As Passive House experts, it’s safe to say we spend a lot of time thinking about the operational energy use of our structures. What you might not know, is that we spend just as much time thinking about the materials that go into our buildings. Aesthetics, feel, utility, durability, and cost are always critical components of any decision in the construction world. We add a few more qualifiers, and make sure they don’t compromise the rest.
One of these critical qualifiers is embodied carbon, the energy used to extract, manufacture, and transport a material to the build site. There are a number of reason’s to care about embodied carbon, but one thing that doesn’t get talked about enough is that these materials are frequently cost comparable or less costly than highly processed alternatives that are shipped from far away.
Let’s take a deep dive into some of these considerations and zoom in on a new material that has just hit the New England market: Glavel.
Embodied Carbon
Globally buildings account for 39% of CO2 emissions. 11% of that comes from embodied carbon. Embodied carbon is mostly an upfront carbon cost (most emissions are released in extraction, production and transportation), while operational carbon costs pay out over the lifespan of the building.
Embodied carbon refers to the greenhouse gas emissions produced in the extraction, manufacturing, transportation, installation, and disposal of a material.
Lowering the operational energy of our buildings is critical to the long term viability of our built environment, yet to meet our climate goals in 2030, we need to put considerable focus on the embodied carbon of our structures.
If we do not account for embodied carbon in construction, it is entirely possible to build a structure with a larger carbon footprint despite its lower operational energy use.
Life Cycle Assessment
Life cycle assessment (LCA) is a method of quantifying the carbon emissions of a material over the full span of its life from extraction to decomposition. There are several software programs that can be used for this purpose, but comprehensive data is still lacking for most building products. There is a growing list of certifications and labeling systems for building materials aimed at tackling this challenge. Declare labels from the Living Future Institute are one good source, but the tool we are currently most excited about is the Building Emissions Accounting for Materials estimating tool, otherwise known as BEAM. BEAM accounts for the emissions associated with turning raw materials into building products (the first three stages of the LCA measurement). Developed by Builders for Climate Action, the goal of this tool is to provide relevant data on the most common building products in our structures (think: concrete, steel, drywall, wood, insulation).
We hope to integrate the use of BEAM into our operations in the future, but for right now we want to share the core considerations MPH uses to make design decisions that are carbon conscious.
Supply chain, location source, regeneration rate, and potential for carbon sequestration are among the most important considerations when reviewing material selections.
1. Supply chain & location source
A significant portion of the embodied carbon cost of building is in the extraction, manufacturing and transport of materials to the build site. The less processed materials are and the shorter the distance between the source of the material and the build site, the less harmful that cost is.
Currently there is no widespread accounting process through which transportation emissions can easily be compared, partially because some of this measurement depends on where the material is being used. Our global supply chains are so complex and integrated, it can be nearly impossible to find the true cost of a material sourced beyond the immediate local environment.
(If you have a minute, I highly recommend this Ted Talk from a designer who attempted to track down every element of a toaster & build one from scratch).
It’s also unrealistic to expect every single element of a modern home to be sourced locally. So what can we do? Anytime there is a choice between a material that travels from far away or requires significant energy to be processed and a material that is locally sourced or less processed - we choose the latter. Examples of easy choices here are siding, flooring, shelving, and even insulation.
This is not a new approach. Prior to our industrial-globalized era, structures were almost always built with resources available from the immediate surrounding environment. In Maine, we have tremendous timber resources, so it should come as no surprise that many of the same building methods (timber construction) used by peoples of this land for hundreds of years are still the most cost effective and produce the lowest level impact on the environment.
The above map is from Local Wood Works, an excellent source of information on lumber and forestry in Maine and the surrounding New England area.
2. Resource Regeneration Rate
In addition to paying attention to the source location and supply chain of material selection, it is also important to consider the sustainability of the resource. The word ‘sustainability’ has come to serve as a buzzword for all kinds of greenwashing campaigns, diminishing its utility and meaning as a descriptor. The use of the term here is only to reference the rate at which a particular resource is regenerated. Specifically, can the resource be replenished at a rate that keeps up with the harvesting and use of that resource?
This is a very important element to consider when talking about wood. Certifications that evaluate forestry practices like the Forest Stewardship Certification (FSC) are great indicators that a resource is managed well. Like all certification programs though, the administrative burden is sometimes too much for small producers to keep up with. Many small sawmills throughout Maine are prime examples of this. Just because they don’t have a certification, doesn’t mean they aren’t using responsible production methods.
Maine Traditions Flooring is a great example of an exemplary local company that dropped its FSC label a few years ago because the cost of maintaining the certification didn’t necessarily make sense (not enough buyers were looking for this stamp). They haven’t changed their operation methods though; as a third generation, vertically-integrated company, it’s in their interest to continue harvesting in a sustainable manner. All their maple and birch come from the forests surrounding Rangeley and Jackman, Maine, and all their hardwood flooring products are manufactured in Maine.
Maine Tradition’s Team at their manufacturing facility in Solon, ME.
3. Carbon Sequestration
Carbon Sequestration is the process of capturing and storing carbon. Carbon sequestering materials are those that capture more carbon than they release. Take wood as an example, the tree captures carbon throughout its lifespan and stores it in the wood. When you cut trees down, you prevent them from continuing to capture carbon, but if that wood is preserved in a structure, it still serves as a store for that carbon. The key to the efficiency of wood as a carbon storing material is tied to the rate of replacement of the resource. Thus, if forests are managed in a sustainable manner, wood can be a good choice for carbon sequestration. Other great material examples are hemp fiber, cellulose, wood fiber insulation, and compressed straw.
Source: GWP numbers provided by BEAM
Note: These are industry averages! They do not take into account source locations or specific manufacturing locations that may be using renewable energy sources - information that is KEY to understanding the full embodied carbon footprint of a material.
There are plenty of great materials with low or negative embodied carbon metrics, but if they are produced far away, the cost and carbon impact of shipping them can void the benefit of using the material.
In the following material highlight, we will outline the use of an insulation product that is new to the North American market, but has existed in Europe for decades. Up until now, the carbon & monetary cost of shipping the material across the Atlantic prevented us from the using the product. Now, this material is produced locally in Essex, Vermont - game changer!
Material Highlight: GLAVEL
When looking at the construction of a single family house, the materials with the highest carbon footprint are typically in the foundation. Steel, concrete and foam board are some of the most energy intensive products, as well as the most difficult to substitute. For years we’ve wished there was a better cost effective solution for sub slab insulation. Typically we use EPS foam, which has a similar kg CO2e/SF to mineral wool. It’s better than XPS foam board, but it’s still foam; the lifecycle impact of the product extends far beyond the energy required to generate it, as it takes hundreds of years to decompose.
When we were planning and estimating a project in Gorham NH, a new factory came online in Vermont. One that produced Glavel, an insulative aggregate made from recycled glass and produced with renewable energy. To say we were excited about the onset of production of this product in the US, and in Vermont no less (3 and half hours from our build site), is an understatement. Glavel is manufactured with an electrified kiln – the first in the world, actually. There is no BEAM data available for the Vermont product just yet (they are waiting for verification via a third party), but it’s safe to say the material definitely has a lower carbon footprint than foam.
Two questions loomed: Will this product fit our slab on grade application? And can this product stay within our budget?
The Approach
We originally planned for 8” of EPS foam sub slab, with denser foam set below structural footers and the slab edge. We adjusted our slab design to accommodate 14” of Glavel in the field of the slab, while keeping dense EPS foam under the slab edge. We kept the foam under the perimeter of the slab for two reasons. Partially because there was some concern about water permeating the Glavel around the perimeter of the building and freezing, but mostly because we did not have a hard boundary to compact the Glavel against at the edge of the area. Keeping the foam enabled us to pour a 10” footing around the perimeter of the slab and at key structure points. Once those were poured, we were able to infill the under slab area with Glavel.
4” of EPS foam was set on the exterior of the 10” footing. The EPS protruded above the footing to our set slab depth, serving as our forms for the slab pour.
Process:
Stake building, excavator preps slab area with 12” gravel & sand in areas where plumbing runs sub slab.
Set EPS foam and form footers for slab perimeter and structural points, working with subs to install conduits for septic, electrical, well line, etc.
Pour footer.
Sub slab rough-in of plumbing, etc.
Install Glavel & compact as specified by the manufacture.
Install vertical EPS on footer perimeter, taping seams. This foam insulates the edge of the slab, and also serves as the form for the concrete slab.
Backfill.
Lay non-woven textile, and vapor barrier, sealing around conduits and J bolts at perimeter. The non woven textile prevents the Glavel from breaking the VB underfoot. (leave enough VB to wrap up the edges of the slab & seal under the sill plate).
Pour Slab.
The Budget
We came in $265.81 under the estimate number we had prepared for an all-foam sub slab. This number includes labor and materials. A few important notes:
The straight comparison of material cost between EPS foam and the Glavel equivalent was within a hundred dollars. Because we still had to use high density foam under the perimeter for our slab on grade approach, which is more expensive, our overall material cost was more using the Glavel. Our labor was less though because we did not have to cut and fit foam across the whole foundation.
Our overall costs could have been lower if we removed the foam from the design altogether. In order to achieve this, we would have had to pour a frost wall, thus using more concrete. Aside from the carbon implication of this, that would have cost slightly more too, perhaps offsetting the savings on foam.
Takeaways:
All things considered (cost, carbon, complexity of design - aka, also cost!), a frost wall is probably the way to go if you are looking for the easiest way to use Glavel without adding more steps to your process.
Site really matters. If you can access the site with a semi truck, it is probably a good option to use Glavel. If you cannot (unless you have a good excavator who's willing to move substrate twice), Glavel is probably not the best fit for your project. If the material cannot be delivered in a bulk order, it will be shipped in bags and cost more. This means plastic waste and more labor.
Bulk delivered Glavel is cost comparable to sub slab EPS foundation.
We will continue to improve our method of using Glavel with a floating slab. All in all the installation went well, the numbers worked and we finally were able to get the vast majority of the foam out of our foundation! Stay tuned, as we hone the details on our next build!