The first thing I should say is that I’m currently up to the 60 or 70th iteration of this design (and it’s still changing). Of the three years I have been planning, most of my time and effort was put into learning to use a 3D design tool called ‘SketchUp’. I would urge you to do this too, even though it involves a fairly steep learning curve, because it lets you ‘build’ your studio digitally and iron out potential problems in advance. It also has tools for estimating quantities of materials and there is still a free download version available (as of March 2020, look for ‘Sketchup Make’ here:
I have been told that the free online version is not worth bothering with). All the illustrations on this blog were drawn in SketchUp.
The only really effective way to achieve good sound insulation on a budget is to build an airtight room inside another airtight room. The air trapped between the two layers of mass (or ‘leaves’ as studio builders refer to them) creates a cushion (or spring) which progressively inhibits the transmission of sound waves. Because of this you will most definitely need to install an HVAC system (heating, ventilation, air-conditioning). Some would-be project studio builders might consider this as an unnecessary expense; regarding it as a refinement or luxury.
It is (and I can’t stress this enough) absolutely essential!
Firstly, without it, you won’t be able to breath (or sing or play properly) and secondly, your studio will rapidly become damp, mouldy and infested by insects and vermin. Trust me, I have worked in a ‘studio’ with inadequate ventilation and the four day session left me and the other musicians in the band with chest infections that took weeks to shake off. So be sure to leave enough money in your budget for HVAC – a project like this simply can’t be done properly without it. I have found it’s also by far the most difficult part of studio design to understand, for a number of reasons. As we already know, we’re making an airtight room inside an airtight room. But because ventilation is needed, we have to knock at least two holes through the outer leaf and another two through the inner leaf for the intake of fresh air and exhaust of stale air. Luckily there is a lot that can be done to mitigate the loss of isolation this causes and yes (you’ve guessed it) it involves more thought, planning and sums! I’ll go into more detail about this later, but in short you need to build silencer or baffle boxes to control both airflow and isolation loss in the ventilation system.
The space I want to insulate is a double garage next to my house. It’s in the South East of England which has a temperate climate, is situated in a residential area, on a hill, and among woodland. The garage is at the edge of a leveled area cut into the side of the hill and the South-Eastern aspect of the building is built into the earth to a height of 131cm (4’4”). It sits on a 4” (10cm) concrete base and the internal dimensions are 4.85m x 4.98m (15’11” x 16’04”). There is a half-hipped roof which is 4.46m (14’7”) at the highest internal point. The walls consist of a single tier of brick and are buttressed on all sides with breeze block and brick columns (or piers), roughly at the centre point of each wall. There is a structural beam which runs from from the North-East wall to the South-West wall at a height of 2.24 M (7’4”). The North-West wall has an outward opening door and window and the South-West aspect has two large openings for the garage doors.
I have measured the ambient sound level in the area surrounding the garage at 35dB on a windless day and up to 68dB when the wind shakes nearby trees. Passing traffic sometimes elevates the level to 70dB and the occasional light aircraft passing nearby will give a reading of 55dB.
Typically, the loudest instruments I am going to record and play are drums and electric bass guitar. I have measured the drum kit peaking at up to 116 dB. Local noise regulations are non-specific when it comes to defining an actual level at which sound becomes a nuisance, but as we have neighbours at both sides (6m and 12 metres) I am aiming for a sound transmission reduction of 55dB or greater and while this is ambitious, transmission loss calculations suggest that it’s possible (although it’s approaching the limit of what is achievable for a home build studio). I’m going to undertake as much of the work as I practically can (although I will not attempt any electrical work, fitting the air conditioner or acoustic windows or doors – I would rather pay experienced professionals to do those parts of the job).
I plan to build a single room within a room consisting of two leaves (where possible). The outer leaf will consist of the existing single tier, solid brick wall which will be sealed, up to a height of 221cm, then a combination of 18mm OSB and 12.5mm cement fibre board to meet a ceiling of similar construction, supported by the existing ceiling chords.
It’s important to remember that sound insulation is dependent on something called ‘mass law’. Broadly speaking, the more mass you add, the more you raise the level of sound insulation that can be achieved ( it also depends on how the mass is arranged, but we’ll get to that later). Be sure to ask a qualified structural engineer if your existing or planned building will support the extra mass that you will be adding. Again, this is not something to be guessed at! I commissioned a report from a structural engineer who advised that with the correct reinforcement to the chords and lowest beam, this would be both possible and safe. He suggested forming a ‘flitch’ beam (i.e. adding a 10mm steel plate with two staggered rows of bolt holes, sandwiched between another identical beam and held together with M12 bolts).
The existing ceiling chords also need be bolted to the joists with M12 bolts.
The South-West aspect of the building has two large “up and over” garage doors which will need immobilising, sealing and damping. Then the gaps will be framed with timber, insulated with rock wool and an inner wall of one layer of 12.5mm cement board and one layer of 18mm OSB with green ‘glue’ in between.
The inner leaf structure will be a conventional stud frame supporting timber framed modules which will be capped with one layer of 12.5mm cement board and one layer of 18mm OSB with green ‘glue’ in between. The remaining space within the frame of each module will be filled with rockwool. This will be anchor bolted to the concrete floor with an air gap of at least 20 centimetres between the leaves, which will be loosely filled with rock wool.
The inner leaf ceiling frame will need to be reinforced on either side of the main beam with two steel 152x89x16mm universal beams in order to support the inner ceiling in a single span. These will need to be pre-drilled in order to attach the connecting timbers.
The inner leaf ceiling will be built using the same ‘inside – out” design as the walls. The ‘backbone’ will support timber framed modules which will be capped with one layer of 12.5mm cement board and one layer of 18mm OSB with green ‘glue’ in between.
The existing window will be replaced on the outer leaf with a fixed one, glazed with 16mm laminated glass and one on the inner leaf using 12mm glass, conforming as closely as possible to the design in chapter 5 of the second edition of Rod Gervais’s book. The existing door will be removed and two, triple sealed doors (similar to Rod’s “super door”) will be installed with closers.
Which brings me to HVAC – but I think that needs a post all on it’s own.
© John Steel 2020