isolating a room with windows

[bivis]

Hi,

I am relocating my business and want to have a room dedicated to recording podcasts, some occasional VO perhaps..

The building is 20 years old, solid build, concrete & steel, located between a taller building and a not very busy street. We do get some occasional scooters passing, that i want to ‘’mute’’.

The office is on top floor (only two floors), ceiling 3,5m high concrete, also concrete floor with parquet finish.

The room in question is overlooking a street, concrete wall with rebar, other walls are simple drywall with insulation, light steel framing, 10-13cm thick.

The windows are in aluminium frame, 73cm x 220cm, normal glass 4mm-16mm-4mm.

I could use the room for recording as it is, but want to achieve additional isolation.

my starting points, (got the ideas from mr.Gervais book and great info on studio construction forums):
▪ replacing the window panes with 4 - 12 - 4+SC+4(ext side) (local glass supliers, said thicker glass would require new frame alltogether.

▪ increasing mass of the existing shorter PB wall
⁃ remove one layer of PB, adding another light steel frame, fill with insulation, cover with 2 leafs of PB on both sides
⁃ caulk

▪ increasing mass of the existing PB wall with the door
⁃ remove the outside PB
⁃ build a new light steel frame 2cm away from the existing
⁃ build and and reinforce the opening for the new door
⁃ add insulation
⁃ add 2leafs of PB on the new wall, and another one on the inside

▪ additional PB wall in parallel to the exterior wall
⁃ adding insulation on bare wall??
⁃ build new light steel framing 2cm away from the wall
⁃ build and reinforce openings for second windows,
⁃ add insulation (pink fluffy rockwoll)
⁃ add 2 leafs of PB
⁃ caulk

I would add another wall inside the room to make a small storage room.

thanks for your comments in advance,
attached the floor plan as it is

[gullfo]

welcome! so are you trying to create a room-within-a-room or just mass enhancement with some additional damping? for example, are the statements regarding remove PB and add frame and then double PB meaning create a separate frame with new PB mass and insulate? or something else? if the former - then leave a slight gap between the frames, fill with insulation, then gwb. on the concrete walls, just another frame, slight separation from the wall, then insulate and mass on the frame. this creates the walls. bigger issue is the ceiling - in addition to the span, contemplate your HVAC (early and often) and the above-the-ceiling situation and possibly mass enhancement there as well. otherwise, frame joists onto the new walls and possibly need isolation suspension for support.

[bivis]

Hi glenn,
Thanks for the warm welcome and advice.

Yes, the idea is to get the room in a room design.
The office is on top floor, the ceiling is concrete with steel rebar. 3,5m high, so i have some space to suspend the ceiling with iso hangers and double PB, backer rod and caulk in the boundaries offcourse.

Hvac, there will be a AC inside, no ventilation, because i want to keep the natural light and fresh air in with opening the windows when necessary, prior/after recording.

Regarding the windows, i was thinking,
-repair and caulk the outer side of the existing windows/frame,
-replace the glass,
-build the new frame with double pb and insulation,
-reinforce the new window openings, (the window guy, said i should make the frame about 10cm wider on all sides, so he can fit the new window frame better, and more airtight.

Should the existing window niche and the new one connect? Or should i leave them, totally decoupled?
The reason i am asking is more aesthetic,If i am going to open the inner window i would not like to see the insulation and the gap between the concrete wall and the new frame.


Regarding the material, should i consider the special, heavier and denser PB? Knauf insulation is pretty popular around here, also fermacell.

[gullfo]

the inner window sits on the inner wall, and the (enhanced) outer windows sits on the exterior wall. the gap between them - use a jamb extension with a 1/4" gap between them. use cloth between them. use that combination. but whatever you choose don't connect them.

same for the walls - use isolation sway bracing, do not use hard framing to support and connect them. otherwise you might as well skip the isolating walls...

use lighter insulation in the walls, preferably a glass wool product as long fibers and air combine to improve TL over denser mineral chip type products. use the mineral wool inside the room where some density can be beneficial to LF absorption.

[bivis]

Hi,

thanks for the suggestion on the window.

You suggest sway braces for supporting the second wall via the first wall?
like this?
https://arcacoustics.com/product/vibro-ws/

I was thinking building a totally separated second framing 5cm away from the existing (remove PB) and use neoprene pad underneaath the top/bottom/left/right profile
It would touch the existing wall, only via screws.

[gullfo]

definitely not the product you linked to... seems like magic BS which is not a good thing... "VIBRO-WS is a homogeneous rubber support system for gypsumboard partitions. The semi-cylindrical modulation at their base and the transversal holes provide the necessary space for the rubber expansion to increase the deflection and consequently the vibration insulation. VIBRO-WS decreases the flanking noise transmissions and interrupts the heat-bridges and the increase of moisture between humid floors and walls."

no, something like these products:

https://kineticsnoise.com/arch/
https://mason-ind.com/isolated-walls/
https://mason-ind.com/ceiling-hangers/

to fully isolate the walls from the floor - you would want to know the weight of the assemblies and calculate the deflection of the isolation product needed and to use decoupled lag bolts or equiv to secure it. this will reduce the wall into floor structural transmission a bit however the overall TL will be dictated by the floor - placing a subwoofer on the floor, bass amp, drums, etc would eliminate the expense of the wall decoupling.

[bivis]

Thanks,

thanks for the link, they also have neoprene rubber pad product,

https://mason-ind.com/sww/

''Walls should be resting on a continuous SWW pad, if not on the floating floor and sealed at the top with AB-716 angle brackets.... All of these devices use neoprene as the isolation media or natural rubber if specifically called for by an acoustical consultant.''

I also found the same item on both companies websites;

- https://mason-ind.com/wic/
- https://arcacoustics.com/product/vibro-sc/

I want to be sure, Isnt it better to just build the second frame of the double decoupled wall completely isolated from the first (existing) frame?

[gullfo]

definitely better to have a separate inner room frame decoupled from the exterior. and by decoupled with mean structural, wires, ducts, sway bracing, etc etc. for example using wiring which is tightly connecting the frames or hard conduit, or plumbing pipes, hard ducts etc all bridge the "decoupled" walls and ceilings. so attention is paid for all possible things that can wreck the TL of the inner walls.

as far as "floating the walls" off the floor - as noted - depends on the situation and other factors like sound source coupling etc. i think too many people over think and thus over spend on isolation tactics while thwarting it all by structural bridging, sound sources coupled to flooring or walls etc. vibrations from machines located somewhere else... etc

like football, fundamentals matter. worrying about whether a silver bullet is going to solve something is really just wasting time and money, and if you had both, you'd be building this in a completely different location and way...

hvac matters. commercial zones may have fire and other safety requirements regardless of your intended usage. someone else in the building might be running equipment which causes vibrations or electrical noises. and if you haven't checked for those, then once you do get to some level of isolation, you'll suddenly be aware of them and now what?

take the time to assess and plan. listen to the noises in the floors and walls - contact mics, mechanic stethoscope, etc check for electrical noises, etc. if you're getting a lot of sound through the structure, then either consider spending much more money on the project or do what's needed to get a decent level of isolation, and just use that. not all locations are good for studio building...

[bivis]

Hi,

i spent some time in the offices past few days.
Found a huuge ''sound isolation weak spot'' i would really like to take care of, before continuing.

The existing windows (220cm x 75 cm wide) are fixed in an opening on the concrete exterior wall (top and bottom) however on the sides they are screwed only to a separate vertical steel frame. This makes it possible that there is a gap between the window frame and the ext. wall. The gap is covered with one sheet of PB to look nice, however sound is passung through this gap.

my thoughts on tackling this problem, to achieve the best isolation around the existing windows:
- remove the pb on the sides completely.
- fill the air gap with fluffy insulation
- insert a ''plug'' between the window frame and the lightsteel frame (MDF, glued to the sides and caulk)
- cover with PB
- caulk

[gullfo]

i'm not sure what i'm looking at here. i'm presuming its a top down view. ultimately you need your windows to match the mass of the walls they're set into.

here's what you need it to look like when its done:

[bivis]

Thanks,

Yes its top view

Ineed to place a jamb between the frame and the concrete wall.
Was thinking:
Mdf cut to size, glued to all sides and caulk, finish with another layer of pb, inner side.

Glue because i will have trouble screwing anything due to limited space.


Equaling mass of the window with the wall would be achieved i guess with another window frame, which is my next step after i get rid of the weakest link.

[gullfo]

if you have moisture - no MDF. proper pressure treated rough frame. even heavy duty commercial windows would do it. it's not clear (to me) why you have 2 concrete walls connected with framing. is this because one outer wall is the "sheathing"/"weather" layer? or the inner isolation is hard coupled to the outer isolation? (which would be bad in terms of isolation).

[bivis]

No moisture present on the outersurface of the pb, which was there 20 years.
It would be even easier to fill the void with pb strips glies together?

Yes the outer wall is only sheathing. Concrete blocks that look nice but habe zero thermal or sound isolation capabilities

[bivis]

Would MLV be an option here?

To glue it on the concrete wall and the outer window frame? The air gap would be filled with fluffy insulation.

Simce i have to put in a new pb, would it be better if i use a denser one?
Normal pb 12,5 mm has density about 665 kg/m3, the premium (12,5) has around 1000kg/m3

[gullfo]

you could try the MLV but if the walls are effectively one unit, then why not extend the pb to the window frame. use denser.

however, if the exterior wall is vented (water drainage etc) then you'll want to make sure the venting stays intact otherwise you could end up trapping moisture. in which case, perforations would be desirable in the extensions.

or as a final approach - rebuild this - a thinner outer window on the exterior sheathing, and a heavy window on the interior wall. and skip the intermediate stuff.