How the sunlight score works

Step 1: Orientation estimate

Everything starts with figuring out which direction the front of the house faces. This single data point determines which windows get morning sun, which get afternoon sun, and which barely see direct light at all.

Building footprints (best case)

Our first move is checking building footprint data from OpenStreetMap. When a footprint exists, we can identify the longest wall segment and determine which compass bearing it faces. This is the most reliable method because it's based on the actual shape of the structure, not assumptions about lot layout.

Building footprint coverage varies by area. Dense urban neighborhoods and newer suburban developments tend to have strong footprint data. Rural areas and older neighborhoods sometimes don't.

Road geometry (fallback)

When footprints aren't available, we look at the nearest road segment. Most houses face the street they're addressed on, and road geometry is well-mapped almost everywhere. We identify the road's bearing and assume the front of the house runs parallel to it.

This works well for standard residential streets. It's less reliable for corner lots, cul-de-sacs, and properties set back on long driveways where the house might be angled differently than the road.

When data is thin

Sometimes neither source gives us strong geometry. Rural addresses, brand-new construction, and properties with unusual lot configurations can all produce weaker signals. When that happens, we mark the confidence level lower and give you a compass slider to adjust the direction manually. Pulling up satellite view on Google Maps for ten seconds will tell you which way the roof ridge runs, and you can set it yourself.

Step 2: Sunlight timeline calculation

Once we know which way the house faces, we calculate the sun's exact position in the sky for every half-hour block from sunrise to sunset. This produces the hourly timeline you see in the results.

Sun position math

Two numbers define where the sun is at any given moment:

• Azimuth—the compass bearing. The sun rises roughly east (~90°), passes through south (~180° in the Northern Hemisphere) at solar noon, and sets roughly west (~270°). "Roughly" because the exact bearings shift significantly by season.
• Altitude—the angle above the horizon. At sunrise and sunset, altitude is 0°. At solar noon in summer at 40°N latitude, it reaches about 73°. In winter at the same latitude, solar noon peaks around 27°.

We calculate both values for the property's exact latitude and longitude at every half-hour mark throughout the day. This isn't an approximation—it's standard solar position geometry that astronomers have used for centuries.

How half-hour intervals work

The sun moves about 15° per hour across the sky (360° in 24 hours). Half-hour intervals give us a granular enough picture to show meaningful changes—the difference between "sun is hitting your kitchen windows" at 8:00am and "sun has moved past the kitchen" at 9:00am matters when you're deciding if you need overhead lights for breakfast.

Direct vs. indirect light scoring

For each half-hour block, we check whether the sun's azimuth aligns with any window direction on the house. A south-facing window gets scored for direct light when the sun is anywhere in the southern arc of the sky (roughly 120° to 240° azimuth). The closer the sun's bearing matches the window's facing direction, the higher the direct light score.

Indirect light is everything else—the sun is up, the sky is bright, but the rays aren't aimed at that particular wall. Rooms still get ambient light from a bright sky even without direct sun. That's why a north-facing room isn't a cave during the day (usually), even though it rarely sees a sun patch on the floor.

How window direction affects the timeline

Each cardinal direction produces a distinctive light pattern:

• East-facing windows: Strong direct light from sunrise until late morning, then indirect light the rest of the day.
• South-facing windows: Direct light for the longest stretch—roughly 10am to 4pm depending on season. The most total sunlight hours of any orientation.
• West-facing windows: Indirect light all morning, then strong direct light from early afternoon through sunset. This is where you get that golden-hour glow, and also where you get overheating in summer.
• North-facing windows: Minimal direct light year-round in the Northern Hemisphere. Consistent, soft ambient light that photographers and artists love but that can feel dim in winter.

Step 3: Seasonal variation

The same house feels genuinely different in December than it does in June. This isn't subtle—we're talking about the difference between a room that's flooded with light and one that barely gets direct sun. The season toggle exists so you can see that shift before you sign anything.

Why the sun's path changes so much

Earth's 23.4° axial tilt means the sun traces a completely different arc across the sky in summer versus winter. Here's what that looks like at common US latitudes:

At 40°N, the winter sun barely clears the treeline. It hangs low in the southern sky all day, which means south-facing windows get deep, penetrating light (great for passive solar heating) but east and west windows get far less than they do in summer. North-facing rooms essentially lose direct sun entirely from November through February.

Winter solstice vs. summer solstice

On the winter solstice (around December 21), the sun rises late in the southeast, takes a low arc through the southern sky, and sets early in the southwest. Total daylight at 40°N: about 9 hours and 15 minutes. The sun never gets higher than 27° above the horizon—roughly the height of a two-story building across the street.

On the summer solstice (around June 21), the sun rises early in the northeast, climbs to nearly overhead, and sets late in the northwest. Total daylight at 40°N: about 15 hours. The sun peaks at 73°, nearly straight up.

That 46-degree difference in peak altitude changes everything about how light enters a home.

Spring and fall equinoxes as baseline

The equinoxes (around March 20 and September 22) split the difference. The sun rises due east, sets due west, and reaches about 50° altitude at noon. This is probably the most "average" representation of how a home feels light-wise over the full year—which is why it's useful as a mental baseline when you're comparing the seasonal extremes.

The real-world impact

A south-facing home in Denver that scores Excellent in summer might drop to Good in winter—not because anything changed about the house, but because the sun is lower, the days are shorter, and the light enters at a different angle. Conversely, a west-facing home that feels blinding in August might be perfectly comfortable in January. The season toggle shows you both realities so you're not surprised after you move in.

Confidence scoring breakdown

Every result comes with a confidence label. Here's what each level actually means and when you should pay attention to it.

High confidence

A clear building footprint was matched. The orientation estimate is based on the actual shape of the structure. You can generally trust the direction within a few degrees. The sunlight timeline will be a reliable representation of what windows facing that direction would experience.

Medium confidence

Orientation was estimated from road geometry. The house is assumed to face the street, which is usually right but not guaranteed. Corner lots, angled driveways, or houses that sit at an odd angle to the road can be off by 20-45°. Worth verifying with satellite imagery before making decisions based on the score.

Low confidence

Map data was sparse. The orientation is a rough estimate and could be significantly off. This happens most often with rural properties, very new construction, and addresses in areas with limited OpenStreetMap coverage. Use the manual compass adjustment, and treat the timeline as directional rather than precise.

What lowers confidence

• No building footprint in OpenStreetMap for that address
• Multiple buildings at the same address (apartment complexes, duplexes)
• Ambiguous road geometry (cul-de-sacs, T-intersections, curved roads)
• Address geocoding that lands slightly off-target
• New construction not yet reflected in map data

What this tool cannot know

Being honest about limitations is more useful than pretending they don't exist. The sunlight score is based on orientation and sun math—two things we can calculate reliably from outside the house. Here's what stays outside the model.

Interior layout and windows

We know which direction the building faces. We don't know where the windows are, how big they are, or which rooms they open into. A south-facing house with tiny windows on the south wall and a massive picture window facing north will feel different than the score suggests. Floor plans aren't part of the input—yet.

Window treatments and finishes

Tinted glass, low-e coatings, blackout curtains, light-colored walls, dark hardwood floors—all of these change how bright a room actually feels. Two identical houses facing the same direction can feel dramatically different inside based on finishes alone. The score tells you how much sunlight is available at the building envelope, not how it plays out in the living room.

Trees and vegetation

A mature oak tree in the front yard blocks more light than a two-story building. Deciduous trees are especially tricky—they provide heavy shade in summer (when you might want it) and let light through in winter (when you need it). But they're invisible to our model. Check satellite view and street view for major trees near the property.

Neighboring buildings and structures

A three-story building going up across the street next year will tank your southern exposure. Construction cranes don't show up in sun math. Even existing neighbors matter—a tight lot with a tall house to the south will block winter sun that the score assumes is reaching the windows.

Renovations and additions

Building footprints reflect the last time someone mapped the property. If an addition was built, a porch was enclosed, or a dormer was added, the footprint might be outdated. New construction is the most common blind spot here.

Microclimates and weather patterns

The score assumes clear sky conditions. If your area is overcast 200 days a year (hello, Seattle), the raw sunlight score overstates how bright the house will feel. Similarly, fog-belt neighborhoods, mountain shadows, and proximity to large bodies of water all create local light conditions that pure sun math can't capture.

How to use the results

The score isn't a grade on a report card. It's a tool for making better decisions. Here's how to get the most out of it.

Reading the hourly timeline

The timeline shows you when direct sunlight would hit each side of the house, in half-hour blocks from sunrise to sunset. Look for the times that matter to you personally. If you work from home and your desk would face east, check whether that side gets morning glare. If you host dinners, check whether the dining room side gets good evening light.

Comparing seasonal views

Toggle between summer and winter. If a house looks great in summer but drops significantly in winter, ask yourself which season matters more. In a place like Raleigh, winters are short and mild—a winter dip matters less than it would in Minneapolis. In the Pacific Northwest, winter light is everything because summer is already abundant.

Sharing with your agent or partner

Export the result as a PDF. It's a useful artifact to send to your buyer's agent before a showing—they might not have thought about light direction, and it gives them something concrete to check during the tour. It's also an easy way to compare listings with a partner without both of you needing to run the tool.

Using alongside a tour visit

The best workflow: run the calculator before the showing, note which direction the house faces, then pay attention during the tour. If the tool says the kitchen faces north but the kitchen is bright at 2pm, there's probably a skylight or a large window you couldn't see from map data. If the tool says the living room faces south but it feels dark, look for obstructions—a big tree, a nearby building, small windows. The score sets expectations; the tour confirms or corrects them.

Try it yourself

Paste any address, Zillow link, or Redfin URL and see the full sunlight analysis—orientation, hourly timeline, seasonal comparison, and confidence score. It runs in your browser and takes about ten seconds.