How to Install Screed for Underfloor Heating

Underfloor heating is an immensely popular heating system for home owners, and property developers. It is a great, cost-effective way to increase the comfort levels of a property, while maximising energy efficiency, and unlocking greater control over indoor temperatures.

What’s more, with the addition of screed, underfloor heating systems in concrete flooring can achieve the same pristine, flawless finish as any other type of concrete flooring.

So, if you’re looking to invest in concrete flooring with underfloor heating, this guide is just for you. Below, the team at iMix Concrete have shared a comprehensive installation guide for how to apply screed for underfloor heating.

Insulation for Underfloor Heating

Before the underfloor heating system is installed, you will need to add insulation to the flooring. Insulation is designed to maximise the performance and efficiency of the underfloor heating system, long into the future.

Insulation for underfloor heating goes under the heating system.

Electric Underfloor Heating

As with all underfloor heating, you need to insulate the sub floor before laying the heating system. As electric systems are lighter and thinner than hot water systems, the insulation is also thinner and lighter.

Foam insulation boards are the most common insulation for electric underfloor heating – and you depending on the height of the floor, you can get these from 3mm up to 20mm. The foam insulation board is similar to that of foam used in model aircrafts.

Hot Water Underfloor Heating

According to UK building regulations, the primary pipework (which transports the hot water from the heat source, to the flooring’s domestic hot water cylinder) must be insulated. However, for the best results, we recommend insulating all of the flooring’s underfloor heating pipework.

When insulating the pipework, we suggest that you use polyurethane insulation (at a minimum thickness of 50mm). Then, on top of the insulation, it is advisable to add a layer of between 65-75mm of screed.

Preparing your Floor for Screed

Once your underfloor heating pipes / cables have been laid and installed, you can start preparing to pour over the floor screed.

To ensure the best results, we recommend taking the following preparation steps:

Electric System

• Check that the subfloor is clean and dry
• Check that the subfloor is even, and if there are any cracks or uneven areas, repair them
• Test the system
• Check the electrical connections to the mains
• Check the thermostat is installed and linked with the system
• If required, install a vapour barrier on top of the subfloor

Hot Water System

• Check that the subfloor is clean and dry
• Check that the subfloor is even, and if there are any cracks or uneven areas, repair them
• Pressure-test the pipes
• If you have a hot water system, check that the pipes are full of water (this will ensure that any issues are identified and fixed, before the screed is poured and set)
• Check the thermostat is installed and linked with the system
• If required, install a vapour barrier on top of the subfloor

Applying screed for concrete flooring with an underfloor heating system

iMix Concrete can supply screed for concrete flooring with underfloor heating systems. Our specialist, premium quality screed ensures that properties achieve the maximum thermal efficiency, and a sleek, flawless result for their new flooring.

Choosing the right type of screed

For underfloor heating systems, we suggest using a high quality self-levelling screed, with added thermal conductivity.

Pouring the screed

Pour the screed over the pipework.
Stabilise the screed with a chemical spray.
Tamper the screed, to ensure a smooth finish and that all elements are uniformly covered (unless the screed is self-levelling).

You can also enlist the iMix Concrete team to mix and pour the screed on your behalf, to ensure a perfectly even, flawless finish.

Allowing the screed to dry

Screed needs to be left to dry for at least 7 days. It is critical that you wait for this period of time before you attempt to walk over the surface, or add heavy loads.

After the 7 day mark, you should also turn the underfloor heating on at its lowest temperature. Then over the next week, you should keep gradually increasing it, bit by bit.

What are the most efficient layouts for underfloor heating?

The most efficient layout for underfloor heating (how the tubes and wires within the system are placed) is outlined in BS EN 1264.

To achieve the most efficient results, the pipework should:

• Achieve an even spread
• Towards the room’s perimeter, the spacing may be reduced (to address the extra heat loss that these areas experience)
• Be laid out in accordance with the guidance of the system manufacturer
• Be kept at least 100mm away from the walls
• Have a maximum loop length of 110m
• Have the control pack, manifold and wiring centre positioned in a central point in the building
• Not extend across to the very edge of the flooring
• Not continue under the floor’s skirting boards
• Not continue under units (such as kitchen units)

The most effective underfloor heating layouts, make the most of the space available. Depending on the wattage you use, there are different spacing sizes.

• 50mm gap between cables for a 200w per m² system
• 60mm for 165w per m²
• 65mm for 150w per m²
• 75mm for 130w per m²
• 100mm for 100w per m²

Having the heating cables / pipes laid out in a back-and-fourth design maximised the heating efficiency.

Electric vs Hot Water Underfloor Heating Systems

There are two primary types of underfloor heating: underfloor heating that uses electric cables, and systems that use hot water pipes. Both of these are suitable for screed to be poured on the top.

Each of these systems offers its own specific strengths and best-fit use cases.

Electric Underfloor Heating

Electric systems consist of a series of wires or heating mats that are heated by electricity, and connected to the electrical mains. Heating mats have the wiring laid out on a mesh sheet, that usually comes as a roll around 1 meter wide. You can also get a heating wire on a drum to layout manually.

Compared to a water heated system, you need to be extremely precise with your measurements for electric underfloor heating, as you don’t want to run out of cabling, or have the order another mat.

The advantages of electric systems:

• Ideal for use in renovation projects
• Perfectly suited to small spaces or single rooms
• Affordable installation costs
• Can be installed rapidly (even as quickly as within 30 minutes)
• Can be powered by renewable energy sources, such as solar energy or wind panels
• Quick to cool down
• Can be used as either a primary or supplementary heat source

Hot Water Underfloor Heating

Water is heated and then pumped throughout an underfloor circuit of pipes. Laid out across the floor, this system takes a bit longer to install compared with an electric one.

The advantages of how water systems:

• Ideal for use in new-build projects
• Perfectly suited to larger spaces
• Low running costs in the long term (compared to electric systems)
• Is compatible with a wide range of heat sources
• Can be powered by renewable energy sources
• Heats efficiently (especially across larger areas) and has a high level of heat retention

If you have any further questions about screed installation and its benefits, or you would like to enlist our team of skilled concrete specialists to support your upcoming project, contact our team today.