endorka wrote:Source of the post As a standard 4x2 stud wall with 12.5mm plasterboard on either side it's the weakest boundary out of room 1. At least it has insulation in it!
How much are you prepared to do to improve isolation here? If you need a reasonalbe improvement, then your plan of adding an extra layer (pr two!) of drywall with Green Glue compound would help somewhat, especially with with the low end. Going further: you could take off the existing drywall, seal up all gaps and edges with caulk all around inside, put up isolation clips (eg: Genie clips, RSIC clips, etc.), put hat-channel in those, stuff the cavity with insulation, then put on two layers of 16mm drywall, with Green Glue compound.
That's a bit more drastic, yes, but if you need a large improvement, that might be the way to go.... as far as the wall itself is concerned...
endorka wrote:Source of the post The existing door is ceramic core FD30 fire rated, mass per area of 27kg/m2. Adding 18mm MDF will add about 12 kg/m2. A layer of code 3 lead between them would add 15kg/m2. Adding both will double door mass and allow multiple perimeter seals. The door jamb is specifically for a fire door, is over 32mm thick and is tough as old boots; presumably ok with the extra mass if I use sturdier hinges.
Doors are always weak points: especially the seals. Beefing up a door will improve isolation, yes, but perhaps not as much as you'd like: doubling the surface density will get you an increase of maybe 5 dB, realistically (6 in theory). Improving the seals can get you anywhere from just 1 or 2 dB to maybe 10 dB or more, depending on how bad the situation was, and how well you do it.
That said, beefing up a door with high mass is more than just adding on some dense layers: as you mentioned, there's also things like hinges to think about: you'll probably need to replace the existing hinges with heavy-duty hinges, and also add a couple of extra ones: I always use at least 5 hinges on a medium studio door, and 6 (or more) is also common for heavy ones. When you think that a good door might weigh 120 kg, and each hinge only has four screws in it, the typical 3-hinge arrangement means that each screw is supporting 10 kg just in vertical weight, but the screws in the top hinge are also supporting the "leveraged load", of the entire door weight trying to pull them straight out of the jamb, where the bottom hinge is the fulcrum and the width of the door is the lever arm with the full weight of the door on it.... well, there's a hell of a lot of force on those screws, as you can imagine! It's a good idea to put a couple of hinges close together up near the top of the door, a couple more spread a little further part around the middle, and the last one (or two) down towards the bottom, spread even further apart. And use extra-long screws, to resist the high "pull-out" forces
Plus, it's not just the door, jamb, and hinges: all of that is attached to a stud frame inside the wall, which was likely originally only intended for a typical house door. Even though that might be able to take the vertical weight of a studio door, there are also some rather major forces that it wasn't designed for, trying to twist it out of shape: And as you open and close the door, you move those forces around, swinging them through 90°: With the door open, you have that same "leveraged load" trying to tip the wall over towards you: It won't actually tip the wall over, of course, but it certainly can bend the framing a little. Over time, the door will sag, twist, warp, bend... and end up not sealing properly, and probably binding against the threshold and the jambs.
The solution is to beef up the framing. Here's how I often do the framing for studio doors:
There's two king studs on each side, plus a jack stud on each side under the header, then outboard of that there are additional noggins that help transfer some of the load to adjacent studs, and also provide extra rigidity. Not visible here, is the "backer" that runs up behind the three studs on each side, inside the cavity. That might be just a strip of 19mm OSB or plywood, or better still is a 2x6 turned sideways. That thickens the support column, and provides extra rigidity and strength for when the door is open. If you look at Tom's thread, you can see how we did that for his isolation wall.
The final part of that, is to then use OSB or plywood as the first layer of sheathing on that part of the wall, then put the drywall over that for the final layer: both OSB and plywood are very good with sheer loading, so the add extra structural integrity, strength and rigidity to the whole "sandwich" of stuff that is holding up the door, and keeping it straight and true.
Here's a couple of examples from actual studios built by clients:
How serious you have to get with that depends on how heavy your door is, but anything over about 50 kg or so needs some extra care. And if you are getting up around 100 kg or more, then it's time to get very serious.
Then there's seals: For typical home studio doors, I suggest two complete full-perimeter seals, and for high isolation three complete seals. By "full-perimeter" I mean that there is a continuous rubber seal that runs completely around the door, unbroken: header, threshold, and both sides. No gaps. Yes, there can be joints in the seals (such as where the vertical side seals meet the horizontal threshold seal), but when the door is closed they must all be pressed together properly, so there are no cracks. For example: if you have a drop-down seal embedded in the bottom edge of the door, then that must not only seal tight against the threshold when it drops into place as the door closes, but it also needs to seal against the rubber running up the sides. Small gaps and cracks can leak a lot of sound.
If you're framing very rigidly, and are certain that your framing won't budge, sag, twist, etc, and the door is mounted with "overkill" heavy duty hinges, then it's OK to just use fixed rubber seals glued to the jambs. But if there's a chance that things could sag or shift over time, then it's better use adjustable seals, such as those made by Zero International. Those allow you to simply pull off a small dust-cap, insert a screwdriver, and adjust the seal for a tight fit, any time you notice that it isn't sealing well. They aren't cheap, but that's the best solution if things might move out of plumb and square over time. It sure beats modifying the jambs to compensate for the load shift!
A realistic prediction? Comments welcome!
If you do "all of the above", then you could maybe get as much as 10 dB improvement in isolation, maybe even a little more. If you can only do some of it, then likely around 4 to 6 dB improvement. In perspective: 4 dB is noticeable, 6 dB is very much noticeable, and 10 dB reduces it the level by about half, subjectively.
- Stuart -