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    Review of 'The influence of ground slab permeability on wall moisture in a historic building'

    The influence of ground slab permeability on wall moisture in a historic buildingCrossref
    A useful but inconclusive monitoring exercise in a case-study building.
    Average rating:
        Rated 3 of 5.
    Level of importance:
        Rated 4 of 5.
    Level of validity:
        Rated 2 of 5.
    Level of completeness:
        Rated 2 of 5.
    Level of comprehensibility:
        Rated 3 of 5.
    Competing interests:

    Reviewed article

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    The influence of ground slab permeability on wall moisture in a historic building

    When impermeable ground bearing slabs are installed in old buildings without a damp-proof course, it is a common belief of practitioners within the conservation industry that ground moisture will be ‘driven’ up adjacent walls by capillary action. However, there is limited evidence to test this hypothesis. The accumulation of moisture in walls can promote the decay of the wall materials, decrease the thermal performance of the building envelope and adversely affect the comfort and health of occupants. An experiment was used to determine if the installation of a vapour-proof barrier above a stone flag floor in a historic building would increase moisture content levels in an adjacent stone rubble wall. This was achieved by undertaking measurements of wall, soil and atmospheric moisture content over a three-year period. Measurements taken using timber dowels showed that the moisture content within the wall did not vary in response to wall evaporation rates and did not increase following the installation of a vapour-proof barrier above the floor. This indicates that the moisture levels in the rubble wall were not driven by capillary rise.

      Review information

      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.

      Architecture,Materials science
      masonry,capillary rise,evaporation,Built environment,conservation,historic building,wall moisture,renovation,soil moisture deficit,timber dowel

      Review text

      The paper presents the results of in-situ monitoring in a case-study building, analysing the influence of reducing the floor vapour diffusion on the moisture balance of a surrounding wall. The analysis of the case study shows that the wall moisture content did not change as a result of sealing the floor area with a polyethylene membrane, and the monitoring results were found to be in contrast with the numerical results from a sharp-front model on capillary rise. Below are some more detailed points that need addressing:


      1. The paper doesn't provide information on the hygrothermal properties of the existing building materials considered in the analysis. A geological map is mentioned (please add a reference), but there is no information on the hygrothermal properties of the materials used in this house for the wall and floor.
      2. The concrete slab is represented by the installation of a polyethylene sheet; however, there is no comparison between the two:
        • In the method section, please add information on the hygrothermal properties of both, at least on the vapour resistance.
        • It is likely that the polyethylene sheet has a lower vapour resistance than the slab; also, construction moisture is not considered in the analysis. In the discussion section, please add a discussion point on the difference between the two.
        1. The title refers to "ground slab permeability "; it is more appropriate to rename it to "ground floor vapour permeability"
      3. In the methods section, some points are unclear:
        • Why were monthly intervals considered? For some of the methods considered, a more frequent sampling is possible, and this could have been beneficial for the analysis. Also, other measurements could have been considered for this analysis.
        • Are all the measurement points presented? A Tinytag logger was mentioned in the results section, but it is not clear if it's the indoor logger or a new logger beneath the polyethylene sheet .
      4. Most of the text found in the discussion consists of the results of a sharp-front model on capillary rise and the comparison with measurements:
        • Please move this part to the result section
        • Introduce this comparative analysis in the methodology. E.g. "The wall moisture changes were then calculated using the potential evaporative drying measurements, and the results of this calculation were compared with the wall moisture measurements".
      5. In figure 10, it would be best to refer to WME (wood moisture equivalent); the text already explains the limitations of this reading. Also, if this chart presents unreliable measurements (as mentioned in the text), what is the value of having it in this paper?
      6. The discussion section is very limited; expand the discussion section,  elaborating on the relevance of these results and limitations, including the following:
        • Is the polyethylene sheet appropriate to represent a concrete slab? Some vapour accumulated initially, but there is not information on the moisture levels under the polyethylene sheet in the long-term, nor any discussion on where the initial vapour might have transferred to (absorbed by the floor material? Through the polyethylene sheet?)
        • The available ground moisture is measured considering the soil moisture deficit; please add information on how this compares with other locations. Is this a location with particularly low water table or is this representative of an average ground moisture?
        • Is the timeframe of this analysis long enough? The conclusion refer to long-term changes, but moisture can build up in years, and three years is possibly not long enough.
        • Is this measurement method the most appropriate? How could this methodology be improved for more conclusive results? How have other researchers tackled similar problems?
        • What can be the causes of discrepancy between model and measurements? Is there something that the model is missing?


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