Should You Insulate the Interior or Exterior of Your Home?

How to Add Wall Insulation in an Old House without Damage - This Old House

Making sure that your house is properly insulated can significantly reduce your monthly bills, as well as increase the thermal comfort in your home. But how do you decide which side of the walls to insulate? Read on to find out which are the cases in which interior or exterior insulation is the best choice for your home.

Interior insulation

You should consider insulating the interior of your home if:

You live in a condo or apartment

Technically speaking, you only own what’s contained within the interior walls of your unit, and the Condo Association won’t allow you to make any modifications to the exterior of the building. Party walls (walls that are shared by two or more owners) also go better with interior insulation, not just because this reduces noise from neighbors, but also because fire-proof insulation prevents fire from spreading quickly from unit to unit.

You have sufficient space in your home

Adding interior insulation will reduce the space of your home by several inches per wall, depending on the materials chosen. If you live in a home that is large enough or is open-style, insulating the interior might be best. Also, it might turn out to be cheaper than the external.

Your exterior walls are unsound

If you live in a house where your exterior walls are unsound or can’t be repaired easily, or even if you just don’t want to alter their design, it might be best to apply insulation on the inside. External insulation relies on scaffolding, as well as drilling into the walls, so it’s best to get advice from a contractor whether it’s applicable in your case.

You live in a listed building

If you live in a historic building, or in a historic part of town, applying exterior insulation might cause aesthetic damage to the façade, and there’s a good chance you won’t get the permits needed to perform the job. Even if a permit is granted, you might have to match the already existing design, which will be very costly. In such cases, insulating the interior is your only alternative.

You’re also redecorating the interior

Applying interior insulation can be disruptive to your household, even if you chose to do one room at a time. You will need to remove door and window frames, electrical boxes, skirting boards and other fittings during the process, as well as clean the floors and tiles when you’re done. So if you’re already scheduled for redecorating your home, now is also a good time to work on the internal insulation.

Exterior insulation

It’s better to consider insulating the exterior of your home if:

You live in a detached house

Because your house doesn’t share any exterior walls with other buildings, you’re more likely to lose heat. If you also have an attic and basement, insulating the exterior is a must, as heat will escape both ways. Also, many of the older houses lack interior insulation, while also having too little space to allow it, in which case insulating the outside will work best.

You live somewhere noisy

Although soundproofing can be applied both inside and out, it has better results on exterior walls. It’s also good to bear in mind that sound travels through walls, so it will be difficult to create a good soundproof barrier with interior insulation. With exterior insulation, you can increase the thickness of the layers considerably without having to worry about losing space. Consider this type of insulation if you live close to highways, airports and flight paths, or even just neighborhoods that get a lot of traffic.

You have issues with dampness

Adding interior insulation makes the walls colder, which will result in condensation both inside and on the surface of the wall, causing mold and mildew. Exterior insulation is much better in this regard, as it prevents dampness from penetrating the walls, without affecting their temperature on the inside.

You live in a cold area

Both interior and exterior insulation will improve the energy efficiency of your home; however, if you live somewhere with cold winters, insulating the outside has more uses. It will not only protect the outer walls, but it will also reduce the risk of condensation when windows are open for airing your home.

You’re building the house

Obtaining permits for exterior insulation can be difficult and even impossible in some cases, so if you’re in the process of building your home, now is the best time to add it. It’s also easier to install exterior insulation on basements at this stage, as you won’t have to worry about excavating and exposing the foundation later on. Now is also a good time to apply insulating material to the middle wall, which will be a more difficult job otherwise.


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