What lets in light better – a double hung window or a window with a central mullion?

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We are talking about the windows in the children's rooms. They are the second windows in each case, which means another floor-to-ceiling window on the gable in each case.

The windows in question (with roller blinds) are on the eaves side (south side) in the jamb (height inside the finished room is 1.80 m) and are currently planned for 2 m x 70 cm (BH 72 cm) (known to require fall protection). The children's rooms are 15 square meters, so there is more than enough lighting.

Meanwhile, however, we are no longer convinced that 2 meters is not too wide, we are now leaning towards a width of 1.76 m. However, the windows are low, which probably makes up for the width.

The only question now is whether we should use a double hung window for better light transmission or a window with a center mullion. Load transfer through the window doesn't have to be guaranteed.

Has anyone installed windows like this and can share their experience? Or how the light transmission is actually between the two versions?



We had windows with center mullion in the apartment and now deliberately chose forend (to get rid of the stupid mullion).

Special solutions (only tilt?) I would not want, I would take completely normal windows. With or without forend.


We have a mullioned window at the top and a mullioned window at the bottom. The increased light yield of mullioned windows is certainly measurable, but in my opinion not necessarily decisive. The driving rain resistance is better with windows with center mullions, but you have a roller shutter against driving rain. There is still the advantage that you can perhaps bring in a sofa with the crane at some point in the future.


The front and center mullion don't differ much in light transmission. By the way, there is also a third option: one section of the window is fixed and only the other section opens. This is probably the most cost-effective solution.

  • While cleaning fixed glazing, except on the first floor, is always more difficult than opening a window.

Forend or mullion is practically an optical difference of a few centimeters of frame width in the middle. Landscape format, in my opinion, looks more consistent intentionally, if you do not divide it in width. Tilt-only is not a special solution: this is the same window with a slightly cheaper opening mechanism, nothing more. Just in contrast to the fixed element suitable for external cleaning without the need for scaffolding.


Where should the light flow come from? Edge and center sashes have 2 sashes – 1 or 2 cm more or less, doesn't matter.

Whether the room is bright enough depends, of course, on the orientation, the color of the room, and the furnishings. I would put the width measurement in relation to appearance.


They should not differ appreciably in light output. With the front, you can only tilt one sash and only open the "second" sash after the "first" sash. With a webbing/middle mullion, you can tilt and open both sashes independently of each other. With the fore-end you can make one large opening, with the remainder you can make two openings next to each other.


What is supposed to be good/bad? Forend/center post has no influence on your concerns now. I would do without a forend: what's the point?

Forend windows are used when you have a patio door and the middle mullion is a nuisance.


The practical consideration of cleaning the fixed glazing cannot be dismissed.

Nevertheless, just as food for thought: we have so many and in the dimensions unusual windows that we (have to) have a company come to clean them. This is not sooo expensive either, if you don't do it monthly. The idea of aligning the beautiful house design with the cleaning possibilities of the windows would not have occurred to me.

BTT: Take the normal windows with center mullions. Are a little more common in manufacture and therefore slightly cheaper if necessary, a little more stable in the frame construction and – as already mentioned above – the wings can be tilted independently.


Thanks for all the contributions. We have now decided to go with center mullion windows and reduced the width to 173 instead of 200. Still looks the same from the outside appearance – so no measurable loss.

By the way, the windows were "slightly" more expensive compared to the forend, but the extra price was waived for us due to insignificance.

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