Leaf me alone: is this 2 or 3 leaves

Howdy all! I've got a studio build coming up and have a quick question in regards to the existing walls. Firstly, this is in Dallas, TX at what was formerly an auto-body shop. The old shop had 2 large garages whereby 1 in this project is being converted into a control room. There is a medium sized gated parking lot in the front of the building (North), another auto shop about 30 yards to the West of the building, a tattoo parlor about 30 yards East of the building, and an empty lot/convenience store to the south of the building. The auto-body shop to the West primarily focuses on paint jobs and do not generate much noise. It is a busy area but the street noise is pretty low in the building apart from commercial airlines. My concern is that the East and South walls are brick, the North wall is cinder block, and the West wall is a finished wall about 7.5 feet high with 1/4 inch boards nailed into the tops - the adjacent room to the West is the kitchen and about 15 West of the doorway heading into the kitchen, above, is the A/C unit. When constructing the room, will these outer walls act as leaves whereby to achieve a 2 leaf system I am to finish with gypsum board only the interior framing? Or should I also attach the drywall to the outer framing and ignore the "leaf role" of the existing brick, concrete, and half wood walls. Also, the roof is aluminum with 16 inch steel beams supporting it and the height of the control room will be 9ft Floor Plan (South Orientation): Room Dimension (South Orientation): Southest Corner: North Wall: West Wall: iPhone App we wrote to calculate ratios, dimensions, etc but what is displayed is not the dimensions for this room: Happy Holidays!

welcome! please update your profile with your location. the iphone app looks interesting. if it's just a control room and it's basically an isolation shell within the space and it seems well short of the existing ceiling, you should be OK to build some massive walls (3x 5/8" on 2x6) and ceiling (3x 5/8" on 2x8 or 2x10 as dictated by the final span calculations). limit the penetrations to the entry door and HVAC baffle boxes. if there is any significant LF noise in the structure you might consider floating the isolation walls and a decoupled/dampened interior floor.

Thanks, Glenn - profile updated! A question that keeps popping up is whether or not we should construct the walls with gypsum on both sides of the framing or just one side. You mention massive walls - is your suggestion to to do 3x 5/8" drywall on both the inner/outer framework or just the inner? For some reason the proximity of the proposed wall to the existing wall makes me suspicious of creating a nasty resonant cavity if we do both sides of the framework. I am worried that the existing walls will behave as a 3rd leaf (if both sides of the framework are finished with the drywall suggestion) and compromise the economic/performance curve of the room. My analysis of the room was to build the walls with gypsum on both sides as massive as it is safe. A colleague of mine has used green glue on some projects and recommends using green glue instead of adding layer upon layer of drywall. I know how busy you must be and greatly appreciate your feeback! Cheers!

on the sides closet to the existing block walls, building it one sided (inner side) should be OK. on the bottom side i'd out it on both inner and outer since the wide gap is effectively a hallway and you'll need something to complete the MSM. even on the top side - inside and above the joists consider drywalling both.

Thanks again Glenn for the great advice. How do you feel about 2 layers of 5/8ths separated by a limp mass like "green glue"? You guys have been great!

Green glue is certainly useful but in this case you might be better off with another 5/8" layer.

gullfo wrote:

Green glue is certainly useful but in this case you might be better off with another 5/8" layer.

Surprisingly, this isn't so: http://www.greengluecompany.com/greenGl ... rywall.php

thanks Ted, that's a great link! what's fascinating is adding almost 3.5lb of GG per 4x8 sheet of drywall (i.e. ~7lb per pair of gwb sheets - each side of the frame) results in a 0.45lb/ft2 lighter assembly instead of a 0.22lb/ft2 increase. :wink: i don't disagree that GG is useful, and if budget permits go ahead, although in this case where building a single leaf, or it has significant space from the other mass, it's probably more cost effective for just the 3x layers on the inner walls/ceiling simply from a pure materials and labor cost. from a increased isolation per $ perspective, GG is a good deal but it is an out of pocket cost versus your total isolation needs.

If he's building walls next to the block wall, the resultant wall is a decoupled double leaf. Block wall + air space + new framed wall with drywall. I'd suggest 3 sheets of Drywall with less GG in between the layers. Split the fixed amount of GG into two thinner layers.

How much isolation do you need? A DD/space-framing ~4" filed with insulation/concrete block wall will have an STC around 65! Green Glue will improve that. Do you need more than a 65 STC partition? From you have written so far, no. Andre

Good question

agreed. it's interesting to note the LF below 80hz, as shown in the GG testing, is slightly better with the plain layers versus the GG wall (although to be fair the testing below 80hz isn't generally considered reliable hence the confidence rating being n/a or blank...)

True enough. Outside of the NRC in Canada, data below 80Hz may show us trends but absolute values are not presumed. Also lab to lab variations are higher below 80Hz. Having said that, damping has been shown to be effective down to the mass air mass resonance frequency

Also maybe an interesting point (maybe not), as we drop in frequency and approach the MAM frequency of the system, elements like decoupling, absorption and damping become less and less germane. You are approaching a point at which the decoupled assembly is now air-coupled and the system is now stiffness controlled. The stiffness gained with the third sheet of drywall now governs the system.

Ted White wrote:

If he's building walls next to the block wall, the resultant wall is a decoupled double leaf. Block wall + air space + new framed wall with drywall.

Would it make any sense or be effective to add anything directly to the surface of the block wall that would be significant in increasing his isolation? So the assembly would be as follows: block wall + mystery material directly attached to the block+ air gap + new framed wall.

Well, that's a good thought. Such a material would only bring practical benefit if it could damp the original wall or add significant mass. The original block is too massive and stiff to damp, and you'd have to add a great deal of mass to make a difference. So from a practical perspective, I don't think there's a product that would inprove things by being added to the block itself. The remaining viable option is still to decouple from the block, and add a massive damped leaf to the assembly. Lightweight absorption in the form of fluffy insulation will help lower the resonance frequency you'd be introducing.