Hemp house rainscreen

montminy | Posted in Green Products and Materials on May 20, 2020 01:24pm

Hello.

I am building a house made of hempcrete walls.

I am looking for a rainscreen to put on the exterior of the walls to provide an air gap and protection.

The idea at the moment is to wood strap (furring) the house, fastened a rigid panel (i.e. cement board) and then apply a cork spray over the board. https://www.corkco.ca/single-post/2017/01/15/What-is-Cork-Spray-

I am trying to find a better option to replace the wood strapping and the cement boards.

What product could be used?

thanks

Answer

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Replies

GBA Editor

Brian Pontolilo | May 20, 2020 03:19pm | #1
Hi Montminy.

I am not familiar with that cork product and it is probably best to ask the manufacturer for recommendation, But my first thought was to use a rainscreen product designed for stucco installations, like those shown in this article: Rainscreen Products for Stucco Installations.
burninate | May 23, 2020 01:57am | #2
Why not just apply a lime render (exterior lime plaster), and then screw through that to attach furring strips, and then your siding? Unlike concrete stucco, lime versions tend to be a lot more flexible, a lot more water permeable, and unlike gypsum, water-resistant enough to be approved for outdoor use.

My understanding is that this is the conventional route with straw-bale (thicker coating) and hempcrete (thinner coating).
montminy | May 23, 2020 12:29pm | #3
Yes lime render was the original idea. however the sprayed cork offer other advantages. https://vipeqcanada.ca/services/

My main concern is to protect the bottom sill and the 6" of exposed insulation that will be above final grade.
The idea mentioned above to fur the house and install board as rainscreen as been dismiss. (too much labour and cost)

Now my builder's option is to build a "sealed box" made of cement board 16" above the sill and covering the exposed insulation and then apply the cork spray, but I read that cement board are not made to be in contact with the ground. What should I do?

I thought maybe I could seal the sill joint with "prosoco" or alike and then have made a flashing with stainless steel which would be fix/glued/seal to the hemp wall maybe 6" above the sill and covering the insulation then apply the cork spay as above. I would need 160 linear feet of SS. (what's the cost of this?? )

I am welcome to ideas.. Thanks