Blockhouse build diary

I am just starting on my practice studio build, details below and have some initial questions before I start the design & planning process. I still have work to do but wanted some initial advice. I am based in Melbourne, living in the suburbs about 15km from the CBD. I have an existing concrete block shed in the back garden that I use to practice electronic drums on headphones mainly, however I want to soundproof the shed to allow the band to practice and also for me to practice acoustic drums. I don't expect to play all hours as I have a day job and a family. Existing building Its a 6mx4m shed located in the back yard, on the boundary, but not close to any neighbours houses. The shed is constructed from series 100 concrete blocks 90x190x390 on a concrete slab. The walls are double block walls with approx 50mm gap between each of the walls, so total thickness of the wall is around 240. The concrete blocks are hollow they have not been filled with anything. The shed has three windows, aluminium sliding ones and a very lightweight door that has a "dog" door in it. Current situation Current situation is that when I play in the shed without headphones or if the guitarist comes round for a jam the noise is quite loud outside so basically there is not much sound proofing going on at the moment. No complaints from neighbours as this has typically been on Sat afternoon and only with the electronic kit but its still quite loud The shed is far from sealed, roof lining is very basic, looks like a compressed cardboard and has plenty of gaps. The shed is mighty cold in winter so there are lots of gaps under the door, in the ceiling and through the windows. Windows are aluminium sliding windows, glass is very thin. There is no plasterboard or any lining at all on the inside walls of the shed so is a giant echo chamber :-). I do have carpet with underlay on the floor. Aims 1. Sound proof, as best I can, the entire room so that band practice can occur (electronic drum kit, bass, guitar, electric piano and vocals). Playing a blues rock, not too heavy. All our recording is done electronically through a presonus desk and associated software. 2. Second aim to to construct a small room within the room for me to practice on my acoustic drums. Not used for the band as its easier to record off the electronic kit, however as a drummer I like to practice on the acoustic kit as well. 3. I will do all the building/construction myself, am competent at woodwork & general construction 4. My budget is limited to around $3000 Oz. Initial Questions I read that concrete blocks act as a 2 leaf system so given its double brick with an air gap I may have a 5 leaf system to start with. I don't fully understand that so wanted to confirm that was true. I'd like to know what impact the double brick wall will have on soundproofing and do I have a good base to to start my project? See image below for the details of the current room.

After some further research on this site and others I think that my shed presents a real problem for me in terms of sound absorption in the walls. My double besser brick walls are a 4 leaf system and from what I have read 3 leaf or more should be avoided and won't provide the best STC. I could create the preferred 2 leaf system if I get the besser blocks filled with either sand or concrete, so I'll need to investigate the costs of doing that, however I'm concerned that the slab may not be designed to take that extra weight, not to mention the costs of getting someone in to pump either concrete or sand into all of the blocks. Needs investigating. Given its the low frequencies for my drums I need to think about and getting an STC around 65, I'm not sure if I can achieve that by adding multiple layers of plaster board to the internal leaf of my 4 leaf wall. Is my best option to build a room within the room that has the 2 leaf wall and put all my energies into getting the STC for that 2 leaf system the best it can be?

"I read that concrete blocks act as a 2 leaf system so given its double brick with an air gap I may have a 5 leaf system to start with. I don't fully understand that so wanted to confirm that was true." No sir it does not. Looking down on a block you can see that it is connected at all corners...there is no break what so ever in this path, so it is only , in a wall assembly, one leaf. Now , why you have a double wythe hollow block wall is beyond me, but you can be assured that the "air space" between the two layers is not an air space since the mortar it took to assembly these walls has coupled the two together...so again, not a four five of even a three, but a coupled assembly.

Thanks Brien, that is easier to understand based on your description of the blocks. I didn't build the shed it was in the garden when we bought the house so agree not sure why they built it with double blocks and the thinner ones at that. I have been doing research before these posts and plenty more since. My primary goal is to have some where for me to practice drums, perhaps thinking I can do the whole room for drums and have the space for whole band is a bit optimistic, not too mention the costs. I think my best next step is to create some plans of what I think would work as a drum room and give me a good STC in the 60's as well as good low end performance for my bass drum and then submit them for review. Am trying to learn sketchup. One question though. Based on the theory of adding more mass would it be sensible to fix two layers of fyreheck directly on the internal concrete block wall via screws & plugs in the wall? or would that only be of benefit using green glue? Was worried that adding plasterboard directly using glue creates an air gap albeit a small one and thats a bad thing for low freq, however thought that this would be a good way to seal up this first internal layer.? Was wondering how you balance the sealing versus not adding extra layers I am beginning to understand how hard this all is :-), there are so many different variables that seem to act against each other.

Not an expert and Im sure Brein or one of the other mods will get back to you but if the 2 skins are connected then maybe sealing the inside skin by rendering or paint and build another skin with plasterboard on some studs might be the way to go, :roll: Did I just say build a third skin :shock:

"Based on the theory of adding more mass would it be sensible to fix two layers of fyreheck directly on the internal concrete block wall via screws & plugs in the wall? or would that only be of benefit using green glue?" Mass law, for every doubling of mass you get 4-5 dB of isolation. Now, if you have a concrete block and add sheetrock of any nature, the mass doesn't add up, so it is not a good idea to add the mass directly to the sheetrock. I think Roguejackal was suggesting to paint or mortar the interior side of the block, and this is a good idea, since the blocks are porous and tend to loose sound in the high frequencies.

Just to confirm what Brien said, with more detail that might help you understand the issue: drywall weighs around 800 kg/m3. Concrete weighs around 3,600 kg/m3. So however much concrete is in those blocks, you'd need to add drywall about five times thicker to double the mass, and that would increase your isolation by a grand total of 6 dB max, and more like 4 to 5 in reality. So let's say that the total concrete in those bricks works out to be the equivalent of 2 inches thick, if you added SIXTEEN layers of 5/8 drywall to the surface of those, bricks, then you'd roughly double the mass, and gain about 4 dB of extra isolation... As you can see, mass law is not your friend. It's not very encouraging. On the other hand, if you put just two sheets of that same drywall on a stud frame an inch or so away from those bricks, you could increase the isolation by 10 or 20 dB, or maybe even more... MSM RULES! :!: :D - Stuart -

wow thats great, thanks for the advice that gives me a solid basis for my plans. I will paint the internal concrete block walls, can happily do a couple of coats and then add a layer of rockwool. Then I'll build an internal frame can separate that from the wall by up to 200mm and then add more rockwool and 2 layers of 16mm drywall (fyrecheck plasterboard to build the internal room. That should give me a good MSM and if I'm careful with the planning, construction, and caulking I will hopefully be able to use the drums. Plans first, I'll get cracking on those and post them back to the forum and see whether I have understood correctly.

That should give me a good MSM and if I'm careful with the planning, construction, and caulking I will hopefully be able to use the drums.

Well, doing one wall alone will not isolate your drums! Isolating a room is like building an aquarium: you have to put glass on all sides to keep the water in. You have to isolate all sides of your room to keep the sound in. Doing only one wall will work about as well as putting glass in only one side of an aquarium frame... :) - Stuart -

"drywall weighs around 800 kg/m3. Concrete weighs around 3,600 kg/m3. So however much concrete is in those blocks, you'd need to add drywall about five times thicker to double the mass, and that would increase your isolation by a grand total of 6 dB max, and more like 4 to 5 in reality." That is exactly what I meant, without all the data...:) I am such a slacker...

Thanks again for the advice. I am making slow progress with sketch up and have uploaded a sketchup file and an image of the plan as well. I have keep the model quite basic at this stage. I have taken the simplest approach where I build a room with a single wall (multiple layers of 16mm plasterboard) inside the shed which will be isolated from the external shed walls as will the roof of the internal room. The air gap between the external besser block wall and the internal walls will be around 300mm (max) and from that I can get a drum room of 3.1 x 2.3m. Ceiling height will be 2.1m inside the drum room. I am a shorty almost 5ft 9 so plenty of room for me. I am not a big hitter on the drums, play in a rock/blues band so definitely not at the thrash metal end of the scale. Would like some feedback as to whether I am on the right track with the internal wall and room and although I have created a MSM barrier not sure if this will suffice. Assuming I generated 90-100db then I'd like to achieve 60db reduction so as not to annoy my wife and neighbours. My house is about 5m away from the shed, our bedroom is about 7-8m away, neighbours houses also about 8-9m away. Would like to be able to play in the evening but nothing past 9pm. I have sound mutes for the kit but playing on those is not the best, I also have the electronic kit as well for late night practice. Will a single internal wall achieve what I want?

You have not mentioned anything about making a ceiling, you are aware for this to work, you have to have a ceiling on the new framed walls of the same mass that is decoupled (like your interior walls) from the exterior? Also, why are you being limited to such a small portion of the shed...your 8X9X6 is going to be small and loud as heck...

Hi Brien, I had planned to do a ceiling as well of the same construction, I just haven't figured out how to add that in on sketch up. The ceiling will be decoupled from the exterior and will be the same mass as the interior walls so I will end up with an internal room that is decoupled from the walls and ceiling of the shed. Hoping that I only need the single internal wall as that will give me more space. Good question re why I am only doing half the shed, my original thought was that I should try something small first, similar to the room I had drum lessons in, but yea is was pretty loud in that small room, was also trying to save a bit of money too. I also have to use the shed to store some furniture and stuff, but that could always be in one end of the drum room. Can always price up doing the full room once I get a design that looks like it will do what I need.