How to Soundproof a Shed

The Concise Oxford Dictionary defines ‘shed’ as ‘a one-story structure, usually of wood, for storage, or shelter for animals, etc. or as a workshop.’ A lot of us think of it as that old rotting, leaking slapped-together wood thing, or beat up tin thing, in the corner of the back yard where the lawnmower and rake get stored–along with an assortment of useless junk. Soundproofing them is easy–a can of diesel fuel, a match, and a trip to the dump.

On the other hand, if your shed is actually a decent structure–both in size and construction–that you want to make more useful, soundproofing it is a positive investment to keep peace with your wife, your kids, and your neighbors.

 

Soundproofing a Wood-Framed Shed

Wood-framed sheds are probably the most common type of shed. They can range from an old pile of lumber that just will not fall down, to something you were building today. Chances are that you are not going to hire anyone to soundproof the building for you–unless you are planning a sound studio and have access to quite a bit of money. (In which case you might want to check out How to Sound Treat a Room.)

How much, or how little, soundproofing you need depends on what you are doing, or using, inside. And if you are trying to keep sound in, or keep noise out. You might have a noisy generator (in which case please check out our article How to Make a Generator Quiet.) Or you might want to do a lot of wood working. Or you might want a man cave.  Or for band practice. Or . . . whatever is important to you and/or your family. You are not doing this to provide peace and quiet for the lawnmower.

Soundproofing the Shed Floor

The floor in your shed will usually be one of: dirt, gravel on dirt, concrete, wood; or a combination of two, three, or all of them.

• Dirt – Regardless of what you are using the shed for, soundproofing the floor is not going to be your biggest problem. You have miles of mass below you, and sound mostly travels upwards and sideways. If you want some sound absorbing material, put down a carpet, moving blankets, or anything else that is thick and heavy. (Note: Cleaning a carpet might be an issue. Moving blankets can go into the washing machine–unless you are married.)
• Gravel – This will act much like the dirt floor. With the added problem of it not being flat. Putting anything down on the floor is going to be problematic. And should not be at the top of your soundproofing ‘To Do’ list.
• Concrete – A concrete floor gives you even more mass. Again, you will not get much noise penetration through the floor, but smooth concrete is much easier to work with. For soundproofing, you can put down QuietWalk Plus or cork underlayment. Then cover either with carpet. If you glue the cork to the concrete with Roberts Universal Adhesive you can use glue down flooring like laminate, or tiles for an attractive and pleasant finish.
• Wood – If the wood is laid on the dirt or gravel (which I have seen–shudder), any of the above options can be used. (Note: I suspect it is not going to be much more level than the substrate it is on.) But, if it is one of those sheds set on 4 x 4 or 6 x 6 pressure treated wood; not only will you have rodents and cats under there, you will have noise travelling through it. Because it is wood you have many more options for soundproofing. If it were my shed, I would add a second floor. Cover the existing floor with 6 mil poly vapor barrier. Attach 2 x 4 on edge at 24″ on center perpendicular to the existing joists. Insulate with ProRox SL 960 Rockwool soundproofing batts and cover with 3/4″ tongue and groove plywood sheathing. Then you can put down QuietWalk Plus, Cork, or Mass Loaded Vinyl (MLV) and finish with whatever you like. (Note: You may have to deal with some door modifications because of the raised floor.)

If you are satisfied with the existing wooden subfloor, you can just put down QuietWalk, Cork, or MLV, and cover it with whatever finish you prefer. Another quick, and inexpensive, option is to put down QuietWalk Plus and Exercise Puzzle Mat. These puzzle mats provide additional soundproofing, are easy to install, and easy to clean.

Other options include surrounding the shed with concrete blocks which will add mass to help keep noise either in, or out. Not very effective because they will move around–especially in any location where the ground freezes giving you frost heaves. Or bank dirt around the shed for the mass. This is way down on my list because it will hold moisture and accelerate any rot.

• Notes: For more information on flooring underlayment please see our article Best Soundproofing Underlayment.

          

Soundproofing Gaps and Cracks

Air is like water. It will flow through the  gaps and cracks. And it conducts Airborne Noise. (That water leak into the kid’s light fixture could be coming from a hole in the roof 20 feet away.) Get lots of  (it is quite inexpensive), and seal every gap you can find. (For bigger gaps you can use spray foam.) In the exterior sheathing. The corners. Between studs and cripples. Around headers. Around all electrical penetrations. I know that this sounds way too anal, but if you have ever been in a well-built new house just before the poly goes on the wall you will see black acoustical caulking everywhere. (The chance of getting in and out without wearing black goop somewhere on your person is almost impossible.) 

It is called acoustic for a reason. Yes, it keeps cold, and/or hot, air from getting in, and/or out. But it also makes the structure quieter. Which, in this case, is the prime reason for using it.  Auralax Acoustics Stopgap will provide an STC rating of 53 when applied according to manufacturers recommendations. 

   

 

Soundproofing the Shed Walls

Generally speaking, there are two types of interior walls to deal with–either finished or unfinished. Unfinished open stud walls are way easier to deal with. I have seen ‘finished’ walls of drywall, plywood, chip board, Styrofoam, 1 x 4, plexiglass, steel, among other weird and wonderful things. And the insulation has ranged from cobwebs, to fiberglass, to foam–all done, half done, and some done. If you intend to soundproof properly, plan to rip a lot of it off, or out, and make a trip to the dump.

• Unfinished Walls – ProRox SL 960 Rockwool batts between the studs will give you great soundproofing–both incoming and outgoing. (Note: Keep in mind that Roxul batts are 24″ wide. If your studs are 16″ on center, or some other weird dimension, your waste factor could be quite high.) Then acoustic caulking, 6 mil poly (don’t forget to seal the poly overlaps with caulking), then drywall or plywood. And Green Glue and a second layer of 5/8″ drywall to add mass. Mud and tape the drywall, then paint.
• Finished Walls – If your walls are insulated and drywalled, then all you have to consider is what to put over them for soundproofing. Seal the gaps. Add 5/8″ drywall with Green Gluebetween layers. Mud, tape, and paint. You can also use Mass Loaded Vinyl between the layers of drywall. MLV will absorb sound but it is heavier and more expensive than the Green Glue sandwich.
• Finished Walls – If your walls are uninsulated, and/or the finishing leaves a lot to be desired, your best choice is to rip everything back to the studs and proceed by filling the gaps and cracks, then treating the building with the ‘Unfinished Walls’ suggestions above.

Notes: The Green Glue test data shows this wall structure with fiberglass insulation will provide an approximate STC value of 50. Roxul inside the wall system will have an STC rating of 45 without the Green Glue and double drywall.     

     

                                                                                                                    

           

Soundproofing the Shed Ceiling/Roof

Ceilings, like floors, tend to be a little less important than walls. Unless deflected, sound will travel in a straight line. Any noise escaping the roof will usually continue straight up where few people live. And other than thunder and planes going over, not much noise will come in through the roof. But soundproofing will not only keep it quieter it will keep the building warmer or cooler. There is no ‘one size fits all’ solution because of the many types of roof construction.

• Trussed Roof – These are the easiest to deal with. Install 6 mil poly to the bottom of the trusses and drywall. You can also double drywall with Green Glue sandwiched between layers. Make sure you build an attic access hatch. You can then get into the attic to put in ProRox SL 960 Rockwool, or (my choice) blown-in cellulose. (Depending on the ceiling/wall composition, cellulose can get you an STC rating of up to 70.) You can usually rent a blower from wherever you purchase the cellulose. With a friend helping feed the blower, you can get both great soundproofing and insulation with 10″ of blown-in cellulose. (Note: Installing the ProRox SL 960 Rockwool or fiberglass batts before the poly has a lot of attraction. But, beware–gravity works. And depending on friction-fit to hold them up while you hang poly can be a large pain in the rectum.)
• Flat Roofs or Rafter Roofs – About the easiest way to add soundproofing to these roofs is with extruded polystyrene (2′ x 4′ sheets in various thicknesses from a home building center) nailed onto the undersides of the joists or rafters after the poly is in place.  For better soundproofing install ProRox SL 960 Rockwool batts first. (Note: Leave at least 2 inches between the insulation and the roof deck. If there is a way to introduce air flow between the roof deck and insulation, make sure you do it. Condensation and insulation are not compatible.) Then the polystyrene, then drywall. For even better STC value–double drywall with Green Glue between the layers.

Notes: Extruded polystyrene should add an STC rating of about 18 to your ceiling system. I have seen claims of STC 50 but do not have much faith in that number.

 

Soundproofing the Shed Window and Door

Make sure you fill the cavities around the window and door. Spray foam the outer 1″-1 1/2″ then finish filling the cavity with fiberglass. Do not pack tight; you will lose both soundproofing and insulation value. If the window and door frames are tight to the framing, caulk the seams with acoustic caulking. Your shed will most likely have a door, but with any luck, it does not have a window, but if it does . . . 

• Windows – Soundproof curtains or even packing blankets are your quickest, and least expensive option. You can change the window to a triple glazed laminated glass unit, but that will only get you an STC rating of around 35 (although my window customers have always raved about how quiet these units are–even on busy streets). If you do not need, or want, light and fresh air from the window; a good option is to take it out and seal the hole. Match the construction to the rest of the building.
• Doors – For a real soundproof door, replace your old one with a solid core wood door. (Note: Make sure you prime and paint it well regularly–especially the edges. Unfinished wood absorbs moisture and warps.) I would get a prehung door with a new frame (preferably wood) because then the hinges will work and the handle cut-outs will line up. Make sure you foam and fiberglass around the frame, and caulk the sill to the floor. Also, make sure that the weatherstrip around the edges of the door and frame seal well. Pay particular attention to the sweep. If it is a rubber fin unit, throw it away immediately and replace it with a mohair sweep. (The rubber does not work very well and will tear.) Other options are a soundproof curtain, or packing blanket, hung on the inside.

 

Soundproofing a Metal Shed

If your shed is one of those units that comes in a flat box and is mostly flat metal panels with a few heavier framing members, and a bucket of bolts and screws–I don’t even want to talk about it. Other than to say that the only way to get any decent soundproofing in the thing is to build another wood wall inside, with ProRox SL 960 Rockwool batts, vapor barrier, and either drywall or plywood interior finish. And unless you are into ‘tiny houses’, you do not have any room for anything but the lawnmower, rake, and some junk.

 

Soundproofing Quonset-Style Steel Buildings

Steel buildings (or sheds) are a popular option for garages, storage buildings, hobby buildings, and work spaces. Many manufacturers are beginning to offer buildings smaller than those huge buildings you see on farms and industrial sites. Most of them (like Toro Steel Buildings) have insulation packages available.

If you have the size of your steel ‘shed’, and maybe a picture; most manufacturers can give you a quote for the material you need to insulate and soundproof (to some extent) your existing building. (Note: If you know the name of the manufacturer–and the company is still in business–go to them first.)

These round wall/roof buildings are almost impossible to insulate and/or soundproof with conventional products–partly because of the way purlins are used in the erection and partly due to the difficulty of attaching product to the skin. Then there are the issues of vapor barrier and interior finishing. (The idea of bending plywood–not drywall–around the interior of a half round or ellipse–after working out how to frame it–will keep you up at night.

So stick with the manufacturer’s bagged product c/w the fasteners they provide. Because I am willing to bet that the DIY options will be just as expensive, take way longer, not work as well, and cost you a lot for antacid tablets. 

 

Soundproofing Rectangular Steel Buildings

I include sea-cans in this section because, other than the floor construction, they are just rectangular steel buildings. People are even building houses with them. Sea-can floors are usually hollow steel capable of spreading Impact Noise. Build a second floor. 6 mil poly tacked to the steel with acoustical caulking, 2 x 4 on edge at 24″ on center, ProRox SL 960 Rockwool soundproofing batts, 3/4″ plywood, and finish with whatever you prefer (with or without the extra soundproofing of QuietWalk of Cork.)

Your best soundproofing option is to build a room within a room. In other words, frame complete new walls and ceiling (if this is a viable option) inside the building. Not only will a wood frame wall allow you to easily add whatever soundproofing you want; it will provide decoupling from the exterior steel box. You will need 6 mil poly vapor barrier between the steel walls and your new wood wall. (Otherwise the condensation from the steel will soak into your soundproofing insulation.)

The best way to accomplish this is to frame the wall on the floor, staple the poly onto it, then lift it into place. (Note: If you plan to use ProRox SL 960 Rockwool, make sure your 2 x 4’s are 24″ on centre to accommodate the batts.) Once all of the walls are up, and stable, you can start soundproofing and insulating.

You can use ProRox SL 960 Rockwool soundproofing batts. Then drywall, mud and tape, and paint. (The inside of my garage is finished with 3/4″ plywood instead of drywall. I like to be able to hang anything anywhere without having to find a stud.) For extra soundproofing, you can double the drywall with Green Glue between the layers. If you opt for the plywood, and still want extra mass, you can also add drywall and Green Glue. 

Note: Do not poly the inside of the wall. You run the risk of sealing moisture inside. If moisture gets into it, there is no way for it to escape. You could accelerate any rotting or mold growth. Not a good option.

Note: You can use spray foam (see Wikipedia for more information about spray foam) on the walls and ceiling of these buildings. It is great for insulation but not for soundproofing. Spray foam provides a little mass and a little absorption, but no decoupling, or damping. And it is sprayed directly onto the steel walls and ceiling so it will conduct the sound vibrations. 

 

Final Thoughts

I have included Sound Transmission Class (STC) ratings for some of the suggestions I have made. Sound Transmission Class is a rating system used to measure how well something (in this case a wall or ceiling) reduces sound transmission. It is a rough reflection of of the reduction of decibels. Please see Wikipedia – Sound Transmission Class where you will find the following chart and more information on Sound Transmission Class.

STC	What can be heard
25	Normal speech can be understood
30	Loud speech can be understood
35	Loud speech audible but not intelligible
40	Loud speech audible as a murmur
45	Loud speech heard but not audible
50	Loud sounds faintly heard
60+	Good soundproofing; most sounds do not disturb neighbouring residents.

The International Building Code recommends an STC of 50 for walls and floors. Some states require an STC of 60 for apartments and condominiums. I think STC 60 is a realistic goal for any soundproofing a person does. You are probably only going to do this once; so why not give it your best shot?