Material Selection for a Net Zero House: Flooring
In a net zero house, material selection can influence a home’s energy performance and indoor air quality. Great attention is paid to the material selection of the building envelope due to different isolative properties, air sealing ability and water barriers. What about everything else in the home, how do you know what products to use? There are many different values that can define a product or material “green”. And what does green really mean when it comes to materials? It is not as easy as selecting the most energy efficient one or organic. It’s much more about understanding the story behind the item and the future it holds. Depending on project goals, different values can have a higher priority then other values and vice versa. For a net zero home, however there is a hierarchy that seems to exist. Flooring options will be considered as an example of how to apply these standards to material selection.
Durability
The first value to consider for material selection of a net zero home is performance. You might think this is obvious but in the attempt to build “green” homes, this has not always been at the forefront of decisions. Durability goes hand in hand with performance. Building materials have an expected service life ranging from 10 years to 100 + years. Conditions affecting durability are moisture, heat, ultraviolet light and insects; with moisture and heat being the most detrimental and constant.
Flooring is affected by moisture in a few ways. First there is source moisture such as in a bathroom or kitchen and secondly there is interior/occupant moisture, a family of 4 producing 2-3 pounds of water vapor a day. Selecting moisture resistant flooring can help elongate service life as well as the ability to dry out. Some flooring options that are naturally moisture resistant include concrete, stone, tile, rubber, naturally decay-resistant wood subflooring like cedar with a wood finished floor (although can warp if moisture and heat conditions are unfavorable for too long).
Heat has an exponential relationship with durability; for every 20 degree reduction in heat exposure almost doubles the life span of the material and the same goes for ultraviolet light. However, exterior materials are typically the only ones exposed to high temperature extremes so for flooring options this does not need to be considered. So when selecting flooring, you want to find the ones that have high performance ability for the function desired of the space and are most durable; meaning will last a long time. Although quality made products that fit the bill may be more expensive, their long life span can actually mean you save money on replacing end of life products.
Health
The next value to consider is the health of the occupants. If product and material selections do not promote human health than the building ultimately is not sustainable. Materials affect human health in a few ways. First there is the harvesting/extracting of raw material and processing to a finished product. This process can potentially expose workers to unfavorable health environments. Secondly, products can affect the health of the occupants in the building. Occupant health is affected by indoor air quality which can be biological or chemical contaminants usually acquired through inhalation of particulates or gases.
Biological contaminants include dust, mold, dust mites, pollen, pet dander and bacteria. Biological contaminants are impossible to permanently eradicate so the best strategy is to reduce source contaminants (such as pets and dirt brought into the house) and provide conditions that are unfavorable for them to thrive. Moisture control, between 45-55% relative humidity, is effective at reducing opportunities for mold proliferation and increasing human nasal defenses. Biological contaminants effect human’s to varying degrees. Some occupants can be completely immune while others can suffer severe allergies.
Flooring strategies to reduce biological contaminants include providing a walk-off mat at the entrance to simply trap large particulates. Also, using hard surface flooring that can easily by kept clean via sweep and mop will help eliminate excessive amounts of contaminants. Area rugs that can be washed are also preferred over wall to wall carpeting.
Chemical contaminants are becoming more numerous as more and more synthetic materials make their way into buildings. There are a few chemicals that are known carcinogens found in many products that should be eliminated from the home through careful selection of building materials. Formaldehyde is one of the more common and harmful ingredients in many building supplies. It can be found in particle board (kitchen cabinets), adhesives and trim. Volatile Organic Compounds (VOCs) are characterized by vapor released at room temperature and cannot always be smelled. VOCs occur synthetically as well as naturally but it is the synthetic ones that pose chronic human health effects. VOCs can be found in, again, particleboard, glues, solvents, paints, carpet and finishes. There are many alternative products on the market that offer low or zero VOC products.
For flooring options, find a floor that is ideally inert or needs little finishing and if it does, use low VOC finishes. Again concrete, stone, tile and wood are all good options. Linoleum made from linseed oil and cork harvested from living trees are also good options. Natural carpet or rug materials can eliminate synthetic VOCs, like using wool, cotton or jute but also some carpet manufacturers are starting to provide low VOC options. Products to stay away from are any plastic/petroleum based flooring like vinyl. Vinyl uses phthalates which off gases from the polyvinyl chloride (PVC) and is a serious endocrine disruptor. To help understand synthetic flooring and indoor air quality, standards have emerged: GreenSeal for paint, Green Label Plus from the Carpet and Rug Institute (CRI) and GREENGAURD to cover everything. Even then, there are thousands of new chemicals introduced into our environment that haven’t undergone serious testing so it’s best to stick with natural materials for flooring.
Embodied Energy: Resource Content & Potential and Proximity
Resource content conveys the longevity of the resource both naturally occurring and its maximum potential. Products made with renewable materials, such plants, are preferred over non-renewable ones, fossil fuels and minerals. Rapidly renewable resources have an even higher preference. However, even non-renewable materials have a hierarchy. Non-renewable materials such as steel are highly recyclable, so a limited amount of raw input can be regenerated indefinitely into new products. Natural flooring options like concrete, tile and stone can be considered highly recyclable, never reaching an unusable phase. Wood flooring is also desirable as it is from a renewable resource and can be recycled many times. There have also been many carpet and rug manufacturers who are producing 100% recycled content synthetic products. Post-consumer recycled content is a more favorable percentage than post-industrial recycled content. Natural fiber flooring (carpet and rugs), cork and bamboo are considered rapidly renewable resources and again can be recycled many times over.
Lastly but not in the slightest the least is proximity. Local resources typically take less energy to find there way into your home and most likely fit all of the above values. So in some ways it makes sense to start with finding the most durable product that is local and go from there. By using local resources you also are usually supporting local economies as well. And for needs that are not sourced locally, at least use your local independent supplier, etc.
Embodied energy is calculations alone, calculated from many factors, should never be used as a deciding factor. It does however encompass the above two values so by selecting appropriately from them you will inherently be choosing product with a lower embodied energy amount.
Conclusion
A net zero home not only needs to articulate the building envelope materials but also must consider whole building design and the impact of material choices. The above values can be reprioritized as needed but generally are a good way to filter through options. The flooring examples are not the only materials with options but every system and material should be filtered through the lens of durability, health and embodied energy (resource content and proximity) to end with a healthy and affordable net zero home.
Resources
http://www.inspectapedia.com/Energy/Moisture_Calculations.htm
http://www.extension.org/pages/Selecting_Materials_to_Resist_Moisture
http://en.wikipedia.org/wiki/Volatile_organic_compound
