EDITOR’S NOTE: This post is part of the Expert Exchange series, an editorially directed and expert-driven platform for information and discussion around leading-edge building science principles and projects. The fourth quarter topic—made possible with support from our sponsor*, Rockwool—is “Choosing Products and Materials for a Green Home.” The series will culminate with a webinar panel discussion among contributing experts on Dec. 7 at 6pm ET. Click to register.
Increasing insulation in building assemblies contributes to greater thermal comfort for occupants. However, if we respond to the desire for increased insulation with petroleum-based products, we overlook a project’s impact on indoor air quality and knowingly contribute to a larger carbon footprint. While it can be said there are situations where foam insulation is the answer, such as in renovations where space is tight, or sub-grade conditions, we are finding more alternatives even in these restricted instances.
While foam will continue to have a place in the building industry for some time, we have found safe and healthy alternatives for our building projects at Love|Schack Architecture. We typically go beyond code minimums for energy performance and see the benefits of carefully considering the materials within. In our cold northern climate (zone 6), we design thick walls and roof assemblies to increase insulation—typically 12 to 14 in. for walls, often more for roofs.
In favor of prefab panels
We commonly employ prefabricated building systems, as they can offer good cost control and are appropriate for remote or rural building sites, where finding labor is challenging. We have sourced prefab walls, roofs, and floors that are filled with cellulose, and also with straw. While these products weigh more than a foam system, and this does impact delivery costs, we find the systems equivalent or better in thermal performance than site-built assemblies with conventional materials; and they are healthier for the crew that installs them.
At Love|Schack, we’re driven to design Passive Houses with high-performance enclosures using more natural products from renewable sources, and that have lower embodied energy. We aim to provide homeowners with optimal thermal comfort without the massive carbon footprint that a conventional building is responsible for.
When the opportunity to design with a cross-laminated-timber (CLT) system presented itself for a project located in Wilson, Wyoming, we felt it was important to use natural materials in the rest of the assemblies; and we explored the options that would help us minimize our environmental impact.
The depth of exterior insulation needed in the walls and roof for this climate was daunting; the conventional response would be rigid foam board. The solution we chose was Gutex compressed wood-fiber insulation wrapped around the structure exterior. While we had to source this product internationally, it will soon be available from North American suppliers, including TimberHP.
Preferred insulation materials
When designing with bio-based materials, understanding how the assembly will handle moisture is critical for a successful outcome. Overall, the goal is to avoid any chance that the air transfer from outside to inside will create moisture within the assembly—something that could cause serious deterioration, if not failure. With the use of smart membranes, vapor-open products, and details that allow bulk water to drain and assemblies to dry, we can confidently specify natural insulation materials in cold climates.
Topping our short list are four products that offer highly effective solutions on several levels, including moisture diffusion and increased water permeability. It should also be noted, they are highly dependent on paint, plaster, and other assembly detailing to achieve vapor diffusivity or high absorption rates.
- Straw bales are recyclable carbon sinks with an R-value of 40, making them eco-friendly yet vulnerable to moisture when left exposed, so proper detailing is necessary. Straw is also inexpensive, renewable, natural, local, and non-toxic, and ranges from an R-value of 2.38 to 0.94 per in. With proper installation and care, homeowners can expect fully functioning straw insulation for decades to come, saving money.
- Cellulose is breathable, acoustic-friendly, fire-retardant, and recyclable. It also insulates with little waste, minimizing end-of-life environmental impact. Loose-fill cellulose outperforms its fiberglass counterpart by 30%, reducing energy bills. An R-value of 3.5 helps reduce energy bills, and its embodied carbon is low.
- Hemp fiber is naturally hypoallergenic; hemp-based solutions offer safe, sustainable insulation from plant-based biomass with added health benefits. Hemp fiber is safe enough to touch and won’t slump, sag, or phase-shift. Hemp’s dimensionally stable R-value of 5, coupled with being a renewable, plant-based, carbon-storing natural fiber, earns it a clean-energy reputation.
- Wood fiberboard, with an R-value from 2.7 up to 3.8, is made from the by-product of wood processing, taking a waste product, combining it with a binder, and creating either loose fill or pressed boards. Like straw, wood fiberboard is fire-resistant due to its density. The flexible fiber boards can be installed on the exterior, without extra cutting necessary, as the edges have a tongue-and-groove style of joining.
It is an important part of our process to coordinate with our construction team on specifying these materials. As architects, we are placed in a position to advocate for materials that will meet the expectations of our clients, and understanding that there are legitimate alternatives is necessary to introduce new materials and methods to the process. While many of these materials seem unconventional in the U.S., they are common in international markets, and our industry is doing its best to raise awareness of these alternatives.
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Lindsay Schack is an architect and co-founder of Love Schack Architecture with offices in Bozeman, Montana; Driggs, Idaho; and Jackson, Wyoming.
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