How to Tame the Afternoon Sun on a West Facing Window

This one comes from a question I answered in a building forum. Someone was planning a window splashback behind their kitchen bench, on a west facing wall. Their living area faced south, so daylight was precious and they wanted to let some in, but they were worried the afternoon sun through that west glass would be a little too harsh.

They were right to worry. They were also right to want the window. Here is the answer I gave, and the thinking behind it.

The short answer: a retractable external blind

I'd recommend installing a retractable external blind. Open it up in winter when you want that sun, and close it down in summer when you want to block it. The one rule that makes it all work: the sun must not hit the glass in summer.

That single sentence is most of what you need to know about west glazing. The rest of this article is why it works, and how to get it right.

Why west sun is the hard one

North glazing is easy to shade because the geometry does the work for you. On the Central Coast the midsummer sun passes almost overhead, so a fixed eave of the right depth blocks it, while the low winter sun slips in underneath. The eave switches the sun on and off with the seasons, automatically, with no moving parts:

West glass gets none of that help. By late afternoon the sun is low in the western sky and shines in almost horizontally: under any eave, under any awning, straight onto the glass and straight into the room. And it arrives at the worst possible time: two to six in the afternoon, when the day is already at its hottest and the house has been soaking up heat since morning. That is why a west window in January feels like a heat lamp, while the same window in July is the nicest light in the house.

So the shading for a west window has to be vertical, covering the face of the glass. And because you only want it there for half the year, it should move.

Stop the sun before it hits the glass

This is the physics that decides where the blind goes. Glass is a trap for heat: sunlight passes through it easily, but once that light lands on your benchtop and floor it turns into warmth that cannot radiate back out. That is the greenhouse effect, working exactly as designed. Wonderful in winter, punishing in summer.

An internal blind or curtain intercepts the sun after it has already passed through the glass. The blind heats up, and that heat is inside the room with you, radiating off the fabric all afternoon. It fixes the glare and does little for the heat.

An external blind stops the sun before it ever reaches the glass. The blind takes the heat on the outside of the building and the breeze carries it away. Most of that solar energy simply never enters the room. Same blind, opposite side of the glass, completely different result.

Why retractable beats fixed

If summer were the whole story you could fix a screen over the window, tint the glass, or spec a very low solar heat gain glazing and be done. But all of those work every day of the year. And in winter, western sun is an asset. It is warm, it is generous, and on a block whose living areas face south it might be the best free heating and daylight the house gets. Permanent shading throws that away.

A retractable blind gives you the seasonal switching that the eave gives a north window, just operated by hand (or a motor) instead of by geometry. Down through the hot months, up through the cool ones. External roller blinds in a mesh fabric are the common choice and still let a soft view through when closed; folding arm awnings, sliding screens and operable louvres all do the same job in different ways.

Two practical notes if you are building or renovating. First, plan the blind with the window, not after it: a recessed box above the head of the window, blocking for the fixings, and wiring if it is motorised all cost almost nothing at design time and are annoying to retrofit. Second, on the Coast, check the wind rating. An external blind on an exposed westerly elevation needs to be specified for it, and a motorised blind with a wind sensor will retract itself before a southerly buster does it the hard way.

The glass still matters

The blind does the heavy lifting, but the window itself is worth choosing carefully. It sets how the window performs on the days the blind is up, and through every winter night. Double glazing slows the heat that conducts back out in winter, and the solar heat gain coefficient of the glass sets how much of the sun that does reach it comes through. I have a full guide to how to decide which window to get that walks through VLT, U value and SHGC in plain language.

Don't let the west scare you off the window

A window splashback over a kitchen bench is a lovely thing: daylight where you actually work, and something better than tiles to look at while you wash up. A harsh western aspect is not a reason to give it up. It is a reason to design the shading and the window as one decision instead of two.

This is a small example of a bigger principle: work with the sun your block gives you rather than against it. If you want to go deeper, start with which way your house should face on the Central Coast and the passive solar design principles that sit behind all of this.

And if you are staring at a harsh western elevation on your own block and wondering what it can become, send me the address for a free site assessment and I will look at the aspect and tell you honestly what I would do with it.