Finishing the straw-cell wall system

Straw cell wall system

Our office building project for the Trillium Lakelands Teachers’ Union features a straw bale wall system that combines conventional wood stud framing with an interior straw bale wall.

Recently, we finished the exterior side of this wall system. This involved placing dense-packed cellulose insulation in the frame wall, filling the cavity so the insulation is blown tightly against the straw bales. With the cavities insulated, we add approximately R-21.5 to the R-30 of the straw bales. Our contractor for the dense-packed cellulose was Morgan Fiene at New Energy Consulting in Hastings, Ontario (705-313-2004), whose care and concern for doing a thorough job was very refreshing.

We then covered the framing with an insulative wood fibre sheathing. This 1/2 inch wood fibre sheathing has an R-value of 4 per inch, and is made from 100% recycled wood fibre and a non-toxic binder. Made by Western Louisville Fiberboard in Quebec, this product is the cleanest sheathing product we could find. Most exterior wood fibre products use an asphalt emulsion coating, but the SONOclimat product uses a proprietary coating that is water based, non-offgassing and meets stringent environmental standards.

As a means to blend conventional wood framing with straw bale walls to achieve very high insulation values, we have been very pleased with the straw-cell system. It marries low impact materials throughout (earthen plaster, straw bales, cellulose insulation, FSC framing and recycled fibre board) with high insulation value and a straightforward construction process. It’s a great way to marry the more unconventional approaches to sustainable building with mainstream approaches.

 

Air tightness details for straw bale walls

Straw bale wall details

Straw bale wall systems have been touted for 20+ years now as a way to achieve higher insulation values with lower environmental impacts. And, having built many straw bale homes and commercial buildings now, we know this is true. However, we have also seen that without attention to air sealing details, many straw bale buildings are quite leaky and fall short of their potential level of energy efficient performance because of this.

Along with many straw bale compadres world-wide, we’ve worked to come up with details that address these issues of air tightness in straw bale buildings. Our latest project for the Trillium Lakelands Elementary Teachers’ Local offices have good examples of easy ways in which a bale wall can be built to be air tight without reliance on whole-wall vapour barriers or other sheet membranes.

Plastered straw bale walls have a naturally air tight nature thanks to the continuous plaster coating. Any crack-free layer of plaster does an excellent job of stopping air movement through a wall. However, where plaster meets other materials (at the top and bottom of each wall, at each door and window opening and around through-wall vents and pipes), just plastering up to these seams does not create an air-tight barrier. All plaster types share the characteristic of shrinking as they dry or cure. Every edge of a plaster wall will pull away and leave a gap as the plaster shrinks. It may not seem like much, but even a 1/16 inch gap at the top of 100 feet of wall area is the equivalent of 75 square inches of “hole” in the wall! Add that same gap around every window and door and at the bottom of each wall and you may have a hole in your wall of up to 1.5 square feet! That’s like leaving an average sized window open full time!

Most homeowners understand that having a window open all winter long would have a negative affect on the amount of energy used to heat the home. But many people do not put the time and effort into “closing the window” around the perimeter of their straw bale walls.

For some, there is a reluctance to build air-tight because of a notion that it is unhealthy to seal a house “too tightly.” However, it is also unhealthy to be drawing outside air into your home through cracks and leaks in your walls. That infiltrating air picks up dust, spores, and anything else that is in the walls on its way into the house. Seal the house properly, and deal with the ventilation that is required in an intentional, clean way.

It’s not difficult to make an air tight bale wall. We will report on our blower door test results for this building as soon as we have performed the test!

Stop motion straw bale and earth plastering

Sustainable New Construction 2014 student Ben Bowman set up his camera and took some great sequences of the construction process at our teachers’ union office project.

Here are the two sequences of straw bale installation and earthen plastering. In many ways, these stop motion videos give a better sense of the process than an actual video, plus it makes it all look so fast and easy!

Ben also captured sequences of our earthbag foundation construction and roof craning process:

 

 

Plan Your Own Sustainable Home: A Workshop for Owner-Builders

November 15 & 16

Note: This workshop is being held in Toronto at The Living City Campus at The Kortright Centre, 9520 Pine Valley Drive, Woodbridge ON. All registrations must be through The Living City Campus.

Workshop Instructor:
Chris Magwood

Workshop Description

The dream of designing and building one’s own home is one of the most deeply held desires in our culture. The dream of designing and building a sustainable home marries that desire with a wish to live lightly (and affordably!) on the planet.

However, many questions face the prospective owner-builder setting out on this journey. To design yourself or hire a designer? To build yourself, or hire builders for different phases? How to choose from a myriad of competing natural building materials? How to choose heating options, water and waste options, electricity options? How to manage budgets and timelines? How to choose a piece of land? This workshop will explore all of these questions in an in-depth way.

The workshop is designed to be an un-biased look at all the options available to the prospective owner-builder, and to assist you with tools to help you assess and choose your way to the house of your dreams. You will leave this workshop ready to handle all the competing claims and information you will face by focusing on your personal goals and aspirations and creating a road map for how best to meet them.

Making Better Buildings book by Chris Magwood

Making Better Buildings by Chris Magwood

This course was the inspiration for Chris Magwood’s new book, Making Better Buildings. The book will be available at the workshop.

Entry Requirements
Open to all

Fee
$350
$630- Couple rate

Includes healthy lunch (vegan and vegetarian options available)

Maximum class size: 12

High-straw earthen plaster recipe

Earthen plaster at Endeavour Centre

It’s no secret that we love clay plasters at Endeavour, and the best case scenario is being able to use a clay soil right from the building site. It just so happens that we lucked into this for the teachers’ union office project!

After digging some test holes on the site early in the spring, we discovered that there was a strata in the site soil that was quite clay-rich and appeared to have almost no stone in it (which is very rare in this part of the world). We made some plaster samples from this soil and found that a wide range of recipes seemed to be viable. We left the samples face up into the elements for the whole summer, and one in particular held up really well so we knew we had a workable site plaster.

Our approach to earthen plasters has changed over the years, with the addition of more and more chopped straw over the years so that we have reached a point where we have a very high-straw content in the plaster. We have found that the high-straw recipe allows us to build up the entire thickness of the plaster in a single application. The volume of chopped straw supplies a huge amount of tensile support for the clay, and means that we don’t need to add nearly as much sand as we used to do when our plasters used less chopped straw.

The result is a mix that is very sticky thanks to the high clay content, and has a huge amount of “inner cohesion” that allows it to be applied at almost any thickness (4-5 inches is not unreasonable, if necessary!) with no cracking.

Rather than applying a very runny slip coat via sprayer or dipping the bales, we’ve found that a layer of the same mix minus the straw works well as a “primer”. We apply the primer to the bales, and then follow it immediately with the high-straw “body coat.” It’s sort of a two-part, one-coat system. It’s great to be able to apply the full desired amount of plaster and achieve the final look we want in a single application. Less time, and much less concern for de-lamination between successive coats.

The mix stays moist for a day or two, so it allows a lot of time to get the walls looking how we want, and the mix is very intuitive for those just starting to learn to plaster, while being fast to apply for those with more experience.

Our recipe (by volume) for this plaster is:

  • One part high-clay content soil
  • One part chopped straw (1/4 – 1 inch)
  • 3/4 part rough sand

There’s nothing like playing in the mud and making a viable building at the same time!

New system for straw bale walls

Straw Bale wall installation at Endeavour Centre

Over 20 years of building with straw bales, I have constantly experimented with new ways to integrate bale walls into buildings that are simple, cost-effective and energy/resource efficient. From load bearing to prefab panels to a variety of framing systems, I thought I’d tried them all.

But we were introduced to a new idea by the excellent builders at New Frameworks Natural Building, and we liked the idea so much we decided to try it ourselves.

Their “StrawCell” approach involves building a conventional stud frame wall for the building which acts as the exterior frame and main load bearing element. One immediate advantage is that this system fits into the regular code structure and should not require special engineering or design considerations, which can really ease the permitting process and help to lower costs. The straw bale wall is then built to the inside of the frame wall, with the bales pressed against the framing. The stud wall cavities are then insulated with dense packed cellulose, and sheathed with a permeable board material. Any kind of siding/rainscreen can be created as the final finish on the exterior.

On the interior the bales are very easy to install. The only framing that interrupts the straw is for window and door openings – very similar to the easy installation for load-bearing designs. At the top of the wall there is no beam or framing to notch around, just a plywood plate on the underside of the roof. We tied each bale through to the framing, so the wall was very straight and solid right away.

While the amount of lumber used in this system was initially a red flag for me, an actual calculation showed that we were using no more lumber than any of the other bale wall systems that use a frame of some sort. A conventional frame wall is actually a very effective and efficient way to use lumber, and only some load bearing systems actually use less lumber than this frame wall approach.

One major difference between this system and other straw bale approaches is the lack of exterior plaster. This can be seen as both a plus or a minus. We have been shying away from exterior plaster finishes for clients, especially commercial clients like the teachers’ union. While we love plaster, it is both a high maintenance finish and one that is susceptible to moisture issues unless well detailed, well protected and well maintained. While we definitely have not sworn off using exterior plaster, we are certainly glad to use siding when the client and/or conditions make it appropriate. On the plus side, this system reduces the amount of plastering material and labour required by half (actually, more than half since the interior plastering is always easier). Interior plastering can happen at any time of year, while exterior requires the right weather conditions.

The addition of the cellulose in the exterior wall brings this wall system into the super-insulated category, capable of reaching PassiveHouse standards even in our cold climate (something a single, two-string bale wall cannot do). The cost of the cellulose and siding together are quite similar to the cost of the material and labour for exterior plastering.

All in all, we like this system so far. We’ll continue to report as we finish preparing the walls for plastering and complete the remainder of the system.

Craning a Finished Roof

Roof craning at Endeavour Centre

Building a roof can be intimidating, and statistically the most dangerous element of making a building. The heights involved add risk, time and a lot of effort.

Whenever we have the opportunity, we build our roof structures – including all sheathing and as much finishing as possible – on the ground, and then use a crane to lift the roof and place it on the building. In this way, we reduce the risks associated with working at heights, lower the amount of physical labour involved in carrying materials to roof height and bring protection to our building faster.

For the teachers’ union office, we once again had enough room on the building site to do just this. We set up two rows of beams on the ground at the back of the property and fully erected the entire roof, including trusses, bracing, strapping, membrane, steel sheathing, light tubes and the full PV array. All of this was accomplished with the fascia less than two feet from the ground!

As we’ve found to be typical, the craning is a relatively quick process. We were slowed somewhat this year by wet conditions on site that made placing the crane in the right position difficult, but we still put all three sections of the roof on the building in a single day.

A quick look at the math makes a pretty good financial case for building roofs in this way. The cost of a day’s rental of a crane and operator is easily paid back by the efficiency and reduced labour time of building on the ground.

It’s not a carbon free practice, but when the site and conditions are appropriate – and particularly when working with student builders – it’s one place that we’re willing to let fossil fuels and mechanical advantage help us out!

Building Science: What every home owner and builder should know

Building Science is a relatively new field of study, emerging over the past decade as architects, engineers and builders examined the results of the new wave of highly insulated and energy efficient buildings. Building science attempts to see a building as a whole system, rather than an amalgam of different elements. Building enclosure (roofs, walls, floors, insulation, windows, doors and barriers) and heating/cooling systems as well as occupant loads and demands are examined within building science to achieve the highest levels of comfort, efficiency and building durability and serviceability.

At Endeavour, we think it’s important that building science isn’t just left to the scientists. Homeowners and tradespeople who understand the principles of building science will make better, more informed decisions at every turn in a project. Whether it’s a minor renovation or a complete new build, the lessons of building science will make the project more energy efficient, more durable and more comfortable.

The basics of heat and moisture movement and material properties are not hard to understand, and armed with an understanding of these basics, homeowners and builders will be able to have informed discussions with designers, building officials and HVAC suppliers and installers.

Builders involved in the natural building movement of the past two decades have played an interesting role in pushing the boundaries of building science. Lessons learned in straw bale, cob and adobe buildings have helped to inform the entire building science community as the field developed into its own branch of study. To date, buildings made with natural materials have often embodied the best principles of building science (whether knowingly or not!)

You can join one of North America’s leading natural building scientists for a workshop on the Fundamentals of Building Science at Endeavour to bring yourself up to speed for your home building project or to help you become a better builder. Jacob Deva Racusin is a principal at New Frameworks Natural Building in Vermont, and a co-author of The Natural Building Companion. His four day course is open to all, and is designed to introduce and develop the concepts of building science in both a theoretical and hands-on manner. You can read the course outline here.

If you intend to achieve a high level of performance in your own home or on your professional projects, this workshop is for you!

Paperstone countertops at Canada’s Greenest Home

Paperstone countertops at Canada's Greenest Home

We spent a lot of time considering our countertop choices for Canada’s Greenest Home. It’s an area with many options, and many factors to weigh when trying to make an environmentally sound choice. Ideally, the countertop material must be durable, aesthetically pleasing, stable, renewable and/or recyclable and not off gas any chemicals into the home.

After much deliberation, we chose to go with a material called Paperstone. This type of countertop is made from 100% recycled paper fibers (complete with FSC certification), bound with a phenolic resin to create a solid, dense material that is certified food safe by NSF and resistant to high temperatures and abrasion/scratching.

One of the main attractions to Paperstone is its workability. It can be cut with typical woodworking tools, allowing us to do our own installation. We were able to shape the pieces we needed, make the sink cut-outs and bevel the edges of the material easily.

Paperstone came in a range of attractive colours, and can be finished with natural sealants and waxes.

The phenolic resin binder gave us some cause for concern. While the material does not contain any petro chemicals or off gas in the home, the resin ingredients are not environmentally benign. However, the company documents its handling practices very convincingly and has received numerous awards for its sustainability initiatives. We would like to see the company apply for Greenguard certification to ensure its claims of zero off gassing are confirmed by a trusted third party.

We obtained our Paperstone from Living Rooms in Kingston, Ontario, allowing us to work with a supplier we know and trust. This is always an important part of any product decision. The material comes in large slabs, and we bought a 5×12 foot slab from which we cut the pieces we needed.

After a lot of use (and abuse), we have been extremely pleased with the performance of the Paperstone. We gave it an initial waxing prior to use, and have not refinished it after 10 months. It is impervious to water, easy to clean, and very scratch and dent resistant. The dark charcoal colour we chose has a nice depth to it, and doesn’t show any signs of staining or wear. Areas around the sink, where many countertops begin to show signs of failure quite quickly, don’t seem vulnerable to deterioration at this point.

The countertop draws compliments from almost everybody who sees it. It looks and feels unique and attractive. While it is not inexpensive, the initial workability of the Paperstone allowed us to do the installation ourselves, saving money. And its apparent durability means that its an investment that will last a very long time. If you can afford it, we would recommend it as a good choice.

 

Framing systems for teachers’ union office

FSC wood framing at Endeavour Centre

Wood framing is a conventional building practice that we use quite frequently at Endeavour. For the teachers’ union project, we are using wood framing for both the floor system and the exterior walls. The walls and floors may not look very different from conventional building, but from a sustainability point of view we’ve made choices that can make a large impact.

First, all the wood framing is certified by the Forest Stewardship Council (FSC), a third party certification organization that helps to ensure that wood products are harvested and processed according to high standards of sustainability. For this project, ensuring FSC certification meant going straight to a FSC certified distributor for our framing lumber and plywood as non of the local lumber yards are FSC certified.

The floor framing uses open web joists from TriForce. These open web joists do not use metal plates, but are finger-jointed and glued, using 2×3 top and bottom chords and 2×2 webs. This uses wood from smaller diameter, fast-growing trees and significantly less wood than solid floor joists, and significantly less glues than wooden I-beams with solid OSB centres. The floor joists are deep enough to allow us to achieve R-46 once they are filled with cellulose insulation.

The 2×6 wall framing is the load bearing exterior wall of the building, and will also be filled with cellulose, adding R-22 to the exterior of our bale walls (more on this hybrid system later), which will be installed to the interior side of the frame.

One of the great advantages of wood framing is the speed of construction and the low cost. When added to the renewability of wood when harvested and processed responsibility, it’s a great combination.