Recently a friend asked me over to see if switching from his gas furnace to heat pumps would make sense—he’d gotten advice from one heat pump installer that his house wasn’t a good candidate, and also got a separate quote of over $60k for an elaborate heat pump system. Why can’t you just switch from a gas furnace to a heat pump?
The thermal envelope, it turns out, really matters. The house in question is a poorly insulated, leaky house—in other words, sorry to say, a typical older house. Houses like that will have rapid changes in temperature inside with rapid changes and heavy winds outside, and require a lot of energy to heat and cool. Most gas furnaces are made to blow a lot of air and heat, so they can respond to sudden demands; but heat pumps are designed to hum along at a fairly even temperature, and don’t have the capacity to ramp up quickly. In other words, residential heat pumps do really well, and are most efficient, in buildings with decent-or-better thermal envelopes.
The other simple problem is capacity: this house had an existing 8-ton heating system (about 100k BTUh) connected to big ducts. There is no 8-ton heat pump you could just plug in to switch from gas to efficient electricity—the biggest I know of is about 4 tons. So you would need to redesign the ducting system to break up the house into two smaller zones, and as you can imagine, complexity, expense, and disruption of the house would increase. The $60k+ quote he got was for—get this—3 outdoor heat pumps with EIGHT indoor units—linesets everywhere, lots of equipment to maintain, and, yeah, expensive. All to heat a poorly insulated house.
What to do– choose a bigger hose, or a bucket that doesn’t leak? This is a good case for insulating first: with insulation and air sealing, the heating load can be reduced drastically, often by 50% or more. This will require some expense and disruption on the house, but once you do it, you need less expensive (smaller) HVAC equipment, and you’ll spend less on heating and cooling forever– you will have locked in that efficiency for the life of the building.
The Expense Equation
Let’s not kid ourselves—the insulation job won’t be cheap either. To do it right means dealing with the roof—probably by spray foaming the underside of the roof deck to reduce stack effect and heat flow, get a few inches of the correct type of insulation on the existing foundation walls, and in this case, with a brick structure, consider putting exterior insulation over the brick with new siding over it. All of that will run in the neighborhood of $60k I should think, and then the HVAC system might now be down around 30k. Good news is there are many incentives out there to offset those costs—with new on top of existing federal incentives for efficiency upgrades, and a $10k retrofit incentive through our local village, the bill may come to more like $50k: less than the wasteful options, with way lower energy bills and a more comfortable house. Maybe I was guessing too low and the total may come out to around 70k after incentives—even so, there would be a tradeoff of lower energy bills for increased loan cost, maybe close to a wash.
Future Energy Costs?
None of the above even takes into account where energy prices are going. Almost as certain as death and taxes are rising energy costs. Between extreme weather, supply chain, and war in Ukraine, it’s been volatile lately, and my hunch is it’s not going to just quietly settle down quickly. To reduce energy use at home, especially with renewables and backup batteries, brings some peace of mind as well as lower bills. I would say it’s worth it.
Following a presentation for Greenbuild today (a free event you can see the recording of), some in the audience asked for the Resource list I had on my last slide. I’m including it on this blog post. TBDA is not affiliated with any of these companies and don’t have any commercial interest in them, but they are all products or resources that we have used in our projects and think are worth considering.
Building Science Corporation: tons of papers, insights, tools, like this article on spray foam, and this one on conditioned and unconditioned attics. Free!
Also from Building Science Corp’s Joe Lstiburek is the Builder’s Guide to Cold Climates, an excellent detail reference for architects and builders.
Building Science Fight Club: great lessons for architects, great Instagram feed.
Passive House Institute US (PHIUS): certification, training, and continuing ed. PhiusCon 2022 will have new thinking on the Revive program.
DOE Healthy Indoor Environment Protocols for Home Energy Upgrades
Rocky Mountain Institute: thinking on efficiency and health, like this article on gas cooking risks
UL’s Greenguard website for healthy materials and products
• 475 Supply (membranes, tapes, ventilation, insulation, skylights, instruction)
• Global Wholesale Supply (Steico wood fiberboard insulation etc)
• Small Planet Supply (membranes, tapes, insulation etc)
• Prosoco fluid-applied air sealing products
• Henry Blueskin peel-and-stick air barrier membrane (exterior air barrier at my house)
• Alpen High Performance Products, US-made triple-glazed, insulated frame windows and doors.
• Also check with your local salvage places like Habitat ReStore for salvaged materials. We’ve used salvaged flooring, old-growth lumber, and some fixtures to good effect.
Payette’s window comfort calculator and also PHIUS’ window comfort and condensation calculator: beyond energy performance, it’s good to know whether windows will be comfortable to be near, and whether they will create condensation in expected temperature ranges.
Come out to Oak Park on June 30th to learn about the second verified Net Zero facility in the State of Illinois. Chris Lindgren, Superintendent of Parks & Planning, Park District of Oak Park and Tom Bassett-Dilley, President & Certified Passive House Consultant, TBDArchitects, will take you on a tour of how the Park District of Oak Park was able to take a 100-year-old facility, add on for more functional programming, and meet some of the most rigorous environmental standards in the industry.
The Park District of Oak Park was awarded a $577,800 grant from the Illinois Clean Energy Community Foundation to achieve Passive House Certification and Source Zero Energy Certification for the Carroll Center expansion project.
This facility generates enough clean energy from the on-site solar array to not only cover the building’s energy needs, but also the entire park. With smart design and engineering tied to thorough construction administration we greatly exceeded our goals of Net Zero. Register for this free event today!
This event is in partnership with AIA Illinois.
I decided to take the leap and decarbonize my 1919 frame bungalow. This was born out of several things: first, we were at the end of service life on the gas water heater, within 5 years of service life on the furnace/AC (inefficient gas, poorly installed), and the soffits and fascias had begun to fall off the house—the squirrels were having a heyday. My walls still didn’t have retrofit insulation, and my enclosed back porch was poorly enclosed in the ‘40’s, with some band-aid level solutions I had installed to make it tolerable. Plus, the house featured an original basement, which is to say, a cracked slab that didn’t keep moisture, radon, or critters out, and no insulation down there. In other words, about 60% of my interior was nasty and uncomfortable, and the rest needed help, too. The driving motivation was a combination of a sense of stewardship and adventure—doing the right thing by my building (which would make for a more durable and much healthier and comfortable living environment), and experiencing first-hand technologies like the heat pump water heater, mini-split heat pumps, induction cooking, and good ventilation with energy recovery. Yes, it’s expensive, but I’m fortunate to be able to finance this given historically low interest rates. This project will teach me a lot, allow me to teach others, and beyond the enjoyment of it for many years, I think it will pay off in the long run. I began with the question, “could I make my house a Passive House?” The answer was yes, but it meant having to replace my roof (which was insulated in 2010, when I had no grand plans and little money), and having to pull out my existing windows (replaced in 2004, when I hadn’t heard of Passive House or triple glazing, and “airtight” was a term nautical designers, not architects used). So, while it was possible, I didn’t think it made sense to spend a lot of money throwing away serviceable items. My next question was, well, if I can’t make all the PH metrics, can I make the PH Source Energy limit? In other words, could I cut down my total overall energy usage to Passive House levels, even if space conditioning energy is a bit high? In doing so I would employ all the PH strategies at my disposal: minimizing thermal bridges, insulating, making the house airtight, using an ERV for ventilation, and using efficient lighting and appliances, plus some solar PV. The answer was yes, it’s totally doable! In fact, I could approach annual Net Zero by adding some more solar.
Check out these visualizations of our energy modeling:
Here are the strategies I employed to get there:
Exterior walls: these are leaky and poorly insulated, and were also covered with asbestos siding. I hired a remediation crew to remove the asbestos; next we will strip off the old siding and expose the original sheathing. We will drill holes in the sheathing so we can pump cellulose into the walls, and then we’ll cover the sheathing with a diffusion-open (meaning it lets moisture “breathe” to the outside) peel-and-stick air barrier membrane, sealed at all penetrations, sealed to the foundation, and sealed as best we can to the roof. We’ll then cover that with a diffusion-open wood fiberboard insulation layer, creating a thermal break at all studs. The fiberboard is essentially a negative-carbon product, having absorbed carbon while it grows, and being repurposed from waste product. Over the fiberboard go furring strips and new siding. This is more than a face lift—it’s like major reconstructive surgery!
Basement: an 850s.f. conundrum. Over the years, whenever I would come up with ideas to expand the house up or out, I always came back to “yeah, but I would have to deal with that basement.” Dirty, cold, wet, and leaking radon (just enough to be concerned), it’s a lesson in why capillary breaks and waterproof insulation are needed. The more I thought about it, the more I realized that insulating the basement plus good HVAC would mean I would have 850sf that I could actually enjoy for art studio, guests, music, laundry, etc. It would mean tearing out the old slab and putting in new windows, but it would really change the way I look at about 40% of the house. Also, replacing the three old wood structural columns with new ones (on stand-off bases) means I don’t have to worry about those degrading by wicking up moisture from the ground. For the windows, I decided to go with Marvin fiberglass double pane; while triple pane is my choice for comfort and energy, especially on larger windows, these are small units in less-used rooms, and I thought it made sense to save over a thousand bucks here.
HVAC and water heating: with a much-improved thermal envelope, I have the opportunity to have a much smaller, energy efficient heating and cooling system; and by replacing the old gas water heater with a heat pump electric type, I will have eliminated most the gas use (cooking and dryer only remaining)—almost there to all-electric! For space conditioning, this meant mini-split heat pumps, of course, like we use on most our Passive House and low-energy projects, since they’re very energy efficient. I wanted the system to function properly, so planned to replace the ductwork so it would be properly sized and well-installed (airtight). I chose a conditioning ERV (the CERV2 from Build Equinox) so that I would have demand-controlled ventilation, good airflow, great filtration, and a modest amount of conditioning when I’m ventilating. The water heater is Rheem Proterra 50-gallon heat pump unit I picked up at Home Depot. It will cool the air in the house in heat pump mode; I don’t see this being a winter comfort problem since it’s in the basement, and the conditioning system will offset the losses—but it will be good to live with it and get first-hand experience.
Appliances and PV: the last remaining items were the range (switching from gas to induction) and dryer (switching from gas to a heat pump condensing dryer). I decided to commit to these with the rest of the project so I could eliminate my gas line. I already have 12 solar panels on the house (kind of jumped the gun, but got them the last year that the Federal tax credit was 30%, before it got reduced) and plan to add some more to offset my increased electricity use (even though everything will be very efficient, I’m using electricity for heating, water heating, cooking, and dryer now, so overall electricity use will go up as gas goes to zero).
Other problem areas: common to a lot of older renovated houses, my front and back porches were enclosed long ago, and were not properly insulated. To fix that, I’m reframing the back porch walls and installing triple-glazed (Alpen) windows; on both, I’m insulating the floors with a few inches of closed cell spray foam for airtightness and condensation control, topped by loose fill insulation (less carbon intensive)—we’re still working out the details of this in light of material availability.
You can follow the progress on Instagram where we upload images from the project. Also, Tom presented this project on the Green Built Home Tour session on “How to Prioritize Sustainability Upgrades for an All-Electric Home” and you can watch that video here.
We’re excited to share progress from our project near Bloomington, IN: we count ourselves fortunate to work with inspired owners and excellent builders. Loren Wood Builders is doing a great job on this—not only did they go get Passive House Builders Training, they are being so diligent thinking ahead about components, assemblies, and the integrity of the air barrier. Plus—they have a drone! Here are some photos of the work in progress—you can see we’re using Zip-R (2.5” insulated sheathing) as our air barrier and continuous insulation, over 2X6 studs with cellulose. The slab and foundation are insulated with EPS, and the roof will be insulated with cellulose over the Rothoblass membrane air barrier. Windows are Alpen Tyrol tilt/turn, great performance (triple-glazed) and value. There’s also a shot of the big cistern going in, which is for rainwater collection for domestic use and irrigation.
More coming soon, as the Thermory (wood) and metal siding and roofing go on!
We have participated in the Green Built Home Tour every year for almost 10 years, and we were excited to include Acorn Glade Passive House as part of the tour this year. Although we missed seeing attendees in person, the virtual tour allowed more people to attend and learn about Passive and green built homes. If you were unable to attend, we have included our portion of the tour below. Enjoy!
The shelter-in-place order meant that homes were far more continuously and intensely used than in the recent past; this makes us consider how well they’re taking care of us. Home offices sprung up in mudrooms, bedrooms, basements; many families are cooking much more; and with parks and playgrounds closed, we look to our streets and yards to provide that much-needed outdoor time and Nature connection. As an architect, three issues I’m thinking about due to these new arrangements are air quality, privacy gradients, and nature connection.
Air Quality: this report from Rocky Mountain Institute sheds light on numerous facets of indoor air quality, including racial and income disparities and impacts on children; gas cooking turns out to be a big issue, even in homes with ventilation. To drill down, here’s a good Allison Bailes article specifically on kitchen ventilation and its flaws. The RMI article makes another interesting point—while we have created standards for limiting outdoor air pollution (the Clean Air Act, for example, threatened by the Trump administration), there are no maintenance* standards for indoor air, and in general, it looks pretty bad—though studies are needed. (*By maintenance, I mean what’s actually being lived in, separate from building code and ASHRAE requirements for ventilation, which do not necessarily ensure good air quality.)
One of the important improvements the Passive House standard makes over a typical home is the inclusion of a balanced, filtered ventilation system. A typical modern house only has exhaust for ventilation at bathroom and kitchen, and of course it only works when you turn it on (see the chart from the California IAQ study); and it doesn’t supply fresh air or filtration to bedrooms or living spaces. But a Passive House ventilation system continuously cleans the air at pollution points (baths, laundry, kitchen), and supplies filtered air to bedrooms and living spaces. These filters can be fine enough to reduce some virus-carrying droplets, as described in detail on this other fine post by Energy Vanguard. In all of our new houses and gut remodels, we design ERV systems; typically we specify MERV 13 filters, though the PHIUS standard requires MERV 8.
So what can you do now? First off, ALWAYS use your kitchen hood when you cook, and use the back burners first. Even boiling water can release CO and other toxins (not the water, the combustion byproducts), and the hood picks up fumes from the back burners better than the front ones. Open windows when you can. Get outside. Consider a finer filter for your HVAC system, but heed the advice on Energy Vanguard’s blog about potential effect on your fan (check with your service tech). Consider installing an energy recovery ventilator (ERV). Here’s the thing: less expensive ones like Panasonic’s spot ERV don’t work below 32F or so—you need to get one that can handle cold weather, like Panasonic’s Intelli-Balance, which means you’ll be into ducting; or you can get a pair or two of Lunos units, very clever retrofit devices; or you can get a unit that will connect to your house’s forced air system like the Renewaire unit (it will require new ductwork from your exhaust locations, but puts fresh air into your existing ductwork); or a stand-alone unit like the Zehnder, or, the gold standard in my opinion, the CERV from Build Equinox, a demand-controlled ventilation system with conditioning and continuous air quality monitoring.
Privacy Gradients: This may sound like architect-jargon; what I mean is that it’s good to have active areas where common activities (cooking) happen and family and friends can gather, and it’s good to have spaces where people can get away from the crowd and noise. It’s a general principle that can result in a space being called “home office” or “music room” or “library;” a good example of this is the “Away Room” or “Place of Your Own” as laid out in Sarah Susanka’s Not So Big House concept. At TBDA, most of our houses, in response to client desires, have include a living-dining-kitchen area that is joined in one big rectangle, L-shape, or other joined configuration; but these houses also feature a quiet non-bedroom space that can be used as office, place for a quiet conversation (or a Zoom meeting, these days. I’m finding in my house that it’s nice to have the kids at the table close to the kitchen (in nearly continuous use!), but the attic studio is a welcome feature when my wife gets on a Zoom call with 20 fourth graders.
What can you do now? Well, if it’s relatively easy, you’ve probably figured out a solution already; maybe you were able to re-think function and see your space in a new light. If it’s not so easy, remodeling may be worth considering, especially if it can solve other problems or otherwise help you upgrade your living environment. Often it’s a matter of space planning expertise and the experience a residential architect brings to see the big picture and make the best use of space, light, and structure.
Nature Connection: This dovetails to the remodeling comment above: it may not be a quick and easy fix. A house can be designed or remodeled to make the outdoors, or a courtyard, feel very much like a part of the home, which is good for us in many ways. Biophilic design is becoming more important as we spend more time indoors—our genetics aren’t that far away from our hunter-gatherer past, so we expect those inputs from the natural world, the variable sounds, smells, air movement, textures, and natural materials and patterns, to be fully alive. Our stress levels rise when we don’t get those and instead get the sound of the refrigerator humming, cars honking, an HVAC system blasting on, the soul-deadening environment of featureless drywall painted with plastic paint.
The concept of home must continue to evolve away from boxes-with-holes to shelter-in-nature; it’s more subtle than a glass box approach, best exemplified by buildings like Fallingwater and other Wright masterpieces; and we must recognize that our neighborhood structure of car-oriented grids with rectilinear family slots leaves much to be improved upon.
I don’t know about you, but I’ve found myself and my family taking more walks around the neighborhood and appreciating the great Spring here; granted, this is in part because we have a new dog, but it’s also because we feel the need to change our environment and can’t go to a gym, library, restaurant, museum, or theater. We’re feeling grateful for our health and for a back yard and neighborhood that are enjoyable to be in. I hope you are (safely!) enjoying good places too, and keeping in good health.
Passive House is more than an energy standard—it’s a way of understanding the technology of high-performance building, and it allows architects to optimize a building’s performance through the design process, regardless of whether an owner wants to pursue certification or not.
The “business-as-usual” approach to design is to focus on program and appearance, then have an engineer or contractor size mechanical systems to condition the building; more sensitive designers may take into account sun angles and daylighting, but for many designers these are afterthoughts as well. That approach usually leads to needless energy consumption, glare, overheating, and thermal bridging. Our approach is to use the powerful Passive House modeling tool to tune the building to the climate as an integral part of the design process.
We begin design with an analysis of climate (temperatures, humidity, sun, rain/snow, wind), vistas and sense of prospect or “belonging” on the site, topography, and neighborhood or natural setting, all to allow the building to speak the language of the site. I think of it as imagining a living thing that evolved to live in that place—its feet or roots in the ground, its back to shelter, its face to the sun, with the right brows, whiskers, or foliage, as the metaphor may be!
That leads to initial gestural designs that become building shapes. As soon as we settle on a general layout, we then bring that geometry into our Passive House (PHIUS) modeling software (called WUFI-Passive), where we can enter values for insulation, window size, orientation, and performance, mechanical system performance, and internal energy use. By trying out different values for these, and by trying different approaches to shading and exposure, we can arrive at an optimal performance level for the building.
Part of the beauty of the PHIUS standard is that the climate-specific metrics give definite targets to design toward. When we optimize for both heating and cooling loads, we set the stage for comfort; when we minimize overall energy (efficient mechanical system, lighting, and appliances), we can design a project to meet annual net zero energy with the smallest solar PV array possible. And from a design point of view, we know the building will have a climatic “fit” that will allow the building to feel true to place.
If there’s one absolute I go by, it’s that Nature is right. I use the PHIUS tools and knowledge to allow my designs have an organic approach to energy, just as I employ biophilic design and understanding of the locality to allow the designs to have an organic, natural countenance and fit with the site. We’re pursuing ecological architecture through both art and science.
For those of us trying to radically push energy efficiency ahead, a strong incentive program can be a blessing. That’s what we now have with the Illinois Clean Energy Community Foundation. Their Net Zero Energy Building Program provides grant money to non-profits, local governments, and colleges/universities undertaking building to site net zero, typically through Passive House or Net Zero/ILFI Certification. Years ago they would provide funding for LEED projects, but as LEED became more common and the need for energy efficiency more urgent (and attainable!), they raised the bar from LEED to Zero Energy. This is huge—we are seeing an amazing increase in PHIUS buildings: aside from our Park District project, there are at least three other schools and park buildings in construction or design as I write this. Given that the only other PHIUS certified projects in the area at this time of writing are our TBDA designed ones and one affordable multifamily project (Tierra Linda), this is a big deal. It’s also a bit worrisome: for the designers and contractors taking this on for the first time, there will be lessons learned and probably some bumps in the road, just as we’ve had on our projects.
To put this into perspective: we just received grant approval for our Carroll Center project, a retrofit and addition for a park district building that will accommodate preschool, after-school, and adult class programming. It’s about a $1.7M build, and the grant of about $577,000 covers the complexity of the retrofit construction (a gut rehab to eliminate thermal bridges, add insulation, replace windows, and redo mechanical systems), upgrade the new addition to Passive, and cover the certification costs (for energy modeling, rater work, and PHIUS review and certification). Without the grant, the park district would not have been able to justify the costs. So, a big thank you to ICECF!