How To Soundproof A Door - Part 2

Last week I wrote about how to build a soundproof door part 1, however, after lots of thinking and designing I have scrapped a lot of what I taught in part 1 of this series. This is an iterative process for me as I am designing the perfect doors for my clients. 

In part two of this series I will go over my new findings and my new design. The entire goal is to create an affordable yet solid soundproof door for all home studio enthusiasts. I have borrowed ideas from Rod Gervais, J.H. Brandt and my own building and design experience to create what I think will be a very effective and affordable soundproof door plan. 

1) The Air Gap and WIC Isolation 

First, I found that the WIC isolation clips made by Mason Industries are 1 1/2" wide. Meaning your air gap between your walls must also be 1 1/2" not the usual 1" I recommend. The reason I am recommending using the WIC isolation clips is that they can each hold up to 250 lb and are much higher quality than the usual I-B3 sway bracing clips I recommend. The I-B3 clips hold 38 lb per clip. This said you could still use the I-B3 sway clips for our doors since the doors each weigh 123.5lb. 

2) Where To Place Your Rubber Seals

The big discrepancy between JH Brandt's door design and Rod Gervais's is in leaving a gap between the double wall or connecting the two with wood. I like JH Brandt's design better because it keeps the integrity of our double wall system, whereas Gervais chooses to bridge the gap at the door with 5/4" wood stock because he feels the doors need the support. I agree with JH Brandt that we can support the doors using the WIC clips and not sacrifice our double wall system. However, if we do leave the air gap, Brandt points out that there will be odors that emanate from the double wall cavity. 

To block the odors we add a rubber seal around all four sides of the door opening. The rubber should extend from the edge of the outer wall to the edge of the inner wall. According to Brandt, you should also place rubber on the floor of the opening and ensure it is sealed against the two sides. I question whether this is necessary and may removed it in future plans, but for now it is part of the design. 

The rubber should be attached with screws, but you also should run three beads of acoustic sealant down the middle and sides of the rubber before adhering it to the studs and floor. You can see the rubber in the diagram below attached to our stud wall and concrete floor. 

*As a side note, in part 1 of this series I had the rubber on the outside of our king studs. I have changed that design because I no longer want to use pre-made door frames. I will explain why later on. 

3) Building Your Door 

The actual door, meaning the swinging wood is going to be made from a solid core door that is 1 3/4" wide. This door should weigh around 66 lb (30 Kg). Now a 66 lb door alone is not enough mass to match our double drywall. 

The two layers of 5/8" drywall equals 4.4 lb per square foot (10.7 kg/ sqm). We need our 36" x 80" door to weight at least 4.4 lb x 20 square feet = 88 lb (40 kg). 

To do this I like to add 16 gauge plate steel to and 1/8" plywood to the back of each door. This is the side of the door facing the inner wall. 

16 gauge steel weighs 2.66 lb/ sq/ft. And 1/8" plywood weighs 0.4lb / sq/ft. The steel and plywood will go on the back of each door leaving a 3/4" gap around the door. The gap is to create a bank vault seal as you can see in the diagram below.  

 Because of this 3/4" gap the weight of our added plywood and metal is about 57.5 lb (26 kg). That brings the total weight of the door to about 123.5 lb (56 kg). This is well over the 88 lb we needed to match our walls. Going over is a good thing, because our doors are a natural week point and we want to beef them up as much as possible within reason. 

So how do we attach the door to the door frame. The answer is with our continuous hinge. I recommend using the ABH A110HD Heavy Duty Full Mortise Concealed Continuous Geared Hinge. This hinge will help with hanging the door plumb with the frame and will hold the added weight of a heavy door. 

Lastly, to finish building our doors, we will need a door lockset. Now from part 1 you noticed I recommend a mortise lockset. The reason is twofold. First, we want something that doesn't fully go through our door and second we want a lockset that can withstand the added weight of our heavy door. I recommend buying the Cal Royal NM Series Mortise Lock. This lockest has a 2 3/4" backset, which is just enough room to clear our bank vault seals. It also fits a 1 3/4" door. This is an important detail to note, your added metal and plywood will have to fit around the door handles in this case. This is not a huge deal, but does require a bit more care when cutting the metal and plywood to fit the back of the doors. An important detail is to add some thin closed cell foam that will go over the mortise lockset. Poke holes where the handle lever will be. This will create one more solid seal to prevent air and sound from traveling through the mortise lock. 

That covers the door itself. As a side note, it is a good idea to hang the door with just the solid core door first and then add the metal and plywood after it is hung. You can add the lockset towards the end as well. It might be easier to cut out the mortise for the lock before hanging the door. 

4) Building Your Door Frame 

In part one of this series I had said to use a pre-made steel frame, however, after much thought and consideration I have decided to stick with the tried and true method of building your own door frame. Because our doors are so heavy we are going to use 5/4" wood stock to frame our door. The frame will attach to each 2x4 stud in the rough opening and will protrude out 1 1/4" to run flush with the two layers of 5/8" drywall. See the diagram below. 

After we have build the frame we need to add our first set of bank vault seals. I like to make these out of 1x3" lumber. I then attach 3/4" Frost King Weather striping to the ends of the 1x3" to create a tight seal against our solid core door. See the diagram below for an idea of how this works. 

5) Adding Zero International Seals Around the Door 

Now that you have the frame, the door, our added metal and plywood on, you are now ready to seal up the door completely. To do this we will use Zero International seals. I like these seal because they are high quality and have excellent acoustic ratings. The seals I recommend are: 

• Zero International Heavy Duty Surface Mounted Automatic Door Bottom - $157.58
• Zero International 770AA Adjustable Perimeter Gasketing Acoustic Door Seal Set - $538.64

These seals will go over the metal and plywood of the door. See the diagram below to see how the perimeter seal works. 

These perimeter seals can be adjusted to fit snugly against the door ensuring no sound will enter or exit the door. 

The door bottom is a very important part of the this door system. The door bottom I recommend is a drop seal and will seal the air gap below the door when the door is fully closed. See the diagram below. 

Once you have installed the door bottom your door should be air tight and ready to go. You can add some trim around the outside and seal it with acoustic caulk to finish off the door. Now you just have to repeat all the step for the second door and you will have your communicating door system. 

6) Adding Rigid Insulation Between Your Door Frames

The last step to finishing our doors is to fill the gap between our two stud walls and rubber with rigid 3lb per square foot fiberglass batts. I recommend using either Corning 703 or Knauf Ecose insulation. Cut the fiberglass batts down to size so that the first layer fits snug up against the rubber and the two 2x4's in our framed wall as well as the two headers. 

Next, we will add the second layer of insulation, but this time we will wrap it in acoustic fabric such as Guilford Of Maine. This will fill the gaps between our 1x3 boards around all three sides of the entryway. It has the added benefit of increasing isolation and making our door look nice and clean between the walls. 

 J.H. Brandt recommends adding two acoustic panels on the back side of each door in the air gap. He says this can increase the doors attenuation by 10 dB. I would recommend this if you have the budget and the space between your doors.  

7) How Much Does This Door System Cost

If we add up all the costs not including the framing of the wall itself we get the following: 

• Home Depot Solid Core Door - $124
• Neoprene Rubber Strips - $27.89 (for 10')
• Cal-Royal NM Series Mortise Lockset - $206.96
• ABH A110HD Heavy Duty Full Mortise Concealed Continuous Geared Hinge - $85.05
• Zero International Heavy Duty Surface Mounted Automatic Door Bottom - $157.58
• Zero International 770AA Adjustable Perimeter Gasketing Acoustic Door Seal Set - $538.64
• Frost King Weather Striping - $13
• 5/4" Wood Stock - $24
• 1x3" Wood Stock - $22
• 16 Gauge Metal - $120.43 
• 1/8" Plywood - $18.98

Total Cost Per Door = $1,338.53 or $2,677.06 per entryway. 

Could you build these doors cheaper. Sure, you could get a cheap door handle, forgo the added perimeter gasketing. However, every corner you cut is a weak spot in your entire design. I try to balance cost with budget and things like the mortise lockset and perimeter seals are important in my opinion. 

*if you build your doors right, but don't use green glue you will have saved the cost difference anyway and will have a better soundproof room in the end.