The call always comes in the same shape. One room in the house is fine all morning and unusable from about two o'clock. The air conditioning is running. The blind is down. It is still unpleasant, and the room next door is perfectly comfortable.
Nothing is broken. It is geometry, and once you see it the fix becomes obvious.
Why the afternoon is worse than noon
At midday the sun is high. It strikes a vertical window at a steep angle, and a good deal of that energy glances off the glass rather than passing through. Your roof and your overhang do real work.
By late afternoon the sun has dropped. Now it is coming in almost horizontally, straight at the pane, with nothing above it doing any shading at all. More of the energy passes through, and it passes through for hours rather than minutes because the sun is tracking across the window rather than over the roof.
This is why a room can be worst at four in the afternoon when the outdoor temperature peaked an hour earlier. You are not feeling the air temperature. You are feeling direct solar gain through glass.
Why it is the bedroom that suffers
Here is the part that confuses people. The complaint is rarely about the room with the big window. It is about the bedroom upstairs.
In a two storey with an open rear elevation, the main floor glass collects the heat, and the heat rises. The stairwell works as a chimney. By early evening the upper floor has been receiving warm air for hours, and unlike the main floor it does not cool down overnight because the building fabric has absorbed it.
Then you go to bed in it. That is why the bedroom is the room people finally do something about, even though the bedroom window is not the cause.
The same thing happens in a different form over an attached garage. That bedroom has a warm space beneath it, less insulation than it should have, and often a west-facing window of its own. It is the single most complained-about room in the subdivisions around Alcona and the newer parts of Aurora.
Three ways to deal with it
Blinds
Cheapest, and the one everybody tries. It works, in that a closed blind blocks the sun. The problem is what it costs you in daylight. A blind that is down every afternoon from June to September is a window you have removed from the house for the sunniest part of the day, and a low sun defeats most of them anyway by coming in under the slats at a shallow angle.
There is a second issue people miss. A blind sits inside the glass. The heat has already entered the room by the time it reaches the fabric, so the blind absorbs it and then radiates it back into the space. It stops the glare well and the heat only partly.
More air conditioning
Also works, also fights the wrong battle. You are removing heat that is still arriving. On the hottest afternoons the system simply cannot keep ahead of a wall of glass in direct sun, which is why the room stays uncomfortable even with the unit running flat out. Every dollar of that is spent after the heat is already inside.
Stopping it at the glass
The only fix that addresses the cause rather than the symptom is to reject the energy at the pane, before it becomes indoor heat.
A solar control covering does that on the glass you already own. Good product rejects roughly half the solar heat while holding around sixty five to seventy per cent of visible light, so the room stays bright and the view is unchanged. From the street the house looks the same, which matters if you would rather not be the one house on the block with obviously altered windows.
Where the room also has a privacy problem, a dual reflective covering does both jobs at once, with a mirrored exterior in daylight and strong heat rejection. It reverses after dark with your lights on, and we say so before anyone buys.
What to check before you call
Two things make the conversation faster.
Which way the glass faces. Stand at the window mid-afternoon. If the sun is on you, it is west or southwest and it is the cause. If the room is bright but the sun never lands on the glass directly, you have a glare problem rather than a heat problem, and that is a cheaper fix.
The age of the house. Anything built since the mid nineties almost certainly has Low-E glass, which changes how the pane handles heat and narrows which products can safely go on it. We identify the exact glass at the site visit, because putting the wrong covering on a Low-E sealed unit is a way to create a much more expensive problem than the one you started with.
The room is not badly built. It is just pointing the wrong way for four hours a day, and that is fixable in an afternoon without touching the window itself.
