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wofati and earth berm

Rodent and termite resistant berm insulation?

R Scott

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posted 3 years ago

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Any ideas? In Tennessee, so sawdust and duff will compost no matter how hard I try to keep it dry. Foam board turns into a mouse subway system. Aircrete eventually sponges up ground moisture until it doesn’t work.

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Jt Lamb

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posted 3 years ago

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Could you sketch and/or describe the construction details (a sectional detail) of what is, so we could all better scratch our heads over what would work, giving you more choices? Also, for clarity, what is being bermed? House, shed, root cellar ... and alternative construction type chosen?

If a mouse problem, I'd barrier up against them, and in addition, set lots of traps to create a bubble/zone around the item needing protection. There are plenty of mice/rats/rodents in the world (the fields around our structures), but they aren't getting into our structure zone ... occasionally, one does, but it is quickly trapped before harm is done. They just don't mix well with human structures ... damage, disease (droppings, fleas), etc., so best to "keep them at arm's length".

Stuff rotting or getting wet needs clear protection from water/elements, like with 6mil poly layers. In addition, perhaps sitework designs or rework that channel water away before it gets a chance to become a problem (similar to mice).

R Scott

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My specific situation is for an Earthship inspired build. Walls on three sides that are bermed to the top with an insulation umbrella that is continuous from the roof down over the portion of the berm that is the thermal mass. Then more dirt on top to protect the membrane from UV and grow enough roots to hold the berm from washout. My roof will be metal for rain collection so my water proofing is simpler than a full roof like a wofati, but the transition details are a bit tricky. I don’t want to leave a direct path from foam to wood under the 6mil or edpm but not create any thermal bridges either.

Mice are one thing, but the real insidious problem is termites. They LOVE chewing through foam board. There are places that won’t insure houses with external insulation, including the required under the slab insulation, because you can’t inspect or repair the damage until it is catastrophic. Or they require a level of chemical prevention that borders on making a superfund site. No thanks.

I am either looking for an affordable non chemical way to waterproof aircrete from rising damp or to termite and rodent proof the whole umbrella.

Jt Lamb

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It sounds like you want a certain building method (earth-berm, wofati), but you are using this in an area of the country really susceptible to termites (the story on these guys is pretty scary reading).

The two things may be too incompatible, given the nature of these little bugs; they need only a 1/32" gap to get in and start doing damage ... moisture (dampness) is another nice-to-have for them.

In researching what blocks termites, a barrier system seemed to be the only real defense, outside of chemical warfare. Folks down under have something called "BTB - basaltic termite barrier", and another reference to it (in Hawaii) is GranitGard. I've also seen references to a certain kind of sand that is the right texture to block termites. The trick is to get it applied in such a way that it stays in place, doesn't get damaged or separated, which again creates access paths.

Everything I've ever read about termites is in relation to above-ground buildings, so with termite shields on the foundation and a good visual gap between ground and walls, you can visually inspect and catch these guys early enough to prevent major damage. Going underground in termite country is the opposite of that ... no way to inspect, no gap, etc.

The Wofati forum might take some careful searching to unearth all techniques used to block termites, but it may be that there still isn't enough history to know what works yet?

Further exploring aircrete, and it's waterproofing methods, sounds like a better track to me ... that's a hard barrier, w/ EDPM and sitework tactics to keep water far away.

More head-scratching needed ...

Aaron Yarbrough

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I'm working on an earth bermed cabin and was thinking about sheathing the exterior of the bermed sides with corrugated metal panels to protect the foam boards.

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Jt Lamb

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It seems like a reasonable barrier, but I would draw up a detail section, and run it past:
- termite pest control folks; if they say they'd "guarantee it", then it seems feasible from termite control perspective.
- a builder/engineer to see if it passes muster as a construction assembly ... building, sealing, back-filling, etc.

After all the termite research I did, I'm not sure I'd put any wood underground, if in termite country. Barriers + chemical warfare, water control, and more ... all would come into play, and I can't find assembly details that seem reasonable, other than conc walls w/ insulation panels on the inside; if insulation panels on the outside, then you ring the dinner bell for termites.

R Scott

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That is great for rodents but I’m not sure it will work with termites. At least not for a long as I want it to.

Aaron Yarbrough

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What if you used cement backer board as well?

So the wall from inside to out would be

Studs infilled with insulation
Plywood Sheathing
Polyiso foam board
Cement backer board
Peel and stick waterproof membrane
Corrugated metal cladding

I don't know if you could find masonry screws with a gasket for attaching the metal panels to the backer board.

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R Scott

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Aaron Yarbrough wrote:
I don't know if you could find masonry screws with a gasket for attaching the metal panels to the backer board.

I don’t know but I do know you can get 3 inch long screws to go all the way through to the studs if you keep the foam board thinnish

I am leaning toward making aircrete with plenty of lime to kill/repel the bugs and rodents and waterproof it with 6 mil poly top and bottom.

As for the roof, I will use steel wool to plug the ribs in addition to the usual trim

William Bronson

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Do boric acid or borax work as ways to stop mice and termites?
If it does then woodchips,cardboard, papercrete and more become viable choices.

As to wetness, anything that can't recover from getting wet seems like a potential problem.
Rockwool can, and while we are at it, sand,charcoal or fill dirt could as well, though not as easily.

What if the walls were steel studs filled with borox treated Rockwool and coveres inside and out with cement backerboard?
A peel and stick water barrier could be covered with a second layer of backer board.
That could be covered with treated woodchips, either piled loosely or as woodcrete.
6 mil plastic, sandwiched between layers of carpet would come next.
A cement slurry trowled onto the outer most layer would be followed with seed and soil.

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M Broussard

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R Scott wrote:My specific situation is for an Earthship inspired build. Walls on three sides that are bermed to the top with an insulation umbrella that is continuous from the roof down over the portion of the berm that is the thermal mass. ...

I am either looking for an affordable non chemical way to waterproof aircrete from rising damp or to termite and rodent proof the whole umbrella.

Pumice (with fines screened out) has been used as very durable insulation in underfloor settings in natural buildings the western US. It does absorb some water, but also is much better at drainage than aircrete and doesn't have the rising damp issue in that context, though I am not certain how it would act in a berm wall. Pumice also has the advantage of being unpleasantly abrasive to small mammals. Something to consider!

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R Scott

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Location: Kansas Zone 6a

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I had forgotten about pumice, THANK YOU for the reminder. That is probably my first choice for under slab insulation if it isn’t outrageous. It solves multiple issues at once. On top of that will be a vapor barrier and soil cement or cob floor.

My current thought on the berm is to use aircrete with lime and copper sulfate. Both should be permanent non leaching omri approved deterrents for bugs and mold. I will be careful to keep it out of the topsoil and only under the umbrella.

Greg Martin

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There's commercially available closed cell glass foam. It is a barrier, is insulative, is critter proof, is LONG lasting and is strong such that it can take a compressive load.

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R Scott

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Greg Martin wrote:There's commercially available closed cell glass foam. It is a barrier, is insulative, is critter proof, is LONG lasting and is strong such that it can take a compressive load.

And WAY out of my price range for this project. I do want to experiment with some, I think it would be great for under the RMH bench

Aaron Yarbrough

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Aaron Yarbrough wrote:What if you used cement backer board as well?

So the wall from inside to out would be

Studs infilled with insulation
Plywood Sheathing
Polyiso foam board
Cement backer board
Peel and stick waterproof membrane
Corrugated metal cladding

I don't know if you could find masonry screws with a gasket for attaching the metal panels to the backer board.

I was able to find a supplier in my area who has Rockwool Comfortboard 80 which per Rockwool's website is used in areas where probability of termite infestation is 'very heavy'

It is pricey a $64 per 1.5" thick 4' X 8' Sheet. A 2" thick 4' x 8' sheet of XPS in my area is $40.

Revising my wall system above I'm thinking about the following for my earth sheltered build:

Studs infilled with cob

3/4" Ground Contact Plywood

Peel and stick waterproof membrane

1.5" Rockwool Comfortboard 80 panels

Polytheylene Sheet

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