by Christopher Gonzales
Thick walls with triple-glazed windows. Air-to-air heat exchangers. Solar hot water. Is this the new face of affordable housing? In 2010 Habitat for Humanity International US Council mandated that by 2015 all new houses built by local affiliates be constructed to meet energy efficient standards. The impetus for the board‟s decision came from homeowner feedback. Most families found themselves financially challenged with escalating utility costs. “If we can reduce a $200-per-month utility bill by half, that amount could significantly improve the quality of life for our families,” said David Magistrelli, Executive Director for Habitat for Humanity of Gallatin Valley. Reducing utility costs while maintaining comfortable levels is a direct result of two main factors:
Given Montana‟s heating-dominated climate, increasing insulation R-values is the most cost-effective strategy. R refers to resistance to thermal conductiv-ity loss. So, plan for more R-value in a home‟s ceilings, walls, floor and fen-estrations.
Since air infiltration or air leakages through a house cause heat dissipation, air-tight construction reduces heat loss. Healthy „24/7‟ ventilation is efficiently achieved with a heat exchanger. There are several energy-efficient standards from which Habitat for Humanity can choose:
• The 2009 International Energy Conservation Code (2009 IECC) with Montana amendments is the minimum requirement for all new house construction in Montana. Insulation levels under this program call for a respectable R-49 ceiling, R-21 wall insulation, R-30 floor, R-10 slab perimeter insulation and R-• The Northwest Energy Star Program increases these numbers slight-ly: R-49 ceiling, R-23 wall, R-38 floor and R-10 full (under) slab insula-tion, and R-3.33 windows. In addition, allowable air leakage is limited to 2.5 air changes per hour.
• The Passive House Standard as applied to Montana presents a significant increase: R-100 ceiling, R-70 walls, R-50 slab, R-8 windows. Allowable air leakage does not exceed 0.6 air changes per hour. In choosing to build to the Passive House Standard, the Board of Habitat for Humanity of Gallatin Valley set an attainable goal for affordable housing. “We wanted to build something that would make an impact,” said Lou Moro, Project Coordinator for Habitat. The projected additional cost to build a Passive House at 1202 Idaho Street in Belgrade would be about $35,000 more than a code-built home. But the projected annual energy utility expense for a family of six would cost only $600 to $700. So the potential savings would be almost $150 per month—a 75% reduction in energy utility costs. That savings could be applied to reducing mortgage principal or invested in the family’s needs.
In the Idaho Street Passive House the goal of sustainable eco-design through energy conservation dovetails nicely with affordability.
The Passive House design with its high performance windows is able to capture heat from solar gain and retain it by virtue of its increased insulation. Natural daylight brightens the home’s interior with a warm glow from south-facing windows. Internal heat gains from people and appliances are modulated via a heat exchanger with a continuous supply of healthy outdoor fresh air throughout the year. A draft-free comfortable 68˚F interior temperature is maintained year round. Minimal backup heat may be needed. In the colder winter months, heat is supplied by a mini-split mechanical system and radiant electric heaters. Hot water production for domestic use is economized using solar thermal collectors.
Altogether, the Passive House Standard promotes energy conservation and reduces carbon emissions while making it easier on the pocketbook. So when it comes to the bottom line, eco-living is that much more sustainable
Passive House – Affordable Eco-Habitats
by Christopher Gonzales