How To Install Foam Board Insulation On Interior Walls

Can I add foam insulation to the inside of a wall instead of exterior?

Shawn, Because fiberglass is so porous to air and vapor, it used to be required by code to have a poly air/vapor barrier installed. In accordance with current code requirements, fiberglass batts must have an air barrier on all six sides, which is a difficult and frequently impossible condition to meet. Additionally, the R-value of fiberglass drops as the temperature goes below or increases above room temperature, i.e., when it is most required. In addition to being a proven carcinogen, fiberglass frequently contains formaldehyde as a binder, which is a key sensitizer or trigger for multiple chemical sensitivity, as well as for asthma.

Fiberglass is usually always a breeding ground for insects and rats, with rodent excrement and dead rodents amassing over time as a result of their presence.

Furthermore, fiberglass batts are frequently related with moisture, mildew, and decay in the walls.

This is especially true when compared to the extremely low footprint of alternatives such as recycled blue jean batts or, even better, densified-pack cellulose (DPC).

It is sufficient to use 1×3 strapping.

The DW is fastened to the strapping.

Walls With Interior Rigid Foam

Energy-related musings from a nerd

When remodeling an older home, it sometimes makes sense to install rigid foam on the interior side of exterior walls

Some remodelers choose to place stiff foam on the inner side of external walls rather than the outside side. While rigid foam is often installed on the outer side of a wall, this strategy cannot always be employed on an existing house because of the limitations of the structure. Image courtesy of: Iso R Plus (Image1)

More Musings of an Energy Nerd

When it comes to decreasing thermal bridging via studs, there are two major options: building a double-stud wall or installing a continuous layer of rigid insulation on one side of the wall. When installing a continuous layer of rigid insulation, the vast majority of builders utilize rigid foam (polyisocyanurate, expanded polystyrene, or extruded polystyrene); only a tiny percentage of builders employ semi-rigid panels of mineral wool as insulation. When rigid foam is installed on the walls of a new structure, the foam is typically installed on the outside side of the wall by the construction crew.

  • Because there are fewer interruptions on the outside side of the wall (such as electrical boxes and partition junctions), it is much easier to apply an unbroken layer of insulation on the exterior than it is on the interior. Rim joists can be effectively insulated using rigid foam applied to the outside of the building. The use of outside rigid foam helps to keep wall sheathing warm and dry during the winter.

Remodelers, in contrast to new house builders, do not have the luxury of starting from scratch. In most cases, the external foam alternative is prohibitively expensive for remodelers who wish to eliminate heat bridging via studs — especially if the siding is in good condition.

“Why can’t I install the stiff foam on the inner side of the wall?” a large number of remodelers inquire. The answer is yes, you certainly can.

Back to the 1980s…

When most cold-climate builders were trained in the 1980s, they were taught that walls needed to be vapor retarded on the inside and be capable of drying to the outside. When a few early adopters began placing stiff foam on the exterior of buildings, others questioned whether the technique was safe. As several old-time builders pointed out, “Rigid foam is a vapor retarder, hence it should be used on the inside.” “Exterior stiff foam is dangerous, unless you live in Florida,” says the author. It’s a vapor barrier on the wrong side of the wall.” It took some time before experts demonstrated that these builders were incorrect.

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Recent Questions and Replies

Rigid foam board insulation may be used in a variety of applications around the home, although it is most commonly seen in basement walls. This will most likely be your first experience with closed-cell rigid foam if you are a do-it-yourself homeowner who is finishing your basement on your own. When utilizing stiff foam, the proper approach is to run continuous 4-foot by 8-foot sheets of the foam across the concretebasementwall between studs, as shown in the illustration.

When to Install Rigid Foam Insulation Between Studs

The placement of stiff foam between studs in below-grade spaces can have a number of advantages, particularly given the fact that wood has certain insulating characteristics. With regard to wood-frame walls, the makers intend for the insulation to be applied on the exterior, rather than the inside, of the braced framing or structural sheathing. As a general rule, any insulation is preferable to no insulation, as long as the insulation does not cause you any further issues in the future. Fiberglass insulation against a vapor-heavy concrete wall is an example of a well-intentioned refurbishment that may end up causing additional issues in the future.

The insulating capabilities of moisture-logged insulation are drastically reduced, and the appearance of mold indicates that the insulation must be removed as soon as possible.

While rigid foam insulation has several drawbacks, the fact that it is unable to properly adapt to the spaces between the studs means that it is still preferable to no insulation.

The use of a low-expanding spray foam sealant to fill in the spaces between studs further boosts the insulating characteristics of stiff foam between them.

Rigid Foam Board Insulation Basics

Basements and other below-grade applications benefit greatly from rigid foam board insulation. Because fiberglass insulation absorbs moisture, it is uncommon to find fiberglass insulation installed below grade. Another situation where this could be appropriate is when you’re insulate a heated completed basementspace against another inside basement area that is not heated. Because you anticipate that this internal wall will remain dry, you may want to consider using fiberglass insulation. Another exception would be daylight wall basements, which are defined as those having three walls against the soil and a fourth wall that opens to the outside at grade level.

Rigid Foam Board Sizes

Rigid foam board insulation is available in sheets up to 4 feet by 8 feet in size, making it easy to quickly cover large walls. Sheets that are smaller and more manageable in size, such as 2-foot by 8-foot and 4-foot by 4-foot sheets, are sometimes available for purchase. Large sheets are frequently supplied with shallow slits that make it possible to break the sheets in two without the need for a saw. In most cases, these scores will not be useful for between-stud installation since the scores are not the proper breadth for the job.

Rigid Foam Water-Resistance

In terms of water resistance, rigid foam insulation is regarded to be impenetrable. Mold is less likely to grow in rigid foam insulation than it is in fiberglass insulation. Mold and mildew can, however, still develop on the top of rigid foam insulation, which is a concern. The distinction is that mold and mildew are unable to penetrate hard polyurethane foam. Mold and mildew are able to enter through the numerous open cells in fiberglass insulation.

Rigid Foam R-Value

When compared to fiberglass insulation, rigid foam insulation often has a low to moderate R-value per dollar spent. Rigid foam board insulation is almost twice as expensive as fiberglass insulation per square foot of R-value. The R-value of a sheet of rigid foam insulation that is 1 1/2 inches thick is 7.5.

Continuous Insulation Makes a Perfect Basement Wall

Rigid foam is intended to be used in a continuous fashion. The traditional wall system, which consists of studs spaced every 16 inches on center, does not provide continuous insulation, on the other hand. Rigid foam sheathing is laid on the outside of the home, just behind the siding, to serve as an exterior sheathing. The foam sheets are butted together and taped together to prevent air from getting in between them. Continuity is also vital when it comes to basement walls. There is no possibility of a thermal bridge forming when sheets are densely packed end-to-end.

Preventing Thermal Bridges and Breaks

A thermal bridge is any opening through which unwelcome temperatures, whether hot or cold, are allowed to enter your house. It is possible for a thermal break to be as visible as a crack or hole in the wall. To many people’s surprise, it may also take the form of a solid substance with great heat conductivity. Metal is a good conductor of cold. It is possible to have a thermal bridge if you have any type of unbroken metal running from the exterior to the interior, such as a pipe.

Wood may also act as a thermal bridge, albeit its effect is not as noticeable as that of metal since wood is not a good conductor of heat. Wall studs made of wood can function as a conduit for the transfer of cold into the inside of your home.

Pros and Cons: Rigid Foam Between Studs

  • Installation requires a lot of labor
  • Studs can still transfer cold

Spray foam put by a professional provider may be more expensive than you can afford, making stiff foam the most cost-effective alternative. Furthermore, because basements often have some insulation from the ground they are surrounded by, temperatures are naturally moderated, and the issue of thermal breakdowns created by stiff foam is kept to a minimum. The use of stiff foam, on the other hand, may not be a viable solution if the wall system is already in place: Dismantling the wall structure just for the purpose of installing continuous rigid foam board insulation might not be a desirable undertaking.

Furthermore, because the rigid foam will not cover the wood studs, which can transmit some cold into the basement during periods of extreme temperature—and because wood studs expand and contract, there will be more opportunities for cracks to develop in the foam—as well as during periods of extreme temperature.

How to Install Rigid Foam Insulation Between Studs

  • In order to determine the amount of rigid foam to purchase, measure the full wall surface area. Do not deduct studs from the total. For example, a 30-foot-long by 7-foot-high wall may be constructed. Consider that 210 square feet is the total amount of rigid foam insulation that has to be purchased.

Measure Individual Cavities

Each bay should be measured separately. The bay width will be roughly 14 inches if the studs are spaced every 16 inches on the middle line. It is preferable if the foam is compact, rather than huge, because it is more difficult to shave down foam that is too large. When it comes to making this project operate properly, one tip is to handle each wall bay individually. Structural studs are frequently positioned at intervals that are not exactly 16 inches apart on center. Like an example, measure each bay individually and write down the measurement, as in this example:

  • Bay 1 measures 16 inches by 7 feet
  • Bay 2 measures 16 1/8 inches by 7 feet
  • And Bay 3 measures 15 7/8 inches by 7 feet.

Mark and Cut the Rigid Foam

  • With a drywall square, trace the measurements of the rigid foam onto the rigid foam with a permanent marker. The firm foam should be cut with a regular wood saw.

Install the Rigid Foam Insulation

  • Each stiff foam sheet should be placed in its own wall bay. However, the fit should be strong without being so hard that the foam’s edge begins to rip or crack. If this occurs, pull out the sheet and use the saw to softly cut the edges down to prevent fraying.

Seal the Gaps in the Insulation

  1. Using a low-expansion spray foam sealer, close any gaps between the foam and the studs.

How to Install Foam Board Insulation on Interior Walls?

Make a mental note to be amazed when you realize how simple and quick it is to install InSoFast foam board insulation on interior walls. Our solutions give individuals and business builders with cost-effective and strong insulating materials that are simple to install and need minimal time and expertise. Insulation from InSoFast, LLC may be applied to any flat surface with success. We have materials that are suitable for both the indoor and external environments and may be applied to floors, ceilings, and walls.

Alternatives to InSoFast insulation installations will necessitate the use of professional skills as well as a significant time commitment.

These restrictions are absent from InSoFast insulating products.

The alignment will remain true and straight, and the system’s strength will increase with each subsequent panel installed.

Construction glue will be used to attach the panels to the wall, and canned spray foam insulation will be used to fill in the gaps, seams, and edges to create an airtight seal once they have been applied quickly.

InSoFast Interior Insulation Options

The InSoFast UX 2.0 insulating panel offers a suitable level of energy efficiency to comply with current and future energy codes and regulations. Although the panels have an R-8.5 rating, the systems often exceed the competition, which has an R-13 rating. These panels are the usual 2’x4′ size with a 2″ thickness and come in two sizes. In this panel, the polypropylene studs are exhibited on a flat surface on the backside. All of our insulating panels have a high level of stability. Because they do not decay or release chemicals as time passes, the R-value remains constant as a result of the material’s long-term stability as an insulator.

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The following characteristics are desirable in any construction:

  • Electrical raceways, drainage channels, and a uniform, stackable panel design are all included in the construction of the frame.

Product lines such as the InSoFast EXi 2.5 product line are made up of 2.5″ thick panels with studs that are more deeply implanted inside the EPS foam than other lines. It exceeds the competition with an R-value of 15 and has an R-level rating of 10 compared to the competition. The notched edges ensure that the panel’s alignment stays consistent, and the panel’s ability to bridge imperfections along surfaces while maintaining its airtight condition is another advantage.

The Power of Embedded Polypropylene Studs

Non-ferrous studs are embedded into the InSoFast insulating panels. As a result, the system is easy and quick to install since the studs offer a secure foundation for application. After applying Loctite PL Premium 3X Stronger Construction Adhesive to the ridges, the adhesive will adhere straight to the wall surface. Once the system is in place, the imbedded studs make it simple to install drywall over the top of the system. Every 16″ on center, the panels are marked with indication lines to make it easier to identify the studs on the panel.

Hang your shelves, flatscreens, and other accessories with confidence, knowing that the built-in frame contained inside the insulating system is equal to the task.

We provide cost-effective insulation that won’t break the bank and removes the need for a professional installation crew to complete the job.

You may also discover a wealth of information on our website to help you get started with your DIY insulation project and keep you going!

rigid foam insulation

Rigid foam insulation acts as a blanket for your home, keeping it warm. It increases the thermal resistance of your home, allowing you to save money on your heating expenses.

Practically everywhere in your home may be used to install it. It also increases the structural integrity of your walls, transforming them into a durable and energy-efficient component of your house.

Step 1–Inspect Interior Walls for Any Problem

When placing rigid foam insulation on an interior wall, make sure to thoroughly check the walls before beginning. If you see any signs of moisture on the inside walls, you should remedy the situation by painting the affected area with a waterproof paint. If you believe that the problem you discovered when inspecting the internal walls is significant, you should seek expert assistance. Keep in mind the ancient proverb, “When in doubt, always inquire.”

Step 2–Attach the Strips

Once you have finished examining and addressing any moisture issues on your interior wall, you may begin connecting the furring strips to the wall surface. Furring strips, which are constructed of wood or metal and are especially designed to support surfaces once they are attached, may be used. Furring strips should be attached to the walls 16 inches apart from one another using glue or a ramset to hold them in place. This type of strip provides a flat surface to which you can adhere the insulation as well as any covering drywall or paneling that you may wish to use in the future.

Step 3–Level the Surface

There will always be irregularities in the construction of walls; thus, you will need to employ a shim material in order to level and repair the uneven walls. Shims are often thin wood wedges that are offered for a low price or recovered wood scraps, but they may also be made of metal. Shimming the furring strips into place will help to level them out.

Step 4–Install the Panels

Get out your measuring tape and take measurements of the rigid foam insulation panels, marking the sizes that are required. Cut the foam using the mark as a guide; you can either use a knife or a saw to complete this step if you choose. Check to see whether the panels are a comfortable fit with the furring strips that have been inserted. After that, insert the panel in between the strips using your fingers. Make certain that there is no room or gap between the insulation boards, which will serve as a protective barrier for your boards.

Step 5–Secure the Foam Insulation Boards

The plastic insulation acts as an additional layer of protection for the rigid foam insulation panels you have installed. As a result, the water vapor is prevented from permeating the panels, preventing additional damage. Make sure to use caution when stapling the plastic insulation and avoid attaching it to the furring strips, which might result in the insulation becoming perforated. By gluing drywall or paneling to the furring strips, you may now cover the insulation with drywall or paneling.

How to Install Foam Board Insulation on Interior Walls

Installing foam board insulation is an excellent do-it-yourself activity for developing new skills. In addition to being lightweight and easy to work with, foam board insulation performs a crucial function. The material is frequently supplied in huge sheets (or boards), which enables the installer to cover enormous areas in a short period of time. Today, we’ll talk about the method(s) that professionals use to rapidly and successfully install foam board insulation on interior walls. Image courtesy of In the construction industry, foam board insulation is a product comprised of polystyrene and polyurethane that is used to insulate interiors from the outside temperature.

  1. An unfinished basement with cement block walls, for example, may serve as an illustration.
  2. A vapor barrier is available in some variants, which is particularly useful in areas where dampness is abundant.
  3. Foam board insulation, for example, can be utilized in place of blown-in attic insulation, batts, and spray foam in some situations.
  4. Block walls, insulated floors, and vaulted ceilings are all excellent applications for foam board insulation.
  5. To simplify things, we will assume that the surface to be covered with foam board is accessible and free of any fasteners for the sake of this article.

A few hand tools are all that are required when working with foam board insulation. These include, but are not limited to, the following:

  • The following tools and supplies are required: a sharp utility knife, measuring tape, straightedge, hammer, framing square, marker, and a caulk gun (if using construction glue).

Wood Framed Interior Walls (Surface Mount)

The first step in installing foam board insulation is determining how much of the material you will use for the project. You’ll need a tape measure and some basic arithmetic skills to complete this task. In most cases, 4′ wide by 8′ long sheets (also known as boards) of foam board insulation will provide 32 square feet of insulation, while other variants may provide 40 square feet of insulation. It is possible to install a sheet without the need for extra trimming if the wall is 8′ high and the wall studs are spaced on 16-inch centers.

Because wall studs are commonly spaced at 12″, 16″, or 24″ intervals, most of the time only the length of the boards will need to be cut.

The sheets can be trimmed with a sharp utility knife if the wall is out of plumb or has an uneven form, though this is not often necessary.

Step 2 Hang the Foam Boards

As previously indicated, there are a variety of methods for hanging the foam boards. Because the material is being put on stud walls in this situation, any of the typical installation methods can be employed, however button cap nails and/or construction glue are the most frequently encountered. Button cap nails will be used in this demonstration. To begin, start with one corner of the board and set it vertically in place with one button cap nail hammered into either top corner of the board. After that, the board is rotated if needed until it is plumb (as measured using a level) with the wall stud to which it will be fastened.

Due to the fact that two boards are attached to the same stud, the boards are connected together and the wall gains lateral strength as a result.

If the insulation and the drywall were to be installed in the same manner, the seams would ultimately come into contact and most likely result in a crack later in the process.

Step 3 Seal the Joints

When it comes to interior installations, sealing the joints is regarded optional, although it is still a good idea to do so. This is accomplished through the application of a special joint tape manufactured specifically for use with foam boards. It is necessary to apply tape over the button cap nails and joint once they have been firmly installed. The tape should be about 2″ broad in most cases. The use of the tape helps to flatten the seam, which makes the subsequent installation of drywall or other wall covering more simpler.

Wood Framed Interior Walls (Inside the Wall)

In most cases, foam board insulation is installed within a wall using 2″ x 6″ walls, which are thicker than the normal 2″ x 4″ wall and hence more energy efficient. This is due to the fact that foam board does not have the same insulative value by volume as expanding closed cell foam in the majority of circumstances. Therefore, 2″ x 4″ walls are typically not deep enough to provide the r-value necessary by most building requirements. The first step is to take a measurement of the distance between each stud.

In this phase, it is critical that the measurements be taken between the studs rather than from outside to inside.

It is common practice in most cases for up to five layers of foam board to be bonded together using construction adhesive before being put between the stud cavities and fixed in place.

Masonry/Cement Block Walls

The fundamental measuring and calculation methods for putting foam board insulation on a block wall are the same as those for installing foam board insulation on a stud wall. The fundamental difference is in the manner in which the foam board insulation is applied. Furring strips, which have been secured to the block wall, are commonly used to attach foam board to the furring strips. When it comes to insulation, it is not suggested to glue foam board insulation directly to the block. Most of the time, this is done because an air gap between the wall and the board will increase the effectiveness of the insulation in most situations.

Step 2 Mount the Furring Strips

Furring strips measuring 1″ x 3″ x 34″ are often installed with a pneumatic nail gun and masonry nails by professionals. Furring strips are put on constant centers, exactly like wall studs, and run from ceiling to floor, similar to how a wall is constructed. The foam board may then be fastened to the furring strip with a nail or construction glue that is suited for the job. It is possible to achieve a 34″ gap between the block foundation wall and the foam board by employing this procedure, which prevents moisture originating from the block from coming into touch with the foam.

How We Turned Our House into a Giant Foam Box, Part I — Wall Insulation — Frugal Happy

One of the most crucial drivers of how much energy your home consumes turns out to be one of the most inconspicuous: the quality of your home’s insulation. I know, insulation is a really unappealing subject. No one ever notices it or gives it any thought. However, imagine being outside on a blisteringly hot summer afternoon. Is it more comfortable for you to seek refuge inside a wooden box or a Styrofoam box? On a frigid, snowy winter day, the question remains the same. Of course, in both circumstances, the foam box would be the best option.

  • Thermal insulation may be defined as any substance that prevents heat from simply passing through it (like foam).
  • The more insulation a building has, the more stable the temperature within the building is (and the less energy is needed for heating and cooling).
  • To put it another way, convert the home into a gigantic foam container.
  • Here’s what the foam looks like now.
  • Chris worked tirelessly for three months to insulate merely the walls of our common areas (part I, what your reading now).
  • As it turned out, it was far larger and more overpowering than we could have anticipated.
  • Because our property had only a thin layer of insulation in the attic for the previous 35 years, and no insulation in the walls or floor, we had to replace it.

When using the air conditioner in the heat, the polar opposite would occur.

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This is not good.

All of the outside surfaces of the home should be insulated with high-quality insulation.

Because Chris is so enthusiastic about this, he chose to have our walls painted R26 and our ceiling painted R46.

Chris conducted extensive study (including reading online and contacting with specialists) to determine the best way to insulate the walls.

Chris did the accurate, to-scale drawings, and I did the child-like calligraphy.

The wall thickness grows from 5.5 inches to 8 inches as the building gets taller (yes, our rooms will actually be a tad smaller after all this is done). Chris did it one layer at a time, despite the fact that it was somewhat scary to make something that sophisticated.

Phase 1: Rigid foam (3 inches)

Before installing any insulation, Chris cut thin long “sticks” from 1/2-inch-thick wood and placed them in the rear corners of each vacant bay to act as a spacer. This produced a small air gap in the event that any moisture (such as rain) were to inadvertently enter the wall assembly at some point in the future. Although it’s unusual in our dry environment, it’s necessary to allow moisture to dry out in order to avoid the possibility of mold or rot in the walls and other structures. My cousin Hank and our buddy Ernie were really helpful during this process – thank you so much!

  • As a result, we need a significant amount of foam.
  • thestackistallerthanmemorningdeliverymeanspjpants Rigid foam insulation is the name given to this form of insulation.
  • However, rigid foam is far more effective than other types of insulation that are more typically utilized.
  • Following the removal of the drywall, this is what our walls looked like at first.
  • A 3-inch layer of stiff foam was to be applied to each bay, according to Chris’ plan.
  • The disadvantage is that it is, shall we say, strict.
  • It will need to be tailored to fit.

That seems like a good time, doesn’t it?

He donned a mask since breaking the foam sent a cloud of fine polyiso dust into the air, which he inhaled.

safetyfirst Chris cut the foam by hand after cutting it with a table saw to ensure that it fit perfectly in each bay.

Then, using a little sledge hammer and a block of wood, he would carefully pound each cut piece into its matching bay until it was securely in place.

It was a long, drawn-out procedure that required patience.

Slowly but steadily, the glittering foil-faced foam began to fill the space between the walls.

Jump in celebration: Before and after photos of a kitchen wall: Chris has now completed all of the bays, which was a long time in the making.

It’s time to AIR SEAL the deal.

If you don’t air seal your foam box, you’ll merely wind up with a foam box full of cracks and holes. As a result, Chris utilized caulk or spray foam from a container to seal every gap around each bay. It’s time-consuming, but it’s necessary! Insulated and air sealed!

Phase 2: Plywood

The next stage was to cover the walls with a layer of plywood to protect them from further damage. This had nothing to do with insulation, but rather with earthquakes, which was the topic of discussion. Since our house was built in 1963, there have been relatively few seismic upgrades, which is concerning given that California is a state rife with earthquake fault lines. It is possible that adding an additional layer of plywood over the building structure will assist give lateral (sideways) support and prevent our house from falling after a major earthquake.

Thank you very much, Charlie!

🙂 Construction progressed more quickly as a result of the collaboration of Chris and Charlie.

We’ll accept whatever amount of good fortune we can receive!

Phase 3: Rigid foam (1 inch)

What’s next now that we’ve got some very spectacular plywood walls? Of course, another layer of firm foam will be added! You might be thinking why on earth we’re putting additional stiff foam in the mix in the first place. We didn’t do this before, did we? Yes, for the most part. But keep in mind that Chris only used stiff foam to line the inside of the bays. In other words, the framework around each bay did not receive any insulation. Let’s go back to my favorite photograph: It’s easy to see that all of the wood studs and blocks are not properly insulated, allowing heat to “leak” in and out of those areas (this is called thermal bridging).

The solution was provided by Chris and Charlie, who placed still another layer of stiff foam on top of the plywood, but this time only 1 inch thick and covered the entire wall constantly.

There will be absolutely no leaks from now on!

Phase 4: Furring stripsservice cavity

The insulation has finally been completed – hurrah! But hold on, there’s more (again). Due to the fact that we require some room below the drywall (a service cavity) for items such as electrical wiring and HVAC tubing, we are unable to immediately apply drywall (the final, completed layer) to the stiff foam layer. Chris’ solution consisted of installing horizontal pieces of wood, known as furring strips, on top of the firm foam to support it. The furring strips form a service space behind the drywall, allowing us to run wiring and other conduits behind the drywall.

Chris and Charlie used a laser level to ensure that the furring strips were properly horizontal and parallel.and I used a laser level to create expressive body art with the furring strips.

Our walls have never looked better than they do now, thanks to four inches of polyiso rigid foam insulation, plywood seismic support, and air sealing twice.

Unfortunately, all of this brilliance will be concealed away inside the wall, where no one will be able to see it.

Chris’s sole proof that he spent three months meticulously insulating the walls is, well, this collection of photographs. That is the way it is with insulation as well. unsunghero The Stratton brothers are ecstatic as they stand in front of their monumental creation.

What is the best way to install rigid foam on interior basement walls?

14th of June, 2021 The most recent update was made on June 16, 2021. This week, I discovered a fantastic price on some old Roofmate XPS insulation, which I plan on putting to use to insulate my basement. I want to achieve R25, therefore I’ll be using 4″ thick R-20 with a second layer of 1″ R5 dispersed throughout the first layer. I have a couple of queries about where this should be hung on the wall. Some possibilities include placing the XPS directly against concrete and attaching it to the concrete with adhesives or furring strips for drywall connection.

Another issue that I am concerned about is the amount of time it will take for the assembly to dry to the inside.

A possible solution that appears to be a decent idea would be to first add 1″ strapping directly to the concrete, which would serve as a nailing surface for the 5″ foam, which would then be secured with long nails or screws.

Although there are no severe water problems in the basement, there are a few cracks that I will repair with hydraulic cement as a precautionary measure before proceeding.

How to Insulate an Old House

For anybody who lives in a place where January temperatures are frequently below freezing, staying in a house with inadequate insulation is a recipe for disaster. That was the situation faced by Christine Flynn and Liz Bagley, owners of the 1916 two-family house that was featured in Season 28 of This Old House, until TOH general contractor Tom Silva came along to help. “People who live in houses built before WWII believe that there is nothing they can do to protect themselves from the cold,” Tom explains.

Interior Wall Insulation in an Old House

Addition of insulation to the walls of a house, if the attic (or roof) is already well insulated, may be the most cost-effective method of lowering heating and cooling expenditures. The fact that many of the house’s walls were going to stay intact, as is the case with most remodeling projects, forced Tom to think about the best way to install the energy-saving material without destroying the whole structure—a process that would have blown the $250,000 renovation budget. His top insulation choice was polyicynene, which is a cream-colored liquid polyurethane that foams up and stiffens after it has been sprayed in place by professionals in areas where walls were left open, such as in newly renovated kitchens and bathrooms and in attic stud bays that had never been covered.

Tom used a slow-pour variant of the foam in the living room and part of the bedrooms. This type of foam is injected into the walls through holes that have been drilled into the walls and expands more slowly, reducing the risk of shattering the existing plaster.

What is the Best Type of Insulation for Interior Walls?

A homeowner wishing to take advantage of a remodeling to retrofit new or more insulation has a plethora of options, including plastics, fiberglass, shredded paper, even denim scraps and wool, all of which are available in a variety of forms. There are differences in the cost, efficiency (as measured by an R-value, which measures resistance to heat transmission), and amount of skill required to install each kind, of course. So, what is the most effective sort of wall insulation? This is the type of email Andre Desjarlais receives on a daily basis, and he says there is no simple solution to it.

However, depending on the site circumstances and budget, one type of insulation may perform better or may be easier to install than another.

Expanding Foam

This insulation, which is made of either open-cell or closed-cell polyurethane (a plastic) or a specific cement, is applied as soft foam or foamy liquid, filling all gaps and then stiffening once it has been set. It can only be applied by specialists, and it is more expensive than other solutions, but it is the most effective in plugging air leaks. Polyicynene, often known as open-cell polyurethane, is a low-density, spongy foam. It’s sprayed between exposed studs and swells to 100 times its original volume in a matter of seconds after being sprayed.

Closed-cell polyurethane foam expands to 30 times its original volume and hardens to form a highly durable shell when dried.


Polyicynene provides around R-3.6 per inch of thickness; closed-cell polyurethane provides between R-6 and R-7; and cementitious foam provides approximately R-3.9 per inch of thickness.

Best used

When you have the ability to see beyond the immediate expense to long-term comfort.


Polyicynene has the potential to break existing walls or to leak out and discolor a floor surface. When polyurethane is exposed to ultraviolet radiation, it becomes unstable. Due to the fact that closed-cell polyurethane and cementitious foam are not flexible, gaps may appear between studs as they expand and compress.


If the wall is open, the cost of polyicynene and polyurethane is around $1.50 per square foot, including labor, and $2.25 per square foot if the wall is already in place. Depending on the density, cementitious foam might cost between $1.40 and $2 per square foot.

Installers can also use a thin layer of foam to seal leaks, followed by a layer of less costly insulation to complete the job. *Please keep in mind that all pricing are estimates for 1 square foot in a 2×4 wall.


Fluffy blankets that come in large rolls or precut pads that are designed to fit between studs are both options. However, you can also buy ones manufactured from cotton (which is actually shredded denim remnants), mineral wool (which is formed by melting blast furnace slag or rocks such as basalt), and real sheep’s wool.


Fiberglass batts can range from R-3 to R-4.3 per inch of thickness; mineral wool provides around R-3.6 per inch; cotton provides approximately R-3.4 per inch; and wool provides approximately R-3.5 per inch.

Best used

In walls that have been taken down to the studs in a do-it-yourself project.


Insulation must be installed at the full loft height, not compressed. Making insulation less efficient by stuffing it around pipes or leaving gaps in odd-shaped places can reduce its effectiveness. Aside from that, the sharp fibers in fiberglass and mineral wool can hurt the skin, necessitating the use of protective clothing and goggles when working with it. Additionally, some types include a formaldehyde binder, which releases formaldehyde fumes over time. Cotton and wool are natural products that do not have these drawbacks, but they are more expensive and more difficult to come by—especially wool, which is only accessible on the Internet from Canadian wholesalers in some cases.


Uninstalled, basic fiberglass batts cost around 40 cents per square foot, while extra-dense batts cost about $1 per square foot. Mineral wool is around 40 cents per pound, cotton is approximately 60 cents per pound, and wool is the most expensive at $2.75 per pound.

See also:  How To Build An Interior Wall In Existing Room

Loose Fill

Dry particles of insulation are blasted into wall cavities through holes ranging in size from 1 to 212 inches in diameter. It may either be installed from the inside of the walls, which necessitates the repair of holes, or from the outside, which necessitates the removal of siding and drilling through the sheathing, increasing the expense of professional installation. There are three main types: fiberglass, which can be treated with formaldehyde (which is produced as a by-product of batt manufacturing) or left untreated; cellulose, which is composed of approximately 80% ground-up newsprint and 20% borate, a mineral added as a fire retardant; and mineral wool, which is composed of approximately 80% ground-up newsprint and 20% borate, a mineral added as a fire retardant.


When permitted to densely fill the space, fiberglass may provide as much as R-4 per inch; cellulose can provide between R-3.6 and R-3.8 per inch; and mineral wool can provide as much as R-2.7 per inch.

Best used

When money is limited, it may be necessary to add more insulation to the attic floor or to install additional insulation inside existing walls.


Cellulose is less expensive to make since it requires less energy, and it is also a more environmentally friendly option in many instances.

The use of fiberglass or mineral wool, as opposed to cellulose, may be a preferable choice in damp or windy places, and particularly in buildings with wood siding, because they do not absorb moisture like cellulose does.


When blown in from the inside, cellulose and fiberglass cost around $1.20 per square foot installed; when blown in from the outside, the cost is approximately $2 per square foot installed. Priced uninstalled, they are around one-third of the cost; a homeowner who wishes to conduct a DIY installation can rent a blower for approximately $70 per day.

Sprayed-on Fiber

A type of loose fill that is only suited for stud walls that have not yet been drywalled or plastered, as opposed to other types. A professional installer mixes the same basic insulation materials with water and glue before spraying the mixture between studs with a hose, which helps to guarantee that all of the studs are covered. Furthermore, the glue reduces the likelihood of fibers settling.


Sprayed-on cellulose and fiberglass perform roughly as well as loose fill, while sprayed-on mineral wool performs significantly better than loose fill, providing an R-4.1 per inch greater performance than loose fill. Any spray-on insulation will perform better than loose fill at sealing air leaks.

Best used

Using open walls when you have a limited budget yet want a professional to handle the construction is a good option.


It is necessary to allow the insulation to cure for at least two days before covering it with drywall in order to prevent mildew from developing.


It costs approximately 50% more than loose fill.

Rigid Panels

Foam extruded polystyrene (XPS) or polyisocyanurate (PIC) boards (“iso board”). These panels can be installed on the exterior of a home, above the studs (which are normally a weak point in an insulation system), but beneath the siding, a technique that is particularly efficient in hot, humid regions since the boards act as an excellent vapor barrier as well. In colder areas, the boards can be installed inside the walls, where the moisture barrier will help to prevent warm air from leaving. Tom used to use polyisocyanurate panels in this manner before switching to spray foam insulation: he would build a 2×4 wall, insulate between the studs with batting (with the paper face removed), then cover the entire thing with foil-faced panels and seal them with foil tape before putting up wall board.


Extruded polystyrene gives about R-5 per inch of thickness. The thermal resistance of foil-faced polyisocyanurate ranges from R-7.2 to R-8 per inch.

Best use

Adding insulation to a 2×4 wall during siding repair or an interior gut project is a common occurrence.


Interior boards must be covered with drywall that is at least 12 inches thick in order to comply with fire regulations. Polystyrene will degrade if exposed to sunlight for an extended period of time, thus it should not be kept out in the sun.


A sheet of 1-inch-thick expanded polystyrene foam measuring 4 by 8 feet costs around $10.

A 2-inch-thick panel of foil-faced polyisocyanurate is available for a little less than $30 on the market.

Tom Silva’s Advice on Handling Half-Insulated Walls

“It is necessary to remove any existing insulation in the completed walls of your home if there is insufficient insulation to keep the cold out. This is because the old insulation can get in the way and reduce the efficiency of new insulation. Find out where you need to make improvements by hiring an energy auditor who uses an infrared camera, or by peering in behind electrical outlets or under trim pieces that you carefully remove from your home. You can cut off a horizontal band of drywall or plaster 12 to 16 inches wide and about halfway up the wall if you locate some insulation.

The loose fill or expanding foam may be inserted via the same hole, however you will need to drill additional holes along the top of the wall in order to finish the work.”

Where To Find It

Fiberglass A certainTeed Corp. is based in Valley Forge, Pennsylvania, and can be reached at 610-341-7000. CottonBonded Logic Inc. Chandler, AZ CottonBonded Logic Inc. Chandler, AZ Natural mineral woolRockwool Milton, ON Mineral wool Sheep’s WoolGood Shepherd Wool Insulation Rocky Mountain House, AB, Canada Sheep’s WoolGood Shepherd Wool Insulation Rocky Mountain House, AB, Canada

Loose fill

Cellulose Applegate Insulation Manufacturing Inc. Webberville, MI Applegate Insulation Manufacturing Inc. Nu-Wool Inc. Jenison, Michigan (800) 748-0128 Owens Corning manufactures fiberglass. 419-248-8000 Toledo, OH (Ohio) Fiberglass that has not been treated Johns Manville Corporation Denver, Colorado Mineral Wool is a kind of wool that contains minerals. Delfino Insulation Co., Bohemia, Delfino Insulation Co., Bohemia, NY631-567-45495

Expanding Foam

PolyurethaneIcynene Mississauga, ON, Canada Icynene Mississauga, ON, Canada It is made of cementitious material and is available from AirKrete in Weedsport, New York at 315-834-6609 or at

Rigid foam

Polystyrene that has been extruded Pactiv Corporation Lake Forest, IL Pactiv Corporation Lake Forest, IL Dow Midland, MI Polyisocyanurate Dow Midland, MI Polyisocyanurate Dow Midland, MI Polyisocyanurate Dow Midland, MI Polyisocyanurate Dow Midland, MI Insulation contractors are those that specialize in insulation.

Anderson Insulation Abington, Massachusetts Anderson Insulation Abington, Massachusetts 800-472-1717 Federal Conservation Group Amityville, New York (800) 675-1660 Federal Conservation Group The phone number for SDI Insulation Inc. Contractors in the fields of insulation and drywall Phone: (785-862-0554) Topeka, Kansas Southland Insulators, Inc., Manassas, VA Andre Desjarlais Building Envelopes Program at Oak Ridge National Laboratory in Oak Ridge, Tennessee (865-574-4160 is grateful for his assistance.

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Installing Rigid Foam Insulation for your Basement

Waterproofing basements is something I’ve written about extensively in my waterproofing section. Basements are chilly, wet environments. Not just any old insulation will suffice in this situation. To be successful in any finishing project, you must be informed of your alternatives and have a game plan in place.

Is Rigid Foam Insulation the Right Insulation for your Basement?

The choice boils down to two options: blanket insulation (also known as fiberglass) or XPS. The most common type of insulation used in houses is fiberglass, but rigid foam insulation, while more expensive, has a few additional benefits. Let’s have a look at this. blanket insulation is highly widespread, mostly due to the fact that it is extremely cost effective. It is often constructed of fiberglass and has some form of face applied to it, such as paper, foil, or vinyl. This was the option of choice in Jason’s basement, and I wouldn’t dissuade anyone from taking this approach in their own situation.

  1. This is what I put in place, and it is also the subject of this post.
  2. Thermal capability is increased by R5 for every inch of thickness.
  3. Although more costly than blanket insulation, the board is more effective.
  4. It took around 35 sheets to cover my typical-sized basement.
  5. Obviously, it’s a substantial sum of money.
  6. Alternatives include loose-fill insulation, which is often blown in, and spray-in foam insulation, which is applied using a spray gun.
  7. These choices are also often not suitable for do-it-yourselfers since they need the purchase of specialized equipment, which makes them much more expensive to install than XPS.

XPS Benefits:

So, what are the benefits of paying nearly twice as much for XPS as you would otherwise? I believe that peace of mind is important. I’ve said that every basement is prone to flooding at some time in its life. Whether the water is actively gathering on your floor (worst case scenario) or seeping through the smallest of cracks in your foundation walls (best case scenario), it is only a matter of time before it becomes a problem. In the event that water finds its way into your basement, it can collect in your fiberglass insulation (among other areas) and cause mold to grow.

At least in comparison to fiberglass insulation, it will not retain the moisture required for mold to form and spread.

As an added bonus, if your basement suffers from a “aquatic event,” you can cut out and replace smaller parts of impacted drywall rather than having to rip out larger sections of drywall in order to repair your insulation.

The majority of the time, by the time you see mold growing on your insulation, it has already gone very far. When you are satisfied that you should install XPS in your basement, what steps do you take to complete the installation. It’s really not that difficult.

Installing rigid foam insulation

Allow me to break down the primary components into their constituent parts. Preparation Work – Basement waterproofing paint is something I’ve discussed previously. I recommend that you do this before installing XPS to give yourself additional peace of mind. I had no trouble applying the XPS to the painted walls in my apartment. With the exception of any additional wall treatments you might want to undertake (I strongly recommend reading my post on internal waterproofing), the prep work mainly comprises making sure you have a clean, dry surface to work on.

Tools/Materials Needed:

Box Cutter – Used to score the XPSDrywall Saw – Used to cut the drywall Although not absolutely necessary, I discovered that with 2″ thick XPS, the box cutter did not adequately score the XPS to allow me to break parts off with my fingers. It performed admirably while scoring along 4′ lengths, but not so well when scoring along 8′ lengths. If you don’t already have one, this Stanley is less than $10 and has received excellent ratings. In any case, you’ll require it while building or fixing drywall.

  1. This will be required in order to apply the glue.
  2. They create a glue designed for putting foam board, and I’m sure there are other adhesives that might work as well as this one.
  3. It is particularly intended to prevent the foam from burning.
  4. On average, I used one tube per sheet of XPS.
  5. I had to make several journeys to HD in order to bring the more than 30 sheets home.
  6. It was necessary for me to secure them to the roof of our Pilot.
  7. In addition, I split the cost of the transaction over two credit card payment cycles in order to reduce the financial load.

Application Tips –

1. Don’t skimp on the glue application. Use a lot of it – especially in the corners and along the edges of a piece of clothing. 2. Use something to keep the boards in place while the adhesive dries to prevent them from shifting. Because I already had all of my framing timber in the basement, I just used that. Not a lot of pressure is required – just enough to keep the board in place and firmly against the wall is sufficient to complete the task. Here’s a picture of my basement wall, which has already been sprayed with waterproofing paint and where the rigid foam board insulation is about to be installed.



Any big openings are potential entry points for air (or escape depending on the season).

To finish the procedure, apply some tyvek tape over the joints of the joints.

Isn’t it straightforward?

In terms of time investment, it’s also rather modest.

It is true that it is more expensive, but if your budget allows it, it is a wonderful insulating alternative that will offer you with piece of mind. In the meanwhile, please post any questions you may have in the comments section below. – Adam et al.

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