Structural Best Practices for a Healthy Home

This blog expands on an early post about the 25 Principles of Building Biology and the Healthy Home Standard Checklist. Here we’ll start diving into the Indoor Air Quality Checklist, and focus on structural best practices for healthy home.

Like so many things… a solid foundation is so important… and following these best practices for structural design are strongly advised for almost every project. Unlike most other green building rating systems, these items focus primarily on protecting occupant health.

Structural Best Practices for Indoor Air Quality

The following measures are strategic healthy building design criteria from the Healthy Home Standard:

• If the house is built on a concrete slab,include at least 4 inches crushed stone as capillary break below slab. This can also be accomplished with a vapor barrier.
  
• If house has a basement, basement is finished with a concrete floor, similarly protected from moisture as a slab.
• If there is an enclosed crawl space, it is a mini-basement with a concrete slab and conditioned or ventilated to the living space as if it were part of the living space. [This can be a tough one to achieve… depending on layout of the building, local building codes, etc.]
• If there is an enclosed crawl space and the crawlspace floor is not concrete, a vapor barrier is installed on the earth, sealed at the seams and secured to the foundation and support piers.
• If house has a basement, a damp proof moisture barrier membrane is installed on the foundation wall from grade level to footer.
• If needed (enclosed crawl spaces & basements), a ventilation system for radon control is installed. (Follow EPA’s Consumer’s Guide to Radon Reduction) [See tips for building a healthy home blog post.]
• If the property is at or below grade, French drains are installed next to the foundation.

French Drain Diagram. If storm water runoff is present, a drainage system is imperative.

• The soil has NOT been treated with chemical pesticides for subterranean termites control. [Soil testing and pesticide removal/mitigation is an option if legacy pesticides remain.]

Pesticide Safety Levels – Building Biology

• The structure has been treated with Timbor a borate (Disodium octaboratete trahydrat) against wood chewing/eating insects (termites, carpenter ants, wood beetles).
• There is either no garage, the garage is detached, or the attached garage has a 100cfm exhaust per bay in continuous operation with a vented garage.

Unlike the Healthy Building Qualification Checklist with mandatory measures, the above structural best practices are optional and count toward the overall Healthy Home Rating.

LEED for Homes Structural Best Practices

LEED-H actually has a lot of overlap with the Healthy Home Standard, and some additional durability measures I like. For instance, additional points are available for locating plantings at least 24″ from the building exterior, installing termite screens, efficient framing, etc. But the focus of the Healthy Home Standard is on occupant health, and therefore the emphasis was placed on moisture control.

I cannot stress enough the importance of good site drainage and capillary breaks as one of the primary structural best practices for healthy home. These measures are very affordable and easy if considered upfront, and if not installed the water damage and restoration can be very expensive. A little planning and extra steps during design can go a long way in preserving the structural integrity AND health of a building. We consider these elements during Building Biology or Building Enclosure Commissioning (BECx) design consulting, and all to often find the results of their absence during Moisture & Mold Inspections.

Pressure treated lumber is another hot issue relating to structural issues and healthy building. In many of our projects we specify composite wood materials or naturally pest- and moisture-resistant woods like construction-grade redwood. Avoiding the preservatives in composite wood is a good idea, especially if the wood will be inside the vapor boundary of the home.

I love the simple Bau-Biologie phrase, “Nature is the ultimate goal.”  It seems so simple, but in reality it is exceedingly challenging to create a home and have the air and EMF be similar to exterior and yet comfortable.

My next best practice IAQ blog will explore heating, cooling, ventilation, and filtration.