[GSBN] using loose straw insulation in roof

Rikki Nitzkin rikkinitzkin at gmail.com
Wed Nov 1 09:00:59 CDT 2017


HI all, 

How interesting this debate!

> One side note. I sent that last email on Oct 27, but GSBN didn’t receive it until Oct 31. Anyone else ever experience a multi-day delay?


I got it today.

The biggest consideration about the insulation value came with the numerous large gaps between bales and trusses that needed to be filled. 

If I were to use entire bales for insulation in the roof (forced into the space between trusses or beams really tight!), I would then cut the strings so that the straw expands a bit and fills in the gaps itself; this way little or no stuffing is necessary. This technique is used in the CUT system and works quite well. If the bales are in really tight they wouldn’t loose much compression ( I understand that dense bales mean less oxygen and more fire resistance, even if the density doesn’t affect the insulation value much).

 In northern Europe it is quiete common to use entire bales in the roof.  It’s curious how cultural differences are important in these decisions. Several people mentioned the extra weight of the bales being  a problem. Here in Spain, this is not true. Trusses are almost never used. Most roofs have a huge “main” beam and then smaller beams resting on the wall on one end and the mother beam on the other (placed at 50-60cm between each secondary beam), and almost all people use tile or green roofs. When trusses are used, they are BIG trusses at large distances, and the secondary beams are placed horizontally. Both systems are “heavy. ” The beams which are dimensioned for these kind of roofs can hold the weight of entire bales with no problem. They are over-dimensioned anyway, so as to be more fire resistant. Here the beams are calculated considering distance, weight and type of wood. Then the size is multiplied by a “safety factor”, depending on the use and type of wood.  From what you all say, I suppose this is not so in the US.

I don’t like the idea of loose straw in the roof, but the only other cheap (non-flamable) possibility I know of is natural sheep’s wool- which has it’s own difficulties in processing. I would never use loose straw in a contracted building, but I think we all know and understand that the needs of low-income self-builders are a bit different. From what everyone has said, I understand that the major problem with the loose straw is not insulation value, but flammability… so I guess each builder has to evaluate if fire is a high risk or not-  especially depending on how the chimney and electrics are installed.

Rikki
p.s. I will be visiting friends and family in Santa Cruz (CA) and New Orleans next month. Anyone know of any projects worth checking  out in these areas? Answers off-list please!

> El 1/11/2017, a las 13:58, Martin Hammer <mfhammer at pacbell.net> escribió:
> 
> Thanks for the info John. I was grasping at the straws of my memory for the story on the “China” fire event (and almost said “or Mongolia”). Not sure if we’re thinking of the same event. Either way the point is the same. In addition to: Don’t install a chimney against insulation (straw or any other). Thus "Section AS107.3 Clearance to fireplaces and chimneys” in the IRC strawbale appendix.
> 
> One side note. I sent that last email on Oct 27, but GSBN didn’t receive it until Oct 31. Anyone else ever experience a multi-day delay?
> 
> Martin (traveling at the speed of straw) Hammer
> 
> 
> From: Gsbn <gsbn-bounces at sustainablesources.com <mailto:gsbn-bounces at sustainablesources.com>> on behalf of John Swearingen <jswearingen at skillful-means.com <mailto:jswearingen at skillful-means.com>>
> Reply-To: GSBN <GSBN at SustainableSources.com <mailto:GSBN at SustainableSources.com>>
> Date: Tuesday, October 31, 2017 at 7:04 PM
> To: GSBN <GSBN at SustainableSources.com <mailto:GSBN at SustainableSources.com>>
> Subject: Re: [GSBN] using loose straw insulation in roof
> 
> Thanks for all that, Martin.  One note, if we're talking about the same incident with Kelly, it was a clinic in Mongolia that caught fire shortly after it was built, because the had installed the fire chimney after the attic and insulation, and right against it.  The fire brigade was quite a distance away, many hours, and because the straw was just smoldering, they had time to move all the equipment and furniture out from the building, without damage, and then the fire in the attic was extinguished.
> 
> John "Insolent Insulator" Swearingen
> 
> On Tue, Oct 31, 2017 at 6:52 PM Martin Hammer <mfhammer at pacbell.net <mailto:mfhammer at pacbell.net>> wrote:
>> Hi all,
>> 
>> Good discussion and advice on this.
>> 
>> The PAKSBAB (Pakistan) SB buildings use 12” (30 cm) of clay-coated straw for insulation above the ceiling (photos and drawing attached) (second photo and drawing courtesy of Darcey Donovan Messner). Andy Mueller and I used a lesser depth of the same “loose straw-clay” for our SB building in Haiti (photos attached).
>> 
>> Both make a noticeable difference in the building's thermal performance in their respective climates. In both cultures thermal insulation of any kind is rarely used. But as happy as I am to use this inexpensive natural insulation in these and similar contexts, I worry about the flammability of the “loose straw clay”. Even if the material resists ignition in the first months or year after installation, I’ve seen evidence over time of clay “dusting”, thus diminishing whatever protection it offered the straw initially.
>> 
>> I remember reading (in a TLS article?) Kelly Lerner describe a straw insulation fire that started (electrical source, as I remember) in the attic of a SB house in China. It was not part of the prescribed design, but I think it was reasoned that if it’s good in the walls, why not the attic? I don’t remember if it was loose or baled straw, but either way it is an indicator of the fire risk of straw as ceiling, attic or roof insulation. This event gave SB a bad name in the region that took time to overcome..
>> 
>> That said, there are many factors at play. I can imagine reasonably fire-safe ways to use straw (with or without clay) as ceiling, attic or roof insulation. (Leaving the structural issues out of it.)
>> 
>> I found the following statement in TLS17 (1997):  "Robert Laporte, timber framer and straw-clay builder, commonly uses straw-clay stuffed loose between rafters as insulation, with the clay discouraging pests."  I don’t know if Robert still practices this 20 years later. His partner Paula Baker-Laporte who is on this list, might be able to say more.
>> 
>> Also, I’ve attached an article from TLS38 (2002) “Bales in My Roof . . . A Costly Decision?” that speaks to some of the identified issues.
>> 
>> Lastly, to the extent that it's relevant, and as far as I know, Rikki is still working is Spain (and maybe neighboring countries).
>> 
>> Martin Hammer
>> 
>> 
>> From: Gsbn <gsbn-bounces at sustainablesources.com <mailto:gsbn-bounces at sustainablesources.com>> on behalf of John Swearingen <jswearingen at skillful-means.com <mailto:jswearingen at skillful-means.com>>
>> Reply-To: GSBN <GSBN at SustainableSources.com <mailto:GSBN at SustainableSources.com>>
>> Date: Friday, October 27, 2017 at 6:57 AM
>> To: GSBN <GSBN at SustainableSources.com <mailto:GSBN at SustainableSources.com>>
>> 
>> Subject: Re: [GSBN] using loose straw insulation in roof
>> 
>> Quite a long time ago we built a house using bales for roof insulation, with site built trusses.The biggest consideration about the insulation value came with the numerous large gaps between bales and trusses that needed to be filled. The building was near a major farmland highway with large trucks passing a few yards away, and the bales did an excellent job of dampening the low frequency noise of the trucks. I would consider them again is a similar situation, but not for insulation; the cost and difficulty of doing a good job is too great, and other good alternatives are available.
>> 
>> This year we have again been up close and personal with fire, this time dealing with melting levels of heat, generating tornado winds in concentrations of timber buildings feeding off of each other. We have four projects that came within yards of the worst fires, but none of them were touched by flames, so we don't have any forensic information to offer.  The closest endorsement we've had came from firefighters who came to defend our house and we showed them our strawbale cabin with a grassy green roof.  They immediately freaked, then looked, pondered, said "no problem" and moved on to check out the wood structures.  Nothing like thick plaster and few inches of wet dirt to slow down a hot fire..
>> 
>> Since we're designing a home in the same fire-prone region of Napa, we've been looking at the weak links that would make a good plastered house vulnerable. In an intense fire, assuming the plaster and roof are good, the weak link is heat transfer (and breakage) through windows igniting the interior, and we're thinking of mounding sprinklers on the exterior within the window cavity, primarily for cooling. We've done this in urban situations when a building has been inside the required setback in lieu of a one-hour fire wall This would be a slightly different use from preventing the spread of fire--primarily to cool the glazing area long enough for a hot wildfire to pass. When firemen show up before and advancing fire, they do a lot of wetting. We've installed large garden sprinklers on our roofs in the forest, and the firemen are big fans of those. Water is their only friend. 
>> 
>> Any thoughts on this? 
>> 
>> John "I'm All Wet" Swearingen
>> 
>> 
>> On Thu, Oct 26, 2017 at 7:13 PM David Arkin, AIA <david at arkintilt.com <mailto:david at arkintilt.com>> wrote:
>>> Hi World:
>>> 
>>> Having just taught a few workshops where we measured the density of bales and discussed the possible reasons for a minimum density, this is a timely question.  We actually had some bales that didn’t pass the minimum 6.5 lbs./cu. ft. specified in the International Residential Code (IRC).  Reasons for a minimum density include structural integrity, insulation properties, and fire safety.  The use of loose fill that doesn’t achieve a minimum density is not supported in this code, but that doesn’t rule out the possibility that some version might be developed that could achieve similar properties to loose fill cellulose and other materials.  
>>> 
>>> For insulation, the IRC and also the IBC specify a maximum flame spread index of 25 and a maximum smoke developed index of 450.  An ASTM E84-98 Standard Test Method for Surface Burning Characteristics test of a Straw Bale in May of 2000 yielded a flame spread index of 10 and a smoke developed index of 350, thus verifying straw bale as a viable insulation material.  Note that this was a test of surface burning of a bale, not loose straw. 
>>> 
>>> Curiously, the IBC notes that Cellulose loose-fill insulation only needs to meet the smoke developed index not exceeding 450 criteria, provided it complies with CPSC 16 CFR Part 1200 and CPSC 16 CFR Part 1404, and further stating that ‘each package of such insulation material shall be clearly labeled in compliance with' [these].  
>>> 
>>> I’ve heard some folks in the UK have been experimenting with a chopped straw insulation infill, but the exact parameters of the processing and the resulting fire resistance I don’t have information on.  
>>> 
>>> That all said, I’ve never done it (put straw in a roof / ceiling), nor do I recommend it, but neither can I say with certainty that it shouldn’t be done.  
>>> 
>>> David A.
>> 
>>>> On Oct 26, 2017, at 4:57 PM, Bill Christensen <lists at sustainablesources..com <mailto:lists at sustainablesources.com>> wrote:
>>>> 
>> 
>>>> In the ASTM tests that Bruce King coordinated back in 2007, one of the walls was clay plastered. 
>>>> 
>>>> Yes, the clay cracked and the straw eventually burned (though the clay plastered wall did better than cement, we believe because it spent the first 20 min or so "firing" as in a kiln, and the chemical changes from that absorbed a lot of the heat).  
>>>> 
>>>> Loosely packed straw might not fare so well once oxygen can get to it.  
>>>> 
>>>> We had a problem because the clay plastered wall had a crack on the exterior, which allowed more oxygen in between a couple bales.  Though we had stuffed and cobbed those spaces maniacally, the fire followed the path back through the wall.  We had to cut the test off at 1 hour because of this - otherwise the clay plastered wall probably would have out-performed the cement plastered one. 
>>>> 
>>>> The guys at the testing facility told us that "Everything burns... eventually.   Everything". 
>>>> 
>>>> I have to agree with the earlier comments in this thread - loose straw as ceiling insulation is just asking for problems, whether hit with clay slip or not.  
>>>> 
>>>> On 10/25/17 4:56 PM, Bohdan Dorniak wrote:
>> 
>>>>> Hi All
>>>>> Graeme – I’d be worried about your statement about a “coating of clay” – in our fire test of rendered strawbales by CSIRO - done in 2002 – the earth rendered bale (render about 50mm thick – Frank Thomas did the rendering) started to show cracking in the render.
>>>>> Wondering whether eventually they would burn? 
>>>>> Other considerations is the weight factor and stronger ceiling structures (if using thicker coats of render).
>>>>> That’s my 2 bob’s worth.
>>>>> Bohdan
>>>>>  
>>>>> From: Gsbn [mailto:gsbn-bounces at sustainablesources.com <mailto:gsbn-bounces at sustainablesources.com>] On Behalf Of Misha Rauchwerger
>>>>> Sent: Thursday, 26 October 2017 8:04 AM
>>>>> To: Global Straw Building Network
>>>>> Subject: Re: [GSBN] using loose straw insulation in roof
>>>>>  
>> 
>>>>> I believe another issue is whether the attic space is vented or not, as well as the kind of roofing.  After the Oakland fires, I remember this being debated furiously, because the codes require attic venting, and going with something like polyisocyanurate rigid insulation without vents was controversial.  Obviously the fire danger will increase if air can mix with flammable insulation fuel (frieze block vents and ridge vents create a perfect means for fully combusting the attic materials) . If it is encased and covered with earth on the outside and inside (plaster on the ceiling), as in a living roof, we can decrease the flammability factor.
>>>>>  
>> 
>>>>> The Lobo fire that swept through our neighborhood recently came right to our friend's straw bale house with only superficial plaster damage on one corner.  Of course there are far too many factors to say it was saved because of being straw bale or not..
>> 
>>>>>  
>>>>> Then again, if you get a fire like just swept through Napa and Sonoma Counties, all bets are off...
>>>>>  
>>>>> Misha 
>> 
>>>>> On Wed, Oct 25, 2017 at 1:38 PM, Graeme North <graeme at ecodesign.co.nz <mailto:graeme at ecodesign.co.nz>> wrote:
>> 
>>>>> This list is a fantastic resource for learned info and is greatly appreciated I can tell you.
>> 
>>>>>  
>>>>> The fire thing is scary - there is no requirement in NZ for single dwellings to have fire resistant ceiling materials, but we do need to have smoke alarms near bedrooms and escape routes.
>>>>> The really scary thing is that the fire people here advise that a dry house with an open attic with light timber rafters or trusses for roof framing will burn from end to end in 60 secs.
>>>>> Goodness knows what adding an accelerant like straw (without a good clay coating) might do. I would advise against it.
>>>>>  
>>>>> I would use straw coated with clay  - pretty much a LEM mix - if my structure allowed it to happen easily and I was considering it for my own house but the work required and extra weight decided against it 
>>>>> and again recently I considered it on another design but the considerably increased extra depth of the roof structure to accommodate it, along with the extra cost, work, and weight, decided against it again so I went with wool insulation in both cases.
>>>>>  
>>>>> I am also not convinced that cellulose/paper insulation with borax retains it fire rating over time - I have seen examples of old (only a few years) cellulose insulation that would not ignite when new,  ignite readily with a match and it seems to keep burning quite happily.
>>>>>  
>>>>>  
>>>>> Cheers
>>>>>  
>>>>> Graeme
>> 
>>>>>> On 26/10/2017, at 5:36 AM, Bruce EBNet <bruce at ecobuildnetwork.org <mailto:bruce at ecobuildnetwork.org>> wrote:
>>>>>>  
>> 
>>>>>>  
>>>>>> Don’t you love it when someone else chimes into these discussions ahead of you, and says everything you wanted to say?  
>>>>>>  
>>>>>> I sure do.  Thank you Derek and John;  what they said.
>> 
>>>>>>  
>>>>>> Bruce King
>>>>>> (415) 987-7271 <tel:%28415%29%20987-7271>
>>>>>> bruce at ecobuildnetwork.org <mailto:bruce at ecobuildnetwork.org>
>>>>>>  
>>>>>>  
>>>>>>  
>>>>>> 
>>>>>>  
>> 
>>>>>>> On Oct 25, 2017, at 7:56 AM, John Straube <jfstraube at uwaterloo.ca <mailto:jfstraube at uwaterloo..ca>> wrote:
>>>>>>>  
>> 
>>>>>>> I would echo Derek’s concerns exactly. Loose fluffy straw burns very quickly and you may as well say you lost the house.
>>>>>>> Adding clay slips will increase the fire resistance to the point is acceptable, as will dense bales with some sort of clay slip top, but once you do that, you have a heavy and labor intensive roof insulation.
>>>>>>> Cellulose with 20%+ borate treatment is inexpensive, gives good R-value, is widely available, and is very good at fire resistance.
>>>>>>> 
>>>>>>> 
>>>>>>> On Oct 25, 2017, at 10:00 AM, Derek Roff <derek at unm.edu <mailto:derek at unm.edu>> wrote:
>>>>>>> 
>>>>>>> I have a different concern about using straw packed at low-densities in the roof.  I think that the fire risk increase is much more of a problem than the decrease in insulation value.  If you have seen flakes of straw or loose straw burn, you will be aware that they are much more flammable than standard bales.  Straw flakes are probably about half the density of a building bale, and loose straw might cut the density in half again.  
>>>>>>> 
>>>>>>> Losing the roof in a fire usually means losing the whole house’s integrity and value.  While enclosing the flakes or loose straw for the roof in plywood, for example, would help somewhat with fire resistance, I recommend against design choices that depend on a few things going right to avoid a catastrophic failure in a fire.  
>>>>>>> 
>>>>>>> An additional consideration that has been mentioned here before, is that while bales may be relatively inexpensive, placing them in the roof requires increasing the size and number of the roof’s structural elements, which will likely raise costs more than the amount saved by using bales instead of other insulation materials in the roof.  Using lower density straw diminishes that problem to some extent, but straw is still likely to be significantly heavier than other kinds of roof insulation, for an equivalent insulation value.  
>>>>>>> 
>>>>>>> Derek
>>>>>>> 
>>>>>>> Derek Roff
>>>>>>> derek at unm.edu <mailto:derek at unm.edu>
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>>>>>>> 
>> 
>>>>>>> On Oct 25, 2017, at 4:34 AM, Rikki Nitzkin <rikkinitzkin at gmail.com <mailto:rikkinitzkin at gmail.com>> wrote:
>>>>>>> 
>>>>>>> Hi!
>>>>>>> 
>> 
>>>>>>> I don’t know if you all remember, but not long ago I asked about the MAXIMUM density of a SB before it begins loosing thermal properties… most people agreed that we should not worry about a bale being too dense..
>> 
>>>>>>> 
>>>>>>> 
>>>>>>> Now I ask about the opposite question: is there a minimum density?
>>>>>>> 
>>>>>>> The other day we were talking about using flakes of straw to insulate a roof. One of the builders insisted that is was important that the insulation cavity was filled with highly compressed straw, and another said that as long as the cavity was properly filled (leaving no big holes for air to circulate) that the density of the infill is not important, as the straw (loose or dense, but enclosed in the insulation cavity) impedes the circulation of air, and that is what insulates.
>>>>>>> 
>>>>>>> Can any of you technicians refer me to studies about insulation properties and how they relate to density? or at least clarify my doubt: Is it important to highly compact the insulation in the roof? and why… so I can explain it better.
>>>>>>> 
>>>>>>> thanks!
>>>>>>> Rikki
>> 
>>>>>>> 
>>>>>>> ______
>>>> 
>> 
>>>> --
>>>> Bill Christensen
>>>> http://SustainableSources.com <http://sustainablesources.com/>http://LinkedIn.com/in/billc108 <http://linkedin.com/in/billc108>
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>> 
>>> 
>>> 
>>> *  *  *  *  *
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>>> 
>>> David Arkin, AIA, Architect
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>>> 
>>> Director, California Straw Building Association
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