General information

 Solid floors are probably the most popular of all the floor constructions that we supply underfloor heating systems for. They are essentially systems where pipes carry warm water through the floor while encased within concrete or screed.

With solid floor systems, insulation is laid below the pipes to prevent downward heat loss. As indicated in the schematic drawing, the pipes are installed on top of the insulation panel (either lightweight polystyrene or polyurethane boards) and the vapour barrier. Depending on the type of insulation used, you might be able to only tape the joints and thereby eliminate the need for this separate layer. Our staff will be happy to discuss the specific situation of your building project.

Above the insulation, a fixing system is used to hold the pipe work in place whilst the screed is being laid. Once the pipe work is installed in accordance to the bespoke pipe layout designs, the underfloor heating system has to be filled with water and pressure tested.

This test will determine that no damage has occurred to the pipe during installation process and can be monitored during screeding to check for damage, should it occur. 

Insulation

The depth of insulation used or specified, can have a direct bearing on the build height of your underfloor heating system. We can recommend a minimum thickness of insulation that you would equire for the underfloor heating. However the final thickness and insulation type will be decided by your building regulations.

Polystyrene or a PIR (foil backed) insulation is commonly used as the main floor insulation type. Edge insulation is also recommended around all external walls to prevent heat being lost around the rooms perimter. It can also combat any expansion of the screed as it heats up.

Screeds and concrete

There are many different screeds available, including anhydrite liquid screeds as well as traditional pumped and mixed screeds. Care should be taken when using liquid or pumped screeds as if allowed to get under your insulation it will float the insulation and pipe work to the top of the screed causing considerable problems. Please consult with the screed suppliers before and during the laying process for any recommendations they might have with regard to their product.

Assuming a traditional 75mm sand and cement screed has been laid, the heating system should not be turned on for at least 28 days. You may be able to get additives to speed up the curing times, but you must then follow the advice of the screed supplier to ensure that their product is being used according to their specifications.

Build up heights

The build up height of the underfloor heating system can vary from job to job, and is very dependent on the types of materials that you use.

In an ideal world, the use of a 50mm PIR insulation such as Celotex with a 65 – 75mm sand cement screed above would be the optimum build up height. You can reduce the screed depth to a minimum of 55mm by using alternative / stronger screed mataerials. The depth of insulation used may also be reduced if you are not covered by building regulations, but this is not recommended as you would be reducing the efficiency of the system.

Temperatures and outputs

Screeded floors have the highest output of all the underfloor heating systems, but at the same time have the lowest water temperature requirement. For example, the water temperature required to run a solid underfloor heating system is normally 40 – 45c; the maximum available output is 100w/m2, which provides a maximum floor temperature of approximately 29c.

In a modern building with high levels of insulation and high specification double glazing, the floor temperature is usually within a few degrees of the air temperature within the room, keeping you warm and comfortable even during very cold weather.

If you have a poorly insulated building with little or no insulation, draughty single glazed windows and open flues, you will find that the system will have to work considerably hard to achieve a comfortable room temperatures in cold weather. We recommend you  refer to the heat loss calculations, which are prepared at the quotation stage of the project, to ensure that any potential temperature issues are highlighted as early on in the project as possible.