Insulation for block wall: RetroFoam Injection Foam Insulation for Block Walls

What Is The Best Solution? — Rmax

When the big bad wolf comes knocking at your door, which building material will you have wished you had chosen? Concrete and masonry are two materials that come to mind as indestructible, even for this notorious storytime character. 

In all seriousness, if you’re looking to build a strong structure that will last a lifetime, concrete masonry units (CMUs)—commonly called concrete blocks or cinder blocks, are the solution. If you’ve chosen CMU for your walls, there are some things to know about the building material and how to properly insulate this wall type.

Concrete Block Wall Basics

A concrete block is basically what it sounds like. It’s a building material made out of concrete that is shaped like a building block. In typical concrete block wall construction, concrete blocks are stacked on top of each other like bricks and held together with mortar. Sizes and shapes can vary, but these units typically come in dimensions of 8” wide by 16” long by 8” height.

Where to Use Block Walls

Concrete block walls are versatile and are used both above and below-grade. Common examples of commercial buildings that are often constructed with CMU walls include grocery stores, schools, and prisons. Below-grade applications are common for residential foundations that form the walls for crawl spaces, and sometimes basements. 

There are many benefits to choosing concrete block walls for your project. A few advantages include the following:

  • Naturally fireproof

  • Less susceptible to mold, moisture, and pest damage

  • Wind-resistance

  • Heavy load-bearing capacity

  • Inexpensive

  • Exceptional security

Block Wall Section Materials

Most times, concrete block walls are made up of more than just a stack of concrete masonry units held together with mortar. For example, a brick cavity wall uses brick veneer attached to structural block. Alternatively, metal wall panels, siding, and other materials can be attached to a backup block wall for a premium finish. A functional CMU wall section often includes a range of components, including:

Insulation Techniques for Block Walls

If you’ve chosen concrete block walls for your project, the next step is to consider which components will make up your wall section. Specifically—when choosing materials, you’ll need to decide which type of insulation to use for your block wall. Additionally, you’ll need to select a compatible installation method. 

Insulation can be installed inside the CMU block wall, on the exterior side of the block, or on the interior side of the wall. Some contractors choose spray foam, blow-in, or injection-type insulations for concrete block walls. These methods can be messy and cause problems if you need to cut through the wall at a later date. An alternative solution to increase the insulation value of your concrete block walls is a rigid insulation, like polyiso.

Polyiso insulation boards typically come in modular sizes, such as 4’ x 8’, and are easy to cut with a utility knife. They install quickly with versatile installation techniques, including:

Rmax Polyiso for Block Wall Insulation

Insulation is a critical component that is often added to concrete block walls to increase the wall system’s overall insulating value. The insulating R-value for polyiso packs the most punch with R6 per inch—meaning that you can achieve R13.1 with a single 2” thick layer (the facer adds to the R-value).

These Rmax polyiso products are for block wall exterior installations:

When insulating the interior cavity of a concrete block/brick veneer wall, foil facers are not always necessary. Polyiso provides a high insulating value per inch for this tight space.

You can also use polyiso insulation for concrete block basement walls to protect waterproofing during backfilling.

Click here to browse all of our insulation offerings by application or installation method.

Let Rmax Help Pick the Best Insulation for Your Block Walls 

Stuck or overwhelmed trying to decide which insulation to use for block walls in your project? Reach out to your Rmax representative today to get expert advice on which insulation solution will complement your design the best. We have a selection of high-quality polyiso products that are specifically designed to meet building code requirements, simplify installation, reduce costs, and accelerate the construction phase of your project’s envelope.

Insulating an Uninsulated Block-Wall Home

Fine Homebuilding Project Guides



Building scientist Joe Lstiburek recommends insulating with rigid foam on the exterior.

By Joseph Lstiburek

Issue 285 – Aug/Sept 2019

Outboard insulation. Retrofitting insulation on block walls is best done on the outside with rigid insulation. Furring strips and 2x4s attached to the wall support the cladding.

Two years ago I purchased a small home near Toledo, Ohio. It was constructed by the owner in the mid 1950s using cinder blocks, and the interior walls are lath and plaster. There is no insulation on the exterior walls, and I want to add some without losing already limited floor space. There’s a less than 1-in. gap between the plaster and cinder blocks, so spraying insulation in there won’t work. The house has a vented crawlspace that’s also uninsulated. I’ve insulated the attic to R-60, but I want to make the home more energy efficient and comfortable, and enhance its future salability. What insulation approach would you recommend for the walls and crawlspace?

—Richard Theriault, via email

Joseph Lstiburek, founding principal of Building Science Corporation, responds: I would recommend insulating on the exterior. This can be done with pretty much any rigid insulation. In your climate zone (zone 5), code requires you to insulate concrete block and other mass walls to at least R-13 if all of the insulation is on the exterior. Before insulating, coat the exterior of the walls with fluid-applied water-control and air-control layers. Then attach 2x4s on the flat directly to the masonry, insulate between and on top of them—staggering the joints in the insulation—and install additional furring on top of the insulation to attach your cladding.

The key decision relates to windows. I would recommend replacing them as well and pushing them to the exterior, turning them into “outies.”

As for the crawlspace, it should either be completely connected to the house and conditioned or completely disconnected from the house. Most crawlspaces are partially connected to both the exterior and to the interior, which is a bad idea. You do not want stuff from the ground or the outside to get into your house. Ideally, treat it like a mini basement. Leave the floor above it uninsulated, vapor-seal the ground below with polyethylene and a thin concrete slab, insulate the walls with a foam-based insulation (such as 4 in. of unfaced expanded polystyrene [R-15]) that allows the foundation to dry inward, and condition the space with air from inside the house.

Drawing: Dan Thornton

From Fine Homebuilding #285


Is Your Exterior Rigid Foam Too Thin?


A Case for Double-Stud Walls



Trusted, comprehensive guidance from the pros for a home that is healthy, comfortable, and energy efficient

View Project Guide

View All Project Guides »

Become a member and get unlimited site access, including the
Insulation Project Guide.

Start Free Trial

Energy Efficiency
  • Understanding Energy and Houses

  • Building Energy-Efficient Homes

Choosing Insulation
  • Insulation Basics

  • Material Choices

Installing Insulation
Water Management

The better to insulate walls made of aerated concrete

Increasing the thermal insulation characteristics of the walls of houses made of gas blocks is one of the main building trends in our country. Autoclaved aerated concrete is very popular with builders and customers due to its thermal insulation characteristics. However, how expedient is it to insulate such walls? What materials are most effective? What insulation options are used? Before starting work, it is important to answer each of these questions.

Do I need to insulate?

Before understanding how aerated concrete is insulated, it is initially important to determine the goals of such work. You might think that the only reason for insulating gas block wall structures is to reduce the cost of heating a house, but this is far from the case.

Among the advantages of insulation:

  • Ability to reduce heat loss by reducing the thermal conductivity.
  • Closing of thermal bridges (thick seams, lintels, armored belts), through which not only heat escapes from the premises, but also moisture penetrates, resulting in the formation of wet zones with mold.

When is the thermal insulation of aerated concrete walls beneficial?

If the payback of insulation is more than 10-15 years, there is no point in such a decision. However, there are situations when the insulation of aerated concrete walls is very beneficial. Here are some of them:

  • Gas or electricity too expensive.
  • Location of the house in a cold climate zone.
  • Walls thinner than 375 mm.
  • There are many temperature bridges in the walls.

According to the norms of SNiP, it is recommended to insulate the walls of houses that are built from gas blocks up to 375 mm thick. For this, vinyl or polystyrene is most often used.

Efficiency of materials

Mineral wool is a vapor-permeable material that helps to remove excess moisture outside through the walls. An excellent indoor climate is created, and the walls do not get wet, while retaining heat as much as possible. The material is non-flammable.

Styrofoam – easy to use, does not cause difficulties in cutting, the cracks are filled with foam. Unlike mineral wool, polystyrene foam is more affordable. However, the material is practically vapor-tight, which is why moisture accumulates on the walls. A house that is insulated with foam plastic needs good ventilation.

How is aerated concrete insulated?

There are various technologies for external insulation. They are carried out strictly according to the instructions. Experts do not recommend replacing materials with analogues in order to reduce the cost of work. For example, some owners decide to replace the special glue with a cheap tile counterpart.

Among the popular methods:

  • “Wet” (thin-layer plaster is used).
  • “Wet” (heavy plaster system is used).
  • Dry (ventilated facade).
  • Three-layer brickwork.

At the final stage, the final plastering and external decoration of the insulated surface is carried out.

outside and inside the house as well as what to do inside and how to choose insulation

Foam blocks are very often used for the construction of private houses, this is due to their affordable cost, as well as high rates of heat and sound insulation.

All house insulation works can be divided into those that are carried out outside and those that are carried out inside the house.

When is it better to insulate the outside of the house, and when from the inside?

It doesn’t matter whether you decide to insulate the walls of the house yourself or invite specialists for this, first you need to decide where it is better to do it, outside or inside?

Both methods have their advantages and disadvantages , and to understand which one to choose in your case, you need to familiarize yourself with them.

Advantages of interior wall insulation:

  • does not change the appearance of the house;
  • such work can be carried out at any time, regardless of weather conditions;
  • small expenses required;
  • work is done quickly.

But this method has a number of significant drawbacks that must be taken into account when choosing it for home insulation:

  • there is a reduction in the useful area of ​​the room, which is very important in small rooms;
  • the dew point shifts inside the wall, from which it becomes damp, and fungus and mold begin to form on the walls inside the room.
  • Carrying out the above works outside the house is also not an ideal option, as it has some disadvantages:

  • the appearance of the facade changes, and this is not always permissible;
  • performance of works depends on weather factors: they cannot be carried out in rain, snow, strong wind;
  • in case of violation of the work technology, after a while such type of finish as plaster may disappear.
  • Among the advantages of this method of insulation, it is worth noting the following:

    1. there is no need to move and take out furniture;
    2. free space of the room is not taken away;
    3. The dew point moves to the outer part of the wall, so the room will always be dry and fungus and mold will not form on the walls.

    [stextbox id=”3_na_zam”]If you want to insulate the walls of your house as much as possible, then it is recommended to do it both outside and inside the room at the same time. [/stextbox]

    outside, so you can protect them from freezing, subsequent cracks and repairs, thereby increasing their service life.

    But if you finish the facade with facing stone or tiles, you will have to make insulation from the inside.

    How to insulate

    Since the foam block has not very high strength, it is necessary to use light materials for its finishing.


    The most commonly used insulation for the exterior walls of the house:

    1. Mineral wool. This is an inexpensive material with high thermal insulation characteristics. It is vapor-permeable, so moisture does not linger inside the blocks, has a long service life, and is not combustible. It is necessary to protect the material well from moisture, otherwise its characteristics are reduced, and it is necessary to work in a respirator.
    2. Expanded polystyrene (styrofoam) . This material is not afraid of high humidity, it is frost-resistant, has an affordable price. Please note that under the action of sunlight, the foam is destroyed, so it requires additional coverage.


    If you decide to carry out these works inside the house, then first decide whether you need to do it.

    Foam concrete has high heat and sound insulation characteristics, and if you additionally insulate it from the outside, then there is no need to do this inside.

    If you decide to insulate only inside, you will get a result in which the walls will freeze through, steam will condense and therefore fungus and mold will begin to develop inside the room.

    [stextbox id=”2_znat”]If you decide to insulate the walls of foam blocks inside, then this must be done outside the house at the same time.[/stextbox]


    basalt wool, and so that you can lay it yourself, it is recommended to take it not in rolls, but in slabs.


    This material acts not only as a heater, but can also be used as a top coat.

    Before using it, the walls must be properly leveled with plaster, they must be clean and dry. The only drawback of cork is its high cost.


    If foam concrete walls are insulated with it, then about 95% of the heat will remain inside the room. Thanks to the foil, heat returns to the room.

    The slabs are laid tightly, and all joints are glued with adhesive tape, after which it is possible to proceed with the installation of the finishing material.

    Polyurethane foam

    This is a foam material with which all cracks and voids are sealed, so cold bridges are not formed.

    Cures this material within 20-30 seconds of application and will last at least 50 years.

    The disadvantage of polyurethane foam is its low vapor permeability and the fact that additional equipment is required for its application.

    Do-it-yourself external thermal insulation

    When insulating walls made of foam concrete, it must be borne in mind that this is a rather fragile material, so experts recommend mounting the insulation not on ordinary screws or dowels, but on glue or plastic screws so that cracks do not form in the block.


    For insulation, it is recommended to use board materials, it can be mineral wool or foam:

    1. first the walls are cleaned of dirt, stains and dust , if required, they are aligned;
    2. the surface of is covered with a primer , which will prevent the glue from soaking into the wall and act as a waterproofing;
    3. for slab mounting, use special adhesive for outdoor use;
    4. a metal guide is fixed at the bottom of the wall, which in its width corresponds to the thickness of the insulation;
    5. glue is applied along the edge and in the center of the slab, after which it is pressed against the wall and held slightly, the work is done from below and gradually moves up;
    6. after installing the insulation, reinforcing mesh is used, which sits on the glue, after which the wall is plastered, instead of plastering the house can be sheathed with clapboard.

    Under siding

    You can do it in another way: first, a waterproofing film is attached to the wall, then vertical guides are mounted, mineral wool is inserted between them.

    Then it is covered with a vapor barrier film, a crate is made to create a ventilation gap and the walls are sheathed with clapboard.

    Thermal panels

    Thermal panels are another way to insulate walls from the outside. This material is a layer of foam that has a finished cement mortar finish.

    You can choose the thermal panel of your choice, it can imitate almost any facing materials.

    The panels are fastened to each other with the help of special locks, and they are fixed to the wall of foam blocks with dowels, after which the fastening points are massaged with a cement mixture.

    Installation of thermal panels can be carried out almost at any time of the year , the main thing is that the walls are dry and even.