Can you put insulation in walls after house is built?

Author: Dr. Howard Kuhlman IV  |  Last update: Sunday, November 23, 2025

It may sound counterintuitive, but yes, absolutely! Existing walls, in old houses and new, can be insulated using a fantastic technology called "drill and fill." (You can learn more about how we use the drill and fill technique on our Insulation page.

Can you insulate walls after construction?

You can insulate any wall after drywall project by first cutting and removing the drywall. Then, apply the insulation, patching (where needed), and finish painting.

How do you insulate a house that is already built?

How to Insulate Walls in an Old House
  1. Apply a house wrap/vapor barrier to exterior walls.
  2. Attach 1-inch foam board insulation.
  3. Install siding over the insulation.
  4. Replace old windows with energy-efficient units.
  5. Caulk window trim and use weatherstripping to reduce air leaks.

Can I insulate my walls without removing drywall?

Insulation can be added without removing drywall. Holes must be drilled to accommodate the insertion hoses, but cellulose and fiberglass can be blown in. Foam can also be added in the same manner.

How much does it cost to add insulation to existing walls?

The average cost to insulate a wall is $2,400, but it often ranges between $1,150 and $6,000, depending on the project scope and materials your installation pro uses.

External Wall Insulation ~ The Ugly Truth?

Is it worth adding insulation to walls?

Energy Savings – Upgrading your wall insulation can help reduce energy loss, leading to better energy efficiency and lower heating and cooling costs. Noise Reduction – Insulation has sound-proofing properties and can help dampen noise. If you live on a busy street, installing wall insulation can make a huge difference.

How much does it cost to insulate a 2000 sq ft house?

The cost to insulate a 2000-square-foot house can range from $2,000 to $6,000, depending on the type of insulation used and other factors.

Why don t builders insulate interior walls?

Interior walls are often left uninsulated during construction because the energy efficiency benefits are less significant than those gained from insulating exterior walls, floors and ceilings.

What is the cheapest way to insulate internal walls?

Thermal lining paper is among the cheapest ways to insulate internal walls. This thick, insulating wallpaper can be easily applied directly to walls, making it a quick and straightforward solution. Costing around £10 per square metre, it effectively reduces heat loss and is perfect for smaller DIY projects.

Do you need a barrier between insulation and drywall?

If you live in a colder climate, you'll be heating your home from the inside to keep the frigid weather at bay. That means most of the humidity will be generated from within, so the barrier should be installed between the drywall and the insulation.

Can I insulate my walls from the inside?

Internal insulation can be fitted when you're planning to redecorate anyway, or to fit a new kitchen or bathroom. You can also spread the cost by tackling one room at a time. External insulation will also cost less if you fit it when you're having other work done to the outside.

What is the best insulation for exterior walls?

Foam Board or Rigid Foam

Foam boards -- rigid panels of insulation -- can be used to insulate almost any part of your home, from the roof down to the foundation. They are very effective in exterior wall sheathing, interior sheathing for basement walls, and special applications such as attic hatches.

Can you over insulate a house?

It is possible to over-insulate your house so much that it can't breathe. The whole point of home insulation is to tightly seal your home's interior. But if it becomes too tightly sealed with too many layers of insulation, moisture can get trapped inside those layers. That's when mold starts to grow.

How to insulate an already built house?

  1. Injection foam: This is a popular option where expanding foam is injected through small holes drilled into the wall, filling the cavity with insulation.
  2. Blown-in insulation: You can also use a blown-in insulation like cellulose or fiberglass, blown into the wall cavities through drilled holes.

Is it code to insulate interior walls?

State and local codes don't call for interior insulation, so usually only in interior walls if the homebuyer specifically asks the builder to include it. If you weren't included in the building process, assume your home's interior walls are not insulated.

What should you not do when installing insulation?

Leaving Too Many Gaps

One of the biggest problems DIY homeowners face is leaving too many gaps in their insulation. Gaps or insulation that isn't secured correctly can leave the building structure open to air and moisture leaks. Spray foam insulation is best for reaching into small cracks and any areas left open.

What is the cheapest way to insulate a wall?

Here are the three cheapest ways to insulate internal walls:
  1. Insulation Boards. Insulation boards are a popular choice for internal wall insulation because they are relatively affordable and easy to install. ...
  2. Battening the Walls. ...
  3. Building a Stud Wall.

Can you add insulation to existing walls?

There are Two Ways to Insulate Existing Walls (That Are Empty) Under the right circumstances, certain types of insulation can be installed directly into a wall through small holes, including injection foam and blown-in cellulose.

What are the cons of insulating interior walls?

If not installed correctly, interior wall insulation can potentially create moisture problems. In some cases, insulation can trap moisture within walls, leading to mold growth and structural damage over time. This is particularly concerning in older homes or in areas with high humidity.

Is wall insulation worth it?

Absolutely. Wall insulation prevents your home from heating up in summer and keeps your home warmer in winter. Around 15-20% of a home's heat loss and gain occurs through the walls. Without adequate insulation in your walls, heat would pass in and out of your wall material without much resistance.

Do interior walls need a vapor barrier?

Not every wall does. A vapor retarder is a material used to prevent water vapor from diffusing into the wall, ceiling or floor during the cold winter. Whether or not you need a vapor retarder hinges on three main factors your climate, your home and the location of the wall you're insulating.

How much does labor cost to install insulation in walls?

Most installers charge between $40 and $80 per hour to install insulation, so the more complex the project, the more it will cost. A few complexities that may increase the cost of labor include: Your installer needs to install insulation in hard-to-reach areas.

How many bags of insulation do I need for 1000 square feet?

For example, if the square footage of the room you're planning on insulating is 1,000 square feet and you want to achieve an R-value of 60, you will need approximately 17 bags to fully insulate your room. If you are using loose fill insulation, the coverage varies based on the R value that is needed.

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