The next step in soundproofing the garage was to address one of the major weaknesses - the window. As any soundproofing article will tell you, ideally the room should have no windows at all as this will inevitably be more soundproof - but a closed box with no natural light doesn't make for a very comfortable and productive atmosphere, so for me, the one existing window was essential.
Fortunately, the garage already had double glazed windows, so this provided some level of acoustic isolation, but this was nowhere near enough. These windows also opened, which meant that they weren't sealed completely. Here is a picture of the existing window from the outside:
Although there is lots of information online on soundproofing windows, in general these refer to internal windows between the control room and live room. As I was dealing with an external window, I had to come up with a slightly different construction strategy.
My plan was, therefore, to both add as much isolation to the existing window in the outer wall as possible, and then to also create another window on the inner room, with the two joined together with a kind of tunnel effect. This would prevent noise from leaking into the air gap around the window. The internal window will be discussed later on in "Windows Part 2".
In order to implement this, I decided to permanently fix the window in place so that it could no longer open. I did this by removing the hardware from the window frame (handles and locks), and then creating wooden battens that I screwed both into the window and down into the window frame, thus locking the window in place. I then used Green Glue Sealant (not to be confused with regular Green Glue which goes between layers of plasterboard), to seal up all the joins between window and frame, to get it as air tight as possible. The battens and sealant can be seen in the picture below:
After this, I used mortar to seal up the bigger gaps that existed around the top of the frame where I could see that light was getting in. Any smaller cracks or gaps were filled with sealant. I then painted the windows as I was going to cover it, so it would look nice from the inside.
I then did something which, in hindsight, was unnecessary and potentially actually counter-productive, but I will discuss it here so that you aren't tempted to do the same. I ordered a piece of acrylic sheeting that was 4mm thick and the same shape as my window, and basically added a 3rd glazing layer on the inside of the window, using sealant to make an air-tight seal. Given the very light nature of acrylic compared to glass, and the fact that I was going to then add a further window on the inner room anyway, I probably ended up with a triple leaf effect and would have done better to omit the acrylic! Anyway, here's a closeup of the acrylic sheet screwed in place on the right-hand side of the window frame:
After this, I also added some steel security bars in front of the window before moving onto the inner window, but I will discuss that in Windows Part 2.