New build from scratch

[jobody]

Hello all,

I am a mastering engineer in the UK. In January, weather permitting I plan to begin construction on a build from the ground up. I have good construction skills (and a dad with a digger) and I would say a basic / intermediate grasp of acoustics, REW, soundproofing and speaker placement etc - but I am no expert, so.. hello and thanks for taking the time.

The size of the external shell will be 5.4l x 4.3w x 3.2h and I estimate after construction the internal shell will be 4.9l x 3.8w x 2.7h

Due to building restrictions I will have to dig down to make sure the building does not exceed the maximum allowed height of 2.5. For arguments sake lets say 1m will be underground and 2.2m will be above.

I won't ask everything in one go, I'll just start with a couple of construction questions if that's ok.

I need isolation as we are in an urban area, my monitors go down to 25hz and I work on electronic music..

In my initial plans I was thinking of having the external concrete block wall on it's own foundations, and then a separate concrete slab within that to build the internal box. Does that make sense or is it overkill?

As the building is sunk and not attached to any other building I assumed I would not need a floating floor as any sound transmission going down would dissipate into the earth. Am I right here? Can I just build my internal shell on the concrete base?

In my mind the walls will be as follows. This is an inside out wall design inspired by John's small studio wall design.

100mm Concrete block > 50mm air gap > 25mm 2 layers plasterboard > 100mm insulated wall structure (thicker at the rear) > fabric

I hope that would be enough to give me decent isolation. And would do the bulk of the room treatment at the same time (there will be more where needed) . Any thoughts or suggestions on the walls?

One last question for now, when working out room modes etc, should I enter the internal dimensions of the concrete wall as that is the 'sound barrier', or do I do it with the dimensions of the internal box? i.e the drywall/plasterboard? I guess the ratio stays the same so does it matter?

I hope to get some drawings done pretty soon so will be back with those.

After I get some clarity on these points I would appreciate some advice on building my speaker wall.

Many thanks

[DanDan]

Isolation, your air gap is kinda small. But whatever size you end up with, don't leave it just air. Fill the gap with light fibre, have it lightly touching the plasterboard to damp it. Put in some wires or whatever to make sure it doesn't sag downwards over the years. Your treatment plan needs work.

[jobody]

Thanks DanDan, noted on the gap. That is helpful.

Yes the plan for treatment is much more comprehensive than I've outlined, just I didn't want to make an overwhelming first post with all the details.

Cheers

[DanDan]

Good plan. Too much is too much. The firm PUR? insulation is three times better thermally.
Also, I am no builder and damp is a black art, but I suspect placing your bigger amount of thermal insulation on the inside may create a dew point on the plasterboard....

I hope Paul, Gregg, others with build experience will join in here.

Here's an unfinished sketch of a proposed wall design for a Garden Studio. Note the studs are not attached in any way to the concrete wall. I have suggested including a layer of PUR 50 or 75mm at the render. This would not touch but protrude into the stud frame. The remaining 100-75 mm within the studs filled for damping as ever.

Wall with PUR.png

[jobody]

Thanks DanDan.

Do you know how much isolation this would give? (assuming the building is well sealed etc)

[DanDan]

You could estimate it from test data knocking around. But isolation is frequency dependent, a spectrum. Also the build details can influence it. Many brick walls do not have a full contiguous layer of cement between the bricks. Swiss cheese.

[jobody]

Hi again

Change of plans for my build.

After much planning and thought (even applied for a lawful development from the council) me and my wife were still really apprehensive to build it in our garden.. as it took up around 1/5 of the space - we have 2 kids so it's their space really.

Then along came my parents who have a lot of land and said - why don't you build it here ? It's around 30 minutes drive which is a small price to pay

My dad is a builder, mainly from wood - think garden structures, decks, anything really.

So he would prefer to build from wood rather that concrete block - (yep he is going to help me build it too) I have one initial question which I'm sure will be a simple answer, or perhaps not. I have searched hard for this kind of wall design but I can't find anything the same - may be there is good reason for that !

Could I build the walls + ceiling without a gap? So from the outside it would be wood cladding > 2 x OSB fixed to the 8x2 studs (filled with insulation) and then 2 x plasterboard on the inside - all fixed together. A single leaf ? See pic

Obviously with all the appropriate sealing and a waterproof barrier - this would be an isolated building built from scratch.

Bear in mind I am mastering, and I care for my ears so the levels are not drum kit loud. (yes I need an SPL meter) also my parents will be the closest neighbour around 50 metres away and the next closest is 100 metres away.

BUT also bear in mind I don't want my parents to regret this offer and be annoyed with this noisy rumbling shed down the garden if this design won't work for isolation at all. My speakers go to 25hz and I know the lows are the hardest to isolate.

If I need to do a room within a room then I can but I just don't want to spend extra time and money if I don't need to.

Any thoughts MUCH appreciated even if you say I'm crazy to even think this.

We are clearing the area to start building in the coming weeks.

Thanks !

[jobody]

Just measuring with my SPL meter (APP) and it's reading 76 max (C weighted) - If I crank it up like I sometimes do it's reading 90 max. As I said I don't master at this level, just occasionally crank it up.

[gullfo]

excellent! this means you can design and build it to purpose. if you don't already have Rod Gervais' book "Build It Like The Pros, 2nd Edition", that is your first stop

since you have significant distance to your parents and nearest neighbors, you probably don't need a room within a room, but you should construct it with heavy mass walls - so triple OSB, and triple drywall. earth-damped foundation/floor. since the structure will have a lot of mass, use the correct lumber and proper construction for vertical stability. getting squashed with several tons of drywall and other bits can have a negative impact on your day.

you'll need fresh air, so keep in mind a hyper-insulated structure needs fresh air and likely cooling (even if its outside air) because body heat, equipment, solar, etc. and it will need to run continuously while occupied. an ERV and a mini-split for a single room will work. figure on 8-10 air changes per hour.

build the interior to a well-known ratio of ceiling-width-depth. then work your way to the outside from there. this will help with the acoustical treatment later. if you decide on angled walls, take the average of the wall for your room width in this calculation.

[jobody]

Thank you Glenn !

I have an acoustic designer to take care of the insides so I am confident with how the room will perform but of course I don't want to make any mistakes in the construction that might hinder the rooms performance. Mini split is in the basket, as is a small MVHR unit.

Ok that is great info thanks. The one thing my dad is keen on is not having a concrete slab. It's partly environmental and also it is quite impractical. But if we have to we will.

So my question is, if the the floor is made from timber (sat off the ground on concrete spots) how would I go about making sure the floor performs well..? Obviously it needs to take a fair bit of weight and I don't want it to resonate and clearly it doesn't have the advantage of being sat on the earth like a slab.

Is this possible or is it more work and poorer results ?

[gullfo]

one option would be to create a floor you can fill with sand - this will create a self-damping mass - you will need dry sand, and you'll need to protect it from moisture. also will increase the number of supports because it will be heavy depending on how thick the floor is. so - runners across posts, then plywood sheathing, joists. line openings with moisture barrier and fill with dry construction sand, seal
with moisture barrier on top, finally 2x ply subflooring, and finish floor.

[jobody]

That is interesting, thanks Glenn. I have just been reading about kiln dried sand this evening. It does seems slightly backwards to do extra work on to keep the sand dry and to support all that extra weight when a concrete slab directly on the earth would be easier. Would you agree? Can you tell which way I'm trying to sway my dad

One question about the sand filled floor.. where does thermal insulation come into this design?

[gullfo]

concrete slab. plus i'd separate it where your rooms are divided (if you have more than one, or a utility closet) which will increase isolation between rooms as longs as you can also do some framing / structural separations as well. but definitely hands down an earth damps concrete slab will be a much better approach.

[jobody]

I thought as much. Luckily it's just one mastering room so that simplifies the slab. I'll break the bad news to the old man.

Thanks Glenn.