Garden Drum Room - Query on external walls

[Flapper]

Hello,

I'm a drummer who is looking into building (or having built) a discrete drum room in my garden. For the interior space I am hoping to get H2.2m x W2.51m x L3.06 (this follows one of Sepmeyer's ratios as set out in Rod Gervais's book). Thus externally I think it will be approximately H2.5m (this is as high as you can go in the UK without getting planning permission) x W3m x L3.5m - possibly smaller if we can build it with suitable isolation from the interior structure.

I have a builder coming to look at the job tomorrow. He has built a drum room before, but I am not sure if he is completely up to speed with the current thinking on sound isolation. I've been reading Rod's book and the posts in this very helpful forum.

I am intending to build using the 'two leaf' system - a room within a room, and will finish the interior with a 'Green Glue Sandwich' between two lots of 15mm plasterboard.

I would like to get as much sound proofing as possible given the size constraints set out above. Depending where we site the room, the neighbours will be approximately 10m away. I am more of a funk/jazz drummer but occasionally play rock so 100db is my guess as sound level. I would like to play in the daytime without annoying the neighbours. Possibly some early evening playing. The dimensions are too small for optimum recording, but I've had reasonable results recording results in a 2.3 x 1.8 x 2.4 space by killing the room sound completely. I'll probably do the same with this room.

My questions regard the treatment of the first leaf which would be built of dense concrete blocks (100mm thick). See the figure below.

Optimum.JPG

Q1. - As far as I can see this is a two leaf build. How should I treat the interior side of the concrete block wall (see A)? Does anything need to go on here (rockwool?, plasterboard?, mass loaded vinyl?)
Q2. - I guess the cavity marked A should be as large as possible (while maintaining the footprint within the approximate measurements above?

I will consult with the builder but there is a possibility we could re-purpose one of the already standing garden walls. See the figure below.

Existing Wall.JPG

Q3. - Would this be a problematic 'three leaf' situation, as the current garden wall already has two leafs with a small cavity tied with wall ties?
Q4. - As above, if we were to repurpose this wall, how should I line it?

Answers to these questions will help me to consult with the builder tomorrow. Many thanks for your help.

[Soundman2020]

Hi there flapper, and Welcome!

For the interior space I am hoping to get H2.2m x W2.51m x L3.06 (this follows one of Sepmeyer's ratios as set out in Rod Gervais's book).

This is a drum room, not a control room, so ratios are irrelevant. They only make sense for control rooms. For a drum room, just make sure that not two dimensions are the same, or a multiple of each other, nor within 5% of being the same or a multiple.

H2.5m (this is as high as you can go in the UK without getting planning permission)

Well, yes and no. Under "Permitted development" rules, you are limited to 2.5m max IF your building will be closer than 2m to the property line. If your building is further away than 2m on all sides, then you can go up to as much as 3.5m for a gable roof, as long as you keep the eaves to no more than 2.5m.

On the other hand, there's no restrictions on how far you can dig DOWN, so in reality you can have your ceiling as high as you want, as long as the EXTERNAL height remains with specs, relative toe ORIGINAL grade!

I am intending to build using the 'two leaf' system - a room within a room, and will finish the interior with a 'Green Glue Sandwich' between two lots

of 15mm plasterboard.

I am more of a funk/jazz drummer but occasionally play rock so 100db is my guess as sound level.

You play VERY quietly then! Typical rock drummers hit 110 dbC without breaking a sweat, can do 115 dBC if they try a bit harder, and can even head for 120 dB if they really go crazy...

Q1. - As far as I can see this is a two leaf build.

Q1. - As far as I can see this is a two leaf build. How should I treat the interior side of the concrete block wall (see A)? Does anything need to go on here (rockwool?, plasterboard?, mass loaded vinyl?)
Q2. - I guess the cavity marked A should be as large as possible (while maintaining the footprint within the approximate measurements above?

The entire "cavity A" should be completely filled with suitable insulation: aprox. 30 kg/m3 for fiberglass, 50 kg/m3 for mineral wool. And the depth of "cavity A" should be calculated! It's a tuned system. You tune it by varying the mass on both leaves, and by varying the depth of the cavity. You tune it to get the resonant frequency at least an octave below the lowest frequency that you need to isolate. Having a cavity larger than you need is fine, as it forces the frequency down even lower, but it wastes space. So only make it as big as you need it to be.

Q3. - Would this be a problematic 'three leaf' situation, as the current garden wall already has two leafs with a small cavity tied with wall ties?

Shouldn't be a problem. Yes it is sort of two-leaf, but the leaves are firmly tied together, and the mass of both is high.

Q4. - As above, if we were to repurpose this wall, how should I line it?

Same: cavity filled with suitable insulation.

- Stuart -

[Flapper]

This is a drum room, not a control room, so ratios are irrelevant. They only make sense for control rooms. For a drum room, just make sure that not two dimensions are the same, or a multiple of each other, nor within 5% of being the same or a multiple.

Ah! Ok. So avoid anything that's cuboid, or near cuboid. Got it (I think). [EDIT - actually avoid any square or nearly square relationships]

Under "Permitted development" rules, you are limited to 2.5m max IF your building will be closer than 2m to the property line. If your building is further away than 2m on all sides, then you can go up to as much as 3.5m for a gable roof, as long as you keep the eaves to no more than 2.5m.

Right, interesting. It looks like we might use the side of the existing house as one of the walls so we would still be limited to 2.5

On the other hand, there's no restrictions on how far you can dig DOWN, so in reality you can have your ceiling as high as you want, as long as the EXTERNAL height remains with specs, relative toe ORIGINAL grade!

Tempting, but my mate did this and had trouble keeping out moisture so I think I'll stay ground level.

You play VERY quietly then! Typical rock drummers hit 110 dbC without breaking a sweat, can do 115 dBC if they try a bit harder, and can even head for 120 dB if they really go crazy...

Right! I'll assume 115db.

The entire "cavity A" should be completely filled with suitable insulation: aprox. 30 kg/m3 for fiberglass, 50 kg/m3 for mineral wool. And the depth of "cavity A" should be calculated! It's a tuned system. You tune it by varying the mass on both leaves, and by varying the depth of the cavity. You tune it to get the resonant frequency at least an octave below the lowest frequency that you need to isolate. Having a cavity larger than you need is fine, as it forces the frequency down even lower, but it wastes space. So only make it as big as you need it to be.

Very interesting, thanks. Is there a calculator for this that you can point me towards for the void?

Q3. - Would this be a problematic 'three leaf' situation, as the current garden wall already has two leafs with a small cavity tied with wall ties?Shouldn't be a problem. Yes it is sort of two-leaf, but the leaves are firmly tied together, and the mass of both is high.

Good to know - we're probably going to build inside this wall now though.

I've spoken to the builder (A) - as he showed up this morning! He doesn't do brick building so I'll have to get a different contractor (B) in to lay the slab and to (probably) build three dense concrete block walls attached to our house (as the fourth wall), with a flat roof (slight rake 2.5m down to 2.4m). Builder A will then come in and build the room within a room. He was talking about using resilient bars to attach the plasterboard to the timber stud wall. From what I've read that's not necessary if the inner stud wall is truly isolated from the external concrete walls. He couldn't grasp this!

Builder A is set on using one of our house walls to attach the internal timber frame onto - in this case I guess resilient channel would be needed as we wouldn't have a true double frame build. Similarly he seemed set on using them to decouple the ceiling of the internal box from the roof.

I guess I am compromising from a true double frame build if aspects of it are attached - albeit with resilient channel - to the existing house wall and the new roof.

Many thanks for your response above. It's been helpful already.