Home Improvement

How to Insulate an Old House

In a climate in which temperatures for January are consistently at or below freezing, you do not want to live in a home that isn’t insulation.

However, Christine Flynn and Liz Bagley aunt and niece owners of the house with two families built in 1916 which was featured in the 28th season of This Old House, faced the same problem until general contractor for TOH Tom Silva came along. “People in houses built before WWII think there’s nothing they can do to protect against the cold,” Tom says. Tom. “Or they just don’t realize how much more comfortable their house can be.”

Interior Wall Insulation in an Old House

If a home’s attic (or roof) is already well-insulated, adding insulation to the walls could be the best option to lower the cost of cooling and heating. Like the majority of remodeling projects, a lot of the walls of this home were expected to remain in place and, therefore, Tom was forced to think about how to best upgrade the insulation without tearing the whole structure down–a project that would have cost the budget of $250,000 for renovations.

In areas where the walls were exposed, like in the bathrooms and kitchens that were renovated such as, for example, and in attic stud bays which have never been covered before–he chose his best insulation choice: polyicynene. an emulsion of cream color that is a foam that stiffens when experts spray it onto the walls.

However, getting the fine foam behind walls with old ones is much more difficult. In the living areas and a few bedrooms Tom decided to use a slower pour version which is put in through holes in the walls. It takes a bit longer to expand, which reduces the chance of cracking existing plaster.

What is the Best Type of Insulation for Interior Walls?

If you’re a homeowner who’s looking to benefit from a renovation to retrofit new or more insulation can choose from plastics, fiberglass, shredded paper or even denim scraps wool, and more–in various types. The price and effectiveness (expressed by an R-value, which is a measure of the resistance of heat exchange) and level of expertise required to install the various types of insulation differ. Which type of wall insulation is the best?

“That’s the e-mail I get every day, and there’s no simple answer,” says Andre Desjarlais, director of an initiative in the Oak Ridge National Laboratory in Tennessee that is focused on the best ways to construct better structures. When considering site requirements and financial budgets, a certain type of insulation is likely to perform better or is more straightforward to install. To figure out which type of insulation will best fit your project take a look.

Expanding Foam (What it is?)

The insulation is composed of open-cell, closed-cell polyurethane (a plastic) or a specific Cement, this type of insulation is put in as a foaming liquid or soft foam to fill all spaces, it then becomes stiffer. It is only applied by professionals. it is more expensive than other options , however it’s the most effective for sealing air leaks.

Polyicynene, also known as poly-open cell polyurethane is a very low-density soft foam. It’s sprayed onto exposed studs and expands up to 100 times its size in just a few minutes. When walls are finished, builders put a less tastier version of it through small holes. It grows over a period of time to 60 times the volume. Closed-cell polyurethane foams up to 30 times its volume , and is dried to form a hard shell.

Cementitious foamthat acts like shaving cream, but it will harden over the course of time to meringue like consistency, requires mesh between the studs to hold it back.


Polyicynene provides around R-3.6 for each inch; polyurethane that is closed cell between R-6 and and cementitious foam R-3.9

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If you are able to consider more than the initial cost, you can enjoy longer-term security.


Polyicynene could crack the walls or leak and stain floors. Polyurethane isn’t stable in the presence of UV radiation. Both closed-cell polyurethane as well as cementitious foam don’t have elasticity which means that when studs expand and shrink, gaps can be created.


Polyicynene and Polyurethane cost about $1.50 per square foot which includes labor when the wall is not open or $2.25 each square foot for walls that are already in place. Cementitious foam is priced at $1.40 or $2 for a square foot. Installers can also apply an even layer of foam in order to stop leaks, and then cover with cheaper insulation.

Note Prices are all approximate one square foot within the form of a wall that is 2×4.

Batts (What are they?)

They are fluffy blankets that are available in long rolls or cut pads that can be placed between studs. They are typically composed of fiberglass, however there are also ones constructed from cotton (actually pieces of denim that have been cut up) or minerals wool (made by melting blast furnace slag or rocks, such as basalt) as well as genuine sheep’s wool.


Fiberglass batts range between R-3 and R-4.3 in thickness per square inch. Mineral wool is about R-3.6 per inch while cotton is R-3.4 per square inch wool R-3.5 each inch.

Most effective

In the walls that have been stripped to the studs for DIY jobs.


The insulation has to be placed at a full loft, not compressed. The insulation that is stuffed around pipes and leaving holes in oddly-shaped regions will reduce its efficient.

Also, sharp fibers from mineral wool and fiberglass can cause skin irritation, so you should wear long gloves, sleeves, mask and goggles when handling it. Certain brands contain an formaldehyde binder that releases gas in time.

Wool and cotton are both natural products that don’t have these disadvantages however, they’re more costly and difficult to locate-especially wool that is available only on the Internet through Canadian distributors.


Basic fiberglass batts are priced at around 40 cents for a square foot without installation The more dense ones cost around $1. Mineral wool costs about 40 cents. Cotton costs approximately 60 cents and wool is the highest priced item at $2.75.

Loose Fill (What it is)

Dry insulation pieces that are blown into the wall cavity through holes ranging from 1 to 2 1/2 inches in width. It is either blown into the inside walls and requires patching holes and from the outside that requires tearing up siding and drilling holes through the sheathing. This adds the cost for professional installations.

There are three primary kinds of fiberglass: which is either coated by formaldehyde (made as a byproduct of the manufacturing of batts) or untreated made up of around 80 percent ground-up newspaper and 20 percent borate. Borate is a mineral used to make an anti-fire agent as well as mineral wool.


When it is allowed to fill the cavity may provide as much as R-4 per inch. cellulose is that ranges between R-3.6 between R-3.8 per inch Mineral wool R-2.7 in an inch.

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For a better insulation of the attic or to add insulation inside walls when budgets are limited.


Cellulose requires less energy to make which means it is less expensive and is a more sustainable choice in many situations. However, mineral wool or fiberglass could be a better choice in windy, wet areas especially in homes with wood siding because unlike cellulose, they do not take in moisture.


Cellulose and fiberglass cost around $1.20 for each square foot when they are blown into from the inside and $2 per square foot when blown in from the outside. If not installed, the costs are approximately one-third of the cost homeowners who are performing a DIY installation could hire a blower for around 70 dollars per day.

Sprayed-on Fiber (What it is?)

A variant on loose fill, which is suitable for walls with studs that aren’t yet plastered or drywalled. Professional installers add adhesive and water to the basic insulation materials , and then uses a water hose to spray the mix between studs, helping to make sure that the wall is completely covered. Additionally the adhesive makes fibrous materials less likely fall.


Sprayed-on fiberglass and cellulose are about the same as loose fill. However, mineral wool sprayed on is more effective than loose fill at R-4.1 for every inch. Spray-on insulation can seal air leaks more effectively that loose fill.

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In open spaces when you’re working on a tight budget, you’ll need an expert contractor to take care of the installation.


To prevent the growth of mildew To prevent the growth of mildew, the insulation should be dry at least for two days prior to when it is covered in drywall.


More than 50% greater than filling with loose.

Rigid Panels (What are they?)

Boards made of extruded Polystyrene (XPS) as well as polyisocyanurate (“iso board”). These panels are able to be put on the outside of a building, above the foundation (typically an area of weakness in the insulation system) but underneath the siding. This method is ideal for hot, humid climates, since they act as a water barrier.

In warmer climates, the boards could be placed inside walls, where you need the barrier against moisture to prevent warm air from getting out. Prior to switching towards spray foam insulation Tom was using polyisocyanurate in this manner. He built a 2×4 wall and then insulate the studs by using batts (paper surface removed) and then cover the entire thing with foil-faced boards and cover them by using foil tape prior to putting up the wall board. The R-values of both batts and board on a 2×4 wall was higher than that of batts by itself on a 2×6 wall and he could gain an extra bit of space in the space.


Extruded polystyrene is a good choice for R-5 per inch. Foil-faced polyisocyanurate provides from R-7.2 up to R-8 for every inch.

Best use

When replacing siding or an interior gut job to provide insulation to a wall made of 2×4.


To comply with fire regulations it is necessary to cover your the interior of your building with drywall that is at least 1/2-inch thick. Polystyrene breaks down when it is exposed to light, which is why it shouldn’t be exposed to sunlight for all day.


A sheet of 1-inch thick expanded polystyrene foam is about $10. A 2-inch-thick foil-faced polyisocyanurate is less than $30.

Tom Silva’s Advice on Handling Half-Insulated Walls

“If your home has insulation in the walls, but it’s not enough to shield you from the cold, you’ll have to take it off before adding more, as the old insulation may block the path and reduce the efficiency of insulation.

Determine where you’ll require more energy by hiring an energy auditor equipped with an infrared camera or by checking between the electrical outlet or in between trims are removed with care. If you spot some insulation, remove an inch to 12 inches horizontal strip of drywall or plaster halfway to the wall. After that, you can remove the insulation.

If you opt for the loose fill or expanding foam you can put it in through the same hole. However, you’ll need to drill additional holes on the edge of the wall for the final step.”

Where To Find It

Universal Insulation Doctor

1616 Centerville Turnpike Suite 215
Virginia Beach, VA

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