What is a cavity wall? What is a solid wall? How to recognize them?


You are neither a mason, nor a plumber, nor a professional needing to work on a wall, yet you still have questions about the insulation of your home? Or are you wondering if it is possible to pierce one of your walls? Or simply, you just want to hammer a nail in to hang a picture and you don’t know what to expect? Before embarking on one of these three actions, it would be relevant to see what your wall is made of? Is it empty or not, is it load-bearing or not, in other words is it a hollow wall or, conversely, a solid wall?

What is a cavity wall?

Cavity walls were developed in the first half of the twenty-first century to reduce humidity. Quite simply, instead of having a thick brick wall between the interior and exterior of the house, a cavity wall has two layers of brick with a gap in between. The gap can be 20-100mm wide and therefore means cavity walls tend to be much wider than a solid brick wall. With the naked eye, you can tell if your wall is hollow or solid just by looking at the exposed bricks. If all of the bricks are the same length (i.e. they were all laid lengthwise), you probably have a cavity wall. You can also look at the width of the wall – if it’s more than 270mm, there’s a good chance you have a cavity wall.

How do you insulate a cavity wall?

Cavity wall insulation is fairly inexpensive and only takes a few hours in an average home. The space between the bricks is filled with one or more insulating materials. We calculate the cost per square meter. It all depends on the material you choose, but cavity wall insulation is generally inexpensive, easy to do, and can save you a lot of money on your energy costs.

There are different types of insulation. You can choose glass wool or polystyrene beads or polyurethane foam. Traditionally, the option of insulation with glass wool is cheaper. Polystyrene bead insulation is more expensive but has a higher performance. There are grants available for cavity wall insulation, so you can easily get help, or if you do it right, very inexpensive or even free.

What is a solid wall?

A solid brick wall is exactly as the name suggests. It is usually made of two bricks wide, with each row of bricks interlocking to form a completely solid brick wall. There is no space between the bricks to be insulated, so you have to either add insulation inside your home or do it outside. These types of walls can again be identified by simply looking at the masonry. If the bricks alternate between a mixture of short bricks and long bricks, you are facing a solid wall. Check the width of the wall. If it is less than 260 mm, there is a good chance that the wall is made of solid brick. The vast majority of houses built before the 1930s are made of solid brick.

How do you insulate a solid wall?

Whether you choose to insulate inside or out, solid wall insulation is expensive. There are funds available for this form of insulation, but you will likely have to make your own contribution and will likely receive less assistance than for cavity wall insulation.

How do you determine if your wall is solid or hollow?

You have undoubtedly seen this gesture of bending an index finger to strike it gently against a wall in order to listen to the noise that “the wall makes”. Professionals quickly know from the sound obtained whether the wall is solid or hollow. If the wall resonates, then there’s a good chance it’s hollow, which is good news if you want to knock it down or at least create an opening. If by this manipulation you really cannot determine the nature of your wall, then all you have to do is consider a discrete area – perhaps at the back of a wall where you can drill your wall. Depending on the material that will result from your breakthrough, you will be able to determine what your wall is made of and from there whether it is solid or hollow.

What look and what color to dust when you drill your wall?

  • If you get a fine, white chalk-like dust, you’re dealing with plaster.
  • If the powder obtained is also fine but rather gray, it is concrete.
  • If the dust is more like sand, beige or gray, you are in the presence of stone.
  • If the residue is a powder in orange tones, then the pierced wall is brick.

Once this is done, you can determine which tool to choose because it is also the material of your wall that determines whether it is solid or hollow. If it’s stone or concrete, there’s a good chance your wall is solid. Conversely, if it is brick or plaster, everything suggests that your wall is hollow.

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