Is Insulating Plaster Walls a Good Idea?

Amy Pawlukiewicz
Written by Amy Pawlukiewicz
Updated November 9, 2021
Home with plaster walls
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Stop sky-high heating and cooling bills for your older home with plaster insulation

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You’ve noticed recently, or maybe not so recently, that your house tends to let the cold in during the winter. Or perhaps it’s inviting in more heat than it should be during the summertime. Whether you’re dealing with one or both of these problems, the answer may be to insulate your plaster walls. Learn whether or not insulating your home’s plaster walls is the right decision for your home.

What Type of Houses Have Plaster Walls?

If you live in a home built before the 1950s, it likely has plaster walls. A common problem with plaster walls is that they can crack and break away from the lath—thin, closely placed strips of wood—in chunks as they age. But if yours are in good condition, they can add some historical allure to your home.

Why Should I Insulate My Plaster Walls?

You can sum up the answer to this question in two words: energy efficiency. Older homes are often beautiful but drafty, as they tend to allow air into the house through the cracks in the walls. Since most new homes didn’t have central air-conditioning until the late-1960s, this was a way to keep the homes cooler during the summer months.

But nowadays, adding some insulation to your plaster walls can help regulate your home’s temperature and decrease your heating and air conditioning bills. Insulation helps keep your home cooler in the summer and warmer in the winter by not allowing the air produced by your HVAC system to escape as easily through the walls. On average, homeowners save 15% or between $200 and $600 a year on utility bills once they insulate their homes.

DIY vs. Hiring a Professional

Professional installing insulation in home
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Adding insulation to your plaster walls is definitely a task best left to the professionals. An experienced insulation professional can tell you where you need to repair large cracks in your plaster. They will also be able to retrofit your home properly without damaging the structural integrity.

While it may be tempting to simply drill holes into your plaster, blow in some cellulose, and patch them back up, this method can cause major problems down the line. Moisture can build up inside the walls, causing mold and wood rot, both of which are costly to repair and potentially damaging to your family’s health.

How the Pros Insulate Plaster Walls

To insulate your plaster walls, the contractor will blow or inject loose fill or foam insulation, and then install proper sealing and a water-resistant barrier. They may also add cladding, another layer of insulation that sits between the blown-in insulation and the outer walls. Ideally, they will then install a rainscreen layer to ensure that moisture doesn’t get into the walls. Once everything is in place, they will carefully seal any holes they cut to ensure that air doesn’t get into the walls. Finally, they will repaint the walls using a vapor-resistant primer.

There’s also a possibility that your walls will need a little TLC to repair large cracks before and after the insulation job. Your insulation professional can help you find a qualified plaster professional to deal with those cracks so they don’t become a problem in the future. The cost to hire a pro to plaster a wall runs between $200 to $1,200.

Cost of Insulating Plaster Walls

The cost of insulating plaster walls is usually $1 to $4 per square foot. According to HomeAdvisor, blown-in insulation is the easiest way to insulate walls since it only requires cutting a hole in the wall instead of taking the wall down and rebuilding it. However, the labor cost for spray foam is higher than other types of insulation because it requires more preparation and experience.

On average, spray foam insulation costs $0.45 to $1.50 per board foot. Blown-in cellulose is a little more expensive at $0.60 to $2.30 per square foot. Board feet is a measurement of volume, taking into account height, length, and width, while square feet only accounts for surface area.

As far as return on investment (ROI) for home projects, adding insulation has one of the highest ROIs. Not only can it increase the value of your home when you sell it, but you’ll also save on utility bills since you’re not allowing your air to escape anymore.

Do I Need a Home Energy Efficiency Audit?

If you’re looking to increase your home's overall energy efficiency by retrofitting your walls, you may want to invest in a home energy efficiency audit. An auditor will come out to your home and evaluate its energy efficiency. They’ll point out where you’re losing energy and inform you about your home’s overall usage. They can also provide recommendations on what you could do to increase your home’s energy efficiency.

A home energy efficiency audit can cost between $100 and $1,650, with an average of $407, depending on where you live. Some cities offer incentives for upgrading your home’s energy efficiency, so be sure to check with your utility company to take advantage of any rebates or tax incentives.

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