Tag Archives: healthy insulation

Light clay straw insulation

On April 10, a workshop at Endeavour led participants through the theory and practice of making wall insulation from light clay straw (also known as straw/clay, slipstraw, or EcoNestTM).

This is an insulating technique we’ve used numerous times on building projects at Endeavour, and we appreciate the extremely low carbon footprint, simplicity, lack of toxicity and simple installation process of this insulation.

Here is an introductory slide show about light straw clay insulation:

Clay slip versus dry mixing
During our workshop, we used the typical mixing approach for light clay straw insulation: mixing our clay into water until we had a thick, “melted milkshake” consistency. This slip is then poured onto the straw and mixed in until the slip evenly coats all of the straw, so that a handful of straw can be squeezed into a shape that reasonably retains its shape. Whether mixed by hand, in a mortar mixer or in a purpose made straw/clay tumbler, this is how we and other straw/clay builders typically prepare the insulation.

 

For this workshop, we also tried a mixing technique more similar to that we use for hempcrete. When mixing hempcrete, the hemp hurd and the binder are added together when dry, mixed until the powdery binder coats all the hemp, and then lightly misted with water to make the binder sticky. So we tried sprinkling dry powdered clay over the straw, stirring, and then adding water. This didn’t work so well, as the clay powdered sifted down through the straw and ended up at the bottom.

Dry mixing, version 2
For our next batch, we reversed the process and gave the straw a light misting of water and then sprinkled in the clay powder and stirred. This seemed to work very well, as we ended up with a clay coating on the straw that was much stickier than slip mix and allowed the clay/straw to be packed into the forms easily. This process used 25-50% less clay, and more importantly 25-50% less water, which should reduce drying time in the wall dramatically. Having placed both slip-mix and dry-mix side-by-side in the same wall system, there was no appreciable difference in quality in the finished appearance of the insulation, but the dry-mix showed about 25% moisture content on our moisture meter, and the slip mix was up at 36%. Given that slow drying time is the main hang-up for straw/clay insulation, we will use this technique in the future to reduce the wait for the insulation to dry!

NEXT STRAW/CLAY WORKSHOP: OCTOBER 30, 2016

Hempcrete Workshop

Saturday, April 9, 2016 – WORKSHOP FULL

Saturday, October 29, 2016
9.30 am to 4.30 pm
Endeavour Centre, Peterborough

Note: This workshop is being offered twice in 2016. Be sure to register for the correct date.

Workshop Instructor: Chris Magwood

Workshop Description

Come and discover how a simple mix of natural materials can create a remarkable thermal insulation!

Hempcrete (or hemp-lime) construction uses chopped hemp hurd (the woody core of the hemp plant) mixed with hydraulic lime to create an insulation material with excellent thermal, moisture-handling and structural properties.

In this workshop, participants will learn about the components of hempcrete, see a slideshow of various Canadian and international hempcrete building projects, and gain an understanding of how, why and where hempcrete is an appropriate material choice. In the classroom, we will look at the costs, sourcing and building science of using hempcrete on new building projects and renovations.

 

In the hands-on component of the workshop, participants will learn how to assess the necessary materials and create a mix that is appropriate for a desired end use. We will use mixing machinery to create batches of hempcrete, and learn how to place them in a wall, floor and/or roof. Different types of framing and shuttering (or forming) systems will be shown, and every participant will leave with a hempcrete block they cast themselves.

After this workshop, you will be able to undertake a hempcrete project of your own!

Entry Requirements
Open to all

Fee
Early Bird – $125
Regular – $150
Includes healthy lunch (vegetarian and vegan options available)

Maximum class size: 12

Building with Hempcrete or Hemp-Lime

A group of lucky participants was treated to an excellent weekend workshop on building with hempcrete (or hemp-lime), led by UK architect and hempcrete pioneer, Tom Woolley. Tom is the author of Hemp Lime Construction and Low Impact Building, and has been involved in many hempcrete and sustainable building projects throughout the UK.

The weekend began with a classroom session, during which Tom covered the materials and techniques for successful hemp-lime building, and showing the group photos and details of a variety of building projects, including his charming hemp-lime cottage.

We then moved on to making some sample mixes to demonstrate the combination of materials. We were working with two different mix types, and made a sample of a third type of mix. For all three mixes, the weight ratios of materials were the same:

  • 1 kilogram of chopped hemp hurd (also known as shiv)
  • 1.5 kilogram of powdered binder (natural hydraulic lime or hydrated lime and metakaolin)
  • approximately 1.5 kilograms of water

The chopped hemp hurd or shiv needs to be fairly course (particle sizes ranging from 1/4 to 1 inch) and be relatively dust- and fiber-free. We were able to source Canadian-grown and processed hemp hurd from Plains Hemp in Manitoba.

Most UK-based hempcrete builders work with a natural hydraulic lime (NHL) as the basis for their binder. There is no North American source for NHL, so it tends to be expensive to import from Europe. We used an NHL 3.5 from St. Astier as one of our mix options. For a more locally-sourced version, we used a typical North American hydrated lime and a fired kaolin clay (called metakaolin) called Metapor. The NHL is a lime that chemically sets (hardens) through a reaction with the water content of the mix. North American hydrated lime does not set hydraulically (with water), but when mixed with a pozzolan like Metapor the two materials together have a hydraulic set.

The dry ingredients (hemp hurd and lime) are mixed together so that the powdered lime is covering all of the hemp, and then the water is introduced. Having done some work with hempcrete at Endeavour, we were surprised at how little water Tom uses in his mix. The final mix is just moist enough to lightly hold together when squeezed in a hand.

With some small scale mixes placed into test cones, we then moved on to installing hempcrete in some larger wall panels. These panels were built by Sarah Seitz for her PhD research work at Queen’s University, where she will perform tests to help determine the thermal insulation properties of hempcrete.

The panels simulate a typical double-stud construction, with a 2×4 frame on the “exterior” side of the panel and a 2×3 frame on the “interior” side.

As one group mixed batches of hempcrete in the mortar mixer, the others placed it into the forms and lightly tamped it into place. As the forms fill up, they are moved up the wall. The hempcrete retains its shape after less than 20 minutes in the forms. The filling and tamping continues right to the top of the wall. Once everybody was settled into their roles, it took less than 1.5 hours to fill a whole wall form.

In the end, we placed 40.25 cubic feet of hempcrete into the two walls. We used seven 40-lb bags of hemp hurd and seven bags of powdered ingredients to reach that quantity. With the small amount of water used in the mix, we’re anticipating a drying time for the 14-inch thick walls of about 2 weeks. This is much shorter than for the wetter mixes we have made in the past.

Cost-wise, we used $63 of hemp, $42 of hydrated lime and $21 of metakaolin, for a total material cost of $3.13 per cubic foot of insulation.

We will share Sarah’s thermal testing results when she has completed them. We are expecting to find their performance to be around R-2 to 2.5 per inch, meaning that our 14-inch wall would surpass current code requirements for thermal insulation.

This was a fun and informative workshop, and we’d like to thank Tom Woolley for sharing his deep knowledge of this subject with us!

Dense-pack Cellulose Insulation

There are several portions of Canada’s Greenest Home that do not have straw bale walls. While we believe strongly in the advantages of straw bale walls, we also want to show our students a more mainstream way to achieve high energy efficiency with low environmental impact: double stud framing and dense-packed cellulose insulation.

These sections of the building are framed with 2x4s and are the same depth (14 inches) as the bale wall cavities to give the house the same wall thickness everywhere. Since the dense-packed cellulose has a better R-value than the straw bales, these sections of the building will be very well insulated!

The cellulose insulation we used is made nearby in the Ottawa area from shredded, recycled newspaper and borax. It is a low embodied energy, local material with no real drawbacks environmentally.

Our first inclination was to use wet-sprayed cellulose, as we thought that this would be the best way to fill the cavities and prevent settling. However, the extra thickness of the cavities would have meant that the wet-sprayed cellulose would have had to be applied in several “coats”, adding time and cost to the installation. Our installer, Air Barrier Insulation, suggested dense packing as a better option.

A fine mesh is applied to the interior side of all the studs, which will let air out of the cavities but retain all the cellulose. The cellulose hose is then inserted through a slit in the mesh and the heavy blower (operating at about 60 psi) packs the cavity full of the insulation. The operator continues to pump the cellulose until the blower can no longer force any more into the cavity. At high densities (around 4 pounds per cubic foot) the insulation will not settle.

The directory of property management companies is much more powerful than the typical rental units we’ve used to loose blow cellulose into attic spaces. Having seen this unit in operation, I’d definitely use this type of machine for retrofit applications as well in the future.

The application was quick, relatively tidy and surprisingly less dusty than anticipated. With such an excellent option available to any builder doing conventional stud framing, an affordable and environmentally friendly wall insulation option is an easy choice.

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