brick - insulation - brick. What next?

Hi fellas, I have an old service station that I'm converting to a studio .lovely place. semi-rural setting. 4.2 metre high ceilings. fantastic for drums etc. Of course, being a service station its close to a highway (about 7m away) - and this one has 4 lanes of quite a bit of heavy truck traffic measuring peaks at about 80db. I started with the live room - which suffered from 2 old roller doors 3m x 3m wide and leaking so much air that it was indistinguishable from being outside. hard even to talk... I removed the roller doors and bricked them up with acoustic maxi bricks to be flush with the external 20cm thick ferrocrete wall ( an old school construction style - a sandwich of thick render, concrete, timber and steel frame). I then rendered the external brick wall with about 30mm of render. I then built an internal brick wall to the ceiling that joins to the side walls (not the wall facing the highway). I left a 100mm cavity and filled with rockwool. This is quite a big wall. 7m long and 4.2 high with a brick pier 1m wide filled with concrete in the middle to keep it up. the wall depth now is about 50cm out to 70 cm at the pier. It has about 8 tons of bricks in it, plus another couple of tons of mortar and render.. Thankfully its done a great job on the road. I figured I had a big problem so I went with the most solid construction style I could use and went with the highest STC ratings I could find. I haven't pulled out my mics to test ( too much dust around ) but I'd estimate that even without having done my ceiling yet that I've knocked out between 50-60db. Maybe more. Normal speech now drowns out the loudest trucks. Ceiling is next. I'm hoping it will get to be near silent in there. I'm still a bit concerned that it won't be enough. Thing is , when I've finished my ceiling I'd like to do a little more to the big front wall (as well as build a cavity/drywall inside the other external ferrocrete walls. My plan is to use the cavity between the internal pier and the brick returns ( about 200mm) to stuff with insulation and put up a stud frame with 2 layers of drywall. Then it would all be flush. (see attachment) This is most definitely a triple leaf, I fear. I've read every post I can on it but it seems to be something that depends on the amount of mass and the width of the cavity. I'm wondering if the sheer mass of my wall and the doubling of the size of the internal cavity would do the trick and make the resonance/bass loss less severe. What do you think? If the addition of a new cavity is a problem what would be the best solution to give my wall just a bit more stopping power? Just add more mass to the wall? Is there an advantage in rendering the internal wall as well ? Perhaps doing it in reverse- with drywall attached straight to the internal brick wall and then hang absorbers on it. Any benefit in using resilient channel here ? I fear with such a massive wall that I'm in a position of diminishing returns but I'd like to achieve something that will a) kill anything that may still be getting through. b) look better than the internal bricks c) tame a bit of internal inflections. any suggestions?

My plan is to use the cavity between the internal pier and the brick returns ( about 200mm) to stuff with insulation and put up a stud frame with 2 layers of drywall. Then it would all be flush.

Why - you already have a solid 2 leaf system - just fix the roof.

Thanks John. I guess I was heading for a bit of overkill. I will do my roof next and then have another listen.

This is most definitely a triple leaf, I fear. I've read every post I can on it but it seems to be something that depends on the amount of mass and the width of the cavity.

Yep, it would be a triple leaf for sure, but in your case triple-leaf isn't something I'd be worried about: You have so much mass in that wall that it is probably a moot point, and adding a few layers of drywall to it is not going to do anything much to change that. The resonant frequency of that wall is already way down low enough (about 6 Hz., theoretically) that a few sheets of drywall isn't going to trash it. (You'd have to add something like 40 (yes, forty!) layers of drywall just to equal the mass of one leaf of that existing wall.) So I agree totally with John: Deal with your roof, which is doubtless your weak point right now, followed by doors and windows. Then if you still need more isolation afterwards, just build an entire separate de-coupled inner leaf using a couple of layers of drywall, and that should take care of pretty much all noises, short of an atomic bomb right outside your front door! - Stuart -

Soundman2020 wrote:

(You'd have to add something like 40 (yes, forty!) layers of drywall just to equal the mass of one leaf of that existing wall.)

Thanks Soundman. That makes me feel happy about not having to have gone in the drywall direction! Yes - the roof is my weak spot. Its old style corrugated iron over tarred timbers ( like a clinker-built ship) and then a cavity with dreaded asbestos sheeting. No doubt I am going to find some evidence of termite and rain damage and may have to replace some of the rafters. And properly seal it. The corrugated iron is still in good shape. Could probably do with a paint of that rust proof stuff but not gain to get up there until I've really inspected the state of the wood. Most of all I haven't been looking forward to dealing with the asbestos. Its the bad stuff from the 50s. Was thinking of getting some of those very sci-fi looking whole body suits and mask etc and lining the whole room in black plastic, wetting each sheet and then pulling them out of there, put in some insulation sarking and finish off with drywall. Thats the plan anyway...

I'm thinking that if I was in your situation, I'd probably bite the bullet and pay a qualified contractor to take off the old roof completely, asbestos and all, and dispose of it properly: Then I'd build the new roof properly, with plenty of mass, as I'd be trying to get close to the surface mass of the walls, or at least in the ball park (pretty hard to match it!). I don't think I'd want the hassle or risk of trying to rip out the old roof myself, and even if I did, then I'd still have to pay a qualified contractor to come take away the rubble and dispose of it correctly. You might even find that there are legal issues in trying to do it yourself... have you looked into that? Are you even allowed to do that, under Australian law? - Stuart -

Sorry Stuart but that is total over kill - the studio is in the country - his only problem is rain noise. You can easily line asbestos with drywall and it's problem goes away - removing it is unbelievably expensive!! Forest can you offer some pictures of the building especially the ceiling as it stands?

John Sayers wrote:

Sorry Stuart but that is total over kill - the studio is in the country - his only problem is rain noise. You can easily line asbestos with drywall and it's problem goes away - removing it is unbelievably expensive!!

I know that, John, but he already said that he plans to remove it! My point was that if you are going to remove it, then perhaps doing it yourself isn't the best way of going about it, and possibly not even legal. He did say "Most of all I haven't been looking forward to dealing with the asbestos. Its the bad stuff from the 50s. Was thinking of getting some of those very sci-fi looking whole body suits and mask etc and lining the whole room in black plastic, wetting each sheet and then pulling them out of there, put in some insulation sarking and finish off with drywall. Thats the plan anyway..." If that's the case, and it does need removing, then firstly is it even legal to remove asbestos yourself in Australia? And secondly, even if it is legal, is DIY asbestos removal really a good way to do it, or would it be better to call in the professionals to do it? That's my point. I'm just assuming that he is right, and the asbestos does need to go. - Stuart -

I'd still like to see some pictures of the ceiling structure.

Thanks for the comments and suggestions and I really appreciate your help. Yes you are both right. It is rural but I do have road-trains passing not far from the studio, as well as rain.The roof is a problem - the passing trucks are making that roof cavity resonate slightly and the asbestos is doing nothing. I've attached a couple of pics. One shows 2m x 1m squares of asbestos held in place with cross-braces of asbestos. A mammoth plastered steel truss bisects the main live room ceiling and supports the 3m joists. I'm guessing that this was strong enough to suspend a car from - as my live room is the old workshop area of the garage. The pit has been filled with sand and concreted over. One asbestos sheet has a hole in it and thats how I can see how the roof is fixed to tarred rafters with a 20cm cavity. Asbestos is very thin and, from much experience, does almost nothing to stop sound. And its kinda a bad vibe that I'd rather not have hanging around. Its been suggested to possibly seal it in with another sheet - but its brittle stuff and I think its better to simply get rid of it now. Drilling, nailing through etc is bound to create a bunch of dust and breakages anyway. Right now its not sealed very well to the wall and is vibrating when music is played. In Australia we are aloud to self-remove as long as you remove and dump responsibly. John is right. The cost is prohibitive to get the asbestos professionals in. It would cost a huge part of my entire build budget to go that way. Its a big building with around 200 square metres of ceiling. It'll be many thousands. I can't get a firm quote but I figure going DIY and just being careful. Empty the place, black plastic it, wear a suit and mask and keep everything wet. I will have to do it myself if I'm gonna keep the budget down and be able to pay for the good materials. Plus - I'm having a great time building and learning this stuff. Yes soundman is right about needing to replace the roof. Due to the ages of the building - the poor state of the flashing and possibly some termite damage I will have to replace the roof, the flashing, some of the gutters, and remove some dodgy repairs of the last owners. Once again I'd really rather do it myself and see the whole budget go to materials. You can see from the outside photo of the front corner just how flat the roof is. The overhanging section is the cavity. The plan is do the asbestos first, coming at it from below, so that I can judge the state of the timber in the roof before getting up there. Its a flat roof so not extremely complicated to work on. I was considering putting up thick batons screwed into the frame around the top of the roof and fixing the new roof to them. That will mean that I can get a better seal and have more confidence in what I'm nailing the sheets onto. Soundman - I'm interested in what you would recommend to add mass to the roof. I don't know much about the other options but I was considering possibly doubling up the corrugated iron - making it 2 sheets thick- one on top of the other. Or would you suggest another roofing material? The existing iron is in ok shape and seems to be thicker than what they sell these days. Under the corrugated iron is a solid wooden roof of jarrah boards (jarrah is a heavy local hardwood) which have been tarred over to be air/watertight. This is all connected to the central steel truss. I figure its not a bad starting point, almost as good as a wall in itself, and I'll make sure its all sealed. Perhaps I could lay another layer of something inbetween this tarred roof and the corrugated iron? I'd pack the 20cm ceiling cavity with insulation (to protect from the summer as much as the road) then at least 16mm drywall as the new ceiling. The book from the local drywall shop (gyprock) here lays out a system that can take as many as 3 layers of 16mm. Before doing this I was thinking of continuing my new internal brick wall all the way to the roof so as to stop more direct sound from the road getting through to the cavity in the first place. Please let me know if you think there is a better way I could tackle any of this. Cheers Forrest

Forest - I'd replace the iron on the roof and I'd make sure it sits on foil backed insulation to reduce the rain noise. I would not consider the iron as a leaf as it will have airflow under the eaves. Then I'd remove the fibro joining pieces and plaster straight over the fibro with a double layer of 16mm Gyprock Fyrchek. That with the brick becomes your outer leaf. I'd paint the brick internally to seal it. Then build a separate structure within that outer shell for your studio.

Thanks for the advice John and appreciate you taking a look at this for me. Cheers