August 24, 2022

Applying screed over underfloor heating requires careful consideration of both the screed and underfloor heating. In this article, we discuss the different types of screeds and key considerations to ensuring professional application over underfloor heating.

The pros and cons of underfloor heating.

Over the past few years, a drive toward ‘greener’ building systems in the UK has led to increasing popularity of underfloor heating, which is now used in many sectors, including residential, healthcare, education and leisure. The move toward more energy-efficient heating systems, such as condensing boilers and ground source heat pumps, is indicative of the greater emphasis being placed on energy efficiency. All these trends favor the adoption of underfloor heating, which is ideally suited to run in conjunction with condensing boilers. In order to avoid problems, it is important for surveyors to be aware of the relationship between underfloor heating systems and the associated floor screed.

Which screed should I choose?

An underfloor heating subfloor can be made up of a layer of water pipes fixed to the insulation in an appropriate manner, such as with tacker staples or a clip rail.

There are two types of screed:

  • Semi-dry screed is applied by hand and then is finished with a trowel.
  • A liquid screed is often pumped over the pipes and spread to a certain depth.

Screeding is the process of creating a smooth, level and firm base for a floor to be laid on. Screeding is done by leveling the subfloor and adding cement-based screed. The screed can either be applied directly to a concrete slab or over an underfloor heating system that has been installed previously. It’s important to remember to let the screed cure before slowly preheating the floor as part of the commissioning process. Once this process is completed, the underfloor heating can be turned on and the floor finish can be applied.

Key Considerations

When laying a floor screed over underfloor heating, it is important to consider the following steps:

  • The floor should be smooth and level before you begin installing underfloor heating. You will also need to make sure that you have the correct screed zone or floor build-up before installing the underfloor heating and screed package.
  • The correct screed is specified, and of the right thickness, after considering heat output, point loading (the amount of weight placed on a given area of floor), the size and scale of the floor area, and the chosen floor finish. Thermal movement caused by heat from underfloor heating also needs to be taken into account when choosing the screed type.
  • You’ll follow the project specification to install expansion and perimeter strips, and you’ll mix and apply the screed according to the manufacturer’s instructions.
  • Placement of movement or expansion joints in the screed, needed to prevent cracking in the floor, is carefully considered at the design stage.

It’s also important to remember the impact this type of heating can have on screed, and how screed reacts when heated.

When designing a heated floor system, there is often an aspect that is overlooked by design teams: the subfloor zone. This area can be vital to the overall efficiency of the system and should be considered when designing the heating components. It is a common problem that installations in the heated subfloor zone often fail. If you install heating in this zone, you can expect to have unhappy clients and damaged reputations. In the UK, there have been many studies about the problems with heated subfloor zones. It is not uncommon for experts to be called in to inspect cracks, which are often a fault of the screed. However, in most cases, cracks are a symptom of a problem with the subfloor zone. In the course of an investigation of a drawing marked up with the positions of cracks – overlaid on the ‘as built’ drawings of underfloor heating layouts – a lack of proper design and poor layout may be revealed.

If you need more information you can always contact a professional company Screed London.