Moved into a new house and have to install blinds on all windows. Some of the windows were single, and I was able to mount the blinds on inside to the wooden frame. However, we have a few of these double and also triple window sets with a small 8 inch tall window-lettes (is that a word?) that complicates things.

enter image description here (The preferred location of blind mounting brackets is displayed with a red X)

We want to keep those small windows at top open, and mount it where the bottom up windows start, just below the first mullion.

As far as I can tell the mullion and joining frame is plastic on top of a thin aluminum structure.

I read somewhere that this is actually a structural piece and should not be drilled into. For the blinds we want to use two blinds with separate head mechanism.

Now the question :) How do I mount it? The ends can go into wood. What I am worried about is the middle. If I can’t drill into the mullion how do I support the middle and take the weight?

Worst case, we can move it up and cover the small windows and drill into wood frame, but since it is non standard size, the cost is almost double :(

Dimensions of one window: 34.5 inch W x 69 inch H. Mullion width is 1 inch.

  • Could you maybe add a photo with rectangles drawn on it showing exactly where you want the blinds to cover?
    – Armand
    May 23, 2022 at 4:24
  • Sure. Updated the picture.
    – ad1988
    May 23, 2022 at 10:50
  • Is this a window between two indoor areas? The other side of the window appears to be indoor, but, the wall we see on this side seems to be indoor as well. If it's an indoor window, maybe a very light curtain instead of blinds so that you can hang it only from the edges instead of the middle. If we're looking at the outside of the window, a picture of the inside would help, since you'll be hanging the blinds on the inside.
    – FreeMan
    May 23, 2022 at 11:00
  • Thanks for checking. Yes, it is a view from inside. I just realized it looks like interior window since it opens onto the covered porch.
    – ad1988
    May 23, 2022 at 15:51

2 Answers 2



Ended up getting 84inch length blinds and cover the transom as well :( cost around 25% more.

While speaking to a contractor, he mentioned that usually people have a wood block between transom and window for that, since they are not here the only options are curtains (outside mount), cover transom with inside mount, hang a steel cable in the middle and secure it to the top wooden beam and two ends of side by side blinds.

I floated another option to use the powder coated pipe (the one popular in building shelves) and instead of wire from top,secure to the base and also the ends of two blinds in the middle.

Longer blinds won, everything else vetoed by better half :) seems the cleanest option.


Had the same problem and I was advised to use a Palladian Shelf. Purchasing from Blinds.com but this will allow me to have single shades on the double hung windows. My width was 70".

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