straw as insulation for masonry? is that a thing?

Hi All,

I've been off the forum for a little while, busy being internet free vacationing and exploring my property between contracts.. mapping, visioning, and all that which leads me to this question!

Some background info: My property is rife with fieldstone. SO MUCH STONE it is crazy. Its 100% woodland and the trees grow very well despite several large veins (or 'brows' as I call them) of bedrock that punch through the earth creating a rolling geography to the place. Between these veins and smaller ripples of Bedrock (which are also covered with a couple inches of nice black loamy stuff) is filled with nice but very rocky dirt. So much rock that I feel the labour involved in sifting enough the earth to do some earthbag work or to cover an oehler/wofati style structure would be extreme. This has led me to consider building the main structural walls of stone. There is, at the ideal building site (chosen for southerly exposure) so much stone available both loose and buried close to the surface that I actually believe the labour of constructing a stone wall might be less than the previous techniques without importing material.

So, if after further research that assumption appears correct there are still many challenges. The most serious of these in the Canadian climate is insulation. Stone is bad at this.

SO the questions:

Has anyone used straw bale to insulate on the INSIDE of solid masonry walls? If so what techniques work? If the strawbales are stuccoed on both sides with a breathable lime based finish, and a non cement based and therefore breathable mortar is used, could the bales be set in contact with the masonry without any worry of condensation?

If the masonry wall is not breathable, or not breathable enough (more likely anyway) and the structure itself is well enough ventilated by air tubes to daylight could bales be used, again stuccoed and in contact with the stone but fully breathable.

Is clay/straw slip a better idea?

do any of these situations actually require an air gap and venting between insulation and masonry to avoid moisture building up via condensation?

I can hear some folks already asking why not just build a structural strawbale or straw bale with a timber frame but I don't think my seasonally very wet climate (east coast) and rather exposed (clifftop) location make this a good idea. I am therefore exploring other exterior wall possibilities but would like to keep the insulation an organic, and local material.

I have also considered doing strawbale and cladding it with reclaimed steel roofing (with an airgap for ventilation of course) in order to protect it from the elements..but that's for another thread.

THANKS!

j

Strawbale as insulation for masonry is possible but tricky to do right at best and comes with a painful final wall thickness. One should try to get thinner walls if you value passive solar or overall natural light.

"Breathable" walls is probably poor terminology. Walls dont have lungs and breathing includes both air movement and moisture. Although they are related, its best to break things into different measurable components to gain more control over the big picture. Its best to describe air and moisture movement in building assemblies as air infiltration which is always bad and permeability which is sometimes good and sometimes bad. Although some natural builders make indoor air quality IAQ claims pertaining to these mechanisms, CFMs of outdoor air should be the main measurement of IAQ.

A masonry wall in your situation is appealing due to the availability of materials. Labor is the main problem. Its practically a lost art and pretty tough DIY although the right combination could end up with a durable, attractive and low-impact wall. Protecting the mold food of strawbale from rain soaked masonry is the other significant problem. I think in a cold enough climate, a vapor barrier protecting the strawbale could work with the other right conditions. Its possible a simple airspace could work but would want to see some other successful examples before investing too much of anything. There are LOTs of variables with perhaps the most important being how good is the stone work at keeping bulk water out?

Since the future energy costs are probably the bigger environmental footprint or wood burning risk and hassle of a home, I would strive for more R-value and look to using the rocks some other way perhaps as exterior hardscape or interior aesthetic thermal mass, perhaps a small portion of water table or exterior veneer. It would be great for you or others to experiment with and share the results.

I think the strawbale with metal cladding is a better proposition and the airspace is debatable depending on the details. Have you seen the other threads in here on air tubes/ground tubes for supplying fresh air? Its very unproven and risky in your climate. What type of woodlands do you have, any usable timber?

Thanks for your input Brian.

No doubt I'm missing some key concepts and mixing up terminology so thanks for the extra info. My main concern with this whole idea in theory was condensation forming where stone meets insulation whether it be straw or pink or anything. I've been doing some reading on stone home construction (a harrowsmith publication by a couple of DIY'ers who built a stone home in Ontario in the late 70's early 80's) and they left an air gap as far as I can tell and vented the stone with little broomstick sized grates every so often. Its an inspiring little softcover but the labour is still huge and they still did full stick frame with insulation inside the stone walls.

Given all that you mention (vapour barrier to keep damp from transferring from stones to the interior of the wall, gap and venting to avoid condensation building up) and given that it is my understanding that we want strawbale buildings to be able to..not breath, but remain somewhat permeable, allowing moisture to flow into and out of the wall mass (this being achieved through the use of permeable lime render...i think) does it not follow that these two, wall thickness aside, are just not a good combo ever? Won't any vapour barrier over strawbale make for a mold factory? OR can this moisture build up be negated with proper humidity control/ air exchange?

I have read quite a bit on air tubes on here and it seems like some are being employed to great effect in Vermont ( Walter Jeffries I think..) which is a pretty similar climate, maybe not quite as wet (we get something like 50" of rain per year). But imagining that they won't work for me, could not a conventional air exchange system designed to keep humidity at an optimal level inside the home also 'drain' a strawbale wall with a traditional moisture permeable finish on the interior of any excess moisture and thus prevent the buildup of condensation on masonry and moisture within the wall? And yes let's assume for the sake of argument that the stone does shed water properly.

I do have LOTS of timber on the property which I fully intend to use, but insulating and figuring out vapour barrier and air exchange without using conventional materials and techniques is name of this exercise - I should probably start a new more generalized thread.

Anyway for the sake of this thread I'm still interested in any 'natural' means by which to insulate stone or other masonry - it may not be the most practical building method, but for the sake of study I'd love to know what has been done other than what seems the traditional method of nothing at all, or what may in theory work.

Thanks!
j

I dont think you could say that these two walls should never be combined but I think its an enormous challenge to do successfully in a rainy and humid climate. Stone and stucco is considered a moisture reservoir cladding and will tend to drive its moisture inward during certain conditions throughout the year. An air gap is probably a good idea but very difficult to execute the details like around windows and top and bottom openings (how many and how often for the grates?). A vapor retarder between the stone and straw would be necessary and I tend to doubt a traditional lime rendering or stucco coat would do the job even with an air gap.

It seems to me that your on-site timber would be the better choice for building materials. Do double stud walls, Larsen/riversong trusses, or insulative sheathing and your home could end up very well insulated. Blown cellulose is one of the most eco-friendly insulation choices available, being mostly recycled newspaper. I wouldnt discount conventional forms of construction if they make sense for your situation.

question: why not do external walls in extra thick rock with cob as a cementing materials? This would stop air movement through the walls. Then, if needed, you could put a thin layer of mortar mix and oil on exterior walls to seal against all that wet?I know that isnt exactly "permie" but sometimes you gotta do what you gotta do.

Jay Peters : It sounds to me that Brian Knight is Talking about Rainsreen Cladding, see the Wikipedia article by that name. Somewhere in my house I have a book titled
' Houses are designed by Architects, and built by Gorrilas 'This is a quite new use of modern materials and I would worry about it being installed correctly, this is a
job for a master builder !

For centuries we lived in mud huts, cob timber frame, ramed earth, and brick houses, these are all materials that hold tremendous amounts of water ,also these houses
were not very tight allowing enough moisture carrying warm air to leak out, and cold drier air to enter our homes, mold and mildew problems were minor,with the Energy
Crises of the 70's people started asking for tighter houses and moisture problems blossomed up over night !

Add in the new materials that are supposed to be insulating, but actually trap water vapor against outside walls where it can collect,reduce insulation values to zero ,bad!
Delaminate or rot all types of wooden materials, BAD, Freeze, BAD ! And create mold and mildew problems, Bad! and then there is the whole out gasing of materials issue-
certainly not good !

There is good news,hopefully you realize that you still have much to learn, and will take the time to figure it out! Any home in our latitudes should not only be well insulated
AND tight it should have some kind of simple heat exchanger Scavenging the heat from exhausted air and warming incoming air, In europe they are building 'Passivehouse's
that use no fossil fuels for heating and cooling, and this is a great goal, lets push you in that direction !

Please goto> cchrc.org , The Cold Climate Housing Research Center is an arm of The University of Alaska, Fairbanks, you and I know Cold, They know COLD ! On their
site they have articles and videos to explain how to build for all types of Circum-Polar housing needs ! The videos can also be found on their channel on you-tube !

It is possible with great care to have a house sealed with vapor (only) permeable walls, placing the Thermal Mass Rock walls on the inside and all the insulation on the outside
of the building allowing for 'rain walls', or 'rain screening walls' that allow excess water to condense and weep out of your exterior walls without freezing ! In many places where
the only way to get # 2 home heating oil to where you live, ( and everything else thatncan't be grown or shot!) is burn Aviation gas to get it there, this brings the price of a gal.
of fuel to $10.00 U.S. multi generational houses with 4 or more people burn 120 -170 gal during a long 'heating season', there is your measurable success!

Any article that you really like consider posting to these forum threads, Even Better ! Start a new Thread ! For the good of the craft ! Big AL !

Al called it for sure.

Round stone is a huge thermal mass and a perfect shape to radiate comfortable heat in an effective way during a passive cooling cycle it's really wasted completely on the outdo side of the building. I would think incorporating it into certain walls like bathroom and kitchen or wherever really would be ideal on the interior of the building.

In the last half century people have really gone down the path of in-sulation, I thnk most good research is now showing that out-sulation practices are far superior in colder climate for a myriad of reasons so a lot of the practices of the 1970/80s are dated in that they often use the in-sulation mindset.

Straw is a great material so long as it isn't exposed to the air. So a simple air gap on the exterior of your straw to me is a major fire hazard.

IMHO stone walls are not desirable in our Canadian climates unless maybe you're in certain parts of BC but even still if thnk they are far better suited to more southern climates.

Ah Yes!! This old thread. I've been meaning to get back to this for a while and hopefully I won't lose the reply just before posting this time :S

Al: I'd been recently (around the time of your post..if you can call that recent. HA!) thinking as a result of further research and the info above that the best use for all the stone might be in interior walls as a thermal mass as well. I'd even been thinking a stone wall *could be used as a main structural wall and thermal mass in a trombe wall system.

Anyway, I've been successfully convinced that stone is best not used as a cladding/ outer wall in my climate. I'm definitely not willing to go to extra trouble just to incorporate it. I would say I'm looking for ways to take advantage of it. So maybe its time to rename this thread: Uses for stone as a building material in a northern, 4 season climate

Other uses i've thought of are:

-uninsulated constructions such as a well house
-retaining walls in terracing/ keyhole beds etc. - good as thermal mass and structure!
-inside walls (floors?) and generally as thermal mass in a passive solar situation or in conjunction with RMH or other heating
-foundation and stem wall - there are MANY examples of this that are over 100 years old in my area that are in great shape. I can't imagine if done properly this can't be at least as good as concrete for the purpose - less lateral strength but seemingly not enough less to matter?
-drive/pathway paving - a friends dad has done this on his very steep driveway just down the road and since he finished he has had no erosion where annual spring thaw used carve gulleys in his gravel/crushed rock driveway....a big job but it serves a purpose and looks great.

To reiterate I'm definitely not interested in forcing this issue but want to take advantage of any of the natural resources already present on my property if/where they are suited..especially if they can replace something that would be purchased or is otherwise 'undesirable'. Undesirable things include things I need to buy new and can't scrounge, and things that are manufactured in energy intensive ways and/or come from far away. I intend to build a modest sized, timber framed, energy efficient home that takes advantage of passive solar, and heats actively with only wood. There is just no way I will ever purchase heating oil. I have 50 acres of trees and could heat the place many times over from the annual deadfall from only part of the property. Also, in NB one company has a near monopoly on the print media, oil and gas, and pulp and paper as well as a dozen or so other smaller corps and they don't need any more of my money than they already get. We should all just say no to heating oil!

Sean: In terms of out-sulation vs in-sulation from some of the practices i've observed there can still problems when out-sulation is applied and like everything it seems its all in the way its done. Having said that I do think the potential for bad things happening when its done right are minimal. I don't really like the idea of rigid foam insulation too much, so I'm hoping to find an alternative to applying it anywhere I don't have to which may mean no out-sulation for me depending on what that constitutes. All I've seen has been a rigid foam product or another though I see a new rigid rockwool product is out now as well and seemingly intended for the purpose. Since, at this point I'm thinking timber frame, with possibly a stone perimeter/stem wall, or rubble trench foundation there would then need to be some kind of 'sulation, possibly inside a larsen truss as it seems that blown cellulose is common and 'affordable' in this situation. I can out or in-sulate using something with less manufacturing and trucking I would.

Part II : this has nothing to do with stone, only straw!

So the question has become, given the chosen parameters (timber frame..that's pretty much all I'm holding onto at the moment) I'm thinking straw insulation could work - I've seen images online but have yet to do a full on permies search on the subject. The issue I see is again the possibility of OUTSIDE damp getting into the wall...keep in mind this is not the west coast. Most of our precipitation comes in the form of snow, not rain so its not perpetually rainy and damp. Never the less, I had at one point thought, as mentioned way above that (working from inside to outside) something like this could help keep the outside damp from getting into a straw wall: timber frame infilled and beyond with straw > lime render on straw > air gap (1/2" ?) >aluminum or steel sheathing with sufficient venting to allow moisture to escape should it build up. The aluminum or steel sheathing could likely be had recycled, but could also be replaced with (vented?) vertical board and batten since cedar is so abundant on the property and is weather resistant. I never thought of leaving any straw exposed to air even within the wall but always imagined I would rent a stucco gun to blast on the render not bothering for a smooth finish, and cover that with some kind of sheathing mounted on vertical battens off the surface of the stucco to allow for airflow under the cladding.

The burning question inherent in the above paragraph is: Do I even need to worry about cladding rendered straw to protect from weather? Is my climate wet enough to warrant it or will it just cause problems...?

I do want to incorporate air tubes for a heat-exchanging air exchanger and power it with the draft from the woodstove of some variety but, again that's another can of worms. I only mention it to say that I am thinking about ways to mitigate any INSIDE damp from moving to and building up in the walls.

Sorry for the detour in the second half of the reply..

THANKS!
j

I initially thought Out-sulation was a flawed system that caused vapour build-up, mould etc, but I've since learned better. The major problem with our cold climate is that typically we simply don't have enough insulation and we come from a tradition of compensating for the lack of insulation with brute force. The real issue is due-point but we can go into it more later.

If you want to use straw the only system I feel good about is strawbale, I've discussed this with others that I work with and its pretty much a consensus that the sweet spot for people like you and I is R50 walls, R50-60 foundations and about R80 in the roof roof systems go a bit further north and those numbers continue to increase. The only straw system that comes close to this is straw bale. R20/30 is nowhere close to where we need to be. So you can do a cob, slip straw whatever and unless you're getting close to R50 out of your wall system that home is going to take brute force to keep it warm in the cold months and cool in the hot ones. Some people will preach that thermal mass can overcome insulation and most of those people have no idea what happens when a building is 50-60C warmer inside then the weather outside and the ground freezes 5-8' down, Once the momentum goes to the cold side of the walls you're back to forcing heat into the earth again which is a total waste.

So yes make use of whatever you can find but don't compromise the building science for ignorance and ideals. Our ideals need to be able to stand up to the reality around us. Just because you burn wood instead of oil or gas, if you're using brute force to overcome a lack of insulation then you're again wasting energy. The idea we need to hold onto is that we must start with the envelope then address energy. Passive solar is awesome but it won't keep a northern house from freezing by itself in the dead of winter, maybe we can design a system that can make that work but if you have a major snow storm and you can't get the sun for a few days of severe cold the home can freeze and thats never a good thing. So to that end I can't recommend that your only source of heat be wood, wood only works if you're there to feed and monitor it. I would highly recommend some sort of electric backup space heater that can keep a super insulated building above freezing till you get back, there are other off the grid solutions that can work as well and you need to make some good hard choices about this.

Use the stone to make walls inside the house, I'm not totally sold on trombe walls in our climate but some thermal mass in key areas and things like a masonry furnace are great options. Hope I've been helpful and good luck!

Sean:

Yep - I'm talking about straw bale at this point...sorry i was not clear on that. You're right - nothing else could possibly do in my/our climate I've come to discover, and frankly neither cob nor slip appeal to me much anyway.

Regarding heating backup, you make a good point. I have thought about that a bit and since I intend to be off grid electricity seems a little frivolous unless I have good wind or water on the site to supply electricity when the sun is not shinning (water is a possibility that needs exploration as is wind). It would be ill-advised I would think to rely on what's stored in batteries to provide the massive amounts of electricity required to heat a space by conventional electrical means if that bank is not being fed simultaneously.

I had thought that having a specifically placed propane heater/stove on a thermostat could do and is better than heating oil in that it doesn't require being trucked all the way into my property (a large truck won't make it...yet). My current gas stove/oven has a space heater built in (its probably 65-70 years old..not a common feature!)...that kind of thing could also work albeit inefficiently. Something a lot of folks do have in this part of the world in their basements are pellet stoves...though they require a little AC for feeding and igniting it really is very little from what I understand. The fuel (pellets) is cheap and renewable and if only used as a backup, I don't imagine I'd go through too much anyway. I have thought of a heat pump for backup, but I need to look further into it. I do know they are expensive to install and I'd still need a reliable source of electricity to run it.

As far as ideology vs. practicality my ideologies mostly come from a practical place. I have little money, and lots of natural resources. This can be overcome with time but if I don't need to wait or put myself into debt, I won't. I also have a hereditary environmental sensitivity issue. So carpets (everything but wool, jute, hemp more or less) styrofoam, PVC, vinyl window frames, perfume, the dollar store, scented cleaners, general industrial activity, and diesel fumes all set me off into varying degrees of headaches, throbbing eye balls, nausea..my mom has it worse. Point is I want to avoid anything that might be an issue, if possible. I know that straw, rock wool, and wood doesn't bother me any more than the average person so they are preferred.

I'm not anti-outsulation by any means, I even think of strawbale as a sort of outsulation when combined with a timber or stick frame. I think outsulation can be better than traditional insulation in principle BUT this guy 's work introduced me to it and though he's a big proponent of outsulation he implements it in a way that seemingly causes massive thermal bridging (fasteners driven through the outsulation, into the interior..you can literally see frost on thousands of nails on the interior.) Granted his work is far more aesthetic than practical so maybe he's a bad example, but other than big box stores and the like this is my experience with out-sulation so far. That is what I was talking about. Not that it can't be done well, but I have not seen it implemented well. In all of these cases there also seems to be far too little out-sulation (2" of rigid XPS or ISO) applied for the climate...especially if R50 is the ideal.

Regarding R-value ratings...it seems there is some disagreement on r-values on the web. I've found a plastered bale of straw to sit at about r30 on average..some say more, some less (25-35). According to multiple resources the BEST performance of the average rigid foam board is r10 for a 2" thick piece of 4x8 XPS and that's dow chemical's own number so I think its probably a bit optimistic. That would require 6" of thickness to match a strawbale at about $0.90 a square foot per 2" and that's not even approaching the r50 mark. Clearly I have a LOT more research to do, but it seems like it would be very difficult to obtain r50 using out-sulation alone. I look forward to learning more on the subject at any rate.

Also Sean, I've found your new home build thread and am getting caught up. Lots of good info in there.

I think this thread has more or less been exhausted under its original title. Time to do some more research and move on to new questions.

Thanks all!
j