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Architecture/Sound insulation

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QUESTION: It's not easy finding the right person for this question, but here goes: In our Mexican home we recently built a separate apartment over a flat cement roof. I thought adding an inch of styrofoam over the roof before the topping of leveling cement (light weight cement) would isolate the upper floor (topped with ceramic tiles) and reduce sound transmission. It didn't. We hear ordinary movements like a chair being moved as if someone were rolling rocks. My opinion is the approx. 2" isolated covering of cement/tile is acting as a drum and amplifying and transmitting the sound out to the walls. I'm looking for an engineered solution. Thinking even of cutting a groove in the cement around the perimeter of the floor to completely isolate. Others say maybe just drilling a few holes around the edges would mitigate. Your thoughts?

ANSWER: Paul,

Just like you, I would have expected that a layer of gypcrete over insulation would limit the sound transmission to an acceptable level.  Two methods of changing the frequency and absorbing sound are to add mass (such as light weight concrete) and creating an air gap between to layers of materials (any type of insulation should accomplish this).

My theory is that there is still a strong connection between the finish floor above and the ceiling material below.  Very much like talking some distance using two tin cans connected by a steel wire.  Unless you can identify what is acting as the "steel wire" in your case, then there is not much sense in adding more material or drilling holes.  Is your ceiling exposed concrete?  If the ceiling is more than 8 feet in height, then perhaps add acoustical tile or some type of suspended ceiling.

For what it is worth, my typical floor-ceiling assembly involves 1/2" resilient hat channels applied at 24 inches on center to the bottom of the wood floor truss.  5/8" drywall is screwed to these hat channels.  On the top side, we lay down 3/4" tongue and groove plywood and then 3/4" gypcrete.  This is considered "good enough" for my standards, but a layer of carpet padding and then a plush carpet floor is always sufficient to keep things quiet.

Good luck,

Richard Burton, AIA
Registered Architect
ICC Certified Plan Reviewer
NFPA Certified Fire Plan Examiner
www.arrow-architecture.com

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Floor Plan
Floor Plan  
QUESTION: Other than the walls shown in the attached floor plan, the entire floor has an inch of styrofoam under the leveling coat. The "strong connection" you mention has to be the wall connections. I agree that hanging sound insulation under would probably reduce sound in specific rooms below, and your scheme for doing that is I'm sure effective, but the first floor continues on for another 30 feet or so and the sound from the apartment transmits throughout the entire house, on both floors. It appears I've created a sound board that does the opposite of what I intended. It would be a monumental job to insulate all the ceilings below and we would still hear the ringing in the upper floors and walls. Is there an instrument that would give us precise measurement of vibration or conducted sound? Whatever action I take, I want to be able to measure the before and after objectively.  And what about the idea of cutting a grove around the perimeter of the apartment floor to totally isolate the vibration? Or maybe just putting rugs, etc on the apartment tile floor might be a solution. Your thoughts?

Answer
(1)
For $2,000 you can purchase a
BRUEL & KJAER SOUND/NOISE LEVEL METER 2238 MEDIATOR
Measure the sound level before and after you apply your solution.

(2)
I agree.
Cut the perimeter of the concrete floor down to the insulation board to interrupt the horizontal transfer of sound vibration into the walls.

(3)
Add acoustical tile ceiling throughout the lower level.

(4)
Add carpet throughout the upper level.

Good luck.

Richard Burton, AIA
Registered Architect  

Architecture

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Richard Burton AIA

Expertise

A combined total of 25 years experience with construction, architecture, and building code enforcement. Ask me about residential and commercial design. Ask me about design aesthetics, structural methods, and building something that will withstand severe weather conditions. Ask me my opinion about YOUR design ideas and I will tell you the merits of good design and challenge your thinking about practical issues. Ask me how to best find and work with your local architect and approach general contractors to get the most value for the least amount of headaches. You can ask me about improving your energy efficiency and things that are both green and practical. But don't ask me about solar panels and wind turbines unless you are currently paying your utility company 35 cents per Kilowatt. Otherwise the math does not justify the initial cost and return on investment. Ask me any building code question and how to get a building permit from the most difficult enforcement agencies.

Experience

Here in the midwest, we design and build "green" in ways that make sense. My construction methods prioritize weather resistance, ease of maintenance and durability. While a graduate student in San Diego, I taught drafting and history of architecture. After working ten years for other architecture firms, I have started my firm Arrow Architecture in 2008. More than half of my work involves commercial office buildings. But my portfolio of work also includes custom homes, residential additions, home remodels, and second story additions.

Organizations
President-Elect of American Institute of Architects - Lincoln, NE

Education/Credentials
B.S. Architecture - (Interior Design) University of Nebraska Lincoln 1997 Master of Architecture - (Urban Design and Professional Practice) NewSchool of Architecture - San Diego 2004 Graduated Summa Cum Laude ICC Certified Building Plans Examiner

Awards and Honors
AIA Henry Adams Medal and Certificate

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