While visiting the construction site of a net-zero project WTW designed last winter, I witnessed something that I never thought possible. I wanted to share this experience, during which I discovered an obvious but overlooked incentive for developing a Passive House building.
For those who do not know, a Passive House project is designed to attain a quantifiable and rigorous level of energy efficiency within a specific quantifiable comfort level, according to the Passive House Institute of the U.S. I could try and sell you on how you should build a passive house building to help save the planet and make a better world for our children, but I’ve been around long enough to know that project budgets — more often than not — rule. Instead, I’m going to tell you why it doesn’t cost as much as you’re probably expecting: if you factor in life cycle costs of the development (including operations and maintenance) as part of your initial budget, developing to Passive House standards will save you money.
In the winter, the construction site for a four-story residence hall project will utilize at least one torpedo heater at the center of each floor — if not two — and large blower fans pushing heat throughout the building. This is done to keep the inside temperature of the building above 50 degrees to avoid drywall cracking and allow the contractors to continue work in cold weather.
Until the aforementioned net-zero Passive House project, I’d never been able to walk through one of those buildings in the winter without seeing my breath and seeing most workers wearing coats, hats and sometimes gloves. It came as a great surprise at this site visit to see only one torpedo heater on the bottom floor heating the entire building. What was even more shocking than not seeing my breath was that, even on the fourth floor, workers were wearing t-shirts. This was before the building was entirely finished and airtight! Imagine what this would do to your heating and cooling bills once the building is complete?
This story perfectly illustrates that by designing and constructing to Passive House standards, building owners can expect to save 90-95 percent on heating and 60-70 percent on cooling bills. In addition, occupants will be healthier and more comfortable due to less outside air infiltration, drafts and more comfortable, consistent temperatures along outside walls. Construction costs alone for a project of this size would normally budget $100,000 for temporary heating in the winter. Now reduce that by 90 percent just for construction energy costs alone.
So what about those added construction costs, surely there has to be a cost and magic formula to create these savings, right? If you have a knowledgeable architect, it’s easier than you would think to develop a Passive House building, as we demonstrated in designing a net-zero energy-ready building. We have found that the energy savings associated with designing to Passive House standards are the most economical way to provide net-zero energy results. By focusing on reducing the biggest energy usage in the building — heating and cooling — we were able to achieve net-zero.
The five major principles of Passive House construction are super-insulation, high-quality windows, elimination of thermal bridging, an air tight building envelope and heat recovery. It is our experience that three of these principles have a significant cost impact:
- Exterior Insulation: In the case of one of our projects in central New York, our wall performance was double the typical R-value found in a student housing project. Getting to such a high R-value isn’t quite as simple as doubling the cost of your insulation, but it’s a good start for early budgeting purposes. However, evaluation of how the building needs to adjust to accommodate the extra insulation should be considered as this can impact that budgetary number. If it’s entirely inside of the building envelope, the exterior wall cavities likely need to get thicker. You might have to use deeper stud walls and lose usable space inside. If it’s outside of the envelope, care must be taken with applicable codes that limit what materials can be used for both the insulation and the cladding, depending on what is being used as a base design. Selection of insulating materials (which may be more expensive) can also help reduce the extra space required.
- Windows and Glazing: For budgeting purposes, a simple change to triple-pane glazing in curtainwall or European style windows (for punched openings) is necessary. Traditional storefront and residential windows (double hung, sliders, casement) simply don’t have the thermal properties required to meet the thermal break requirements.
- Structural Thermal Breaks: Putting extra effort into increased insulation and glazing won’t pay off if all of that heat is drained through a few structural elements. Think of structural thermal breaks like a straw — if you don’t have them, warm air from inside of your building can travel right through the tube of the straw to the outside of your building, wasting all of that heat. By cutting the straw in half, all of that warm air (and your money) can’t be sucked out of the building. This means that a structural thermal break material needs to occur anywhere that the building structure penetrates the building envelope.
Passive House design can and should be a realistic goal for your project from a budgeting perspective. For this practice to be successful, other details like the orientation of the building or ensuring continuous and properly installed air and vapor barriers are critical. These details should not add to construction costs — they should be standard practice on all construction projects. The first step is finding a knowledgeable architect that is willing to walk you through the process and explain things to you.
— Brian DiPietro, Associate Principal, WTW Architects