Towards a better tinyhouse

Inventing to freedom?

lighter soundproofing

with 2 comments

One of the biggest complaints people living in FEMA trailers had was the amount of noise that gets through a trailer’s wall.  That is one of the key differences between a tinyhouse and an RV, that the walls are much thicker and heavier, and therefore more soundproof, thus making it a much nicer place to live.   I bet some people don’t really realize this is why they find tinyhouses more comfortable, but I bet it is a big part of it.  Zoning codes usually specify a certain degree of soundproofing because noise can be pretty bad for you, causing stress and lack of sleep etc.  Now obviously zoning codes are not always based on anything so sensible, as I’m sure most anyone reading this is aware….

But for portable tinyhouses, they do require pretty big vehicles to tow around, so it would be nice to reduce the weight a bit, while retaining the desired soundproofing, or even increasing it.

You can read up all about soundproofing on the web, but it might seem a bit opaque at first if you have no technical experience. There is a lot of kind of sloppy explanations out there in which people make it sound a lot more complex than it really is.  I recommend wikipedia, though, starting with the entry on Sound pressure level, and then Sound transmission class and OITC.

Anyway, basically a cheap way to improve the sound isolation of a tinyhouse without increasing the weight would be so-called decoupling.  Instead of attaching the inside wall to the outside wall, “staggered studs” could be used (google, sorry I shoudl have explained that better, you can find pics with a quick google though), complicating construction a bit, but not increasing the materials cost much.

Another thing would be to use plywood rather than tongue and groove walls.  Tongue and groove walls of course have cracks in them through which sound can travel.

Windows are the first place soundproofing usually goes, because they are the weak spot on the walls.  If the walls are decoupled, rather than putting a single window in, which would itself cause some coupling between the walls, the normal double glazed window could be attached to the outer wall and another single pane of glass used in the inner wall. For just soundproofing a piece of glass on the outside wall instead of the double glazed window could be fine, but then condensation could be a problem. Condensation can be a problem for double glazed windows, too, though, so all that needs to be worked out and planned for, to prevent any potential for mold growth. Triple glazed might make more sense, or some way to provide some ventilation around the outer window’s inner side, like a “trickle vent.”

Acoustic rockwool insulation could also be used, instead of foam.  It’s pretty cheap stuff, actually.  Incidentally, decoupling the walls and putting insulation in where the studs used to be touching can increase the insulation of a a wall quite a bit, because the studs conduct quite a bit of heat.  Not that heating bills are a big concern in a tinyhouse anyway, but it could be used to help achieve a house so well insulated it would be passive.  That extra pane of glass would help, too.

The floor is a problem, it needs to be decoupled too, but of course it has to support all that weight.  There are various products sold to try to provide some decoupling, including rubber “joist caps” and “quietfoam.”  None of them are, of course, as good as an air gap, but short of some sort of inflatable cushion….  Another option is rubber vibration isolation equipment mounts.  Also, because the house is to be moved, it still needs to withstand lateral forces, the walls I would think could stand up on their own, but the inner room will, since it is no longer connected to the outer walls, of course slide around if not restrained.  Obviously you don’t want that… One approach to solve this problem could be to use cables or chains to keep things in position, without conducting sound the way a rigid connection would. EDIT: I have been looking for some rubber isolators that have this sort of ability to withstand high peak stresses encountered during transport, without compromising on acoustic isolation. You could, for example, have an otherwise ordinary rubber isolator, but design in metal pieces to provide backup strength, which would only touch when the rubber is deformed quite a bit. So it can provide strength, and isolation, but not both at the same time (but it doesn’t need to), because to provide strength the metal has to touch. There seem to be some rubber mounts available for engines that have this feature, made for mobile applications, but it would be nice to have a thicker layer of rubber, because the thicker it is the better isolates (small compressions result in less transmissions of force). One example.

Suppose you imagine 2 boxes, one inside the other.  The inner box is resting on the floor of the outer box, but otherwise not touching.  Attach a cable to the inner box at the lower lefthand corner nearest to you.  Attach the other end of that cable to the outer box at the lower righthand corner nearest to you .  Do the analogous thing to all the other 7 corners of the inner box.   Great, now it’s restrained  against lateral movement.  Now lift the inner box up a bit relative to the outer box (let the cables get a bit longer.) This represents the separation between the floor of the inner box and the outer box caused by the floor joists and whatever piece of rubber or foam was used provide decoupling.  Now you’ll notice that in order to prevent the inner box from tilting you might want to add some short cables between all the lower corners of the inner box and the point on the floor of the outer box which is located directly below each corner.  All this would prevent the inner box from sliding around and so on while still leaving the floor pretty well decoupled, I think. Sorry, the drawing isn’t very good, but my graphics card doesn’t support sketchup, and I figure paint is good enough for rough drawings.

This sort of thing would be particularly useful for a tinyhouse that is going to be used as an office (perhaps in addition to as a home.)

Another thing is viscoelastic damping using something like Green Glue or Quietrock, or Serious Materials also sells Quietboard, damped plywood. It’s probably pretty expensive, though.

The ultimate would be vacuum soundproofing panels. I might do a post on those at some point. It is possible to block sound in a practical way using a vacuum, and it gives you a wonderfully light and highly effective soundproofing layer, even 70 decibels or more. Their weakness, of course, is the potential for leaks, but leaks can be detected and patched by various means.

UPdate:
I also recently found out about Noise Reduction Rating, Sabine, and other stuff related to soundproofing with fibrous material like fiberglass and rock wool. here are some links form my bookmarks:

http://www.soundproofingcompany.com/library/articles/the_dead_vent/
http://paulmadison.com/baffle.html
http://www.ironmongerydirect.co.uk/Products/Bolts_Stops_and_Accessories/Vents/2103/Hit_and_Miss_Vent_Plastic
http://www.passivent.com/cs_hotels.html
http://www.bobgolds.com/AbsorptionCoefficients.htm
http://books.google.com/books?id=f19_6NFg4jkC&pg=PA399&lpg=PA399&dq=random+incidence+absorption+coefficients&source=bl&ots=_3HAlABpLz&sig=1oqAvqgXXRwwWnrkjrjVW8suweI&hl=en&ei=ugEYTZKaF4OcnAfey6CoDg&sa=X&oi=book_result&ct=result&resnum=10&ved=0CGQQ6AEwCQ#v=onepage&q=random%20incidence%20absorption%20coefficients&f=false
http://en.wikipedia.org/wiki/Attenuation_coefficient
http://www.encyclo.co.uk/define/Sabine%20absorption
http://forum.studiotips.com/viewtopic.php?t=1632
http://www.webref.org/acoustics/s/sabine_absorption.htm
http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=801-31-10
http://en.wikipedia.org/wiki/Absorption_coefficient#cite_note-3
http://www.acoustics-engineering.com/sabin/wcsabine.htm
http://stason.org/TULARC/physics/acoustics-faq/4-2-What-is-the-sound-absorption-coefficient.html
http://www.sae.edu/reference_material/pages/Coefficient%20Chart.htm
http://www.engineeringtoolbox.com/sound-propagation-indoor-d_72.html

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Written by gregor

August 3, 2010 at 17:44

Posted in Uncategorized

2 Responses

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  1. […] is important to have this feature. The problem is, normal soundproofing is *heavy*. Very heavy. I previously mentioned decoupling, and […]

  2. […] is important to have this feature. The problem is, normal soundproofing is *heavy*. Very heavy. I previously mentioned decoupling, and […]


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