Floating Walls??

Hi all, I have a couple of questions about floors and walls and what might be best in my case. My original post is here - http://www.johnlsayers.com/phpBB2/viewt ... highlight= and I got some great design advice from John here - http://www.johnlsayers.com/phpBB2/viewt ... highlight= I have read (and am re-reading) Rod's book where he mentions his views on building floating floors - eg. unless it's done properly it might cause you more trouble. My building has a solid and flat concrete floor which the guy who built the place told me has 'insulation under it', whatever that means. I think I am in the situation that floating a floor might be pointless from the sound isolation point of view (considering the roof and the remote setting of the building), so how should I approach putting my walls up on the existing floor? I was going to use neoprene pads at the bottom of the walls to isolate them from the floor, but should I use one long strip along the whole length of the wall, or just pads at regular gaps? If so what should the gaps be? Also, I've read here that screwing the wood to the floor via the rubber pads reduces the worth of the pads.....but I need the fix the walls to the floor somehow, otherwise it might not pass building regs... :) Any help would be greatly appriciated. Thanks, Jamie.

The point Rod was making in his book is that structure-born flanking (leakage) from airborne noise via a concrete slab on grade is likely to be minimal and probably less than the leakage through the walls anyway. In other words, unless you're going to build something so massive that slab flanking is the source of your noise leakage, there's really no point to floating a floor/slab, and that doing so might actually make isolation worse and not better. The problem I see with most methods to achieve a decoupling between floor and wall is that they compromise the structural integrity of the inner leaf walls, which is especially important when those walls are holding up the inner leaf ceiling. The issue is magnified in areas that are subject to seismic or hurricane risks. Bear in mind that if you attempt to "float" your walls on elastomers (e.g., Neoprene pucks), but then nail or bolt your soleplates to the slab for stability and to meet building code requirements, you've completely ruined any benefits you'd hoped to achieve with the elastomers because the fasteners end up becoming the transmission path between wall and floor. FYI, never use screws to attach your framing -- always use nails. Hope that helps... --Keith :mrgreen:

Hi Keith, Thanks for the swift reply. Can I just say that you're thread is truly an education in itself.....if you can make it all the way through that is! :? I take your point concerning Rod's attitude to floating floors. This was pretty much what I had understood although I also had it in my head that he also mentioned sound problems inside the room (once built) with resonating frequencies. Either way, I quite believe that it's pointless me building one. However I think I'll need walls :lol: So what do you think would be my best course of action - building the walls straight onto the concrete floor with no rubber buffers? I suppose that if the floor will receive sound / vibration anyway, attaching walls directly to it shouldn't make too much difference should it? Or does this mean that more sound will be channelled into the floor and potentially to other rooms / the external structure / the outside? Thanks for the point about using nails instead of screws. I anticipated using nails to build the walls, but I was told by a carpenter friend of mine that when building 'standard' house walls they always use heavy duty screws to fix the base plates to the floors. I know this doesn't mean that I necessarily should but surely nails won't do this job will they? Just to let you know....I am planning to build a double leaf ceiling hanging from the current ceiling joists (although I do still need to check that the structure can support this) but I'm working on the assumption that my walls will not need to support either leaf of this ceiling. Thanks in advance, Jamie.

Glad to help, Jamie. :-) The "heavy duty screws" you're referring to may be a product we have on this side of the pond known by their brand name: Tapcon. That may be OK, BUT i'm a bigger fan of anchor bolts: use a hammerdrill with a masonry bit to drill 5/8" holes in the slab a couple of inches deep, insert the 1/2" galvanized anchor bolt, drill a hole in the pressure-treated soleplate (a.k.a. base plate), set the plate on the floor with the bolts penetrating the holes, use a large and thick square galvanized washer and galvanized nut, then tighten: the upward force on the bolt causes the ring at the bottom of the bolt to slide up to a thicker area on the shaft, locking it into place. The only thing better is L-bolts set into the concrete when it is poured. I think the anchor bolts are the best retrofit method, especially here in Earthquake-prone California. Remember that a slab on grade or a basement has complete firm contact with the rock and soil on which it sets, so resonance of the slab is dampened naturally. If we were talking about an extremely heavy duty slab on an upper floor of a commercial building, I'd be singing a very different tune, advocating a floating concrete slab on top of that slab. But for slab on grade or concrete basement floor, forget it. :-) What's your vertical clearance? If you can afford the height, support your inner ceiling on your inner walls. Only go with the method of resilient hanging if you have no other option and are certain you don't overload. --Keith :mrgreen:

This may vary by locale, but in New England it's fairly common to attach the bottom plate to a slab with a Remington charge-fired nail gun. It uses nails like shown below, and makes the job quick -- no drilling -- but loud (hearing protection definitely required). - Andy

Hey guys, Thanks for the replies - I'll look into the best type that I can get over here, and the costs of course..... Just to mention that we don't get many earthquakes over here - the last 'natural disaster' we had was a tornado in outer London, which destroyed about two houses and that was on the news all over the country! :lol: I don't mean to rub your faces in it, I'm just saying that my walls probably won't need to be earthquake ready. I'm not exactly sure what you mean Keith by 'slab on grade' but I'm pretty sure this is what it is anyway! It's built right on to the earth as a basement would be. I'm assuming that this means that any sound travelling through the concrete floor from the live room to control room will be pretty minimal? My vertical clearance is 9 foot at the moment - from the concrete to the one layer of plasterboard that is currently on the underside of the exsisting joists. Thinking about it, I won't really loose too much height if I do as you suggest and make the inner leaf supported by the new walls. What do you think about the idea of attaching the outer leaf of plasterboard to the top of the existing joists, then putting new joists in (supported by the new walls) and the inner layer of plasterboard attched to the bottom of these? This way I would get the maximum distance between the two leaves but not loose more than maybe 15cm of height (some of which I'd have lost anyway with the RC). Basically as you would do if they were two walls. Sorry if what I've written above is obvious, but I was sort of thinking it through as I went along! :oops: What does anyone think to that? Jamie.

Yeah, you definitely want to have two and only two leaves overhead. I'm curious -- what do you have on those joists now? Some drawings are in order now. Maximizing the distance between leaves is a big advantage. Yes, "slab on grade" means a concrete slab poured onto the soil, with deep haunches around its perimeter. --Keith :mrgreen:

Hey Keith (and anyone else who may be reading), I've attached a couple of pictures which will hopefully give you a better idea of what I'm dealing with. The joists actually look pretty minimal to me (not that I've got any experience) considering there's only 6 for the whole thing. In the picture below the guys are putting up the only layer of plasterboard and you can see that they've put in extra timber to bridge the gap between joists, but still the whole ceiling must rely on just these joist to keep it up - now I think about it attaching four layers of plasterboard to it might have been a little silly. :oops: I've still yet to actually check, but I'm pretty confident that this single layer of plasterboard has some basic insulation on top - not sure what size though. I basically thinking that the roof is almost pointless for sound insulation and so I'm not really considering it as a leaf. Therefore I'm planning on building the two leaves necessary on top and below the joists - as you suggested probably on a new inner ceiling for the inner layer. I did at one point consider trying to line the inside of the trusses (I think?) with plasterboard to give me more space between the two layers and extra ceiling height, but I soon realised that this would be a pretty big job and so settled for two flat leaves closer together. As my Dad was around when the place was being built I've got access to the original plans. The description of the concrete floor reads (excuse any mistakes as it's quite hard top read)- '125mm concrete slab mesh reinforced Jamb proof membrane 150mm stone hardcore blinded' Let me know if that sounds potentially bad for sound! :D Thanks again for all the advice, Jamie.

Those trusses in the PHOTO look prretty hefty. :-) The bottom chord is made of larger dimension lumber than the rest, which I think may be a good sign. Unfortunately, a simple joist span calculator cannot be used to determine the maximum load. Instead, you'll ned to get the specs for the trusses and/or check with its manufacturer. If they weren't engineered trusses and were homemade, then a structural engineer consultation would be in order. FYI, you can't just "will away" the third leaf effect... Although the volume of the cavity between second and third leaf, coupled with its liberal venting, should mitigate its effects. It may actually help for some frequencies, just not the pesky low-end ones. Is that a pnumatic nailer being used to attach gypsum walboard overhead? :roll: I don't have any concerns about the concrete, as long as the site of the pour was properly prepped and compacted. Have you heard of Green Glue? You may want to consider it, especially for your ceiling. The constrained layer dampening method would give you performance akin to four layers of board with only two layers with Green Glue sandwiched between them. --Keith :mrgreen:

Ok, you've lost me there Keith. What's the bottom chord? Being a guitar player I would think it's an open E, but I could be wrong. :D So if I knew the spec of the trusses I can work out the maximum load myself? I'll get onto the guy who should know where they came from, thanks. Are you sure I can't just 'will away' the third layer effect? :cry: Fair enough then, but is there anything else you know of that I can do to get better results apart from what I proposed previously (without doing lots more work)? Am I to take it that you shouldn't use a pneumatic nailer to fix plasterboard overhead? Sorry, but I'm new to this you know.... I've heard a lot about Green Glue but I was slightly put off by how much it was.... and slightly dubious about how well it works. Call me sceptical, but I've got such a tight budget I didn't want to spend anything unnecessarily. However, I read this link http://www.johnlsayers.com/phpBB2/viewtopic.php?t=7851 this morning and it made me think about just using it on the ceiling... as you suggested to stringbender! I'll go and do some more pricing.... Cheers, Jamie.

Jamie M wrote:

Am I to take it that you shouldn't use a pneumatic nailer to fix plasterboard overhead? Sorry, but I'm new to this you know....

No, no -- it's fine, really. As long as you don't intend to ever stand underneath it. :wink: Plasterboard is normally attached with drywall screws. I'm surprised the nailer didn't just send the nails right through it. - Andy

Cheers Andy, I'll bear that in mind when I start to put the plasterboard up. Can you tell I'm not in the building trade? :lol: Jamie.

Jamie M wrote:

I've heard a lot about Green Glue but I was slightly put off by how much it was.... and slightly dubious about how well it works.

Completely understandable. You are right to be skeptical; many people fall for the marketing tactics of a lot of soundproofing product purveyors. Green Glue, however, stands apart from that crowd. They have impressive and credible third party lab tests that prove their claims. I think that's one of the reasons it's more expensive. Those tests aren't cheap. That, and the stuff actually works as advertised. --Keith :mrgreen:

Hello everyone, I'm starting to build this week and immediately I've got a few more questions!:lol: Having gone through my plans with my experienced handy man / builder / carpenter (who also happens to be my Dad) he was confused why I wanted to erect all the stud walls directly onto the concrete and then lay a floor, rather than doing it the other way round. I was going to use laminate flooring (or something similar), with no attempt to float anything, but my Dad thinks that it would be much easier if we put down the floor first (while the space is still a good rectangle). I've got no problem with this if it's going to be easier, provided that we cut the flooring to separate the different floor spaces once the base plates for the stud walls are in place. Is there any reason not to do it this way? Secondly, I'm a little confused about the whole caulking idea. Have I got this right?..... You use standard caulk and tape to cover each of the plasterboard joins and then go around the edges with acoustic sealant with backer rod behind it. My areas of uncertainty are.... Does the caulk used have to be different to normal decorators caulk? I'm sure I've seen mentions of 'acoustic caulk' on these pages but I'm struggling to find anything here in the UK. I've seen some websites advertising acoustic sealant (which I think is different to the caulk?!), but again, it doesn't seem readily available from the standard suppliers. Can any UK people point me in the direction of what I should be buying? So to sum up.... Floor before or after walls? Acoustic sealant / caulk suppliers in the UK? Thanks guys, Jamie. PS Once we've actually started to build something I'll put some pictures up!

Hi Jamie, congrats on the build! In U.S.A. terms (don't forget the A), we're practically neighbours! Warm regards, and much success. Lou. 8)

Jamie M wrote:

Having gone through my plans with my experienced handy man / builder / carpenter (who also happens to be my Dad) he was confused why I wanted to erect all the stud walls directly onto the concrete and then lay a floor, rather than doing it the other way round. I was going to use laminate flooring (or something similar), with no attempt to float anything, but my Dad thinks that it would be much easier if we put down the floor first (while the space is still a good rectangle). I've got no problem with this if it's going to be easier, provided that we cut the flooring to separate the different floor spaces once the base plates for the stud walls are in place. Is there any reason not to do it this way?

You absolutely should not attempt to install new inner leaf wall frames on top of a laminate floor. You'll crush and/or damage the laminate. I hope this doesn't lead to confusion, but laminate floors are meant to "float" freely so that they can expand and contract through the seasons. If you install walls on top of it, not only will you surely damage the laminate in the process, but the floor will buckle or pull apart, depending on the amount of humidity in the air. Laminate floors need about 1/4 inch (2/3 cm) margin around the perimeter of the room, and the gap is covered with baseboard or "quarter-round" shoe moulding.

Jamie M wrote:

Secondly, I'm a little confused about the whole caulking idea. Have I got this right?..... You use standard caulk and tape to cover each of the plasterboard joins and then go around the edges with acoustic sealant with backer rod behind it.

Yes... (Except, not caulk and tape -- it's supposed to be mud and tape. "Mud" = joint compound, like plaster, using a wide putty knife.)

Jamie M wrote:

My areas of uncertainty are.... Does the caulk used have to be different to normal decorators caulk? I'm sure I've seen mentions of 'acoustic caulk' on these pages but I'm struggling to find anything here in the UK.

Yes. The two are NOT the same. Acoustic sealant is a lot like caulk in the way it is applied, but it never fully hardens, so it's less prone to cracking and shrinkage over time. This is critical to maintain your seals. --Keith :mrgreen:

Hi guys, Thanks for the advice Keith. I wouldn't have built straight on top of laminate, but my Dad is talking about another type of wood floor that fits together in much the same way but with much larger sheets. This stuff can apparently used for semi-industrial situations and he thinks it'll be fine with the weight. I suppose what I was really asking (although not too clearly :? ) is that is there any reason (for sound isolation) why I shouldn't build the walls on top of a strong suitable flooring, instead straight onto the concrete? Thanks for clearing up the caulking thing. I'll get hold of some regular 'mud' to do the joints and order some acoustic sealant on line for the edges - I managed to find two suppliers last night in the UK who look like their selling what I need! Lou - thanks for the words of encouragement. We need more Brits on here! Let me just ask one further question...... The small gaps that you should leave between the plasterboard on any connecting walls / floors / ceilings....I'm assuming that this is to allow the plasterboard to move a little without effecting another surface, but does this also aid in better isolation buy not transfering any structure sound vibrations from board to board? I'm just thinking ahead, as my ceiling will be supported by my walls (so there will be direct contact between the timber anyway) is there still an advantage in doing this? Thanks, as ever... Jamie.

Jamie M wrote:

I suppose what I was really asking (although not too clearly :? ) is that is there any reason (for sound isolation) why I shouldn't build the walls on top of a strong suitable flooring, instead straight onto the concrete?

Jamie, mind you that I will begin this by saying that I have never tested this to see the effect - BUT - my experience tells me that my best isolation would be with the wall directly to the concrete and then the floor inside of that assembly.

The small gaps that you should leave between the plasterboard on any connecting walls / floors / ceilings....I'm assuming that this is to allow the plasterboard to move a little without effecting another surface, but does this also aid in better isolation buy not transfering any structure sound vibrations from board to board?

Nope - you are mistaken in that respect - the amount of transfer you could get into an edge of a sheet of drywall (lengthwise) is next to non-existant. BUT - it is absolutely critical that you leave that open joint- (/4" to 3/8") so that the joint can be caulked - You are then stopping the possible movement of air through the joints - and THAT is critical for sound isolation - without that, STC 54 walls quickly become STC 30 in real life. Rod

Hi Rod, Thanks for the swift reply. We've now decided to stick with my original plan of the walls going straight onto the concrete and the floor going down afterwards. I suspected that this might be slightly better in terms of isolation, but it's good to hear a similar opinion expressed by a professional! I really got a great deal from your book by the way (the only shame being that certain sections weren't really applicable to the UK), but definitely recommended. I only hope the work I'll be doing will live up to the standards I've read about! I'm now off to find some backer rod, or the english equivelant....whatever that might be. Cheers, Jamie.

Hello all, Just want to ask your advice regarding sliding glass / patio doors.... My studio plan incorporates two of these in the independent walls between the control room and live room. Although I know these are not the best in terms of sound isolation, I thought that they would probably be best for my design, providing me with great communication between spaces and the necessary doorways. I have, however, been offered today four double glazed units for free by a conservatory company who work on the site (and who are good friends of my Dad's). These units are 1980mm x 1350mm, all double glazed with 4mm toughened glass 12m gap and then another 4mm of glass, and are left over from a job that never happened. I know that if I used two of these in my walls then I would be putting together a four leaf section, which isn't good, and that 4mm glass is far from ideal for sound isolation. However, since I was going to build a very similar four leaf system by using double glazed doors instead (at quite a price) is this something that I could consider doing? Basically my questions are... Would the size of the glass units make them a major weak point in my walls (which are currently 2 x 12.5mm plasterboard on individual wooden stud walls 25cm apart)? As I can have four of the units would using all four in some ingenious manor help to improve their performance, or am I just ignoring the facts? I'm sure anyone who has built anything on a budget will understand how I'm feeling....it seems like a great opportunity, but is it just the easy way? Thanks guys, Jamie.