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Author Topic: Mounting plexiglass to soundproof old sash windows?  (Read 3707 times)


  • Guest
Mounting plexiglass to soundproof old sash windows?
« on: May 29, 2017, 10:35:06 PM »

Hi, new member here (so go gentle!)

I just moved to a house that have lovely original Sash wooden frame windows, which look nice, but pass sound as if there's a giant open hole in the wall.

Quotes to replace them in the bedroom (the most critical area as my neighbors driveway is 6 foot away and the kinds have a habit of yelling down the length of it at 7am) were over 4 grand, so that's out the question.

I stumbled across the idea of mounting plexiglass but want to check I'm planning it right.

The windows have traditional style shutters on the inside which thankfully means the windows already have a a perfect 1/2" "lip" as a frame around them on the inside. I was planning to attach 1/2"  wide adhesive magnetic tape to the frame, and then apply the tape to the perimeter face of the plexiglass to hold it snugly in place.

Firstly, is that tape, assuming I'm very accurate with it, enough to create a seal for the soundproofing advantage? Do I have to use any foam/caulking or is the tape enough?

Secondly, what plexi should I use? All the hardware stores around me sell just Optix brand, and the thickest I can still use (while being able to close the shutters by getting larger swing hinges installed) is going to be 1/4". Is that thick enough? Do I need some special type of acrylic (i.e. extruded vs cast or other?).

Finally,the largest and worst offending window, could also have a sheet permanently installed on the outside too (making it a 3 pane window total). I'd have to do some millwork and nail the frame with the sheet in place, but would there be any benefit to this extra pane?

Thanks and any pointers greatly appreciated!


Randy S

  • Guest
Re: Mounting plexiglass to soundproof old sash windows?
« Reply #1 on: June 05, 2017, 06:35:55 PM »

The magnetic tape is actually supposed to go on the acrylic and the steel L-frame is to be screwed into the window both entirely around all 4 sides of the window.
1/4" standard acrylic will work, 3/8" is diminishing point of return.

Here is the link to the magnaseal instruction page.

If there is a gap between the L frame and the window box then you would caulk any gaps.

On the final window you are looking for the greatest size air gap you can get..

Randy S.