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Dark afternoons
Updated
In December the shutter can be down from late afternoon without anyone missing useful sun. That is the easy winter win.
What the glass admits
The worked opening for Dark afternoons is 3.2 m wide by 1.2 m high, 3.84 square metres of glass. This figure puts 595 watts per square metre on the pane and uses a g-value of 0.76, about 1736 watts into the room if the curtain is up. An opaque external shutter, taken as stopping 90 percent of that gain while it is fully down, leaves about 174 watts and keeps about 1562 watts out. That is a noon figure for comparison. An internal blind does not get the same reduction. For Dark afternoons, use the noon figure to compare two openings on the same house, then let a measured survey replace the figure.
An internal blind does not get that reduction, because the energy has already crossed the glass.
The hot part of the day
Tie it to the lights coming on, not to a summer clock left in the motor from August.
Dusk in January
Winter figure for Dark afternoons: glass at 2.6 W/m2K, 3.84 square metres, a 12 degree inside-outside gap and eight night hours. The bare pane is about 0.96 kWh a night on that crude sum. A closed shutter cutting about 30 percent of the flow leaves 0.67 kWh and saves about 0.29 kWh a night, only while it is down. Open it when you want winter sun.
Leave it if
Stop Dark afternoons if the door is an escape route and the motor has no way to open when it is dead. A photograph is not a manufacturing size.
Milton Keynes is only a setting for Dark afternoons. The streets there are not the product.
How to use the figure
The 3.2 by 1.2 metre opening inside Dark afternoons is there so a quote has something to disagree with. If the tape gives a different size, the tape wins.
The example drive is a solar motor, and the illustration is £3,551. A belt, a wired motor and a solar motor can share a curtain and still be different jobs. Compare those lines, not a single bold total.
What the survey still has to write down
For Dark afternoons, ask where the box lands, what colour reference will be ordered, and how the curtain opens when the motor is dead. Those three answers move the job more than a rounded price.
Leave the lantern, the side light and the next elevation off the order unless they are drawn. Dark afternoons covers one kind of opening. The house may have three.
When I would not order yet
Dark afternoons should wait if the opening is an escape door with no way to raise a dead motor, or if the front is the elevation a conservation area was drawn to protect.
A photograph is not a manufacturing size. Two quotes for Dark afternoons only compare when the slat, the box and the drive are the same kind of thing.
Questions worth asking the fitter
Is the price on this page a quote?
No. £3,551 illustrates Dark afternoons for a 3.2 by 1.2 metre opening with a solar motor, at September 2026 rates. Your survey replaces it.
Does the shutter cover every pane?
It covers the opening it is built for. Here that example is 3.84 square metres. A roof lantern, a side light or the next elevation is another line.
What if planning is unclear?
Do not pay the factory for Dark afternoons until a listed building, a conservation front, a flat or a shopfront has a written answer. Ordinary rear walls on houses are sometimes simpler.
What should two quotes share?
The same openings, the same slat type, and the same drive. Dark afternoons uses a solar motor in the example so you can see how much the motor choice moves £3,551.