Our green building adventure began in 2013, when I came across various Passive House and high-performance projects in the book, Prefabulous + Almost Off the Grid, by Sheri Koones. The red house featured on the cover and built by GO Logic, in particular, seemed like a striking departure from conventional homebuilding as practiced in the U.S.
Arguably, in both cases, these homes have too much glass on their south elevations, both in terms of potential overheating of the interior and in purely aesthetic terms. Nevertheless, using south-facing glazing to bring in the sun during the winter months while getting some Btus of free heat made a lot of sense to us, especially in a heating-dominated climate like ours here in the Chicago area.
Evaluating potential problems
By the time construction began, we had settled on what seemed like a significant number of windows and a kitchen door for our south elevation. We felt the layout would be appropriate in terms of passive solar heating, aesthetics, and daylighting.
Moreover, by addressing the main weaknesses of the original Passive Solar movement of the 1970s, namely the lack of air tightness and sufficient levels of insulation, we hoped that we could strike a balance between enjoying the seasonal movement of the sun in and out of our home, while decreasing the risk of overheating, even during shoulder seasons.
Since our build, however, there appears to be growing concern about just how effective this design strategy really is for Passive Houses—or high-performance homes, in general. We find ourselves asking: Are the potential savings on a heating bill really worth the risk of temporarily overheating interior spaces?
“Don’t bother with the passive solar. Your house will overheat in the winter. Yes, you heard that right. Even in Chicago. … You should go with very, very low SHGCs, around 0.2, in your glazing. If this sounds familiar to those of you who are as old as me, it should.
“We were here in the late 1970s when ‘mass and glass’ took on ‘superinsulated.’ Superinsulated won,” Lstiburek continued. “And superinsulated won with lousy windows compared to what we have today. What are you folks thinking? Today’s ‘ultra-efficient’ crushes the old ‘superinsulated,’ and you want to collect solar energy? Leave that to the PV.”
Clearly, he’s not entirely wrong, especially when some of the early failures in the Passive House movement revolved around this very issue of overheating. If you were an early adopter of the Passive House concept, especially if you were the homeowner, and you ended up with comfort issues because of too much glass on your southern facade, it certainly would make you doubt the purported precision of the Passive House energy modeling.
However, with careful planning, it is possible to avoid this issue of overheating while still getting to enjoy most of the benefits associated with passive solar design. In our case, this meant limiting windows on the north side—net-energy losers—to our daughter’s bedroom, while glazing on the east side is limited to the front door.
In addition, we avoided any potential for overheating from our west-facing windows by using self-tinting Suntuitive glass in our master bedroom and family room. The SHGC in this glass fluctuates between .08 and .18, depending on whether it’s in the fully tinted or clear state, which depends on the surface temperature of the glass.
With the other three sides of the house accounted for, we were able to concentrate all of our attention on the best window layout for the south side. The utility room, which is on the southeast corner of the house, needed only one small window, so we went with a single 3-ft. by 5-ft. unit. In the kitchen, the window above the sink was already going to be limited because of the lower cabinets, and was mainly for a view while doing dishes. This unit ended up being 4 ft. by 5 ft. In the kitchen, we went with a mostly glazed door with privacy glass, which has worked out well. It lets in an abundant amount of daylight without overheating the room.
The real challenge was getting the family room window on the south side of the house sized correctly. The temptation was to go too large because we had the space to do it. We kept in mind that even the best window is still a lousy wall (e.g. R-40 wall vs. R-6 window), and decided to retain some empty wall space for artwork on either side of the window.
In the end, we went with a 3-ft. by 9-ft. window on the south-facing side of the family room and put it 32in. off the finished floor in order to gain a little more privacy. On the west-facing windows we maintained a lower height of 27 in. off the finished floor to maximize our views. This 5-in. difference may not sound like much, but it has a dramatic affect on the perspective when standing at these windows.
In terms of wall area on our south facade, the windows and kitchen door account for just under 15% of the total area. That’s not a crazy amount, and obviously nowhere near the amount of glass in a curtain wall.
The sun’s path month to month
For those who haven’t directly experienced a space that utilizes passive solar design principles, it may be helpful to see in photos the affect they have on a home from month-to-month.
In our case, we have a long interior wall that runs east-west along the longest axis. This wall effectively separates the private areas to the north (bedrooms and bathrooms) from the public areas to the south (family room, kitchen, and utility room). For context, this wall stands almost 16 ft. from all of the south-facing windows.
In our kitchen and family room, here’s what the sun looks like near midday in January:
By the middle of February, the sun is already making its way toward the windows, barely able to reach the couch, but it still adds plenty of sunshine and warmth to the kitchen and family room areas:
By the spring equinox, the sun has continued its slow march across the family room floor toward the south-facing windows:
Although we chose to forego any windows on the east side of the house, mainly for privacy and energy loss reasons, the small amount of glass in our front door still allows our entry area to be bathed in early-morning light without contributing a significant amount of heat gain:
The seasonal path of the sun also can be marked on the exterior by its progress up or down the facade of the south elevation. By mid March you can see the shadow line formed by the substantial roof overhang beginning to make its way down the siding—just above the windows and kitchen door. This invisible curtain will cover the window glass entirely by the end of June, completely denying the heat of the sun direct entry into the structure.
By the time of the summer solstice in June, the sun has been pushed outside completely, limited to the metal sill pans on the exterior of the windows.
With significant and thoughtfully placed windows on the south side (combined with a substantial roof overhang), we’re able to enjoy views to the outdoors year-round, allowing us to maintain an unbroken connection to nature in our yard, without any of the heat or glare normally associated with the summer sun.
Also, since the transition from winter (welcoming the sun in) to summer (denying the sun entry) has proven to be seamless, we’ve been able to avoid installing any curtains or window treatments. This invisible curtain effect of passive solar design means we enjoy all the benefits of traditional window treatments without any of the hassles (routine opening and closing, cleaning, maintenance, and repair), all while maintaining an unobstructed view of the outdoors. This is especially rewarding during the long winter months when we are starved for sunlight and extra warmth, but it is equally pleasurable as life begins to hum in the yard with the return of spring and summer.
In the photo below, the family room window (on the left) and the kitchen door are protected from the heat of the sun by the roof overhang. The window on the back wall (facing west) is protected by self-tinting Suntuitive glass, which also allows us to enjoy unimpeded views of our backyard without the need for curtains or window treatments, even on the sunniest and hottest days of summer.
On the exterior, by the middle of June, this shadow curtain has fallen over the entire face of the south-facing windows, denying the sun entry into the home where it could cause unpleasant glare and unwanted heat gain (these windows have a SHGC of .54), which would needlessly increase cooling loads for our Mitsubishi heat pump system, while also reducing overall occupant comfort.
After slowly making its way back into the south-facing living areas by November, the sun is once again approaching the back wall in the family room and kitchen:
Even in the basement, where it’s more difficult for the sun to make its way into the space, with our oversized window wells and two large windows, the sun manages to get very close to the center of the space. The light pouring in helps keep us connected to the outdoors, mostly eliminating the cave-like feel normally associated with many below-grade spaces. Even on the coldest days in winter, this daylighting effect makes the basement a warm, inviting space.
Some final thoughts
We were expecting to enjoy the seasonal movement of the sun, watching it progress in and out of the main living space, warming us in the winter while also helping to moderate summertime AC demand. One surprise, however, is how effective our window layout has been in maintaining a high level of daylighting, even on the grayest of days.
Short of a menacing thunderstorm that turns the skies nearly black, we almost never have to turn on lights during the day. The kitchen door, because it consists mostly of privacy glass, contributes a great deal of interior light in both summer and winter, and we’re extremely happy we didn’t choose a more opaque door.
We are also pleased with the amount light that comes in on full-moon nights. The moonlight creates a soft, beautiful light as it falls across these interior spaces.
In terms of shoulder seasons, when sunlight still has some access to the interior but outdoor temperatures are mild or even occasionally warm, we haven’t really noticed a problem. In spring, if outdoor temps should reach into the 70s during the day, it is is welcomed because we are starved for warm sunshine at winter’s end. In the fall, if there’s an occasional too-warm day, we simply open a couple of windows.
If there’s any failure in our set-up, it would be the family room couch. From the end of December until the end of January, if it’s a sunny day, regardless of how cold it gets outside, sitting on the couch is uncomfortable, if not impossible, because of the heat gain. Thankfully, we’re almost never on the couch. Having said that, if this family room were dedicated office space, and I needed to be sitting at my desk from 10am-2pm, it would be extremely uncomfortable. This is a good example of how individual spaces need special consideration in a floor plan scheme, particularly when it comes to HVAC-related comfort based on how occupants will use the space.
Although this design strategy may not be as applicable in the hottest climates, where the goal is generally to keep the sun out, passive solar has proven to be a great source of enjoyment for us, particularly during our long winters. If given the chance, we would definitely design the same way again.
This post is one of a series by Eric Whetzel about the design and construction of his house in Palatine, Illinois, a suburb of Chicago. A list of Eric’s previous posts appears below. For more details and more photos, see Eric’s complete blog, Kimchi & Kraut.
Other posts by Eric Whetzel
- Basement Paint Splatter
- Tile Floors
- Installing Hardwood Flooring
- Completing the Wall Assembly
- Charred Cedar Siding
- Exterior Insulation and a Rainscreen
- The Blower Door Test
- Choosing and Installing a Ductless Minisplit
- Installing an ERV
- Choosing Windows
- Attic Insulation
- Installing an Airtight Attic Hatch
- Air Sealing the Exterior Sheathing
- Installing a Solar Electric System
- Prepping for a Basement Slab
- Building a Service Core
- Air Sealing the Attic Floor
- Ventilation Baffles
- Up on the Roof
- A Light Down Below
- Kneewalls, Subfloor and Exterior Walls
- Let the Framing Begin
- Details for an Insulated Foundation
- The Cedar Siding is Here — Let’s Burn It
- An Introduction to a New Passive House Project