Shade for South-Facing vs West-Facing Patios: What Sun Geometry Means for Your Awning
On a south-facing patio the summer sun is high, so a retractable awning's projection does most of the work and a 10 ft (3 m) awning shades most of the space under it at midday. On a west-facing patio the problem sun arrives low in the late afternoon and slides under any awning, so projection alone fails exactly when you want shade: you need a drop valance or a vertical screen. This page shows the geometry with computed numbers so you can size for your orientation instead of guessing.
Key takeaways
- A south wall at the equinoxes sees a constant "profile angle" all day, equal to 90 degrees minus your latitude; that makes south shade unusually predictable.
- At 40 degrees north, a 10 ft (3.05 m) awning with its front bar at 7.5 ft (2.29 m) shades about 7.8 ft (2.4 m) of floor at a June noon, but only about 3.7 ft (1.1 m) at the equinoxes.
- On a west patio the same awning shades about 6 ft of floor at 2 pm solar time in June and essentially none by 4 pm.
- For west exposures, a vertical screen or drop valance of about 3 ft (0.9 m) does more for seated comfort than adding 3 ft of projection.
- The Department of Energy notes awnings can reduce solar heat gain by up to 65% on south-facing windows and 77% on west-facing windows, so both orientations are worth shading, just differently.
The one angle that matters: profile angle
For any awning, what decides how far shade reaches is not the sun's altitude alone but its profile angle: the sun's elevation as seen in a vertical plane perpendicular to the wall. When the sun is straight in front of the wall, profile angle equals altitude. When the sun is off to one side, the profile angle is steeper than the altitude, because the rays come in at a slant. The formula is tan(profile) = tan(altitude) / cos(difference between sun azimuth and the wall's facing direction).
Once you have the profile angle, the shade edge on the floor is easy: the shadow of the front bar lands at a distance of (front bar height / tan(profile)) back toward the wall from the front bar. Subtract that from the projection and you have the depth of shaded floor measured from the wall. If the result is negative, the floor under the awning gets no shade at all and the shadow falls on the wall.
You do not need to do this by hand: the shade calculator computes it for your latitude, date, time, projection and mounting height, and the shade coverage tables list precomputed depths for common latitudes and projections.
South-facing patios: projection does the work
In summer the midday sun is high in the southern sky, so its profile angle on a south wall is steep. Better still, as the sun swings west in the afternoon, the profile angle on a south wall gets steeper, not shallower, because the sun moves off to the side. In June at mid-latitudes the sun actually passes behind the plane of a south wall by mid to late afternoon, and the wall goes into its own shade.
| Latitude | June solstice | Mid-April / late August | Equinox (March / September) |
|---|---|---|---|
| 30 N (Houston, Jacksonville) | 9.1 ft (2.8 m) | 7.5 ft (2.3 m) | 5.7 ft (1.7 m) |
| 35 N (Memphis, Albuquerque) | 8.5 ft (2.6 m) | 6.8 ft (2.1 m) | 4.7 ft (1.4 m) |
| 40 N (Denver, Philadelphia) | 7.8 ft (2.4 m) | 5.9 ft (1.8 m) | 3.7 ft (1.1 m) |
| 45 N (Minneapolis, Portland OR) | 7.0 ft (2.1 m) | 5.1 ft (1.6 m) | 2.5 ft (0.8 m) |
Two patterns stand out. First, a south awning is self-regulating: deep shade at the summer solstice, shallower in spring and fall when some warmth is welcome, and fully retractable in winter to let low sun into the house. Second, the shoulder seasons are where south awnings feel short. If you want shaded lunches in September at 40-45 N, a 13 ft (4 m) projection or a front drop valance helps more than you would expect.
The real south-patio problem: the west end
Because the summer afternoon sun is far to the west, a south awning casts its shade shifted east. People sitting under the western end of the awning get sun coming in from the side, under the end of the fabric. The fix is width, not depth: extend the awning 2-3 ft (0.6-0.9 m) past the seating on the west side, or add a side screen at the west end. That is why the usual rule of "awning 2 ft wider than the seating" should be applied asymmetrically on south walls.
West-facing patios: the sun gets under everything
A west wall receives sun from early afternoon until sunset. As the afternoon progresses, the sun drops lower and comes almost straight at the wall, so the profile angle approaches the sun's altitude, which falls toward zero. No practical projection can shade a floor against a sun 15 degrees above the horizon.
| Solar time | June: floor shade depth | June: shade at seated head height | Equinox: floor shade depth | Equinox: shade at seated head height |
|---|---|---|---|---|
| 2 pm | 6.0 ft (1.8 m) | 8.1 ft (2.5 m) | 4.3 ft (1.3 m) | 7.4 ft (2.3 m) |
| 3 pm | 3.5 ft (1.1 m) | 7.0 ft (2.1 m) | 0.2 ft (0.1 m) | 5.4 ft (1.6 m) |
| 4 pm | 0.2 ft (0.1 m) | 5.4 ft (1.6 m) | None | 2.1 ft (0.6 m) |
| 5 pm | None | 2.9 ft (0.9 m) | None | None |
| 6 pm | None | None | Sunset | Sunset |
Solar time is not clock time. During daylight saving time, solar noon falls around 1 pm or later depending on where you are in your time zone, so "5 pm solar" is roughly 6 pm or later on the clock: the exact hour most people want to sit outside. Values at 30-45 N are similar in pattern; latitude changes the details far less on west walls than on south walls.
West-patio solutions, ranked
- Awning plus drop screen. A lateral arm awning with an integrated roll-down valance (a second roller in the front bar) gives overhead shade at midday and vertical shade in the evening. See awning accessories.
- Motorized vertical screens on the patio's west face, alone or under a roof or pergola. Solar mesh with 3-10% openness factor cuts glare while preserving the view. See motorized patio screens and screen mesh openness factor.
- Drop arm awning, which angles down to near-vertical and works well over west windows. See drop arm awnings.
- Exterior solar shades on the glass if the goal is mainly keeping heat out of the house; compare exterior solar shades vs awnings.
East, north and in-between orientations
East patios are the mirror image of west patios: low morning sun that slips under awnings. Because most people use patios in the afternoon and evening, east patios are often naturally shaded at the times that matter, and a modest awning or a vertical screen for breakfast is enough. North patios in the US receive direct sun only early and late in summer, mostly at low angles from the northeast and northwest; side screens beat overhead shade there.
Walls facing southwest or southeast behave in between. Southwest is the hardest of all: high-angle midday sun and low-angle late sun both arrive at a steep enough angle to heat the patio. Plan for both projection and a vertical screen.
| Wall faces | Main problem sun | Best primary shade | Add |
|---|---|---|---|
| South | High midday | Lateral arm awning, 10-13 ft (3-4 m) projection | Extra width on west end |
| Southwest | Midday and late afternoon | Awning with roll-down valance | Side screen on west end |
| West | Low late afternoon | Vertical screens or drop arm awning | Overhead awning for midday |
| East | Low morning | Vertical screen or modest awning | Often nothing needed for evening use |
| North | Low early and late summer sun | Side screens | Overhead shade rarely needed |
Heat gain through glass: why both orientations pay back
The comfort question (can I sit outside?) and the energy question (how hot does the room behind the glass get?) have the same geometry. A south awning blocks high summer sun on south windows efficiently, while letting low winter sun in when retracted. A west awning or screen tackles the most punishing heat gain of the day, late afternoon sun striking glass when the house has already warmed up. For estimates, use the energy savings calculator and read energy savings from awnings.
A sizing sequence that respects orientation
- Find your wall's true facing. Use a compass app and correct for magnetic declination, or check an online map. A wall that is "west" may really face 250 degrees, which behaves more like southwest.
- Decide when you use the space. Evening dining on a west patio and midday lunches on a south patio need different designs.
- Run the numbers in the shade calculator for your latitude, the dates you care about and your mounting height.
- Size projection for overhead sun and add vertical shade for low sun, using the orientation table above.
- Measure the wall and check head clearance with how to measure for an awning.
Frequently asked questions
How far should an awning project on a south-facing patio?
For most US latitudes, 10-13 ft (3-4 m) shades the bulk of a typical patio in summer. Use 13 ft at higher latitudes or if you want good shoulder-season shade, and check head clearance at that projection.
Will a bigger awning fix a west-facing patio?
Only partly. Extra projection helps in early afternoon, but in the last few hours before sunset the sun is too low for any overhead shade. A drop screen or vertical patio screen is what solves evening sun.
Does awning pitch change how much shade I get?
Yes. Steeper pitch lowers the front bar, which pulls the shadow edge toward the wall on the floor but can help block lower sun for seated people. The shade calculator lets you compare pitches.
Why is the shade under my awning not directly beneath it?
Because the sun is rarely directly overhead. The shadow shifts away from the sun: east in the afternoon, west in the morning, and toward the wall as the sun gets lower. That is why awnings should be wider than the area they shade.
Is a southwest patio more like a south or a west patio?
It combines both problems. It gets strong midday sun and also low afternoon sun at a steep angle to the wall. Plan for a full-projection awning and a vertical screen or roll-down valance.
Does the season matter for a south awning?
A lot. At 40 N, the same awning shades roughly twice as much floor at the June solstice as at the equinoxes. That self-regulation is a benefit: more shade in summer, more warmth in spring and fall.
Sources and standards consulted
- NFPA 701, Fire Tests for Flame Propagation of Textiles and Films (NFPA)
- International Building Code (IBC), awnings and canopies provisions (ICC)
- Energy Efficient Window Attachments (U.S. Department of Energy, Energy Saver)
- RV awning owner manuals and operating instructions (manufacturer documentation)
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