Deep Eaves and Why a 600 mm Overhang Protects a House

Walk down a street of houses built in the last fifteen years and count the eaves. On many of them you will find almost none: a flat wall running straight up to a crisp roof edge, gutter tucked behind a parapet. Then walk past a 1920s bungalow or a Prairie-style house and look at the roof sailing 600 mm or more beyond the walls. The older house is often the one with drier walls, cooler summer rooms and window frames that still close properly.

Deep eaves are one of the cheapest pieces of climate design in architecture, and one of the first to be cut when budgets tighten or a design wants to look sharp. I want to make the case for them with numbers rather than nostalgia, and show how to size an overhang for a real house.

What Deep Eaves Actually Do for a House

An eave is the part of a roof that projects past the outside face of the wall. A shallow one might be 150 to 300 mm. A deep one is generally 600 mm or more, and in hot climates a metre is common. That projection does three jobs at once.

It keeps rain off the upper wall and the window heads, where most leaks start.
It shades windows from high summer sun while letting low winter sun in.
It throws roof runoff further from the base of the wall and the foundations.

None of those needs a pump, a sensor or a maintenance contract. They work every day for the life of the roof.

Builders understood this long before anyone modelled it. Traditional Japanese timber houses use broad eaves to protect paper screens and wooden verandas from heavy rain. Frank Lloyd Wright's Robie House in Chicago, finished in 1910, stretches its roofs far past the walls so the long bands of windows sit in shade through the summer.

The Sun Angles Behind a 600 mm Overhang

Overhang sizing starts with the noon sun angle, which depends on latitude. At about 51 degrees north, roughly the latitude of London, the midsummer sun at noon sits around 62 degrees above the horizon. In midwinter it drops to about 16 degrees.

That difference is what an eave exploits. A 600 mm overhang casts a shadow about 1.1 metres down a south-facing wall at midsummer noon, enough to shade the glass of a standard window placed just under it. In midwinter the same overhang shades only around 17 centimetres, so almost the whole window takes in low, warming sun.

Eave depth	Summer noon shade at 51 N	Winter noon shade at 51 N
300 mm	About 0.55 m	About 0.09 m
600 mm	About 1.1 m	About 0.17 m
900 mm	About 1.7 m	About 0.26 m

This only works well on walls facing the equator. East and west windows get low morning and evening sun that slips under any eave. For those, vertical fins, planting or smaller glazing do more. Our piece on why building orientation decides a home's comfort covers that side of the equation.

Rain, Walls and the Fifty-Year View

Sun gets the attention, but rain is where deep eaves earn their keep over decades. Wind-driven rain wets the top of a wall most heavily, and that is exactly the zone an overhang protects. Timber cladding, render, mortar joints and window seals near the roofline all last longer when they stay dry.

Repeated wetting is what rots window heads, stains render and lets moisture creep into wall cavities. A house with no eaves relies entirely on its cladding, flashings and sealants to keep that water out. Those are good products, but they are finite. Sealant joints might need attention every 10 to 15 years. A properly built overhang needs paint.

Why Flush Eaves Became the Default

If eaves are so useful, why did they vanish? A few reasons keep coming up when I talk to builders and designers:

Looks. Minimal, sharp-edged forms photograph well, and flush roof edges deliver that look cheaply.
Plot size. On tight lots, every 600 mm of overhang near a boundary can run into setback rules or fire separation limits.
Cost per square metre. Overhangs add roof area and soffit work that do not add floor area to sell.
Faith in membranes. Modern wraps and sealants made it feel safe to skip the overhang.

The Case Against Relying on Better Cladding

The usual argument now is that modern materials make eaves unnecessary. Use a good rainscreen, a quality membrane and high-performance windows, the reasoning goes, and the wall will cope.

I disagree with that framing. Better cladding does handle more water than older materials, but it does not shade a window, it does not keep a summer bedroom cool, and it fails quietly when a single detail is installed poorly. An overhang is a backup layer that keeps working when something else underneath is imperfect. That makes it a resilience feature, not a style choice. Pair it with the strategies in our piece on why passive cooling still beats mechanical air and a house needs much less help from machines.

The fair counterpoint is high-wind and wildfire zones. Deep overhangs catch wind uplift and can trap embers. There, eaves need stronger fixings, closed soffits and non-combustible linings, not removal.

Sizing Eaves for Your Own Project

A simple rule works for a first pass on an equator-facing wall. Measure the height from the bottom of the window to the underside of the eave. Multiply it by a factor set by your latitude: roughly 0.25 to 0.3 in cooler northern climates around 50 degrees, and up to about 0.45 in warm regions. Most ordinary windows land somewhere between 450 and 900 mm.

Then check three practical points:

Will gutters stay reachable for cleaning from a ladder?
Do the boundary setbacks on your site allow the projection?
Does the overhang darken rooms you want bright on grey days?

Put the eave depth into your project brief so the designer treats it as a requirement, not an option to drop later. The guide on how to write an architect brief shows where performance goals like this belong.

FAQ

Do deep eaves make rooms too dark?

Rarely, if sized for your latitude. On north-facing walls in the northern hemisphere you can keep eaves shallow, since there is little direct sun to block.

Can eaves be added to an existing house?

Often yes, by extending rafters or adding a bracketed canopy over key windows. A structural engineer should check the roof can take the extra load and wind uplift.

Are eaves worth it in a cold climate?

Yes, mainly for rain protection. Keep them moderate, around 400 to 600 mm, so winter sun still reaches the glass.

The Practical Takeaway

If you are planning a new house or an extension, ask for at least 600 mm of overhang on the equator-facing side and over any window you want shaded in summer. It costs a little more in roof area and saves far more in comfort, paint and repairs across the decades the building stands.