Most of the time when we’re talking about soundproofing, we tend to focus on dealing with the exterior and shared walls and doors. However, I believe that those of us who live with our families or roommates should pay special attention to interior doors as well. So that’s what we’re going to tackle today: soundproofing interior doors.
Although I do recommend soundproofing shared and exterior walls first, you might as well ensure peace within the household after you’re completely free from outside noises. Since doors are most often the biggest culprits when it comes to leaking sound, that’s where you’ll want to start.
Obviously, many of the tips I’ve mentioned in prior articles are going to apply here. Still, soundproofing interior doors looks a bit different than soundproofing your apartment door. Interior doors are typically much more vulnerable than exterior ones in a host of ways.
Of course, the differences are completely justified when you consider the purpose of the two types of doors. So before I share some modified tips for soundproofing interior doors, here’s a brief comparison of interior and exterior doors.
Interior vs. Exterior Doors: the Build
Because interior and exterior doors serve different purposes, it stands to reason that they would have structural differences. These structural differences determine how effective your door will be at regulating indoor temperature.
However, most manufacturers also take into account the fact that our doors need to protect our privacy. So they pay special attention to exterior doors, in particular. After all, it wouldn’t do to have our neighbors know all of our business, especially in an apartment building. And that’s why most of our front doors are thicker than the doors inside of our homes and apartments.
Interior doors are typically about 1.37–1.75 inches thick, while exterior ones are slightly thicker, ranging from 1.75 to 2.12 inches. There are slight variations, and some doors can be thinner or significantly thicker. However, these are the standard measurements for homes and apartment buildings.
Still, it’s not all about the thickness of the door. As I always say, soundproofing is all about mass and density. A door that’s thick but hollow is low on both of those qualities. Unfortunately, most interior doors are, in fact, hollow.
On the other hand, exterior doors need to be able to keep cold air out of our homes. Not to mention that they should, ideally, prevent outside noises from entering your house. Well, exterior doors are actually built with that in mind.
One of the most common types of such doors has a polyurethane foam insulation core that’s encased between layers of steel. The primary purpose of the insulation is to keep cold weather out.
However, it also makes this type of exterior doors much more effective at soundproofing than interior ones. If you recall, acoustic foam is also made of polyurethane. Between that and the steel layers, exterior doors should be airtight.
Interior vs. Exterior Doors: the Appearance
So, as you’ve just seen, interior doors are neither soundproof nor weatherproof. Sadly, they’re most often just made of two layers of wood, or even worse, fiberboard with a hollow space inside. In contrast, exterior doors are almost always metal, if not steel, layers with some type of filler in between.
Additionally, the two types of doors also tend to have different designs. After all, exterior doors are meant to be looked at. However, they’re meant to be seen from the outside, so many of them actually only have designs on the part of the door facing out.
Most of the time, exterior doors have more intricate designs than interior ones. Still, plenty of interior doors have a stylistic element to them as well. In fact, it’s much more common to see symmetrical designs on the doors inside of our homes than the front doors. At least that’s a point for interior doors.
Another point for them is that they’re cheaper, especially when they’re hollow and plain-looking. However, I certainly wouldn’t say that the amount you save is worth having a door that leaks sound. The lower prices and the design elements of interior doors can sometimes tempt people to consider installing them as a front door.
Well, I’ll be the bearer of bad news if I must. You simply can’t use interior doors as exterior ones, for all of the reasons we’ve just discussed. No amount of weatherstripping tape or draft stoppers will help you if the door itself is inadequate. And unfortunately, interior doors are by and large inadequate — so how can we fix that?
Soundproofing Tips for Interior Doors
This time around, I’ve decided to dispense my soundproofing advice by splitting it into two categories. As you’re probably aware, soundproofing doors, especially ones that are as flawed as most interior ones are, boils down to two things:
- Closing air gaps.
- Thickening the door.
No matter where you’re getting your advice, this is pretty much the standard checklist for both doors and windows. They’re both pretty self-explanatory.
The first category of advice simply deals with the fact that doors are, in essence, huge holes in your walls. So if you’re looking to soundproof your doors, you’re going to have to start by making sure that the door is airtight when you close it.
The second category will deal exclusively with the hollow core of your interior doors. With that in mind, let’s talk about the ways you might close the gaps in and around your doors.
Closing the Gaps
If you take a second to look at your interior doors, you’ll see that the biggest gap is the one between the door and the floor. Fortunately, that one’s fairly easy to fix, and you can do it with different types of materials too.
The first things you could use is rubber door sweeps, which are very effective at completely blocking sound. However, the main issue I have with door sweeps is that the rubber can squeak against wooden floors. Obviously, that’s not what you want if you’re trying to make your home a quieter one. Personally, I’d go for something like the Seal-O-Matic door sweep, which has a mechanism that lifts the rubber off the floor whenever you move the door.
Another option that I really like for closing the bottom gap of a door are draft stoppers (like this one on Amazon). They’re stuffed fabric inserts you slide underneath doors. Actually, I could even say that they’re some of the most effective soundproofing solutions I’ve used. What’s more, you could even make one yourself, as I’ve explained in my article on door sweeps.
Of course, if you decide that your DIY skills aren’t quite up to snuff to make a draft stopper, there are several household alternatives. You can stuff towels, blankets, even old clothes under the door and achieve a similar result. However, a draft stopper does seem to be the ultimate solution here, whether you buy it or make it.
Although the gap under the door is, in most cases, the largest one, there are several others you may need to take care of. Most of the time, exterior doors already have weatherstripping tape either on the door frame or on the door itself. Either way, the rubber tape ensures that there’s no gap between the door frame and the door once you close it.
Sadly, interior doors don’t often come with weatherstripping tape, so you’ll need to install it yourself. Fortunately, weatherstripping tape is cheap and easy to install. It’s just a matter of peeling the protective layer off the back and sticking it on along the three remaining sides of the door.
With the door sweep or draft stopper at the bottom and weatherstripping tape everywhere else, you should now have a completely sealed-off door. The only reason why you’d still hear noise coming through is if your door were too thin (which we’ll deal with in a bit) or not properly installed.
If it’s the latter, you may have more gaps in the wall surrounding the door frame. But this too has an easy fix. Just go along the door frame with a caulking gun (acoustic sealant). After you’ve done that, the only thing left to do is to take care of the thickness of the door.
Thickening the Door
Now, we’ve reached the crux of the matter. As I’ve said, interior doors have several design flaws that allow sound to travel freely. Firstly, they are often made of either wood or fiberboard, which are less than ideal materials for soundproofing. They’re also notably thinner and hollow, unlike exterior doors.
In order to combat these disadvantages, you’ll need to make the door thicker than it already is. Usually, you can achieve that with the same materials you’d use on your walls. That includes using soundproof blankets and curtains, MLV, and even acoustic foam materials. However, I’ll also explain how you can adapt the Green Glue sandwich technique and use it to reinforce your door panels.
So let’s start with the easy ways to add some breadth and mass to your interior doors. The first thing I’d try is to use thick fabrics. The homemade version of this would be just collecting thick curtains or adding grommets to old blankets and putting them up on a curtain rod above the door.
In fact, if you’re going for the homemade solution, I recommend getting double curtain rods that are slightly wider than your door. That way, you can have two layers of whatever you hang up. But remember, you’ll need fabric that’s long enough to brush or pool against the floor. Although, if you have a draft stopper already, this will be an unnecessary precaution.
On the other hand, if you want to use professional methods, you can just hang up soundproof curtains or room dividers. You can read about how these methods work in my previous article on this subject.
However, drapery isn’t the only thing that can reinforce your interior doors. In any case, not everyone would like to have a fabric covering their doors. If you’re one of those people, one thing you could do is to add some much-needed mass to the door with Mass-Loaded Vinyl.
Actually, I’ve got several ideas as to how you could use this classic soundproofing material with a bit of a twist. For one, you can combine the material with soundproof curtains by attaching it to the fabric. Soundproof room dividers, in particular, often consist of two layers of fabric. You can utilize that feature by opening the curtains and attaching MLV inside, then sewing the fabric shut.
The other way to use MLV to thicken your doors is to put it directly onto the door. If you cut the MLV carefully, you can make a single piece to cover the whole door and attach it with glue. Even Green Glue would work, and it would also add another layer of acoustic protection. If you don’t want to see the MLV, you can cover it with foam tiles or a wooden board or fiberboard.
Green Glue might actually be the scene-stealer in this scenario. You can even use it directly with wood or fiberboard (sound deadening fiberboard, preferably). Once you’ve cut your board to the size and shape of your door, you can apply a layer of Green Glue onto it and then paste it to the door.
You will need to take the door off and work on it separately, though. You need to have it in the horizontal position in order to apply pressure and make sure the Green Glue sets well. If you take off the handles before you do anything and fix up the sides afterward, you’ll be able to make the door look as though it hasn’t been tampered with. But at the end of the day, it’ll be much thicker — especially if you add a layer to both sides.
More on Soundproofing Interior Doors
If, after all this work, you’re still able to hear your kids bickering through the door, you may just have to get solid wood doors for your home. However, I believe that these techniques will help you get the peaceful home you deserve. Ultimately, doors really are one of the weakest links in your home, as far as soundproofing goes.
Once you fix those, you’ll be able to hear the difference instantaneously. And in any case, there’s no harm in trying, and the sooner you do — the sooner you’ll be able to bask in the results.