[GSBN] Modeling or measuring mass effect of interior plaster

Wed May 8 17:17:28 UTC 2013

Concerning my last post, there is a very interesting paper about the
colombage building in Haiti:

http://www.wmf.org/sites/default/files/wmf_publication/WMF%20Haiti%20Mission%20Report.pdf

Best

JVK
Portugal

On Wed, May 8, 2013 at 3:32 PM, Van Krieken <vankrieken at gmail.com> wrote:

We put a 12 cm clay bricks  wall on the interior side of the strawbale
> walls, filling the timber framing.
>
> We also leave a 2-3 cm space between the strawbale (also rendered with
> clay) and these adobe bricks. If any condensation is to occur, looked to me
> that's the way to avoid complications. Also, no chimenea effect, as there
> is nothing there to burn.
>
> We have temperatures of 43º C in Summer and -5ºC in Winter, and the inside
> temperature of this house need very little heat on Winter (depends more on
> the sun direction) and no refrigeration al all on Summer. Ofcourse, we need
> good shading on Summer.
>
> At this moment, we are building several houses with his method, using 10
> and 20 cm aglomerated cork painels instead of strawbale, rendered with lime
> mixed with aglomerated cork granulate.
>
> You may see the strawbale/colombage building method we use at
> http://strawhouses.carbonmade.com
>
> The colombage method was very popular in Europe and was known by the
> Romans as the *opus craticium* technique.
>
> In recent Haiti earthquake disasters, it seams that these colombage houses
> -- (the technique was taken to Haiti by young haitian architects graduated
> in Paris in the early XX century) -- were the only ones that did not failed
> down.
>
> In Portugal, we still have many houses like this with more then 400 years,
> and still in good conditions.
>
> However, they did not had a good insulation, so when you add a good
> insulation from the outside (strawbale its also good), the result is
>  amazing.
>
> And simple.
>
> All the best
>
> Jorge Van krieken
>
>
>
>
> On Wed, May 8, 2013 at 1:51 PM, John Swearingen <
> jswearingen at skillful-means.com> wrote:
>
>> One other thought is that the mass on the interior of a plastered SB wall
>>> is more important than the mass on the exterior in terms of thermal
>>> performance.  I wonder if anyone has therefore used a thicker interior
>>> plaster than exterior.
>>
>>
>> Yes, we have, but did not, or could not measure the effect.  We've also
>> put double layers of plaster on stud walls to increase internal mass.
>>
>>
>>
>> On Wed, May 8, 2013 at 3:29 AM, martin hammer <mfhammer at pacbell.net>wrote:
>>
>>>  Great discussion on this subject.
>>>
>>> I often characterize plastered straw bale walls as “a perfect balance of
>>> mass and insulation”.  A generalization, to be sure, but not far off, for
>>> almost any climatic condition.  I also often refer to them as “natural
>>> SIPs”.  Structural Insulated Panels, are usually thought of as having an
>>> insulating polymer foam core between layers of plywood or OSB, but can also
>>> include a similar core between layers of cement plaster (applied in situ).
>>>  These are sometimes called “composite panel building systems” or
>>> “structural insulated reinforced concrete panels”. Structurally, plastered
>>> SB walls (can) function like any of the SIPs, but thermally they perform
>>> only like SIPs with the cement plaster skins. (Though I suppose gypsum
>>> board is sometimes applied to the interior and cement plaster to the
>>> exterior of OSB SIPs, which thermally gets them closer to SB walls.)
>>>
>>> The systems with cement plaster skins usually use a welded steel wire
>>> space frame that ties the skins together through the insulating foam core.
>>>  If you squint hard and ignore petro-chemical insulations and the Portland
>>> cement based plaster (I know that’s impossible), then in terms of
>>> structural and thermal performance its a great system.  This might be like
>>> saying “except for the fact that it’s terrible, it’s great!”, but there’s a
>>> valid point in there somewhere.  And one could presumably use lime plaster
>>> or soil-cement (or even clay plaster?) with one of these foam-wire-core
>>> systems (anyone done that?) that would significantly reduce the
>>> environmental downside but maintain the thermal performance and structural
>>> capacity (with careful consideration of the weaker plasters for the
>>> particular application).
>>>
>>> Of course instead of messing with any of that one could just build SB
>>> walls.  I’m just making a comparison to “similar” industrialized systems,
>>> that to be fair, have certain advantages.  One advantage is SIPs (with wood
>>> panel or reinforced cement plaster skins) can be used structurally for
>>> floor and roof elements and plastered SB cannot (notwithstanding SB vaults).
>>>
>>> One observation on the very good article Bohdan shared, is that the
>>> mid-mass building gets you far in terms of thermal performance (compared to
>>> the low-mass building), whereas the high-mass building then demonstrates a
>>> more modest improvement.  Like anything else, the first steps in the right
>>> direction have the largest payoff, with still-valuable but diminishing
>>> return after that.
>>>
>>> One other thought is that the mass on the interior of a plastered SB
>>> wall is more important than the mass on the exterior in terms of thermal
>>> performance.  I wonder if anyone has therefore used a thicker interior
>>> plaster than exterior.
>>>
>>> Martin
>>>
>>>
>>>
>>> On 5/7/13 5:23 PM, "Derek Roff" <derek at unm.edu> wrote:
>>>
>>> Thanks for posting the article on thermal mass, Bohdan.  I found it very
>>> interesting.  Based on the data it contains, I have a few comments relevant
>>> to Laura's situation.
>>>
>>> As John mentioned, the article emphasizes that it is addressing thermal
>>> mass with direct solar exposure/gain.  However, I didn't see anything
>>> quantifying what amount of time the sun needs to shine on each bit of
>>> thermal mass floor and wall each day, in order to attain the listed
>>> results.  As the sun moves across the sky, some parts of the floor and
>>> walls will receive direct sunlight for only a few minutes, while other
>>> locations will be in the sun for several hours per day.  The amount of
>>> furniture, area rugs, and wall decorations will also affect how much sun
>>> shines on thermal mass.  I'm thinking that as the amount of time in the sun
>>> decreases, the needed surface area of the thermal mass needs to increase,
>>> to get the same thermal mass effect.  The total mass of the thermal mass
>>> might need to increase a bit, too.
>>>
>>> At 6000 sq ft/560m3, Laŭra's project will likely have a higher floor
>>> area to wall area ratio than smaller houses.  By itself, this might
>>> decrease the importance of the thermal mass in the walls.  However,
>>> depending on the number of stories and the floor plan, a large project
>>> might have a smaller percentage of floor and wall area accessible to direct
>>> sun.  That would increase the importance of maximizing the surface area of
>>> the thermal mass.
>>>
>>> Laura didn't say where this project will be built, but I'm guessing it
>>> might have a climate closer to the "cold European climate" listed in the
>>> article, rather than to the alternative Melbourne figures.  The article
>>> quotes Vale and Vale as suggesting 1,200kg of thermal mass for each square
>>> meter of floor area.  It's worth noting that all this thermal mass could
>>> not be in the floor.  If it were, the thermal mass floor would need to be
>>> about .5m/20" thick.  Not only is that absurd from a construction
>>> perspective, but much of the mass in a slab that thick would not respond to
>>> daily temperature variation.  My reading is that walls have to be involved
>>> in the thermal mass equation, to get the results described.
>>>
>>> At the top right of page 7, the article says that temperature modeling
>>> for the three reference building variations (low-mass, medium-mass, and
>>> high-mass) are predicted to have similar maximum temperatures.  However,
>>> the numbers in the chart paint a different picture, as I see it.  Table 3
>>> shows the maximum temperature at the hottest part of the summer as 32
>>> degrees C/90 degrees F for the low mass house, contrasted with 25 C/77 F
>>> for the high-mass house.  To me, that's the difference between the average
>>> American demanding air conditioning (or feeling that they are suffering),
>>> versus a temperature that many would find acceptable.  23 C/77 F is pretty
>>> comfortable, when the radiant surfaces (ceiling, walls and floors) are at a
>>> similar temperature or lower, as they would be in a well-insulated home.
>>>  That temperature can feel uncomfortable, if the radiant surfaces have
>>> heated up to 30 C/86 F or more.
>>>
>>> Table 3 also shows surprising figures for the morning lows in the
>>> hottest month.  The low-mass building is predicted to be at 16 C/61 F on a
>>> summer morning.  Some residents would be turning on the heat in the
>>> morning, and the air conditioning in the afternoon.  The high-mass building
>>> will get down to a comfortable 20 C/68 F on the same summer morning.  To
>>> the extent that covering the walls with barn wood will diminish the
>>> effective thermal mass, as Laura describes, it could have a significant
>>> impact on comfort in the summer.  The winter figures indicate substantially
>>> greater differences between high-mass and low-mass temperature variations.
>>>  I also conclude that Hobart has a pretty pleasant temperature range.
>>>
>>> I agree with David, that uninsulated thermal mass can easily be a
>>> liability.  I'm not sure the same is true for well-insulated thermal mass.
>>>  A large amount of thermal mass combined with a well-insulated building
>>> envelope will result in small daily temperature variations.  At some point,
>>> adding more thermal mass will have little effect, because of the low
>>> temperature swing and the resulting low delta T across the thermal mass.
>>>  After this point, adding more thermal mass wouldn't help much, but I'm not
>>> seeing how it would have a negative effect, either.  Unless the residents
>>> found consistent temperatures monotonous.
>>>
>>> Derek
>>>
>>> On May 6, 2013, at 7:05 PM, Bohdan Dorniak wrote:
>>>
>>> Hi All
>>> This is a note that has been published by the Australian Institute of
>>> Architects regarding Thermal Mass.
>>> I thought that you may find this interesting? Any comments John?? Laura??
>>> Regards
>>> Bohdan Dorniak
>>>
>>> *From:* GSBN-bounces at sustainablesources.com [
>>> mailto:GSBN-bounces at sustainablesources.com<GSBN-bounces at sustainablesources.com>]
>>> *On Behalf Of *John Swearingen
>>> *Sent:* Tuesday, 7 May 2013 9:38 AM
>>> *To:* Global Straw Building Network
>>> *Subject:* Re: [GSBN] Modeling or measuring mass effect of interior
>>> plaster
>>>
>>> Laura,
>>>
>>> Modeling thermal mass is generally difficult because of the large
>>> variable conditions of heat transfer related to air circulation. We've done
>>> this in Energy-10 with some success, and usually our projections have come
>>> out on the conservative side--the temperature swings have been less than we
>>> calculated.
>>>
>>> The other very large variable is climate--temperatures and sunshine at
>>> different times of the year. Everyone I know who does this successfully had
>>> dialed it in from years of experience in one particular climate, with which
>>> they are familiar.
>>>
>>> As to whether the walls make a difference,  the short answer is, I think
>>> it makes a big difference, and that many of the lauded characteristics of
>>> thermal comfort in straw bale buildings may have as much to do with the
>>> thermal mass on the walls as with the insulation.  Modulated temperature
>>> swings can influence occupant behavior positively, reducing reliance on
>>> mechanical systems, over and above straight Btu calculations.
>>>
>>> The ultimate efficiency of thermal mass is tied to the heat-transfer
>>> mechanism for exchanging heat between the mass and the rest of the building
>>> (air).  A floor slab is thick and of limited surface area; bale walls are
>>> thin with a much larger surface area. So floor slabs are longer term
>>> storage, and walls  function very effectively to modulate temperature
>>> swings on a short term (diurnal) cycle which can reduce loads on mechanical
>>> systems and increase comfort in passive buildings.  I don't think there is
>>> too much danger of over-massing, and haven't seen it in our buildings,
>>> because the relatively thin mass of the walls, backed by insulation and
>>> actively transferring heat, stays close to room temperature and so isn't
>>> felt as too cold or hot.
>>>
>>> Temperature modulation can result in significant changes in how
>>> mechanical heating and cooling are used by the occupants: if the building
>>> is slow to cool off at night, for instance, the occupants don't call for
>>> heat early in the evening.  The key here is responsiveness, which is
>>> related to surface area. Mass walls also help to distribute Btu's somewhat
>>> between warmer and cooler areas of the building: cooler walls will absorb
>>> heat more readily than warm walls, so they are somewhat of a magnet for
>>> warm air when located in cooler areas of the building.
>>>
>>> Well, hope this helps!
>>>
>>> John.
>>>
>>>
>>>
>>>
>>> On Mon, May 6, 2013 at 12:39 PM, Laura Bartels <laura at greenweaver.com>
>>> wrote:
>>> Hello All,
>>>
>>> I'm writing to ask if anyone has had experience with modeling or
>>> measuring the mass effect of interior plaster of bale walls versus other
>>> interior finishes. This has come up on a straw bale project in design phase
>>> I've involved in which has a net zero energy goal. The project is large,
>>> about 6000 sf. The owners are interested in  barnwood interior wall
>>> surfaces (over plaster) on all or some walls. With the net zero goal, the
>>> question is what we might lose in having wood rather than exposed plaster.
>>> There will be adobe floors which will already provide direct and indirect
>>> gain mass.
>>>
>>> Anyone tackled this topic or have a guess about how to look at this? Our
>>> team has talked about estimating direct vs. indirect gain wall surfaces
>>> through sun studies in ArchiCAD as a starting point.
>>>
>>> Looking forward to hearing any thoughts on this.
>>>
>>> Laura
>>>
>>>
>>> *
>>> Laura Bartels
>>> GreenWeaver Inc.
>>> 520 S. Third St., Suite 5
>>> Carbondale, CO 81623
>>> 970-379-6779 <tel:970-379-6779>
>>> www.greenweaverinc.com <http://www.greenweaverinc.com>
>>> *
>>> *
>>> *
>>> <image001.jpg>
>>>
>>>
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>>
>>
>> --
>> John Swearingen
>> Skillful Means Design & Construction
>> 2550 9th Street   Suite 209A
>> Berkeley, CA   94710
>> 510.849.1800 phone
>> 510.849.1900 fax
>>
>> Web Site:  http://www.skillful-means.com
>> Blog:         https://skillfulmeansdesign.wordpress.com
>>
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>
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