Window Overhang Calculator

Size an eave or awning that blocks summer sun and lets winter sun in.

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project

Overhang depth (from the wall)

19.6 in

Run it at least 12 in past each side of the glass so morning and afternoon sun cannot slip in at the corners.

Depth range for the goal
19.6 in+ (blocks some winter sun)
Summer noon shade
100%
Equinox noon shade
28%
Winter noon shade
6%
Winter sun reaches into the room
172.4 in
19.6 deep100% shaded
Share of the window shaded, 21st of each month, by solar hour
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Save this overhang as a project: the cut list, bracket layout and materials for a 20 in awning over your 36 in window, tracked in Blueprint. Add every window on this wall in the app.

Save this overhang as a project

Framing lumber: lumber calculator. Cutting the heat that gets through: insulation calculator.

Turn these numbers into a build plan.

  • 20" depth
  • 60" width
  • 73.4° summer noon sun

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Project plan · built from your numbers

Window awning, 20" deep

A 20" deep, 60" wide wood-framed awning mounted 6" above a 60" S-facing window at latitude 40. Goal: full shade at the summer solstice, 10am to 2pm. It shades 100% of the glass at summer noon and lets winter sun in (about 6% shaded in December). Framed with 3 brackets and 5 rafters, roofed with polycarbonate or metal panels.

Materials
$260
Time
1 weekend
Level
Intermediate
6 steps 7 tools 9 materials
  1. 1

    Lay out the awning

    Mark the ledger line 6" above the window head and 12" past each side of the glass. Locate studs or the window header along the line.

    • Check local rules and HOA for exterior additions
    • Mark the ledger line level
    • Mark stud locations
  2. 2

    Flash and mount the ledger

    Slip Z-flashing under the siding above the line, seal fastener holes, and lag the ledger into studs. Water must shed over the ledger, never behind it.

    • Install flashing first
    • Pre-drill and lag into every stud
    • Check level end to end
  3. 3

    Hang 3 brackets

    Fasten the brackets under the ledger into framing, evenly spaced. They carry the outer edge of the awning plus snow and wind load.

    • Space brackets evenly
    • Fasten into studs, not just siding
    • Check each bracket for plumb
01 · Your numbers
Depth
20"
Width
60"
Summer noon sun
73.4°
Est. cost
$260
02 · The plan

6 steps · 7 tools · 9 materials

3 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

Your plan is 60% built. Save it.

3/5

Window awning, 20" deep

Finished in 1 weekend · $260 DIY

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How overhang depth is calculated

  1. Find your latitude. Enter a US ZIP or type your latitude. South of the equator, use a negative number and a north-facing wall.
  2. Set the wall direction. Overhangs work on walls facing the equator (south in the US). East and west walls need fins or shades.
  3. Measure the window. Glass height, sill height above the floor, and the gap from the top of the window to the underside of the eave or awning.
  4. Pick the goal. Full shade at the solstice, full shade all summer (deeper), or full winter sun (shallower).
  5. Read the depth. Depth = (gap + window height) / tan(profile angle), using the steepest-needed sun position from 10am to 2pm.

Worked example at 40 degrees north, a 60 in window 6 in below the overhang, south wall: the noon sun on June 21 is 73.4 degrees high, so depth = (6 + 60) / tan(73.4) = 19.6 in. On December 21 the noon sun is 26.6 degrees, and that overhang shades 6% of the glass. Away from noon, or on a wall turned off south, the profile angle (tan(altitude) / cos(sun azimuth - wall azimuth)) is what sets the shadow line, which is why the calculator checks every hour from 10 to 2.

Overhang depth by latitude and window height

South-facing wall, overhang 6 in above the window, full shade at the summer solstice 10am to 2pm; depth in inches
Latitude3 ft window4 ft window5 ft window6 ft window
25 N1 in1 in2 in2 in
30 N5 in6 in8 in9 in
35 N9 in11 in14 in16 in
40 N12 in16 in20 in23 in
45 N17 in21 in26 in31 in
49 N20 in26 in32 in37 in

Awning vs eave vs pergola

  • Eave: part of the roof, so it is free on new builds but fixed at the roof line; tall gaps above the window make it less effective.
  • Awning: mounted just above the window, so the gap is small and a shallow depth does the job. Wood-framed with metal or polycarbonate roofing is a weekend build.
  • Pergola or trellis: slats or deciduous vines for seasonal shade over patio doors. Frame it with the lumber calculator.

How to measure your window

Measure the glass height, not the frame; the sill height above the floor inside; and the gap from the top of the glass to the underside of the eave or the planned awning. Use a phone compass held flat against the wall to read which way it faces. Once the shade is right, the insulation calculator and the energy savings calculator cover the rest of the cooling load.

Window overhang calculator FAQ

How wide should roof overhangs be for shade?

For a 5 ft window 6 in below a south-facing eave at 40 degrees north, about 20 in shades the glass at the summer solstice and still lets the winter sun in. Lower latitudes need less, higher latitudes more.

Should overhangs be sized for the solstice or for August heat?

August is hotter than June but the sun is lower, so an overhang sized for the solstice lets sun onto the bottom of the glass. Shading May to August at 40 degrees north takes about 41 in instead of 20, and shades some spring and fall sun you may want.

What overhang depth for a 2 ft eave?

A 24 in eave set 24 in above a 4 ft window at 40 degrees north shades 100% of it at summer noon. Full solstice shade there takes about 21 in, so add an awning or lower the head of the window.

What is a metric example?

At 52 degrees north (London, Berlin), a 150 cm window 30 cm below the overhang needs about 98 cm of depth for full solstice shade at noon on a south wall.

Do overhangs work for east and west windows?

Not well. Morning and afternoon sun comes in low, under any practical overhang. Use vertical fins, exterior roller shades, shutters or trees.

Can I use a pergola instead of a solid overhang?

Yes. Slats angled to the summer profile angle block high sun and pass low winter sun; deciduous vines do the same thing seasonally.

How much energy can window shading save?

Exterior shading on sunny windows can cut cooling loads 10 to 25% for those rooms, more than interior blinds, because the heat never gets through the glass.

What about retractable awnings?

They give full shade when extended and full sun when retracted, so the depth calculation matters less. Size the projection here, then retract in winter and storms.

Does this calculator work for the Southern Hemisphere?

Yes. Enter a negative latitude and a north-facing wall. The calculator flips the solstices, so June is winter and December is summer.

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