Comments on: Vapor Barriers

By: Andrew Morrison

Andrew Morrison — Mon, 06 Feb 2012 16:56:21 +0000

I definitely recommend building without a vapor barrier other than the plaster. I would also recommend that you use lime plaster to help mitigate the humidity. Finally, I suggest you install an Energy Recovery Ventilator which will actually draw moisture out of the air and dump it outside of the house. Another plaster option is clay/earthen plaster; however, that is harder to maintain in wet climates on the exterior. That is a fantastic plaster for deal with humidity if you can protect it from the elements (rain most notably).

By: Kristopher Hamilton

Kristopher Hamilton — Mon, 06 Feb 2012 15:19:41 +0000

Hi Andrew,
So…I’m building an addition on my home, (288sq. ft post and beam holding roof). I live in the piedmont of North Carolina where humidity levels in the summer are regularly 80-90%, In a climate like this, is it possible to build with straw and use no vapor barrier other than the plaster?

By: Andrew Morrison

Andrew Morrison — Mon, 02 Jan 2012 22:53:05 +0000

Hi Lynn. I would recommend vapor barriers in the floor and roof but now over the bales. Instead, use a quality lime plaster in three coat (minimum) build up application. This will provide adequate protection against the elements and will allow the walls to naturally move the vapor (the lime will act as the vapor barrier to an extent). Be sure to seal the gaps around electrical plugs and other wall penetrations and the intersection of the wall with the floor and ceiling. Flooring can be anything; however, I suggest something with a high thermal mass to help store heat. Foundations will depend on the local geology so I can´t really comment on that.

By: Lynn

Lynn — Mon, 02 Jan 2012 05:57:54 +0000

Hello, what are your thoughts on a vapour barrier when building up in northern parts of Canada. Like Winnipeg MB, or Regina SK, or around Edmonton, AB. These are areas that get snow 5-8 months of the year. Generally, driving rain is not common, although there is rain, more or less depending on the region, in the summer. However, it’s not raining all the time, nor is it always humid.

So, vapour barriers on the walls, floor, roof? Would a couple layers of lime coating be enough to withstand the snow? What would you recommend as foundation and flooring?

By: Andrew Morrison

Andrew Morrison — Tue, 29 Nov 2011 16:53:27 +0000

Hi Nola. The measurements are in US calibrations. You can substitute white glue (Elmer’s Glue here in the states) for the wheat paste. As an FYI, I am coming to West Wyalong in March and Perth in August to teach straw bale workshops. If you want to learn more about the classes, please visit http://www.strawbaleworkshops.com. Hope to see you there!

By: Nola Poupard

Nola Poupard — Sat, 26 Nov 2011 19:37:41 +0000

I want to make this, but got a couple of questions:1. What can I substitute for wheat starch? Don’t want to buy a whole packet only to use 4 tablespoons.2. Are the measuring cups and spoon American? In Australia, 1 cup = 250ml, whereas in the US, it is 235ml. I don’t have US measuring utensils.

By: Andrew Morrison

Andrew Morrison — Thu, 13 Oct 2011 17:19:35 +0000

Hi Ben. Sorry for the long delay. You can add rock right to the face of the bales as long as you have relatively large chinking (joints) between the stones made of a breathable mortar, preferably lime. I would leave all of the plumbing to interior walls, out of the straw, and only put it in bale walls if you have to. In that case, I would frame out that whole section of wall and put the plumbing in the framed area, again, without contact with the straw. If you want to leave a gap between the bales and the stone, you can, but that means more material use. You would need to provide screened ventilation to that area and be sure to slip coat the bales on both sides.

By: Ben B

Ben B — Fri, 29 Apr 2011 18:24:36 +0000

Hi Andrew,
Thanks for answering all of these questions over the past couple of years. I see a few questions that touched on an area I am having a difficulty working through.

I am planning on building three homes for my family and myself. It sounds a bit much, but will be a phenomenal farm when we are done. We (Really I) am pushing to use Strawbale construction, but we don’t want to have the plaster finish on either the inside or outside.

We want to make use of the stones on the property to affix to the outside wall at least a few feet above grade and we are still debating on what to do above that. If there are enough stone we are not against going all the way up to the roof (They are going to be one story homes). We also want to keep all of the plumbing and electrical work away from the interior of the walls so that repairs can be made easily.

I will be constructing my own 4 x 8 panels that can be removed easily enough to get access to the plumbing and electrical work. That means there will be a least a couple of inches of space inbetween the stud wall and my stone and wood interior panels.

My question is how can we allow the straw bales to breath, if we have stone on the outside. There will be just a simple plaster coating on the bales (inside and out).

Should we leave a gap between the outside frame and the stone to allow for air movement? And would you vent this up through the roof vents?

By: Leana Mcbath

Leana Mcbath — Thu, 03 Mar 2011 16:42:45 +0000

Certainly worth you discussing this educational write-up. Fantastic!

By: Andrew Morrison

Andrew Morrison — Mon, 24 Jan 2011 18:35:43 +0000

The earth bermed part should not be straw bale as it will not do well below grade. Other than that, the inclusion of proper drainage and waterproofing is essential. There are a lot of products out there, most of which are good quality but less than “non-toxic.” It may be a trade off for long term health: i.e. a less than green product up front allows you to build a long term green house. There are some plastic sheet designs, some with rubber membranes, that work well and are about the most green available. Good luck.