Straw Buildings: A Good Compromise between Environmental Sustainability and Energy-Economic Savings

Round 1

Reviewer 1 Report

The manuscript addresses the present trend in the design, construction and implementation of new materials for construction of buildings, from the perspective of the environment, sustainability, energy and economy.  The authors report their study of two straw buildings with different characteristics and types of applications.

The authors consider the thermal performance of the two structures during the summer and winter seasons.

In recommending the acceptance of the manuscript for publication in the Journal, I note that Figures 3-9 do not convey any useful scientific information.  Perhaps, they should be deleted or at best, included in the Supplementary Materials.  I do not see any value, both from the scientific as well as the architecture point of view, in these figures.

From an application stand point, it would be good to include a few sentences along the following lines:

While the straw based construction may provide utility in summer, in winter seasons, it will require additional insulation.  However, the concept of straw-based construction can be a practical solution in tropical countries.  In fact, it is practiced in several tropical countries due to the low expense as well as the low-maintenance. 

Author Response

Thank you for this review. I have tried to improve the text and, in order to be clearer, I try to answer by points:

1) In recommending the acceptance of the manuscript for publication in the Journal, I note that Figures 3-9 do not convey any useful scientific information.  Perhaps, they should be deleted or at best, included in the Supplementary Materials.  I do not see any value, both from the scientific as well as the architecture point of view, in these figures.

I tried to explain better why we inserted this part. These straw houses have the same performance as the other buildings that are built in Europe and the United States. In order to have these performances, the technology used which allows to reduce the thermal bridges and guarantee a good thermohygrometric behavior as well as the duration in time is very important.

2) While the straw based construction may provide utility in summer, in winter seasons, it will require additional insulation.  However, the concept of straw-based construction can be a practical solution in tropical countries.  In fact, it is practiced in several tropical countries due to the low expense as well as the low-maintenance. 

The typology of straw houses treated in this work are detached single-family buildings that are not built in tropical countries but in the United States and Europe, especially in France but also in Italy. They have good performances both in summer and in winter.

Reviewer 2 Report

The paper looks like a case study. The authors must add more data and/or analysis to make it a research article.

Author Response

Thank you for your observation: “The paper looks like a case study. The authors must add more data and/or analysis to make it a research article.”

We have added some technological material in paragraphs "2. Straw constructions" and "3. Case studies" to better explain how these straw houses are made. Then we compared the results obtained with those of the nearly Zero Energy Buildings and with the standard requirements (at the end of paragraph 3). We added paragraph "4. Technical and economic feasibility" in which we indicated costs, construction times and type of incentives that could be used to encourage the construction of straw buildings. Finally, the conclusions have also been modified with further useful information in order to understand in which context this work fits and what repercussions it could have in the Piedmont Region (in Italy).

Reviewer 3 Report

This paper presents a brief review of straw bale construction, a description of two straw bale projects in Italy (one a conventional load-bearing house; the second a small pre-fabricated panel structure), a description of thermal monitoring of each building, and some analysis and comparison of the thermal performance of each building.

I believe there is definitely some interesting and useful data and analysis here and the paper is worthy of publication. The big criticism I would have is in the Literature Review. It is mainly focussed on Europe, which is fine, but the authors should let the reader know this and that there is a wide range of literature from outside of Europe which is not being reviewed.

Other things which need to be addressed:

Lines 32 – 34: These sentences are quite confusing and mis-leading. When you say: “In the United States, the first straw houses had a supporting structure made of steel bars, in order to maintain the straw bales lined up, an electro-welded mesh to hold up the cement plaster and foundations in reinforced concrete,” you are surely not talking about the 1^st straw bale houses in Nebraska! They would not have been using steel, except maybe in the nails! I am not aware of any straw bale houses that used “steel bars” as the main supporting structre. Could you provide more details and a reference.

 

Lines 67 – 70: Your description of “load-bearing” straw bale construction is not consistent with the usual definition. It seems to imply that bare straw bales are used to make up the walls: “This system requires that the bales of straw transfer the loads deriving from the horizontal elements to the foundations …” Load-bearing walls will still be plastered and it is the combination of straw and plaster that creates a sandwich panel that carries loads to the foundations. If you have something else in mind, and have examples, please provide more details and references.

Lines 190 – 193: I cannot figure out what you are saying here. Perhaps an image would help to make it clearer.

Lines 260 – 263: Normally new information is not introduced in the Conclusions. This should be part of the Discussion.

Comments for author File: Comments.pdf

Author Response

Thank you for this review. I have tried to improve the text and, in order to be clearer.

I try to answer by points:

1) I believe there is definitely some interesting and useful data and analysis here and the paper is worthy of publication. The big criticism I would have is in the Literature Review. It is mainly focused on Europe, which is fine, but the authors should let the reader know this and that there is a wide range of literature from outside of Europe which is not being reviewed.

We have specified that the type of thatched houses we have treated allows to have buildings that have the same performance as standard buildings but with less environmental impact (they are not buildings built in developing countries). These buildings are mainly built in Europe and the United States and are very similar buildings. We have added bibliographical references [15], [23] and [24] which describe where these buildings are located in paragraph "4. Technical and economic feasibility".

2) Lines 32 – 34: These sentences are quite confusing and mis-leading. When you say: “In the United States, the first straw houses had a supporting structure made of steel bars, in order to maintain the straw bales lined up, an electro-welded mesh to hold up the cement plaster and foundations in reinforced concrete,” you are surely not talking about the 1st straw bale houses in Nebraska! They would not have been using steel, except maybe in the nails! I am not aware of any straw bale houses that used “steel bars” as the main supporting structure. Could you provide more details and a reference.

In fact, the scenario in the United States is so vast that, not wanting to dwell too much on the introduction, those phrases were confusing and misleading. We have therefore modified the text by focusing attention on the origin of these houses and how they have been the springboard for their development in other countries as well. This work aims, in fact, to deepen the use of the straw construction system in Europe and to encourage its dissemination. This is because there is little reference to literature and foreign examples.

We have rewritten this part:

“The first straw houses were built in Nebraska around 1890, in the central plains of the United States. The scarce availability of timber and sandy soils did not facilitate traditional constructions.
Thanks to the invention of the machine for packing straw, and therefore the transformation of straw into "big bricks", they began to stack them one on top of the other, with staggered joints as in load-bearing walls, taking the name of Nebraska Style or Loadbearing Style. Initially these houses were considered temporary, but the time and the progressive improvement of the construction system made them recognized as durable houses.
A few years later the construction of straw also arrived in France. At the end of 1920 they completed the Maison Feuillette, in Montargis, the oldest known and existing building in Europe that is isolated whit straw.”

 

3) Lines 190 – 193: I cannot figure out what you are saying here. Perhaps an image would help to make it clearer.

We rewrote this part:

“Finally, in order to improve the breathability and thermal and acoustic insulation of the pre-assembled module, a coating layer was added to both sides: lime plaster on the external side and lime plaster or clay plaster on the inner side. The wooden structure also serves as a windward element and is covered on both sides with reed panels, the classic "arelle". This improvement was not considered in the Verrès prototype and, for logistical reasons, it was deemed necessary to opt for an OSB coating on both sides.”

4) Lines 260 – 263: Normally new information is not introduced in the Conclusions. This should be part of the Discussion.

We added the new paragraph "4. Technical and economic feasibility" in which I inserted costs, construction times and type of incentives that could be used to encourage the construction of these thatched buildings.

Reviewer 4 Report

Dear Authors,

first of all I find this paper, very interesting, but some issues (mainly editorial one) need to be considered:

1. The abstract should be more precise and "juicy". It should just point the main idea of the paper, and encourage the reader to explore the subject
2. abbreviations - there are some shortcuts, I think connected with region names, which needs to be developed when you use it for the first time. Not all readers will be from Italia and know where these places are. Also check other abbreviations
3. the presentation of results needs to be improved. The x-axis labels on the charts should be Time not no of measurement. This would give us a better view of this experiment.
4. It would be also interesting to compare results with data for traditional insulation materials like wool or EPS (calculation for the same thickness of the wall).

Besides these issues, please check the grammar and spelling errors, which does not affect the legibility of the text. Please look to the attached text.

looking for revised text.

Best Regards!

Comments for author File: Comments.pdf

Author Response

Thank you for this review. I have tried to improve the text and, in order to be clearer.

I try to answer by points:

1) The abstract should be more precise and "juicy". It should just point the main idea of the paper, and encourage the reader to explore the subject.

We have rewritten the abstract

2) abbreviations - there are some shortcuts, I think connected with region names, which needs to be developed when you use it for the first time. Not all readers will be from Italia and know where these places are. Also check other abbreviations

Abbreviations refer to the Italian provinces; have been rewritten in non-abbreviated form

3) the presentation of results needs to be improved. The x-axis labels on the charts should be Time not n. of measurement. This would give us a better view of this experiment.

We changed all the graphs indicating the minutes instead of the number of measurements made (the measurements were made every 10 minutes); so it is more understandable.

4) It would be also interesting to compare results with data for traditional insulation materials like wool or EPS (calculation for the same thickness of the wall).

We added a sentence after Table 1: " It can be observed that the thermal conductivity of straw is generally higher than a standard insulating material such as expanded polystyrene sintered (EPS) or rock wool with a conductivity of about 0.035-0.04 W/m/K.”

We also compared the thermal transmittance of the straw walls with typical values of nearly Zero Energy buildings in paragraph 4.

5) Besides these issues, please check the grammar and spelling errors, which does not affect the legibility of the text.

The text was proofread and corrected by a native English speaker

6) Lines 67 – 70: Your description of “load-bearing” straw bale construction is not consistent with the usual definition. It seems to imply that bare straw bales are used to make up the walls: “This system requires that the bales of straw transfer the loads deriving from the horizontal elements to the foundations …” Load-bearing walls will still be plastered and it is the combination of straw and plaster that creates a sandwich panel that carries loads to the foundations. If you have something else in mind, and have examples, please provide more details and references.

We probably synthesized this part too much. Now we have modified the text to make it clearer.

We rewrote this part:

“Load Bearing. In this construction system there are not load-bearing structures of wood or other material. This technique requires that the straw bales, together with the plaster that covers them and all the materials that make up the stratigraphic package, transfer the loads deriving from the roof and from the horizontal elements to the foundations, thus guaranteeing both structural support and thermal insulation.”

7) Lines 190 – 193: I cannot figure out what you are saying here. Perhaps an image would help to make it clearer.

We rewrote this part:

“Finally, in order to improve the breathability and thermal and acoustic insulation of the pre-assembled module, a coating layer was added to both sides: lime plaster on the external side and lime plaster or clay plaster on the inner side. The wooden structure also serves as a windward element and is covered on both sides with reed panels, the classic "arelle". This improvement was not considered in the Verrès prototype and, for logistical reasons, it was deemed necessary to opt for an OSB coating on both sides.”

8) Lines 260 – 263: Normally new information is not introduced in the Conclusions. This should be part of the Discussion.

We added the new paragraph "4. Technical and economic feasibility" in which I inserted costs, construction times and type of incentives that could be used to encourage the construction of these thatched buildings.

Reviewer 5 Report

Comments

1. Images shown on Figures 10 and 11 are blurred, not focused. First picture from the left (Figure 11). The first photo from the left - the symbol "~" means the camera is not ready for use, the image was not focused.
2. Why the heat flux is maximum during the minimum temperature difference - Figure 12 and 13. Thermal inertia, if possible, is very unlikely. It should be explained. How the authors explain it?
   
3. There is no information in the study on average outdoor temperatures, number of degree days for given locations, solar radiation (there is only information about temperatures during the measurements). It should be given, because energy performance index EP is recalled.
   
4. Line 259 - EP_H,nd = 23.4 kWh/m²/y - wrong unit, correct unit is kWh/(m²y). Similarly units: W/m/K, W/m2/K are wrong (Table 1,4), W/(mK), W/(m²K).
5. Is energy of 4.5 kW of polycrystalline modules consumed?
   
6. It is difficult to refer to the conclusions. There is only energy performance index. The reader doesn't know:
   
   • what about utility and final energy (without efficiency and with the efficiency of the heating system);
   • what is the heat demand of the building;
   • how the EP ratio was calculated, coefficient of expenditure on non-renewable primary energy (it may be different in different countries), what effect the heat source has on the EP, please explain it;
     
   • what are the unit costs of heat, otherwise the value of 100-150 Euro/y says nothing.

Please note the comments

Author Response

Thank you for this review. I have tried to improve the text and, in order to be clearer.

I try to answer by points:

1) Images shown on Figures 10 and 11 are blurred, not focused. First picture from the left (Figure 11). The first photo from the left - the symbol "~" means the camera is not ready for use, the image was not focused.

The image quality of Figures 10 and 11 is the result of the operator's choice. In this case, the thermographic images were only used to identify a measurement point in the absence of disturbances such as the presence of thermal bridges. The images were taken in visible and infrared overlay mode so that we could remember where the images were taken. With this type of images visible+infrared, the images are just a little more “grainy”. The image with "~" had been put because it was the only frontal image of the building; it has been removed and replaced with another one on the north side where the measurements were taken. Below are the examples of the overlapping images that our thermal imaging camera provides and they all have the same definition in this mode.

Please, see the pdf file attached.

2) Why the heat flux is maximum during the minimum temperature difference - Figure 12 and 13. Thermal inertia, if possible, is very unlikely. It should be explained. How the authors explain it?

The specific heat flow q is measured on the inner wall together with the surface temperatures. Not being in steady state (constant temperatures), we cannot calculate the thermal transmittance instantaneously and therefore we use the method of progressive averaging.

There is a time shift between the heat flow affecting the outer wall and the heat flow entering the room due to the thermal storage capacity of the straw wall. The thermal flow that enters the environment therefore cannot be proportional to the measured difference in surface temperatures. This behaviour of the straw structure can be explained with the equation (3) and can be seen clearly in the following figures: the peak of external temperature does not coincide with that of internal temperature. The time shift has been calculated with formula (3) and is about 19 h. We have added some sentences to better explain this behaviour.

3) There is no information in the study on average outdoor temperatures, number of degree days for given locations, solar radiation (there is only information about temperatures during the measurements). It should be given, because energy performance index EP is recalled.
There is a time shift between the heat flow affecting the outer wall and the heat flow entering the room due to the thermal storage capacity of the straw wall. The thermal flow that enters the environment therefore cannot be proportional to the measured difference in surface temperatures. This behaviour of the straw structure can be explained with the equation (3) and can be seen clearly in the following figures: the peak of external temperature does not coincide with that of internal temperature. The time shift has been calculated with formula (3) and is about 19 h. We have added some sentences to better explain this behaviour.

We added the Heating Degree Days in Table 2.

4) Line 259 - EP_H,nd = 23.4 kWh/m2/y - wrong unit, correct unit is kWh/(m2y). Similarly, units: W/m/K, W/m2/K are wrong (Table 1,4), W/(mK), W/(m2K).

The ways of expressing the units indicated are equivalent: kWh/m2/y is equal to kWh/(m2y); as well as W/m/K is equal to W/(mK) and W/m2/K is equal to W/(m2K). We have removed divisions and brackets from the units of measurement to avoid misunderstandings.

5) Is energy of 4.5 kW of polycrystalline modules consumed?

4.5 kW is the installed power of PV modules

6) It is difficult to refer to the conclusions. There is only energy performance index. The reader doesn't know: what about utility and final energy (without efficiency and with the efficiency of the heating system); what is the heat demand of the building; how the EP ratio was calculated, coefficient of expenditure on non-renewable primary energy (it may be different in different countries), what effect the heat source has on the EP, please explain it;

The EPH,nd was calculated from the design data and this value is on the Energy Performance Certificate. The methodology for the evaluation of the EP and the reference legislation is described in [20] and [25]. We have added these references.

7) what are the unit costs of heat, otherwise the value of 100-150 Euro/y says nothing.

The Casa Cembo has a consumption for space heating of 1200-1300 kg of wood per year that in Italy have a cost of 100-150 €. We have added a sentence in paragraph 4.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Acceptable.