How to Insulate Walls Without Cavities

cavity wall insulation

Home wall insulation is more than essential for homes that want to be protected from cold weather conditions and high heating bills. Most modern UK properties have cavity walls which can be insulated, or probably already have been.

But what about older homes or those built with no cavity walls whatsoever? How do you go about insulating those older properties that are not suitable for cavity wall insulation?

Solid Walls vs Cavity Walls: What’s the Difference?

Solid walls are effectively walls without a cavity, while cavity walls have a space between the internal and external leafs that can be filled with insulation. But what is a wall cavity?

A cavity is any space that separates two layers of bricks or blocks. Cavities can range from 50mm to 100mm in thickness. Their primary purpose is insulation as they offer excellent thermal performance. 

As a result, modern constructions use cavity walls rather than solid walls. The latter used to be common during the early 20th century, but you don’t see them used often in building construction anymore.

Solid walls are just a single layer of bricks or blocks, so they are less effective at helping keep your home warm in the winter or cool in the summer unless they have some other form of insulation added to them.

How to Determine What Type of Walls You Have

With their differences out of the way, let’s move on to how you can determine which type of walls your property has. At first glance, you want to measure thickness. Solid walls are typically thicker than 260 mm while cavity walls tend to run thinner.

Brick pattern is another element to check. Cavity walls show alternating brick patterns since they consist of two walls. Alternatively, solid walls have consistent brick patterns.

Finally, if possible, find out about the age of the building or home you’re in. Remember, as a rule of thumb older houses, usually those pre-1920s, will likely have solid walls and therefore no cavity wall insulation — unless any renovations or additions were made to the property which have considerably altered the construction.

How to Insulate Walls Without Cavity: 2 Simple Methods

After double-checking that your walls are indeed solid, it’s time to decide which method of insulation will work best with them. Generally speaking, you have two solid wall insulation types to choose from — internal wall insulation and external wall insulation:

Method 1: Internal Solid Wall Insulation

This first process involves adding an insulating layer of material to your internal walls. This additional layer can either be a stud wall or be made up of rigid insulation boards.

On one hand, stud walls are metal or wood frameworks. Think of them as partition walls – except you fill in the gaps, or studs, with insulation material. After that, you cover them up with plasterboard.

On the other hand, you can use the right plasterboard to build a rigid insulation layer instead. Choose from foam or polyisocyanurate (PIR), for example. Plasterboards sometimes have a facing as well (like foil) to further enhance their insulation properties.  


  • A budget-friendly option for improving your home’s energy efficiency 
  • Flexibility in insulation choices as there’s a variety of materials to pick from
  • A compact solution that won’t compromise floor space



  • Fixing heavy items to the internal walls proves difficult after insulation


Method 2: External Solid Wall Insulation

Your other choice would be installing solid wall insulation to the walls’ outer surface. Insulating material will be fixed to external walls before covering it with a specialised render or cladding. 

External insulation is an excellent solution if you’re looking for more than weatherproofing. It also improves sound resistance, fills any cracks in the brickwork, and reduces draught.


  • Increase the walls’ lifespan without compromising your floor space
  • Renew the appearance of your outer walls
  • Prevent damp issues by reducing internal condensation




How to Internally Insulate Solid Walls: Steps & Equipment

Decided to go for the more affordable insulation method? Let’s see how to internally insulate walls without cavities, using the two processes we mentioned above.

How to Build a Stud Wall

Stud walls are a relatively simple DIY project. Here are the materials and tools you need:

  1. 2×4 lumber for framing (studs)
  2. Insulation material
  3. Nails or screws
  4. Framing square
  5. Tape measure
  6. Level
  7. Caulk
  8. Insulation tape
  9. Circular saw or handsaw
  10. Drill or driver
  11. Utility knife
  12. Safety gear
  13. (optional) Vapour barrier
  14. (if you have a concrete floor) Pressure-treated lumber for the bottom plate


With your equipment ready, let’s go through the required steps to build a stud wall.

Step 1: Plan and Measure

Determine the length and height of your stud wall. Make sure to use a framing square and a level for accurate measurements. Plan for electrical outlets if necessary.

Step 2: Prepare the Bottom Plate

In case you’re building on a concrete floor, use pressure-treated lumber for the bottom plate. This should help prevent moisture damage. Use a circular saw to cut the lumber to the desired length.

Step 3: Mark Stud Positions

Start marking the stud position on the bottom plate. Space them 16 to 24 inches apart using a framing square. Ensure everything is properly perpendicular. 

Step 4: Cut and Install Studs

With the circular saw, cut the studs to the desired height. Vertically install them between the top and bottom plates. Apply construction adhesive on the edges for added stability if needed.

Step 5: Secure the Top Plate

Attach a top plate to the studs’ upper ends. It should be level before you securely fasten it to the stud with nails or screws.

Step 6: Insulate the Stud Wall

Time to insert the insulation material of choice between the studs. It should snugly fit. Leave no room for gaps.

Step 7: Secure and Finish the Wall

After using a level to ensure the wall is plumb (vertical), secure the bottom plate with fasteners. 

With that, you can finish the wall by attaching drywall, for instance. Seal any joints with caulk and use insulation tape to increase airtightness. 

How to Insulate with Rigid Foam Boards

If the process above sounds rather complicated, consider rigid foam boards instead. The needed equipment is:

  1. Rigid foam insulation boards
  2. Adhesive (has to be suitable for foam insulation)
  3. Measuring tape
  4. Utility knife or saw
  5. Straight edge or level
  6. Caulk and caulk gun
  7. Construction adhesive
  8. Putty knife
  9. Protective gear

The steps are pretty straightforward for this method. Take a look:

Step 1: Prepare the Surface

Your walls should be clean, dry, and both dust and debris-free. Repair cracks or holes as well.

Step 2: Measure and Cut the Insulation

You need the height and width of the walls to determine the size of insulation boards required. Use a level or edge to accurately do this. Then, cut the boards with a utility knife or saw. 

Step 3: Apply Adhesive

Generously apply construction adhesive to the backs of the boards. Once done, position and press the adhesive-coated sides against the wall with firm pressure. Keep doing this until the wall is fully insulated.

Step 4: Seal Joints and Edges

To prevent air and water leakage, seal the joints and edges with caulk, using a putty knife.

Step 5: Reinforce and Finish the Wall

If you want extra stability, try attaching furring strips over the insulation. After, finish the wall as desired. That can include painting or adding a decorative flourish.

How to Externally Insulate Solid Walls: Steps & Equipment

External insulation is more of a professional feat than a DIY one. We recommend you seek our services and have us direct you to a reputable insulation company that’ll do this for you.

If you must do it yourself, here’s the material you’ll need:

  1. Insulation material (EPS, mineral wool, etc.)
  2. Special adhesive for external insulation
  3. Screws or anchors
  4. Reinforcement mesh
  5. Polymer-modified base coat
  6. Exterior render

As for the tools, have the following on hand:

  1. Notched trowel
  2. Spirit and straight level
  3. Electric drill
  4. Mixing paddle
  5. A float

5 Steps to Externally Insulate Solid Walls

Here’s your to-do list to externally insulate any wall without a cavity:

Step 1: Prep the Surface

Clean the exterior surface you’ll be working on. Remove any loose or flaking material and repair any cracks found.

Step 2: Install Insulation Boards

With your notched trowel, apply adhesive to the back of the insulation boards. Press the boards snugly onto the wall. Use the spirit level to keep everything straight.

After that, secure them with the mechanical fixings you picked. Place them at the boards’ corners and edges.

Step 3: Cut and Shape Insulation

Pick up your saw or knife to cut the insulation boards. They need to fit around the windows, doors, and other obstacles around your home.

Step 4: Apply Base Coat and Mesh

Apply a base coat over the entire surface. While it’s still wet, embed a reinforcement mesh, making sure it’s fully embedded. It should overlap at the joints for added strength.

Once done, allow the coat to cure according to the manufacturer’s instructions. It might take several days.

Step 5: Apply Finish Render

Only after the base coat is cured should you apply a final layer of exterior render. Use your float to smooth and finish the render – this provides an excellent decorative finish.

How to Insulate Walls Without Cavity: Wrap Up

Insulating solid walls is easier than you think. All it takes is the right understanding of your needs and budget as well as what insulation materials guarantee you a warm living space.

Whether you decide to internally or externally insulate your walls, we recommend you check with us, Insulation Advisor, beforehand. We’ll put you in touch with trusted insulation contractors who’ll properly take care of your insulation project.

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