Queries for new music room design and construction overview

[Ash]

Hi all, first time poster here!

My partner and I are so glad to have found this site, and the absolute treasure trove of information it contains! We’d love to run our plans past you, and would massively appreciate your thoughts/suggestions/advice, as we’ve never done anything like this before but are enthusiastic and always want to learn. We’ve tried to be as informative and concise as possible, but apologise in advance if it is too long/should have been multiple posts, or if anything is missing. Thank you for your time!

Basic Premise and Sizing:

We’d like to build a Shepherd’s Hut style, detached micro music room / living space. As of now we have planned for it to be a ‘Room within a room’ design, but are unsure if that’s necessary, so it’s not set in stone. To legally sleep in there, it must be classed as a caravan so will be built on top of a trailer we have. We are relying on up-cycling and finding alternative ways to do things, as our budget is only £2,500 GBP excluding the trailer.
I will do the whole build myself, except electrical work.

Our measurements for the build are:
3.40m long x 1.85m wide x Unknown External Height (dependent on barrel roof and whether it is single or double room). The entire plot is 6.29 square metres. We will aim to have an internal height of 2.2m.

Weather and Placement:

We are based in Essex, United Kingdom. It’s often humid, wet and windy, with temperatures between -5 and +28 degrees Celsius. The build will be situated about 30ft from the main dwelling and neighbouring houses. There’s a fence directly behind the south wall, a shed located close to the east wall, and a dense hedge close to the north wall.

Sound Situation:

We’re more concerned about people outside hearing noise from within the build, than vice versa.

The room will be used for practising (with and without amplifiers) and recording, including:
- Vocals (rock, pop, opera tenors and sopranos)
- Cajon / small drums
- Piano
- Bass guitar, electro-acoustic guitar, electric guitar
- Violin
- Double bass and Cello

There could be 1-5 people recording at any one time, with any combination of these instruments played simultaneously.

— — —

General Construction Overview:
(Regardless of the double-or-single wall decision)

Overview Image SketchUp.jpg

THE FLOOR
The base/floor (3.4m x 1.85m) will be bolted to our trailer chassis, and made from pressure treated 2x4 or 2x6, and the top and bottom covered in OSB. This cavity will be insulated (likely with 75 or 100mm rockwool).

WALL FRAMING
600mm stud centres will be used where possible, to allow for 600mm wide batts of insulation.
There will be cladding on the outside, which will cover our vapour membrane (taped), which is to cover the OSB Sheathing (at least 12mm), which will be screwed externally to the timber framed, cavity-insulated walls. On the innermost part of our timber framed wall, we will hang our chipboard ‘drywall’ alternative. Please see the associated drawings below for clarification, and to see the single vs double wall versions.

ROOF
The build will have a tin barrel roof, which will be insulated between the rafters to keep the overall height lower. The vapour membrane will go over the roof rafters, ready for the tin sheets to sit on top.

WINDOW AND DOOR
There will be one (opening) window on the short side (west) wall. It will be 820mm x 820mm, and double glazed. For budget reasons, it will just be cheap stock that is available at ‘Wickes’ or ‘B&Q’. When recording, we plan to use an acoustic blanket as a curtain, or fill it with a plug made from leftover insulation…. or both…
e.g. https://bit.ly/3q4M1dM
The door is partway down the long side (north) wall. It will be handmade: 600mm wide, 1700mm tall, tongue and groove front. 50mm cavity insulation, with a chipboard backing (interior side). For space, it is outward opening. We will invest in lots of rubber seals and draft excluding strips.(See drawing below)

Door.jpg

ELECTRICAL
We will use putty packs, with 3-4 sockets embedded in the walls. This will hook up to a caravan connection point on the outside of the building.

VENTILATION
For all ventilation, I intend to make a ‘baffle box’ to sit either ‘in’ the wall (if double) or hidden in the top of a built-in wardrobe on the short side (east) wall. This will have ducts running through it.
For the internal room (or only room, if single walled), we would have a baffle box with ducts directing air flow.
In either design the window will likely be fitted with an integrated trickle vent to allow for natural circulation
For a room within a room, we would put two ducts through the baffle box - one leading to the air cavity, and one leading to the internal room.
We would hope that for both the double and single room design, this baffle box could have an exhaust/extractor fan fitted to the part outside the build to take air out, and we could rely on air intake from either the window trickle vent (inside) or the area where the corrugated metal sits on our external soleplate and is filled with foam (external room) and is not fully airtight.
When it comes to ventilation we’re most worried about the air cavity circulation (given that we go with that design) and if two baffle boxes are needed for intake and outtake of air. An HVAC system isn’t needed for our build as far as we’re aware so we’ve been looking at passive systems (or small external solar powered fans) and how to naturally keep warm air from accumulating in the roof / the build itself. As well as making sure the system we end up using doesn’t simply let all of the sound out.



Room-within-a-room design specifics:

Including the construction described above, if we decide on building a double room (determined by what you all think would be best for our build) then there will be an air gap between all walls and roof.

We aim to keep the room-within-a-room wall thickness to a total of 200mm or less (excluding OSB sheathing, cladding and 12mm chipboard), due to space limitations.
The internal room frame will also be decoupled from the base/floor of the external frame via a layer of mass loaded vinyl, and the decorative vinyl flooring we will also put down.

Double Room Wall.jpg

Double Wall Cross Section Sketchup.jpg

ROOF CHANGES
The external build will still have a tin barrel roof, with insulation between the rafters and the vapour membrane sandwiched between the rafters and tin sheets.

The internal build will have either a flat roof, with ‘warm roof’ design: rafters, topped with OSB, topped with 75mm insulation, or another curved roof with exposed flat beams allowing for a better aesthetic (please see image below). Regardless, there will be an air gap between this ‘inner’ roof, and the ‘external’ tin roof and rafters.
We require the internal ceiling joists (individually) to take a 150kg load each, but not much more.
(Please note that if we go for the internal ‘barrel’ as well as the exposed flat rafters, the internal ‘barrel’ will not need to hold any weight except for the insulation, so may even be 2x2 pieces of wood).

Double Room Art.jpg

INSULATION VS AIR GAP

Our current issue with having a room within a room design is that we are very limited on space, and are unsure on what configuration of insulation size vs air gap would be best suited for the build.
In an attempt to maximise our internal space, we have come up with these ideas for the room within a room/insulation setup, but would love to hear your opinions/advice/thoughts:

Spreadsheet Insulation Values.jpg

Example of table plan A:
(Please see table above and drawing below)
- External and internal 2x4 walls (89mm wide soleplate)
- Distance of 22mm between soleplates (GREEN arrow)
- 75mm insulation used in all cavities
- 36mm min air gap (BLUE arrow), 50mm max air gap (RED arrow)
- Total wall size of 200mm = 89mm + 89mm + 22mm

Air Gap Example.jpg

Double Wall SketchUp.jpg

Single Room specific information:

If it turns out that a double room doesn’t help us gain any noticeable soundproofing, then we have also come up with a single room build plan.

Below the differences are shown for the wall framing and the roof.
Most notably, the interior walls would be double lined with 12mm chipboard with green glue between them, in the hopes of gaining an adequate amount of soundproofing, instead of the one layer of chipboard used in the double room design.
We may also be able to add more insulation to the roof (e.g. on top of the rafters as well as between) to try to make up for the loss of the double roof. This, however, is not shown in the image below.

Single Room Wall.jpg

Single Wall Art.jpg

Questions and Concerns for both single and double room:

- We need to know at what point an air gap doesn't have any discernible purpose in a soundproofing build. Since our build has to be so small, and as such our max air gap in any iteration is only 100mm with a minimum 61mm, is the air gap even worth it for soundproofing at this point? If so, which is better to prioritize, more insulation or a larger air gap?

- Do we need to ventilate the ‘air gap’, or just the internal room itself? We’re worried about condensation from the metal roof if we leave it unventilated. Also, will two baffle boxes (one on each short side wall) be needed? One being for air intake, and the other being for the air leaving the build.

- Will the trailer base act as a ‘floating floor’ in and of itself? As there will be minimal points of contact with the ground (axle stands and 4 rubber tyres resting on soil).

- Since the door and window will inevitably connect the inner and outer rooms (e.g. the window sill), does this negate the entire point of constructing it as a room within a room?

- Will the chipboard benefit the soundproofing more than acoustic drywall or general drywall? Chipboard has a larger density so I would assume so, and we do not have to worry too much about humidity as there will be no shower.

- Any ideas for a more cost effective alternative to OSB for the sheathing/floor?

- Are any of these designs viable / could they be fairly effective?

- Does the insulation have to be ‘acoustic’? We’ve heard that regular thermal insulation can be similarly effective for most applications. Any recommendations?

- Is 2x3 or 70mm x 45mm (other) timber structurally stable enough to use instead of 2x4?

Note: Sorry for the awful perspective in the drawings, and the pixelation… we’ve been careful to stick within the 750 width constraint as instructed!

Thank you so much for reading, and for any advice!

Best wishes,
Quinn & Ash

[DanDan]

Bless your energy!

- We need to know at what point an air gap doesn't have any discernible purpose in a soundproofing build. Since our build has to be so small, and as such our max air gap in any iteration is only 100mm with a minimum 61mm, is the air gap even worth it for soundproofing at this point? If so, which is better to prioritize, more insulation or a larger air gap?

Larger the airgap the better. Doubling it adds 6dB or so to the Transmission Loss. Air gaps in a MAM system benefit greatly from a full fill of absorbent insulation.

- Do we need to ventilate the ‘air gap’, or just the internal room itself? We’re worried about condensation from the metal roof if we leave it unventilated. Also, will two baffle boxes (one on each short side wall) be needed? One being for air intake, and the other being for the air leaving the build.

I'll leave that one to Paulus or Glenn. Metal Roof..... condensation....


- Will the trailer base act as a ‘floating floor’ in and of itself? As there will be minimal points of contact with the ground (axle stands and 4 rubber tyres resting on soil).

No and it doesn't matter. Floating floors in a studio isolate sound from travelling from floor to wall or vice versa. Yours will isolate from earthborne vibration.

- Since the door and window will inevitably connect the inner and outer rooms (e.g. the window sill), does this negate the entire point of constructing it as a room within a room?

They will be the weakest points.

- Will the chipboard benefit the soundproofing more than acoustic drywall or general drywall? Chipboard has a larger density so I would assume so, and we do not have to worry too much about humidity as there will be no shower.

I am sure that Drywall is denser in general, certainly the enhanced ones.

- Any ideas for a more cost effective alternative to OSB for the sheathing/floor?

Paulus, local knowledge.

- Are any of these designs viable / could they be fairly effective?

The space is very small.

- Does the insulation have to be ‘acoustic’? We’ve heard that regular thermal insulation can be similarly effective for most applications. Any recommendations?

Yes. Kingspan and such hard insulations are thermally 3 times better than fibre, but acoustically useless.

- Is 2x3 or 70mm x 45mm (other) timber structurally stable enough to use instead of 2x4?

Paulus, local regs.

[gullfo]

you'll definitely want to treat the roof ventilation as you would any structure wrt moisture protection.

if you double the windows - one per frame set - you can mostly negate the isolation degradation from a single window. same for the doors but if doing a single door, ensure there is a jamb extension and soft seal that decouple the frame set and don't expose the air gap space into the room or the exterior.

what about leveling of the trailer when you move it?

also, if this is a trailer which can be transported on its own wheels, you'll need to look into rules and constraints on vehicle towed trailers to ensure compliance to the rules and fees for inspections and licensing etc. when traveling, are there roads and other areas with weight restrictions?

air for people inside?

[Ash]

Bless your energy!

- We need to know at what point an air gap doesn't have any discernible purpose in a soundproofing build. Since our build has to be so small, and as such our max air gap in any iteration is only 100mm with a minimum 61mm, is the air gap even worth it for soundproofing at this point? If so, which is better to prioritize, more insulation or a larger air gap?

Larger the airgap the better. Doubling it adds 6dB or so to the Transmission Loss. Air gaps in a MAM system benefit greatly from a full fill of absorbent insulation.

- Are any of these designs viable / could they be fairly effective?

The space is very small.

- Does the insulation have to be ‘acoustic’? We’ve heard that regular thermal insulation can be similarly effective for most applications. Any recommendations?

Yes. Kingspan and such hard insulations are thermally 3 times better than fibre, but acoustically useless.

Hi DanDan,
Thank you so much for your reply!

We'll bear this in mind, and will continue to budget for acoustic insulation rather than the regular stuff!
Given the small size and small air gap (we can't really make it bigger than previously mentioned), would the double room even be worth doing, when we could just do a singular room build and double up the drywall/chipboard?
Thanks again!
- Quinn & Ash

[Ash]

you'll definitely want to treat the roof ventilation as you would any structure wrt moisture protection.

if you double the windows - one per frame set - you can mostly negate the isolation degradation from a single window. same for the doors but if doing a single door, ensure there is a jamb extension and soft seal that decouple the frame set and don't expose the air gap space into the room or the exterior.

what about leveling of the trailer when you move it?

also, if this is a trailer which can be transported on its own wheels, you'll need to look into rules and constraints on vehicle towed trailers to ensure compliance to the rules and fees for inspections and licensing etc. when traveling, are there roads and other areas with weight restrictions?

air for people inside?

Hey Glenn! Thank you so much for taking the time to read over the plans so far.

With roof ventilation, do you think the extraction-muffler-box idea could be adequate? This is the best we've come up with so far and are at a bit of a loss as to what else to research with it sadly!

With the window(s), it is imperative that we can open it (for use as a fire escape), so we are a little worried about trying to put a window into each wall!
We'll be sure to extend the jamb, thank you!

Luckily when it comes to the trailer, we don't need to worry about being able to actually move it or have it be road legal, so no worries there! It will just be sat in the garden --sorry we didn't clarify!

As for making sure there's air for the people inside (we're not in the business of suffocating people..!) we're relying on a good ventilation system, but are unsure of where to go with what we have already.

Thank you again!
- Quinn & Ash

[gullfo]

why both with the trailer approach then? keep it simple and put it on a earth damped foundation.

on the roof - build it the same way houses are built in your area to have a passive ventilation flow which prevents the build up and use the proper vapour barriers. then if you need force venting to reduce heat build up, you can add that.

[Ash]

why both with the trailer approach then? keep it simple and put it on a earth damped foundation.

Hi Glenn,
Sorry for our terribly slow reply!
We need to have it on a trailer as we wish to sleep in it and use it as ancillary accommodation - and for that to be legal in a back garden it has to be classed as a 'caravan' or mobile home, as is achieved by the addition of wheels!

Thanks again,
Quinn & Ash

[gullfo]

do wagon wheels count? it could also be very decorative

[DanDan]

https://www.youtube.com/watch?v=x4oYe7VYCpU