Ventilation louvre hassles

I specified wooden louvre blades

This louvre window installation is described in this earlier post.

Photo of louvre for night purge

Louvre now fitted with glass blades

The automated louvre window that I specified for my system of summer cooling by nocturnal purge had wooden louvre blades of western red cedar 14 mm thick.
I specified wood because I preferred that this louvre should not be transparent, as I did not want to see through it and I did not want it to admit light. I took the risk that wooden blades might not seal as well as advertised.
Other posters on the ATA forum (see link below) doubted that the blades would seal effectively. They were right.

Failure of the wooden blades to seal

When the louvres were closed for the first time, there was clearly no seal at all. The rubber seals fastened to the blades failed to meet the matching blades, leaving gaps of up to 2 mm admitting daylight.

Attempts to rectify

I wrote a letter of complaint on 18/5/2016.
Rectification work on warranty first revealed faults in the gallery of gearing at the side of the window. However, when the gallery was replaced the gaps remained. The photo shows daylight visible on the right side through three of the gaps.

Photo evidence that louvre does not seal

Wooden louvres showing daylight

As the blades did not meet their specification, the company replaced them without charge. When these new blades did not seal any better, the company offered (on 10/10/2016) to replace them with aluminium blades, 6 mm thick. I reviewed the specifications of their blade options, and decided that this was not acceptable. The aluminium blades had little thermal resistance (U-value: 6.55). Glass blades 6 mm thick, with a low-e coating had much higher thermal resistance (U-value: 4.40), almost the same as the wooden blades (U-value: 4.39). The company agreed to provide these low-e glass blades. (In fact, this had been their original suggestion.)

Sealing of glass louvre blade gaps

Map of the gap widths in a louvre windowWhen the new glass louvre blades had been fitted at the end of October, it was clear that they sealed rather well.
I tested the gaps by trying to slide 80GSM copy paper, which is 0.10 mm thick, into them.

As shown on the graph, the paper could not be inserted between the blades at 57 of 80 test points. One sheet could be inserted at 16 points, two sheets at 4 points, three sheets at 2 points, and four sheets at just 1 point. That is to say, hardly any of the gaps were wider than 0.40 mm.

I painted the glass surfaces with detergent solution, thinking that leaking air might blow bubbles. Although the outdoor air was eight degrees warmer, the airflow blew no bubbles.

Photo of bubbles between louvre blades

Louvre test using detergent

In the photo, the middle overlap is the one (S7) that has the widest gap (>0.40 mm) at the right end. The detergent foam does not span the gap there. Where there is foam, the wider gaps have larger bubbles. While some of the areas without foam are caused by wide gaps, some are too narrow for foam to appear.


Although I have done no testing for the rate of air leakage, I am inclined to think that it is not significant for this louvre window with these glass blades. That was certainly not the case for the wooden blades.
In summer time, the transparent glass blades are not ideal: they expose the back of the refrigerator to view, they allow a startling amount of light to enter near floor level in the mornings, and they even let sunshine in at some odd times.
I have considered painting the blades white, but I have been cautioned against it.

This concept is discussed in some depth in a thread in a forum of the Alternative Technology Association (Melbourne) (now re-named “Renew”): “Louvre windows in hot dry summers”.

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