Garden studio construction options

Hi, I wish to build a room at the bottom of our garden which can be used for recording and mixing; it also needs to incorporate a small office. The house itself is on a busy road, but the garden is approximately 55 metres long, and backs on to allotments. While it would be nice to occasionally record drums and electric guitars, I don't generally work loud, so from an isolation perspective, the key issue is keeping out environmental noise, particularly road noise. I would like the music room to be a single space (apart from the office), as I don't require separate control and live rooms. From the point of view of the internal acoustics, I would like it to have a pitched roof with a reasonably high ceiling, at least in the middle. If I keep the floor area under 30 metres squared, I won't need Building Control approval, and I can also avoid the need for planning permission if I keep the width to 4 metres or so. So, assuming the internal dimensions can be worked out appropriately, I'm looking at a building perhaps 4m wide, 7 or 8m long, and 2.5m high at the eaves rising to 3.5 or 4m in the centre. The question is what sort of structure to build. We will be using a builder to extend our house at the same time, so I could ask them to quote for laying a conventional concrete foundation and raising a brick or blockwork shell. I could then build a room within a room using the methods tried and tested here, with an internal division to make way for the office. If done properly I think this should be more than adequate from an isolation perspective, but it will stretch my budget, and quite possibly trash the garden. It would also probably require a fair bit of internal acoustic treatment. So I've been wondering whether alternative construction techniques could deliver something usable in a cheaper, greener and more garden-friendly fashion. One option, for instance, would be to build from straw bales on top of self-draining foundations, with a wooden floor of some sort. Are there any alternative techniques that are appropriate? Or does it always come down to the need for mass which can only really be fulfilled by concrete and similar materials?

Hi Rigby, and welcome the forum! It sounds like you already have a pretty good idea of what you need and how to go about getting the basic structure right, so it would be a good idea if you could put that all down on paper, or rather on "electrons", so to speak. The best way is with SketchUp, which is free software for designing pretty much anything. Regarding floor space: ITU, EBU, AES and other similar specs call for a minimum floor are of about 20 m2 to 40 m2 for a critical listening room, and maximum of 60 m2, so your 30m2 is a pretty good size. The specs also call for a room volume of less than 300 m3, with no minimum specified, but around 45 m3 is the generally considered to be good for a control room. With a height varying between 2.5 and 4m, you certainly have a decent size space for an optimal room.

I could ask them to quote for laying a conventional concrete foundation and raising a brick or blockwork shell. I could then build a room within a room using the methods tried and tested here, with an internal division to make way for the office.

That's the way I would go, if that were my studio. That's a known quantity all around, with no surprises.

It would also probably require a fair bit of internal acoustic treatment.

Treatment is mostly a function of room size, and also of the final finish materials that the walls are made of, not so much the structure behind it. The inner-leaf walls pretty much need to be hard, solid, rigid and massive.

One option, for instance, would be to build from straw bales on top of self-draining foundations, with a wooden floor of some sort.

Over the years there have been a couple of attempts by members here on the forum to build straw-bale studios. Unfortunately, none of them were ever finished, as far as I know. Or at least, if they were finished, their owners never posted the final results. That, in itself, is a good indicator of the "success" they achieved: One would assume that if the studio had turned out great, or even reasonably good, they would have been proud to post the results... So basically you'd be your own guinea pig if you choose to go that path. Firstly, there's very little history of success stories to look at, and see how people resolved issues along the way, and secondly, there's no acoustic data or research on how that might work out: Or at least, none that I'm aware of. There are also the issues of fire insurance (hard to get for highly combustible materials such as straw), structural integrity, long-term stability, etc. Having said all that, if you have the pioneering spirit in you, then there's no reason why you shouldn't be the first to do it! But if the only reason you were thinking of that is to save money, then maybe it would be better to look at less expensive building materials and methods that are known to work. For example, building the outer wall using stud framing with a couple of layers of OSB or plywood and some type of outer sheathing, such as vinyl or fiber-cement siding. That is probably quite a bit cheaper than brick or block, and is also a "tried and true" method.

Or does it always come down to the need for mass which can only really be fulfilled by concrete and similar materials?

You can build up the needed mass pretty much any way you want. Sound waves aren't fussy: all they react to is the final mass, without caring much if it is just a bunch of bricks, or several layers of wood, or drywall, or fiber-cement board, or lead sheeting, or MLV, or whatever. The important things is that there is enough total mass on each leaf, and a big enough gap between them, that the wall can isolate to the level that you need. So if you can do that with concrete, brick, wood, straw, recycled beer bottles, or titanium foil is up to you. As long as the mass and air gap is right, then the wall will isolate, and that's all that really matters. - Stuart -

Thanks Stuart! That makes a lot of sense. The more I think things over, unfortunately, the more problems I see with the romantic ideal of a studio built of green materials that has a low impact on the environment (and the garden). I did manage to unearth some measurements on the sound isolation levels that are achieved by a wall of plastered straw bales. If these are to be believed, they are effective at high and mid frequencies, and rather less so at low frequencies: http://www.thelaststrawblog.org/2009/07 ... acoustics/ I guess one could build a second leaf from some other material within the outer straw bale wall, but straw bales are already almost half a metre thick, so it would not be a very efficient use of space. On the other hand, exemption from UK building regulations is based on internal floor area rather than the total area of the building, so perhaps the building could simply be made bigger to compensate. I managed to track down someone here in the UK who had completed a small straw bale studio build, and he was kind enough to share his experiences with me. On the plus side, he very much liked the natural acoustic qualities of the straw bale walls, and had successfully built the studio himself with very little professional involvement. On the down side, he had difficulty with sound transmission through the floor, which I guess is likely to be an issue in any lightweight structure that rests above the ground. Thanks again Sam

I did manage to unearth some measurements on the sound isolation levels that are achieved by a wall of plastered straw bales.

Cool! That's actually very useful: I hadn't seen that before, and it's a neat addition to my "library". Thanks for posting the link!

I guess one could build a second leaf from some other material within the outer straw bale wall,

From what they say in the article, the straw-bale wall plastered on both sides already acts as an MSM system, and from the graph it certainly appears to be correct, so adding another leaf inside would create a 3-leaf system: therefore your total low-frequency isolation could end up even worse....

he had difficulty with sound transmission through the floor, which I guess is likely to be an issue in any lightweight structure that rests above the ground.

Right! If you can, the best bet for for your place is "concrete slab on grade". That's hard to beat. - Stuart -

Soundman2020 wrote:

From what they say in the article, the straw-bale wall plastered on both sides already acts as an MSM system, and from the graph it certainly appears to be correct, so adding another leaf inside would create a 3-leaf system: therefore your total low-frequency isolation could end up even worse....

Interesting, so the limiting factor on isolation would be the thickness and weight of the plaster rather than the bales themselves? I wonder if they compressed the straw bales. In a building with load-bearing straw walls, the weight of the roof rests directly on the straw bales and compresses them, but I guess they would still contain enough air to act as the spring in an MSM system. Perhaps a better option would be to leave the inside of the bale wall unplastered, then build a stud and plasterboard interior wall. Either way, I think you're right that conventional construction is a safer option!

Interesting, so the limiting factor on isolation would be the thickness and weight of the plaster rather than the bales themselves?

Right! It seems that the straw acts mostly as damping. They even comment in that article: "...loosely packed bales will perform better than very tightly packed bales. Extra thick (>35mm) earth plaster specifically improves low-frequency performance." That certainly sounds exactly like MSM performance to me.

Either way, I think you're right that conventional construction is a safer option!

:thu: It looks interesting, but I think I'll wait until many more people have tried it, and there's enough data out there to be sure of what you are getting in to! :) - Stuart -