Central AC units on roof - stop the vibration?

[Peter Avery]

Hello,

We have a problem in our rented apt. that you might be able to help us address.

We live in a brownstone building with 7 units.  The building has central A/C.  There are seven AC units on the roof.  I believe they are the type with just a cooling unit, and the furnace/blower inside the apt circulates the air.  

Our apt. is on the top floor, back half of the building.  There is a persistent, low-grade vibration (which can be felt in the floor, and into our furniture) and hum (which can be heard throughout the apt.).  Almost immediately outside the apt door is a ladder leading to a metal hatch that opens to the roof. The hatch is just the metal cover - nothing else.  I believe the walls and ceiling of the apt have some sort of insulation in them because the noise is somewhat dampened inside the apt, as opposed to in the hallway right outside the apt where it is much louder.  In the hallway it sounds as if the sound just bounces back and forth like an echo chamber.  

The apt has a skylight to the roof, and the opening is located within about 2 feet of one of the units.  6 of the units sit next to eachother in a row, running from front to back of the building, and one sits alone right near the hatch.  The row ends at the one near the skilight and extends away from our apt, toward the front of the building.  

The landlord responded to our complaint by having the connections between units and roof re-insulated, I beilieve.  A worker removed the tar and insulation right around where the hoses enter the roof.  This alleviated the pulsing nature of the noise, but did little to quiet it.  It did not help with the physical vibration.  The units themselves sit on 2x4s that run parallel like RR tracks.  There is nothing between the unit and the 2x4s.  Under the 2x4s are rectangles of thick tar-type roofing material, and then under that, the roof itself.  

The main sources of the noise seem to be the skilight and what's coming in the door from the noisier hallway, whereas the source of the vibration seems to be just all the walls in general.

Do you have any suggested remedies?  Especially ones that are relatively low-cost - that the landlord would be more likely to take on?

Thanks for your time and assistance.  

[Carlos Rivas]

Dear Peter,

The following product is use in the marine, automovile, industrial field to damp unwanted vibration or noise.

Noxudol-3101 is a water-base, viscous elastic, noise, and vibration absorbing compound. It’s excellent for damping resonances in aluminum, steel, frp, wood, and polyglass. Our product performs better than older technologies, with less weight, less bulk, less material and less labor cost.



I can see that our product is well suitable for your sound proof need, and it contains all the characteristics you have been searching to eliminate your unwanted vibration, and noise in your boats. Noxudol-3101 is dependable, cost effective, and easy to apply; furthermore it has been tested by various authorities in the marine, automotive, and train industry such authorities have certified our product with seal of excellence.



Note: see the attached reference



Please, contact me at (310) 324-0149 or carlos@soshinusa.com



It would be my pleasure to assit you with your soundproof needs.



Best regards,



Carlos Rivas

Noxudol USA



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