Author Topic: help improve my design for exterior single frame wall  (Read 4840 times)

pharmaboy

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help improve my design for exterior single frame wall
« on: April 06, 2008, 09:27:50 PM »
Hi experts.

my situation isa single frame house on piers with 13mm drywall on interior, then 90mm hardwood frame (18" centres) with 1.5" rockwool insulation, sarking/building paper, then weatherboard sidings made of masonite.  The sidings are  very poor as an air barrier and the house is on the top of a hill and exposed to regular significant wind - 40mph + weekly.  when the wind blows I dont sleep, which is a problem especially for other family members!  :)

Now as it happens I want to change the cladding to a plywood 8'*4' rough textured sheet, so my design to help fix the problem is -     
inside to outside existing 13mm drywall, stud, add in extra layer of rockwool insulation, 10mm heavy drywall (7.5kg/m^2), air and vapor barrier stapled and joins taped, 35mm thick battens nailed over existing frame at 2' centres (leave as air gap and drained cavity), then butyl rubber gasket on battens, 12mm plywood nailed through ply and gasket, but nails will stop in drywall and not make it through to main frame.   the gasket should compress to about 2 -3 mm thick.

thus you get ply, 35mm air gap, some isolation from gasket, building paper to stop wind accessing stud wall, thinner drywall, rockwool, the interior drywall.

I am in australia so simply buying product is difficult - it took a great deal of luck just to get hold of the Gasket!.

Yes i have plans to do something for the underside of my floor (when I say something - I've no idea what, but i WILL do something! ), and access under the building for noise, and also some window treatment.

the battens are necessary for the cladding to go from 18" centres to 24"  centres - cladding is weather proof, but you do get condensation behind it and occasional storm would breach it slightly. (just in case people are thinking of stuffing the 35mm void with something, it would have to be water and mould resistant - ie not rockwool.

Am i on the way to a decent result or am i going to be disapointed and double rocking with isolation the interior drywall anyway?

Any feedback greatly accpeted.

graeme

pharmaboy

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Re: help improve my design for exterior single frame wall
« Reply #1 on: April 12, 2008, 02:26:15 AM »
After reading just about everything I could find on the net re soundproofing walls, I have changed the design from a 3 leaf system to a 2 leaf, ie  will be from the inside, now
13mm drywall
90mm rockwool filled air space
35mm rockwool filled air space between the battens (TOTAL 125mm filled air space)
Battens connected over 4mm butyl rubber gaskets (tubing  type stuff)
16mm fire rated drywall
sarking
plywood cladding mounted against more butyl gasket

gasket is endeavoring to isolate wind vibration of outside cladding into the structure - cant be perfect because they must be solidly connected for structural reasons - but it might just be enough to stop the frame creaking in the wind.

advantage of the new design - much more air space

possible disadvantage - there is a small gap - about 2 or 3 mm between the dry wall and the ply as a result of the gasket - it is hard to guess what effect this small space will be, but i've created it to ensure any condensation can drain away rather than keep the cladding wet, plus absorb some flex created by the wind.

The other possible solution, if it will help me, is to use  a 4kg/m^2 mass loaded vinyl instead of the drywall - obviously it will be a bit more expensive in materials ($16 / m^2 versus $7/ m^2 for fire drywall) - question is, is the MLV a better solution?



Mark Daveis

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Re: help improve my design for exterior single frame wall
« Reply #2 on: April 13, 2008, 08:36:10 PM »
125 mm air gap is good but I would use double drywall on each side. If there are any mechanical connections across the air gap then you wont have a double wall design and LF performance will not be good as it will act as a single wall.
Mlv is better for LF problems as it does not resonate except at very low frequencies and is about equivalent as a heavy sheet of drywall but works better if mixed with drywall in a design to help damp the drywall vibrations. Using lots of mlv layers instead of drywall is even better but expensive and the choice is between how much you want to spend and performance.
We have 90+mph winds here in the UK as I live next to the sea which really hammers our windows but does not affect the heavy concrete walls so enough mass is needed to stop these effects. :)

pharmaboy

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Re: help improve my design for exterior single frame wall
« Reply #3 on: April 14, 2008, 06:59:04 AM »
Mark, thx for the reply.

double drywall isnt really an option from a construction perspective, because of minimum fastening depths for the ply cladding/siding (the frame is old and 50mm machine driven nailing is about the limit of fasteners into the hardwood  -would require pre drilling and screwing 1500 screws!)

But i take the point that more is better, so perhaps 13mm drywall fire rated(ie heavier with fibrous layer) AND 4kg/m^2 MLV and the 12mm ply.  Would the MLV be best installed as a limp barrier direct to the battens, or between the drywall and ply?

Rest assured, if I had to build again, it would be concrete block!  ;) - all I'm really after is a an improvment of 10 to 15db - i think the existing wall may be as low as a 15 stc wall as it is - i'm expecting the ply cladding and sarking to make a decent difference on their own just by making the wall airtight on the outside.

cheers

edit  - the reasoning for the butyl gasket, isnt to try and make a defacto double wall design for sound, but to try and dissipate some of the wind energy striking the structure and dampening the wind impact which causes creaks and strains in the building fabric - i'm sort of guessing that any energy absorbed in that manner should help in some way - the highest windload last year was about 132kmh gusts  - but thats a rare event - but i'd like to sleep through 70kmh (40mph) gusts - so i need to reduce noise and increase bracing.

Mark Daveis

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Re: help improve my design for exterior single frame wall
« Reply #4 on: April 14, 2008, 10:46:17 PM »
Definitely if the wind is causing the structure to move and creak then soft rubber materials will absorb some of the energy.
It looks like you have low mass problems and because you don't have much space to fix layers of thick material then I would go with mlv attached limp to the battens and you could go for quite a few layers of mlv as its about 5 kg/msq per layer and its damped mass plus its very thin so takes up little space but a bit more expensive than solid materials such as drywall or board.
Mlv limp works better but still gives good results if more rigidly fixed.
Try and get as much mass as you can to block the sound and wind energy.
When we have really heavy winds we can loose tiles from the roof and the trash cans are blown all over the place. :)

joel

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Re: help improve my design for exterior single frame wall
« Reply #5 on: May 01, 2008, 04:02:02 PM »
MLV is most effective when attached in a continuous layer directly to studs/joists.  Then use the isolation tape and layer of dry wall.  Using the rockwool inside the cavity works well to absorb and block sound, the gasket tape is good for a decoupler and the MLV gives the needed barrier.  You could use a continuous layer of closed cell foam in the small space betweet the outside sideing.  This material absorbs and blocks sound very effectively - that's why it is used in light aircraft soundproofing.  It is also light weight and "waterproof" because of its closed cell makeup.  For info on this material see the first product discussed at  http://www.soundproofing.org/sales/prices.html