Please critique my new build

[sharward]

I realize that building techniques and products vary throughout the world... But I keep proposing dual frame construction (no blocks) because I really do believe that may be best for isolation. Would an outer frame, sheathed with OSB for stability, and then a thick layer of stucco applied to a styrofoam base be an option?

Does it have to be concrete blocks? If so, then fine... But nobody has answered that question yet.

--Keith

[AVare]

Fortunately the type of construction you are thinking of has several similar designs tested by the NRC with the OITC data. OITC IS usefull for comparing music isolation.

Sorry, I don't hve URL but do a google search for NRC an duse their search engine for OITC. That should get you useful results.

NRC also has (literally) hundreds of test results with the TL data but only STC summary analysis. Teh needed info is still there but you have to work it out.

Good luck!
Andre

[Deluks]

I realize that building techniques and products vary throughout the world... But I keep proposing dual frame construction (no blocks) because I really do believe that may be best for isolation. Would an outer frame, sheathed with OSB for stability, and then a thick layer of stucco applied to a styrofoam base be an option?

Does it have to be concrete blocks? If so, then fine... But nobody has answered that question yet.

--Keith

Well I also live in London, and there's no way I'd build my studio with two wooden frame stud partitions, simply because some cheeky bugger will probably try and break in and steal stuff!
Concrete blocks/bricks would offer much better security I would've thought.

[sharward]

Well I also live in London, and there's no way I'd build my studio with two wooden frame stud partitions, simply because some cheeky bugger will probably try and break in and steal stuff!
Concrete blocks/bricks would offer much better security I would've thought.

Someone would, what, bust a hole in 1" of solid stucco attached to styrofoam attached to OSB? OSB is about the same strength as plywood, and stucco is a type of cement/concrete mix. Are we on the same page here?

[knightfly]

Another reason for masonry outer, especially in foggy old London and thereabouts, is WATER retention - masonry can retain approximately 100 TIMES as much water as gypsum before having problems with mold, etc - review Building Science Corp's PDFs (links in the REFERENCE section) for more on this.

Yet another reason - last year another UK member was looking for alternatives to gypsum - seems the stuff cost about 4 TIMES as much there as here, while masonry products were almost reasonable.... Steve

pps - mass is mass; concrete is approx. 3 TIMES the density of gypsum so 4" of concrete would equal about 12" of gypsum, which would REALLY get expensive at $25 or so per sheet

[sharward]

I stand humbly corrected! (Sitting, actually...)

[knightfly]

Standing/sitting corrected is better than laying, rejected

As to wall construction - if you build 4" outer masonry and "4x2" inner stud frame with 2 15mm gypsum, the best way to handle insulation (both for sound AND moisture) is to NOT put insulation against the masonry; instead, try to find some of that fiberglass strap material that's used to band heavy boxes and stuff together - build your inner frame on the floor, add a "4 x 1" diagonal brace (you can leave this in place across the inside edge of the frame), then fasten the fiberglass strapping (it's about 15mm wide, yellow usually) across the inside of the frame, perpendicular to the studs and parallel to the floor. I like to use roofing tacks, at least 1" long - neither Rod nor I trust staples for this.

Place the straps across the studs at about 1 foot intervals, bottom to top - then stand the frame up (if you build the frame so it is 1/4" shorter than the total distance from floor to ceiling, it will just clear when tilting) - or, with new construction you may have these interior walls up before the interior ceiling frame, so no matter. (Keep in mind that you want TWO leaves of mass ALL AROUND, so the ceiling should be similar in construction to the walls in that respect.)

Once your wall frames are standing, you can place fiberglass insulation batts in the stud cavities - if your space will be heated more often than cooled, any foil or paper backing goes to the inside of the space, against the inner gypsum.

The fiberglass strapping across the backs of the studs keeps the fiberglass from pulling away from the inner layer of gypsum, thereby improving the damping of the wall for better isolation.

If you intend to support an inner ceiling frame on the inner wall frame, be sure to double the top plates. IF your bottom plates will rest on concrete, be sure to get some building felt (bituminized paper) and place a layer or two under your bottom plate for a thermal break; keeps any sweating from the concrete away from the wood. Pressure treated lumber for the base plate wouldn't hurt, if it's available.

Beyond that, most of what you need to know is in the first 2-3 threads in the REFERENCE section... Steve

[Wurlitzer]

Steve,

I just spoke to my man who's here today to start digging. Turns out I'm wrong about the building regs. We can either use 190mm blocks, OR use 100mm block with piers every three metres at least for structural support.

We had originally decided against the piers, because we're building right up to the edge of the property and didn't want to lose floor space by allowing the extra space around the building for piers. But now we've come up with the idea of putting the piers on the INSIDE of the outer leaf.

This would mean we'd have a 165mm air gap, but where the piers are they'd jut into that for 100mm. We would only need one at each corner and probably one half-way along each side. My question is - how much would this affect the TL?

I'm presuming that the important thing is the GENERAL distance between the two leaves, and that it's not the end of the world if that distance is shortened in just a few places (as it will be anyway, for example, by the struts for the inner leaf). Am I right?

If this sounds OK, I think we'll definitely go with this design instead.

Many thanks for any help with this. We need to start ordering blocks pretty soon.

[knightfly]

You presume correctly; I doubt your TL would drop by even a dB because of the piers. Just make sure the inner wall frame doesn't actually TOUCH the outer masonry wall... Steve

[Wurlitzer]

Just did some basic calcs on your options - keeping the total wall thickness constant, using 100mm concrete block with the extra 90mm added to the air gap, improves the low end TL by about 5 dB over the thicker block - in each case, the inner leaf was 2 layers 12.5mm gypsum.

The added air gap helps the low end more than the extra thickness of concrete. So as long as your walls won't fall over being only 100mm thick, that would be your best bet. Cheaper AND better isolation... Steve

(this is with 100mm block, 165mm air/insulation, 2 layers 12.5mm gyp)

It now looks like, due to engineering factors brought about by the split foundation we will be using, the total wall thickness will need to be 360mm instead of 300.

So using this revised plan, we'd have 100mm block, 275mm air/insulation, 2 layers 12.5mm gyp.

Question: The air gap is now pretty big. Does that affect the issue of what thickness blocks would be best? ie, for a total wall thickness of 360mm, would we now be better off with 190mm block, 185mm air/insulation, 2 layers 12.5 gyp?

I'm not sure at what point increasing the air gap starts to give diminishing returns, and how it compares to increasing the thickness of concrete.

Many thanks.

[Wurlitzer]

Sorry, I got the maths wrong in that previous post. Also, the positioning of the outer walls has changed slightly again. The two possibilities are:

a) 100mm block > 210mm air/rockwool > 2 x 12.5mm plasterboard

b) 190mm block > 120mm air/rockwool > 2 x 12.5mm plasterboard

Same total thickness (now = 335mm). Which is best?

Thanks.

[knightfly]

(a) STC 78/50 dB @ 50 hZ
(b) STC 83/42 dB @ 50 hZ

The thinner block with wider air gap is better at low end, which is harder to stop. Therefore (A) is your best choice, provided there are no windows to muck it up... Steve

[Wurlitzer]

Hehe - you just addressed the window issue in my other thread.

There's another factor which is that the thinner blocks are considerably cheaper, and easier to carry. (This latter part might not sound important, but I live in a terrace house with no vehicle access to the garden. All building supplies need to be dropped off on the side of the road outside the house, and carried by hand through to the back garden for the building. We're currently working on shifting eight tonnes of ballast for the foundations this way, and not looking forward to the blocks!) So I guess I'll go for that.

But just out of interest - I take it from your figures that the thicker blocks and smaller airgap would be better for mid frequencies, but worse for lows. This is the opposite of what I would have expected, as greater mass is required to control lows. Strange...

Thanks again for your help.

[knightfly]

Just shows how important the air gap can be in msm calculations