review refers to round of peer review and may pertain to an earlier version of the document.