How to Insulate a Concrete Floor

Insulating a concrete floor is no mean feat – compared to insulating walls or roofs, it can be an intensive piece of work with plenty of disruption. However, it can also provide some great benefits both in the short and long term for a property.

The best approach for insulating a concrete floor depends on the nature of the property and the amount of money you’re willing to spend. Generally, it comes down to whether the insulation will go above or below the concrete, but there are many other factors you’ll also want to consider.

Should You Insulate Above or Below the Concrete?

In a perfect world, insulation should always be placed underneath a concrete floor. However, in many cases, it’s much easier to put it above and still enjoy the benefits.

Despite concrete having a reputation for being cold and unforgiving, it’s actually quite good at naturally absorbing heat. Putting insulation underneath allows the concrete to continue taking heat from the air and helps retain it for longer, helping to maintain more stable temperatures.

Putting insulation above concrete still helps to keep rooms cooler, but you lose the concrete’s natural regulating properties. Rooms with the insulation above concrete tend to heat up faster and cool down quicker compared to having the insulation below concrete.

Of course, the major downside of trying to put insulation below concrete is having to remove the concrete itself. If working on a new build, this isn’t an issue, but if trying to add insulation to an existing concrete floor, the potential cost of removing the floor usually far outweighs the potential energy-saving benefits.

One other reason you may consider removing your concrete floor though, is the impact on floor levels. Putting insulation on top of existing concrete will obviously raise the floor level, which can be a problem for doors and electrical sockets. Meanwhile, if you remove the concrete floor, you can dig lower and install insulation without changing the floor level.

Overall, insulating below a concrete floor delivers better performance and is usually the option of choice for new builds. However, if renovating an existing property, the potential cost of removing the concrete floor means that retrofitting insulation on top is often the preferred choice.

How to Insulate Above Concrete

Insulating above concrete is a relatively simple process. However, you want to make sure you’ve prepared the concrete floor and also consider how thick your insulation is going to be, and what impact that will have on the floor level.

1. Prepare the Concrete – Make sure the surface is clean and there are no cracks which could cause issues in future.
2. Install DPM – Cover the concrete with damp-proof membrane to prevent damp rising into the insulation.
3. Install Insulation – Put down your insulation of choice.
4. Add Chipboard or Screed – Add a layer of moisture-resistant chipboard or screed.
5. Add Finish – Place your final choice of flooring, such as wood or carpet.

How to Insulate Below Concrete

Insulating below concrete involves many of the same materials as insulating above, albeit in a different order. Again, it’s fairly straightforward so long as the preparation work has been done.

1. Sand the Base – Apply a layer of sand to the earth base.
2. Install DPM – Place damp-proof membrane over the sand to prevent moisture being drawn up.
3. Install Insulation – Place your insulation of choice.
4. Add Concrete – Pour concrete over the insulation and let it cure.

Key Considerations When Insulating Concrete Floors

Beyond the key question of whether to insulate above or below the concrete, there are some other key factors you need to consider whenever adding insulation to solid floors.

Raised Floor Level

When renovating an existing property, insulation will usually be added on top of concrete floors. If this is something you’re considering, you have to be very mindful of the potential impact on the floor level.

Thin insulation slabs have been designed to minimise the potential impact on floor levels, but you need to be mindful of whether these produce enough insulation for your property (see the next point below). Even a small change, however, can have knock-on effects on things like doors, stairs, plug sockets and windowsills. Make sure you assess every aspect of the room and make any changes required before raising the floor level.

Government Insulation Requirements

As with many aspects of a property, there are specific insulation requirements in the UK that need to be considered when doing any work like this.

If you’re working on a new build, you need to ensure all insulation requirements are met, including reaching the required u-values for floor insulation.

If you’re renovating an existing build, the rules are less stringent and there is leeway if the required insulation value can’t be met due to specific issues with the property – for example, if raising the floor level would cause a significant issue to the usability of the property. However, a general rule of thumb is that if you’re replacing more than half of the floor – for example, by removing the concrete to install insulation underneath – then you must adhere to the modern requirements regarding floor insulation levels.

Different Insulation Types

Another of the big decisions to make when insulating a concrete floor is the specific insulation product you’ll choose. Obviously, this has a massive impact on the potential cost, the thickness and its impact on the floor level (if added above existing concrete), as well as the final result, since some insulations come with additional features.

EPS (Expanded Polystyrene) is a popular choice for new builds as it is lightweight, durable and easy to handle, as well as being budget-friendly. However, its thickness makes it less suitable to putting on top of concrete, which might require a more expensive option such as phenolic foam boards.

When choosing your insulation, you also need to consider its compressive strength, particularly if placing it above concrete. If the insulation has to handle a lot of weight, then you want a board that won’t deform over time and create an uneven surface. You may also consider an insulation’s soundproofing qualities when making your decision.

Ultimately, given all the potential variables that go into insulating concrete floors, it always pays to ensure the situation is thoroughly assessed before making a decision. However, if you can put up with the expense and disruption, having insulated floors can make a world of difference to the feel of a property.