Soundproofing Feedback Needed

[Craig Vollmer]

I am in the process of renovating/finishing off a basement wood shop in my house. My long-term plan is to operate my shop as a business and with full time use on the horizon, soundproofing will be important for the rest of the house. I have been doing a lot of research on this (including some previous posts here) and would like feedback on my plan from anyone with experience or expertise, and have a few specific questions as well that I wasn't able to discern answers from previous posts here.

Some background... My house is an old (1927) two room school house. The part of the basement that will be house my shop was the old gymnasium. The shop space is 21'x46' with one separate 10'x10' room that will be a finishing room. All 4 exterior walls of the shop area are poured concrete. The floor is maple tongue and groove -the original gym floor. The basement extends 4 feet above ground. 6 full sized windows line one wall - I replaced the original single pane wood windows with modern thermal ones. I have gutted everything, but the floor. There are two interior door ways.

With the exception of about half of one wall that I built a lumber rack on, I intend to frame all walls with standard 2x4 studs. I am going to insulate the walls for thermal reasons, but sound transmission through walls is not a concern as they are concrete and not adjacent to active living space except the utility/laundry room, which is on the other side of a concrete interior wall. I am going to apply quiet seal green glue on the stud faces and surface with a single layer of sheet rock.

My main concern for sound transmission is through the ceiling. For the ceiling I am going to install a single layer of Roxul safe n sound in the joist cavities and install resilient channel, covered by a single layer of homasote 440 Sound barrier and a single layer of 5/8 sheet rock . I am also concerned about sound transmission through the duct work, most of which for the HVAC system for the house is in the shop. There will be no heat vents in the shop; I will have a separate heat source for the shop. I am going to enclose the duct work in bulkheads framed with 2x2's. There will not be a lot of space surrounding the bulk heads, but I am going to fill the voids with thinner layers of Roxul, resilient channel, homasote, and double layer of sheet rock. Acoustic putty pads around the electric boxes/fixtures in the ceiling.

My questions:

Will the walls transmit sound upward into the joist where attached to the upstairs or will the quiet seal green glue stop it well enough? Should I install something between the top wall plate and the floor joist above to break the pathway for sound? Use quiet seal green glue or something else?

Is a double layer of draywall on the ceiling better than the homasote/drywall combo for typical high decibel wood shop equipment noise?

I am concerned that the duct work will be a weak point because of the limited framing. I have read about a product called dynamat; I can't seem to find too much from a review stand point. Does it work and should I wrap the duct work in that first before enclosing and packing with Roxul - or am I good with the thin layer of roxul, resilient channel, homasote, and double layer of drywall? Or is there some other product I should consider? Same question here also about the homasote...am I better off swapping drywall for it?

Access to the joist cavity above the main duct is limited for installing Roxul without dropping the duct. If I enclose it as described is that going to suffice to block sound or should I drop the duct and put Roxul above as well?

Any suggestions on the doors? STC rated doors are cost prohibitive. At least the ones I have researched. I have a local home depot, but with their stuff aimed at typical residential use, I can't seem to find too much info on the sound blocking properties. I did see where some companies sell kits to seal the jam and bottom for sound, which I should probably consider, but there is still the door density itself to address. Any sources of cost effective doors that offer reasonable ability to limit sound transmission would be helpful.

I am going to install fluorescent strip light fixtures. Are they secure enough attached to the resilient channel? Attaching to the joists would give sound a pathway, wouldn't it?

Thanks for any feedback and help that anyone can offer. I want to get this as right as I can on the front end of the renovation.

Craig

[Scott Brader]

I'm not going to chime in on the soundproofing part, but I will caution you about the whole HVAC in the shop situation. My shop is in our basement where our furnace also lives. No matter how much DC you employ, fine dust gets into the HVAC system. My HVAC technician recommended that I change the filters at least once per month. That has helped to greatly minimize the dust getting everywhere else in the house.

Scott

[Mel Fulks]

I just did some soundproofing ,used Roxul, cellulose( hand crumbled and packed in ) and some mass loaded vinyl. One of those projects that shows little improvement until it's ALL done, think of sound as being a lot like water. One thing I did not use but hear only good things about is the Quiet Rock drywall, expensive but does the job of multiple layers of the regular stuff.

[Matt McCoy]

It sounds like you've done some homework already, so you probably already know that isolation and mass are going to make the biggest difference and will only be as effective as the sum of all of its parts. This will get expensive fast, depending on your expectations, and since you mention wanting to do it right the first time, you might consider consulting with an expert to help design your shop. Most of the methods you mention are used regularly in the dedicated home theater industry and might be a good place to start. It will be challenging to dampen the high dB of tools and the transmission of mechanical vibrations.

BTW, your space sounds awesome. Hope you can find some time to attach some pics.

[Peter Aeschliman]

I'm building out a soundproofed dust collector closet in my basement.

You mentioned resilient channel- I've read mixed reviews about using it by itself. Look into using the isolating clips with the channel. A lot more expensive, but from what I've read, they make a huge difference. As Matt said, the key is mass and decoupling. More mass means less vibration on the ceiling surface, and decoupling means less of that vibration passes into your joists and upstairs. Insulation is less important than mass and decoupling. Two layers of 5/8 drywall with green glue between them, screwed into resilient channel which is hanging from isolation clips- this is the gold standard. Leave 1/4" gaps between the intersections of walls and ceiling and use acoustic caulk rather than joint compound.

I've read that insulation is helpful at keeping resonance from the drywall from bouncing around in the joist cavity and making its way upstairs. So it's worth doing. But I've also read that if you do the above (mass and decoupling), Roxul won't really outperform regular fiberglass batt.

As for your HVAC, you need to think about noise, dust, and fumes. For fumes and dust, it's important to seal all seams in your ductwork. I recommend mastic. Snap lock pipe has seams along its length- seal those seams too. This will have the added benefit of improving your furnace's performance. You should also build a closet around your furnace, assuming it's the style that pulls its clean air and blows its exhaust outside (not the open hood vent that uses gravity). I think these are called "high efficiency" furnaces. If not, then your furnace needs ambient air in order to function... and you're going to have challenges there.

As for HVAC noise, your best bet is to box in the ducting using the same methods discussed above to avoid vibrations getting to the duct in the first place. I have an air return above the dust collector closet in my shop, so I did load it up with 3 layers of a dynamat-like competitor. It works awesome. Just make sure the matt is butyl based and thick. Avoid the cheap knock-offs that are asphalt based. They are stinky and don't adhere as well when it's hot. I think you'll find that using this stuff on all of your duct will be extremely expensive though.

Another option for HVAC is to replace your round metal duct with hose. Yes, this hurts efficiency so there is a trade off. But it won't pass vibrations nearly as badly as thin metal duct.

That's all I got! Good luck. There aren't any shortcuts on this stuff unfortunately.

[Frank Pratt]

Peter has some very good suggestions here. But Roxul does significantly outperform regular fiberglass batts in sound absorption. There is lots of published test data available on this.

[Peter Aeschliman]

I'm certainly no expert and haven't done exhaustive research (just lots of googling!). I don't doubt that you are correct about Roxul vs Fiberglass, and re-reading my post, I didn't make my intended point very well... which is that the distinction between Fiberglass and Roxul doesn't matter a lot if you decouple and add mass, since those efforts come closer to addressing the original source of the noise (short of not making noise in the first place, which would defeat the purpose!). First most important is to reduce the amount that your drywall vibrates by using mass (two laters of drywall, plus with green glue which is kind of a decoupler in a sense). Second is to decouple the drywall from the joists. These two things will dramatically reduce the noise that enters the joist cavity in the first place.

After that, from what I've read, the distinction between the two insulation materials won't make much of a noticeable difference because mass and decoupling handle the majority of the abatement.

However, it could be that if you don't decouple and don't double up your drywall that the distinction between Roxul and FG becomes more important- that I don't know.

I'm DEFINITELY not an expert at this- I'm just regurgitating what I learned through my own research... echo chamber bigtime!

[Frank Pratt]

This is one area where you definitely have to use belt and suspenders. Mass & decoupling are very important, but without absorption, you'll still get a ton of sound echoing around in that empty space & transmitting to the other side.

I built a room in the basement for the dust collector & did at LOT of research prior to construction. Here is what I did:
Walls: 2 rows of 2.5" steel stud with a .5" space between. Both halves of the wall filled with Roxul Safe n'sound. Both faces of the wall have 2 layers of 5/8 fireguard drywall with GreenGlue between
Ceiling: 2.5" steel studs supported by the inner layer of the walls & isolated from the floor framing above. Cavities filled with Roxul.
Door: 2 exterior pre-hung doors mounted back to back. Each door has a 3/4" layer of MDF with GreenGlue between it & the door. Each jamb was also fitted with a second set of weatherstripping.

Inside the room I have an Oneida V-5000 collector. If I stand 5' away from the room & start the collector, I cannot hear it. If I stand 1' away from the door & start it, I can just hear it. My office is above the room & I can't hear the collector running in the office.

[Craig Vollmer]

Thanks for the info. I think I'll be OK with the HVAC. The furnace is in a separate room separated by a concrete wall and will be sealed off from the shop. I already sealed my duct work joints with mastic to minimize heat leakage and they will be further sealed up in bulkheads.

[Craig Vollmer]

Thanks everyone for some great advice. I really appreciate the specifics and will use some of this info. It is pretty cool having my shop in this old school - can't beat the size of the basement. A lot of work to renovate the shop though and always a challenge to work around an existing structure...and the equipment that can't be stored elsewhere. Unfortunately it's put most of my woodworking on hold while I get the shop functional. Hoping to have it done this year and get back to making dust. Here's a couple pics. It's rough yet. Only one outlet and a couple old suspended ceiling lights dangling from old wire. It has a lot of potential though and can't wait until I can stop working on the shop and start working in it.
Shop 1.jpg

Shop 2.jpg

[Peter Aeschliman]

Very cool! Love the floor.

Good luck- you have a lot of work ahead of you, but it will pay off!

[Craig Vollmer]

Thanks Peter. Tongue and groove maple. Original floor from 1927. Unfortunately I've got some rotten spots. It's fastened to wood strips on concrete. That was before treated lumber. I'll have to patch a few spots, but in good shape overall for it's age. You mentioned a dynamat like product that you used on your duct work. Can you tell me the brand? Thanks.