cause a large part of this variation. What is the R-value of a straw bale wall system? It is hard to evaluate R-values in a wall system like you describe. can significantly decrease the R-value of a wall because the moisture Some lab tests of straw-bale assemblies have found significantly lower R-values in practice. Photography by Laurie Dickson. There are straw board products available; however, I donât know much about their r-value. E11.5. The California Energy Com-mission currently accepts an R-value of 30 for all plastered straw-bale walls. Centimetre for centimetre, straw has similar insulation value to fibreglass batts. Straw bale walls have a minimum R-value of 38, twice that of an insulated stick-built wall, which averages R-19. on the Crest (not the toothpaste) web site. California Energy Commission. Straw bale walls are at least eighteen inches thick. The R-value for a straw Wood and straw have similar moisture-absorbing characteristics; moisture In this part of the world, wheat, barley and oat straw are the most commonly available. R-values vary by board thickness. it would take forty-one days to evaporate 1¼ lb. The article you referenced has a pretty good summary of the work that went into determining a straw bale wall's R-value, and the exact number may have once been a controversy, with some believing that the walls performed in excess of R-50 while actual test data showed values in the middle R-20s for a given wall thickness (18"). is completely redistributed, the moisture content of the straw will be We personally love the marriage of straw bale and cob architecture. absolute humidity. Relative humidity is the percent of moisture available for the redistribution of moisture. transported towards the inner wall must be re-evaporated. A new test of the thermal performance of a wall built with 19-inch straw bales laid flat revealed that the wall had an R-value of 27.5. temperatures become much colder and the water inside the plaster walls temperature and relative humidity are known. Thus he concluded that the insulating value is R-2.68 per inch (0.054 W/m°C) when heat flow is perpendicular to the orientation of the straws (bales stacked on edge) and R-2.38 per inch (0.061 W/m°C) when the heat flow is parallel to the straw orientation. much greater and the R-value of the straw will be significantly decreased. Dew Point: If a surface is cooled sufficiently, The warm As a result of the higher R-value of the straw bale << colder, moisture will begin to condense on the inside of the outer wall. in a redistribution of the moisture within the straw. Gutex R-values for Ultratherm 50 given as R 6.6 for a 1 15/16" thickness. While this relatively high R-value confirms that straw bale construction can decrease heating and cooling energy usages by up to nearly one-third over conventionally built homes, the new R-value is lower than those that have been previously reported. of water requires 1250 Btu’s while an ice layer about ¼” thick. about 16 pounds. A rendered straw bale wall has almost 5 times the R-value of a brick veneer wall. Meet the Panel â the Building Block of the Future. side of the wall was at 70ºF and the cold side was at 0ºF. When laid flat and stacked like bricks in a ârunning bondâ pattern, a plastered straw-bale wall is ±27â³ thick, with an R-value of 1.3 per inch, or R-30 total. 2. In the fall, as the weather becomes Get a free estimate. If bales at 70º F and 14.5% EMC are placed in a wall with a vapor If all the heat flowing into the wall contributed to water evaporating, redistribution of moisture it could take months to reach equilibrium The measurements made may have been accurate, but if the wall had been Paxton, J. The high the R-value the more insulative a material is. for polyethylene foam), or for an assembly of materials (e.g. This adds aesthetic value to the home as thick wall are expensive to achieve with conventional construction. conditions are established, the absolute humidity within the bales will than the energy needed to raise the temperature of a pound of water to Retrieved from https://www.buildinggreen.com/news-analysis/r-value-straw-bales-lower-previously-reported. I recently looked at some ten-year-old conversations on straw bale R-values R value for strawbale walls is often overstated, and there is a lack of reliable duplicable testing, but R-30 imperial (or around R 5 metric) is probably optimistic, and a 6 inch or 150mm thick wall of clay slip /straw will have an R value closer to 1.2 to 1.5 metric or 7-10 imperial. Straw bale homes: Straw bale house ... Bale walls have a very high R-value (around R40) and make for about as environmentally responsible a building material as you can get. may have been considerably higher. cavity2 showed that at the onset of an applied temperature differential, 70ºF. The relative humidity near the The R-value is a measure of the resistance of a material to heat flow through it. Citation, (1998, September 1). The thicker the bale, the better the R-value. The condensed moisture will lower the Relative Humidity: Warm air can hold more water given the several months needed to reach equilibrium, the measured R-value When equilibrium approached and less water is being transferred to the outer wall. Straw bale wall R-value is calculated for 3 unit R-values for straw to cover potential variability. much more moisture. energy flowing through the wall each day. the cold wall. This water when condensed on the cold outer wall will form Study on Energy Efficiency in Buildings Proceedings. A further explanation of the principles governing moisture in insulated freezes on the surface, it produces a pressure difference that sucks barrier on the inner and outer surfaces and the outside wall is dropped relatively dry. These values were reported in, Published September 1, 1998 What Goes on within a Wall Average material thickness across foam block wall sections are as follows: 6 inch foam has 2.9 inches polystryene each side and 3.4 inches of fill. will allow water to be wicked through the outer wall as it is formed, © 2021 BuildingGreen, Inc. All rights reserved except where noted. You can have the insulation you need for colder winters by building with straw bales, and cob can be used on your homeâs interior for absorption/thermal mass, to round out straw bale walls and/or to add sculptures and depth. The worlds most elegant refrigerators are also the world's most efficient! Does r-value have any meaning w/ bales of straw? Daniel Y, I don't think you will find that straw rots like hay does. This much moisture will not Bales are formed by compressing and tying strings around packages of straw. Migration in a Closed only 30 Btu’s flow though a perfectly dry straw bale wall each a straw wall that allowed only two weeks to reach equilibrium. flow. In The bales also provide a highly effective sound barrier. Dry straw has a limited ability While regular brick only has an R-value of 0.80, straw bales are considered to have an R-value of anywhere between 25 and 35. rate of 30 Btu’s/day. 1952. You may login with either your assigned username or your e-mail address. The energy required to evaporate a pound of water is 14 times larger freezes, this process will stop. Equilibrium Time Constant for a Straw Bale Wall A straw bale minimizing the water collected on the inner surface of the outer wall. soaking straw in colored water for a month the water barely rose up the During this time period the measured to R 0.94 per inch. What is R-value? 98% NATURAL RENEWABLE MATERIALS. In Europe the oldest straw bale structure may be the ivy-covered straw bale house in Montargis, France, built in 1921. was considered when looking at how moisture redistribution affects heat bale wall will then be reduced by a higher percentage at the onset of He used a single bale of wheat straw, at 8.3 pounds per cubic foot (pcf) density and 8.4% moisture content, and used a guarded hot plate to determine an R-value of 54.74 for a 23â³ wide bale and R-50.33 for the bale laid on its 16½â edge. The following table lists the thermal properties of rammed earth (adobe). Guarded Hot Plate. R-Value of Straw Bales Lower Than Previously Reported. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Moisture. to 6%, the straw in one square foot of wall will contain 1¼ pounds Straw bale building really performs optimally. more moisture through the plaster. As a consequence of the slow An R-value can be given for a material (e.g. in the air compared to saturated conditions. freezing point. The R-value of a straw-bale wall is between R-32 and R-42, two to three times better than the walls of most conventional homes. In practice this gradual seasonal change in temperature Reputable labs arrived at these measurements; however I have not seen an adequate explanation of the varying results. K). The R-value is the ability of a certain material to resist the passage of heat from one side to another. to the quantity of moisture in the wall and the wall’s R-value. R-value is a measurement of a materials insulating quality, higher the number the more insulating. Straw is defined as the dead stalks of small grain-bearing cereals. The actual R-value of the earth and the compacted straw would not add up to R-40, but then the performance of the entire package could perhaps be equivalent to a good straw bale hut that would be R-40. Thus he concluded that the insulating value is R-2.68 per inch (0.054 W/m°C) when heat flow is perpendicular to the orientation of the straws (bales stacked on edge) and R-2.38 per inch (0.061 W/m°C) when the heat flow is parallel to the straw orientation. R 0.94 per inch to R 2.38 per inch. of moisture. The freezing water then liberates part of this variation may not be due to the straw itself but to the moisture will begin to condense on it. Thermal Insulation (R-Value) A definitive test using state-of-the-art equipment at Oak Ridge National Laboratories yielded an R-value of 27 for an 18-inch-thick straw-bale wall (and, by inference, a value of 36 for a 24-inch-thick wall). cold wall will be close to 100%. data generated for wood can thus be used to determine the moisture content collect on the outer wall in a home. moisture content of the wall will be reduced from 14½ % to 6%. Transactions, ASHVE. I imagine it would not be very good because the vast majority of the r-value in a bale wall comes from the entrapped air inside the bales and the overall thickness of the walls. 1998. The straw bales, finished by plaster, have a high R-value. A 23-inch-thick straw-bale wall has an R-value of about R-33. Much of the published information on the energy performance of straw-bale buildings is based on measurements done in 1993 by Joseph McCabe at the University of Arizona as part of his master’s thesis. Gutex Ultratherm 160 is 6 5/16" thick and has an R-value of 21.5. I initially thought that straw would readily wick water. wall has a constant moisture content per unit of volume, or constant walls can be found in the “ASHRAE Handbook of Fundamentals.”. Refrigerators and Freezers | Models | Vaccine Refrigerators | Home Composters | Composting Toilets absolute humidity within the bales. The phenomenon to a value less than 32º F. The smaller the pores, the lower the If the outer wall dips below the dew point, moisture will Straw will take on moisture and release it, whereas hay will take on moisture and rot do to mold. Compressed straw bales have a wide range of documented R-value. A paper published by the California A typical strawbale wall has an R-value greater than 10. to wick, so this phenomenon is probably not significant. ASHRAE. The temperature where straw. The tested cavity was only 2 inches thick. R-value will be continuously increasing as equilibrium conditions are be constant as it is in a wall made of porous insulating material, and of 1¼ lb. If only sensible heat is considered, the extent to which moisture A âthird generationâ straw-bale technique combines a straw-bale interior wall with an exterior stud wall insulated with cellulose By Ben Graham | November 17, 2014 An exterior stud wall provides room for more insulation. Straw bale insulation is technically a densely packed cellulose fiber. determine exactly how the redistribution of moisture in a straw bale The reported R-value of straw bale walls varies from R 2.38 per inch to R 0.94 per inch. A standard straw bale is 450mm thick with an R-value in excess of 4.8 and up to R9 for a standard bale. Absolute Humidity: Absolute Humidity is the As a consequence, when the temperature of the plaster A straw bale home can save up to 75 percent on heating and cooling costs annually [source: Morrison, Amazon Nails ]. It has an R-value ranging between 30-50, providing cost savings for the life of the home. wall has a considerably higher R-value and also is capable of holding 3. A major can evaporate. This process is similar to the way ice lenses are formed. from completely freezing, so the process can continue. Commins and Stone. The vapor of straw. The moisture content of straw primarily depends on the relative humidity, There are two common sizes of bales⦠When Engineers, Inc. 2. In that report the test results with It would probably be beneficial to do additional experimental work to was observed in sawdust-insulated cavities. Wicking water away from a cold, wet outer wall towards the warm wall Homes insulated with straw bale can have insulation values of R-30 to R-35 or more. Straw bale walls are very well insulated, when built correctly can have an R-value between 40 and 60, depending on the thickness of the wall There are many great resources out there that discuss the insulation characteristics of straw bale . He reported R-values of 48.8 (RSI-8.6) for bale on edge and R-54.8 (RSI-9.7) for the bale laid flat. vapor than cold air. Without an exterior stud wall, most straw-bale walls have an ⦠1. is below 32º F moisture can still migrate through the wall. its latent heat, keeping the boundary between the ice lens and the wall Unlike other more common building materials, the R-value More on Gutex is at FIBERBOARD SHEATHING of water at the can be determined if the absolute humidity is known or if the The dew point R-value is a measure of thermal resistance, or resistance to heat flow. A 23-inch-thick straw-bale wall has an R-value of about R-33. As a result of the drop in the EMC from 14½ % about 2% near the warm wall, and about 13% near the cold wall. A major part of this variation may not be due to the straw itself but to the distribution and redistribution of moisture within the wall. What is the R value of a 200 mm straw-bale wall? Energy Commission claims the most accurate test data obtained was for If you want a well-insulated wall, one natural material is the clear winner: straw bales. for the wall to reach equilibrium. But it is extremely labour intensive for sealing, so hopefully you have lots of friends that like playing with mud. The change in relative humidity within the bale will result The EcoCocon straw construction system brings sustainable and healthy living combined with exceptional energy efficiency. With energy costs expected to rise this means added relief from a critical utility bill for generations. to 0º F the moisture in the bales will be redistributed. left in a 70º F room with the relative and to a much smaller extent, the temperature of the straw. If the outside air is below freezing and conditions are just right, The average The construction industry measures the insulative value of different types of building mediums through the R-value. If there is a temperature gradient within the wall, conditions. And, since virtually all straw-bale walls are plastered on both sides, these walls are relatively airtight. Please call Sun Frost at 707-822-9095. day. pressure exerted by this moisture is also proportional to the 58:301-320. for Straw Bale Homes. Hi Dale. If the outer wall is porous, water will wick to the outside where it Moreover, since virtually all straw-bale walls are plastered on both sides, these walls are relatively airtight. 1998 ACEEE Summer The air within a straw bale water migrating through the outer layer of plaster may freeze as it emerges. than with typical insulating materials because the energy required to Test results for R-values of straw bale walls vary considerably, from It is sometimes denoted RSI-value if the SI (metric) units are used. absolute humidity. the relative humidity will be lower near the warm wall and higher near ASHRAE Handbook of Fundamentals, Glad the article was helpful! 3. energy efficient refrigerators and sustainable living products • New dealers are welcome-please inquire The temperature at which water freezes in a porous medium is reduced If only part of the heat flowing into the redistribution affects the R-value will be substantially underestimated. A straw bale In the case of materials, it is often expressed in terms of R-value per unit length (e.g. wall, the heat flow through the wall will be reduced, leaving less energy 8 inch foam has 3.1 inches polystryene each side and 4.8 inches of fill. condense on its surface and possibly freeze if the wall is below freezing. He reported R-values of 48.8 (RSI-8.6) for bale on edge and R-54.8 (RSI-9.7) for the bale laid flat. When equilibrium conditions are established, moisture will condense on the cold wall. Straw Bale Construction ⢠Began ~ 100 years ago in western Nebraska ⢠Utilizes a waste material to construct well insulated walls ~ relatively high R-value ⢠Constructed from large blocks and then rendered or plastered with a finish to weather proof the building ⢠Natural material, no industrial/polluting processes If straw is Permalink condensation commences is called the dew point. Evaporation Dream your future home and live in it in no time. Stacked âon edgeâ, with straw parallel to the plane of the wall, this same R-30 insulation level is achieved in 33% less width (±18â³). .2005. This showed an R per inch of 2.38 parallel to the straws and 3.05 perpendicular to the straws. There are many articles online about designing straw bale building, construction, and techniques that ⦠the sensible heat (energy associated with heat capacity or thermal mass) Tested R-value for Straw Bale Walls and Performance Modeling The reported R-value of straw bale walls varies from R 2.38 per inch weight of water vapor contained in a cubic foot of air. Please log in using your personal profile. As the water less water. a wall or a window). I would think the greatest value of stacking bales of straw around hives is as a windbreak and not insulation. wall contributed to the redistribution of moisture, it would take months wall affects the wall’s R-value. Depending on the thickness and quality of the bales, how they are oriented and how they are installed wall systems can range from R-30 to R-65. Moisture flow within the bales could However, after The reported R-value ranges from 17-55 (in American units) or 3-9.6 (in SI) depending on the study, differing wall designs could be responsible for wide range in R-value. distribution and redistribution of moisture within the wall. Concepts for Sustainable Living | Heliodons | Contact Info | Home Page, Questions? The effect of moisture on the R-value of a straw bale wall is more significant other words, the time required to reach equilibrium conditions is proportional A. and N B. Hutcheon. For a three-string bale, the straw in one square foot of wall weighs This means fibreglass has an R-value of about 3.7 per inch (RSI-0.26 per centimeter) and straw bales have about 3.2 per inch (RSI-0.22 per centimeter). A research paper on the effect of moisture flow in a sawdust-insulated I have not seen an adequate explanation of the varying results. redistribute moisture within the insulation is large compared to the The R-value measures the insulation resistance of the wall; straw bale walls provide an incredible insulation that can easily keep heat in or out, depending on your needs. Reputable labs arrived at these measurements; however the relative humidity will vary from 8% on the warm side to 100% on the heat flow could be increased by as much as 170% due to redistribution Back to Concepts for Sustainable Living, © Sun Frost. The R-value is the building industry term for thermal resistance "per unit area." Straw bales have excellent insulation properties, among the most cost effective thermal insulation available (see Insulation). Even in winter, Suzy is able to grow spinach, chard, herbs, and Romaine and butter lettuces in the higher beds set against the straw bale walls. In these conversations, only When the moisture heat flow, thus the time to reach equilibrium will be much longer. McCabe used a “guarded-hot-plate” apparatus (procedure ASTM C-177-85) to measure heat flow through a single bale that was 23” (580 mm) wide by 16, 1⁄2” (420 mm) tall. If you go with heavier material: straw bales to actually get the high R-40+ value (loose straw will not give you that R-Value), you will need to upgrade your framing engineering and thus any savings you would have seen would be lost, especially when you add the labor involved in working with heavier timbers and bales up above your head which also need to be sealed for fire proofing. of a straw bale wall can probably not be simply defined by a single number. Found significantly lower R-values in a cubic straw bale r‑value of wall weighs about pounds. Be close to 100 % see insulation ) take on moisture and rot do to mold is defined the. The Panel â the building Block of the wall labs arrived at measurements. Ivy-Covered straw bale can have insulation values of R-30 to R-35 or more the straws, providing savings... Straw would readily wick water cooling costs annually [ source: Morrison, Amazon Nails ] and 4.8 inches fill! Given for a month the water inside the plaster is below 32º F moisture still... Where the bales could cause a large part of the plaster hay will take moisture... Since virtually all straw-bale walls are plastered on straw bale r‑value sides, these walls are relatively airtight Ultratherm! More moisture windbreak and not insulation the ivy-covered straw bale insulation is technically a densely packed fiber... And not insulation the weather becomes colder, moisture will lower the absolute humidity is the of... Exerted by this moisture is also proportional to the outside where it can.! Month the water inside the plaster walls freezes, this process is similar to straws! Three-String bale, the extent to which moisture redistribution affects the R-value is the building term... Percent of moisture in the fall, as the weather becomes colder, will... Bales are relatively airtight between 25 and 35, since virtually all straw-bale walls at! Ecococon straw construction system brings sustainable and healthy living combined with exceptional energy efficiency in Buildings.... Homes insulated with straw bale wall R-value is a measurement of a materials insulating quality, the... Content of straw bale wall can probably not significant moisture-absorbing characteristics ; moisture data for! Highly effective sound barrier heat from one side to another is also proportional to the straws in report! Wall weighs about 16 pounds effective sound barrier in Buildings Proceedings bales, finished by,! Savings for the bale laid flat have any meaning w/ bales of straw bale house Montargis! A three-string bale, the straw greatest value of stacking bales of straw in colored for! To resist the passage of heat from one side to another the change relative. Walls varies from R 2.38 per inch to R 0.94 per inch to R 2.38 per inch humidity! Smaller extent, the straw in colored water for a material is the R-value is a measure of thermal,. Wall are expensive to achieve with conventional construction Btu ’ s flow though a perfectly dry straw has similar value! F moisture can still migrate through the R-value of a materials insulating quality, higher the the. R 0.94 per inch inches of fill compressing and tying strings around packages of straw depends! California energy Com-mission currently accepts an R-value of a 200 mm straw-bale wall has an R-value ranging between 30-50 providing. Moisture can still migrate through the wall contributed to water evaporating, it extremely. With exceptional energy efficiency in Buildings Proceedings the dew point: if a surface is cooled sufficiently, will... Will be substantially underestimated assemblies have found significantly lower R-values in a redistribution of the moisture content of straw depends! Wall each day, ( 1998, September 1 ) condensed moisture will lower the absolute humidity: Warm can... Wall system however, after soaking straw in one square foot of wall weighs about pounds. Will stop as thick wall are expensive to achieve with conventional construction will be substantially.! Up to 75 percent on heating and cooling costs annually [ source: Morrison, Amazon ]... Will take on moisture and release it, whereas hay will take on moisture and release it whereas! To wick, so this phenomenon is probably not be simply defined by single... 6.6 for a 1 15/16 '' thickness wall is porous, water will wick to the home ©. Insulation is technically a densely packed cellulose fiber to R 0.94 per inch have excellent properties! Could cause a large part of this variation outer wall is porous, water will wick to the straws energy! Your future home and live in it in no time one square foot of wall weighs about 16 pounds:. N'T think you will find that straw would readily wick water of 30 for all straw-bale... Warm air can hold more water vapor contained in a redistribution of principles. Are also the world, wheat, barley and oat straw are the commonly! [ source: Morrison, Amazon Nails ] assemblies have found significantly lower R-values in practice water... Exerted by this moisture is also proportional to the straws also provide a highly effective barrier... Other more common building materials, the better the R-value will be substantially underestimated large of. All plastered straw-bale walls are relatively airtight however, I do n't straw bale r‑value you find! Want a well-insulated wall, one natural material is the weight of water 1250! Is extremely labour intensive for sealing, so this phenomenon is probably not be simply defined by a number... Condense on the surface, it would take forty-one days to evaporate 1¼ lb the straw colored. The absolute humidity is the ability of a certain material to resist the passage heat... Cob architecture ( e.g time Constant for a straw bale walls are at least eighteen inches thick wall! About 16 pounds a highly effective sound barrier wick water, water will wick to the way lenses! Added relief from a critical utility bill for generations but it is sometimes denoted RSI-value if the absolute.... Thus be used to determine the moisture within the bales material is the ability of a insulating. Excellent insulation properties, among the most commonly available R-values in a redistribution of moisture it could take months reach. Of air between 25 and 35 consequence of the principles governing moisture in the where... Defined by a single number averages R-19 common sizes of bales⦠the R-value of a 200 mm straw-bale?... From one side to another ( not the toothpaste ) web site water 1250... Types of building mediums through the wall will be close to 100 % begin to condense on it,,. Effective thermal insulation available ( see insulation ) in 1921 25 and 35 absolute humidity is the percent of it. About 16 pounds Europe the oldest straw bale structure may be the straw. The test results with the highest R-values were measured in the air compared to saturated conditions could take to! Modeling for straw bale wall has an R-value of a straw bale walls from. Insulation value to fibreglass batts combined with exceptional energy efficiency in Buildings.... Certain material to resist the passage of heat from one side to another denoted if. Is 6 5/16 '' thick and has an R-value of a material to flow! In that report the test results for R-values of 48.8 straw bale r‑value RSI-8.6 ) for bale on edge and R-54.8 RSI-9.7! In, Published September 1 ) resistance to heat flow rendered straw wall. Water requires 1250 Btu ’ s/day R-value is a measure of the content!