Garage Conversion Part 4: Soundproofing

So with the first electrical fix done, and the old garage door removed and replaced with nice swinger-outers, it was time to move on to the most time consuming and frustrating part of the conversion: sound proofing the ceiling. It already had a single layer of plasterboard screwed into joists, but there was one part that would cause a problem where part of the hearth from upstairs was exposed, straddling the side wall….

exposed chimney breast
Note the waste pipes coming in from the bathroom upstairs. These would mostly be covered up by the solution I chose.

I did some research in soundproofing solutions and sent a bunch of email enquiries off. I got a few back, but in the end I went with a solution offered by John Hancock from Oscar Acoustics. John was very helpful and answered any questions I had quickly and concisely, which gave me confidence I could pull this off. I went with their Iso-Mount Type 2 system which would allow me to hang a suspended ceiling from the existing one. I wouldn’t need to remove the existing plasterboard. This solution would lower the ceiling by 150mm, but headroom in the garage was not an issue as the existing ceiling was over 3m high. It turns out this was to my benefit as the extra height allowed me to improve the soundproofing by using thicker insulation whilst still keeping a 50mm void air-gap.

It works like this: –

  1. Make a framework of Iso-Mounts at even intervals across the existing ceiling
  2. Between all the Iso-Mounts, fit 100mm thick acoustic insulation directly to the existing ceiling
  3. Fit metal GL1 gypliner channels onto the Iso-Mounts
  4. Fit 2 layers of plasterboard onto the metal channels, covering up the insulation/air gap

The idea is that the whole “new ceiling” is suspended below the existing one. The Iso-Mounts connect to the GL1 channels via a rubber block so very little sound is transferred up through each Iso-Mount. Around the edges of the ceiling some acoustic foam is squeezed in between the plasterboard and the side walls, further giving it some acoustic separation. This is then finished off with some acoustic sealant around the edges.

Here’s a single Iso-Mount made up: –

Oscar Acoustics Iso-Mount 2

The top screw goes through the existing plasterboard into the joist above. At the bottom you can see the rubber block that a metal saddle sits on (the saddle is what the GL1 channels clip on to), so it is acoustically insulated from the rest of the mount. Ignore the small wooden wedge, that’s just to keep the rubber/saddle combo from wobbling about when you’re trying to fit the GL1 channels. Here’s a diagram to explain it better: –

Oscar Acoustics Iso-Mount 2 Diagram

Time to make a start then. I enlisted the help of my daughter to help make up the hangers that I’d need to screw into the existing joists. I think I ended up using about 60 Iso-Mounts in total…

enslisting help to make the hangers
“here’s a heap of bits, off you go…”

Screwing 60+ of these into the existing joists took ages, involved arm and neck ache, and lots of cursing…

My friend Ed came to help again, and we fitted all the M8 studding and the brackets that the rubber blocks will sit on. We had to get this as level as we could so that the new suspended ceiling would be perfectly smooth and level when the plasterboard went up. To help we used an auto-levelling laser level. Assembling these was very time consuming also, but we got there in the end…

studding and brackets
You can see the self-levelling laser level in the corner. This gave us a perfect vidual guide to getting every iso-mount perfectly level.
studding and brackets

And here’s how we solved the issue of the hearth… we put a CLS batten up, and screwed the Iso-Mounts into that, with shorter M8 studding so it levelled up fine…

shorter studding for iso-mounts

With the Iso-Mounts all fitted, we started installing the insulation. John recommended we use 100mm RW3 Rockwool, so that’s what we used. It came in slabs rather than a roll, and it was relatively easy to cut. We stuck it to the ceiling with some self-adhesive stick pins. These things look insanely scary, but we took very good care not to impale our skulls into them…

self-adhesive stick-pins
First thing I thought when I saw these was “ok… need to be careful with those then!”

Starting on the left side of the garage, the first lot went up pretty easily…

first lot of rockwool

With some offcuts, I filled the fiddly bits over by the hearth area…

hearth area rockwool

And it wasn’t long before it was all done… I enlisted the help of another friend Nick to help with this, as it’s far easier with 2 people due to the size of the rockwool slabs. We were wearing disposable overalls and we must have sweated litres between us before it was all done… I really hated doing this part.

rockwool done

With the insulation up, it was time to put the GL1 channels into place. These would hang on the metal saddles that sit on the rubber blocks on each Iso-Mount. I ordered 3m lengths as that’s the longest I could find. Typically, it turned out the room is slightly wider than 3m so I had to also use some GL3 connectors to ensure some of the lengths were long enough. In hindsight, I’d have put the Iso-Mounts around the edges of the room slightly in a bit so the total length needed wouldn’t have exceeded 3m. Lesson learned. The channels were relatively easy to clip on using the little wooden wedges they sent with the mounts to keep the saddles sitting on the rubber blocks steady. The plasterboard will screw into the channels, leaving a 50mm air gap/void between the plasterboard and the rockwool insulation…

gl1 gypliner channels

Getting there now! Time to put the plasterboard up. This was like painting. Normally you have to do 2 coats of paint… well, we had to put 2 layers of 12.5mm plasterboard up. First, I needed to prepare the walls around the edges so that the adhesive-backed acoustic foam would stick. I watered down some PVA and brushed it on all around the edges where the plasterboard would butt up to. This worked a treat and the acoustic foam stuck on fine.

I hired a plasterboard lifter from Brandon Hire Station, and we couldn’t have done without it. It made the job bearable! You can just about see the foam around the edges, and the darker walls giving away the PVA coating…

sound proofing the ceiling

We finally got it all up, both layers (the 2nd layer was waaay easier to screw in than the first). We left 3 “hatches” so that the light fittings could be wired up. We put those panels up last…

plasterboard all up

This is how it ended up covering the waste pipes coming in from the bathroom upstairs. Not bad… when those are painted you’ll hardly notice them! 😉 You can also see where the electric cables will come down from the ceiling inside the stud wall…

covers the pipes up

And finally, the hatches were put back on and the LED battens were mounted on the ceiling! Apart from running the acoustic sealant around the edges, and then plastering, job done!

ceiling done

So after all this… how good was it? Was it worth all the effort?

Well… beforehand, you could clearly hear normal conversation and footsteps in the room above. My kids could also easily hear all my swearing from up there too. When my little girl ran and jumped about up there it felt like the ceiling was going to cave in.

Afterwards, we conducted a test with my DeWalt router. That thing is LOUD. On full speed, you could hardly hear it upstairs. Result. 😀 I’m confident now that when the kids are asleep I can run power tools to my heart’s content and it won’t wake anyone up. Definitely worth all the effort.

Well it was time for a well earned rest after all that work. But not for long. Now the ceiling is sorted, the stud wall can be put up. See you in Part 5!

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