Transom Replacement for Acoustic : Toughened vs Laminated

[rideforever]

Hi, it's above the front door of a flat (there is an existing georgian wired that will stay) it's to block noise from people in the shared hallway.
Two question, firstly what deduction to I make from the aperfture width/height to get the glass cut ? Is 5mm okay, it's pretty square imo.
Second question is, I have been offered 6.8mm laminated, but it's a bit cheaper to get 12mm toughened ... from the spec sheets they both say -35db sound reduction. 6mm seems pretty thin to me and I have a feeing the toughened is a better choice blocking deeper noise due to its mass. (-35db could be of any part of the spectrum or just an average). Here it's mostly door slams that are the problem rather than voice.
Thoughts ?
Cheers

 

[JohnD]

12mm will be very thick and heavy. Have you got an adequate rebate?

for sound deadening, generally the heavier the barrier, the more effective it is. In the case of glass, when you have two panes, it is more effective if they are different thicknesses as each will have a different resonance. the georgian wired is probably 6mm

6.8mm laminated is an effective barrier against burglars, as you cannot make it crumble away like toughened.

adhesive glazing tape will hold the glass very securely and is slightly absorbent of vibration.

 

[rideforever]

12mm will be very thick and heavy. Have you got an adequate rebate?

for sound deadening, generally the heavier the barrier, the more effective it is. In the case of glass, when you have two panes, it is more effective if they are different thicknesses as each will have a different resonance. the georgian wired is probably 6mm

6.8mm laminated is an effective barrier against burglars, as you cannot make it crumble away like toughened.

adhesive glazing tape will hold the glass very securely and is slightly absorbent of vibration.

Rebate is 27mm so lots of room ... thanks yeah both being 6mm is not as good as having different thicknesses.
One thing I don't know is when I get the glass cut how much should I deduct from the aperture size? Is 5mm about right?

I am going to use glazing putty around so that it absorbs vibrations from the heavy door underneath. The wood trim is 9mm.

I do have the sense that Georgian wired does almost zero for some reason I don't know if the wires resonate and increase the sound even !!!

 

[JohnD]

5mm sounds generous. cut a piece of stiff cardboard and try it.

keep a sharp chisel handy in case you need to shave any high spots, or blobs of paint, out of the rebate.

I strongly advise the glazing tape. thicker grades are more absorbent, I think I use 2mm which looks neat. It is made of dense butyl rubber like material, with strong adhesive on both sides. It is foamed to accomodate slight irregularities. Your glazing supplier will stock it, but possibly only in large packs. You want the same width as the depth of the rebate, or possibly a fraction less. You can add an ornamental wooden bead painted or stained on the outside.

If indoors, your georgian wired might be glazed dry, with (wooden) glazing bead, allowing it to vibrate.

I learned to putty in wooden and metal windows many years ago, hardly anybody does it now, and I wouldn't recommend it. Even if you have been taught.