underfloor heating on joisted floors

We stock and supply a number of floor systems that provide the same or an improved performance as a traditional underfloor heating concrete ground floor, but for suspended floors.  Suspended floors are typically constructed using timber or steel beams or joists and are above a void or a room below.

These systems include a steel sheet that reinforces and stiffens the floor (being steel it also spreads the heat across the floor and eliminates any cold spots) and allows for a thin screed or concrete to be used over the top.

These systems include:

  • Lewis Deck
    • Typically around 52mm total depth above the top of the joists, but can be as low as 36mm including the underfloor heating.
  • Max4 Therm
    • From just 15mm total depth above an existing floor that can be timber or concrete including the underfloor heating.
  • FastSlab Ground Floor
    • Complete ground floor system including beams, insulation and floor structure.  Underfloor heating pipes are simply clipped to the top of the Lewis Deck before a screed or concrete is applied.
  • FastSlab Foundation System
    • As the FastSlab system but including the complete foundation that utilises steel screw piles and an insulated ring-beam to support the building.
  • Op-Deck
    • Typically a large spanning insulated and high load-bearing ground floor system, also used in load-bearing flat-roof applications.  Underfloor heating can be included within the concrete of the system.

Scroll down the page for links to the various systems.

This video compares the Lewis Deck and Gyvlon Thermio+ screed (top left) against aluminium spreader plates (top right).

There is also a comparison between two ground floors, a 40mm Gyvlon Thermio+ screed (bottom left) and a typical 75mm concrete (bottom right).


The second video shows the reaction time of a Max4 Therm floor, this is 15mm in depth and includes an 8mm diameter underfloor heating pipe.

Available Systems

Max 4

Max4 without UFH

Max4 reinforcing sheets provide a great solution for leveling uneven existing floors with the introduction of reinforced ultra thin light weight liquid screed floors in projects where weights and height restrictions are an issue. The Max4 reinforcing sheets are manufactured from 2 sheets of special profiles steel and designed for use on existing timber or …

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Lewis Deck

Lewis Metal Dovetailed Sheeting Deck with acoustic Sylomer resilient strips

LEWIS Dovetailed metal decking, as part of a joisted floor system, provides a first class solution where acoustics and fire protection are key concerns. The Lewis system works very well with screeded underfloor heating and cooling systems, allowing them to work more efficiently than without the sheets in place. LEWIS provides a number of solutions …

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The FastSlab Ground Floor system is designed to make it quick and easy to replace existing suspended ground floors with an insulated concrete or screeded floor. This gives the solid feel of a concrete ground floor with the benefit of maintaining the ventilated void beneath to prevent moisture issues in the existing walls. The FastSlab …

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Op-deck is a lightweight insulated floor and roof system. The advantages of composite metal deck concrete floors and traditional rib floors have been combined in this unique patented floor/ roof system. This insulated concrete floor/ roof system (ICF) is based on traditional concrete installation but with optimal design and installation flexibility. It is suited to …

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FastSlab Foundation

FastSlab foundation system

The FastSlab Foundation System is a fast track method to construct foundations and ground floors, ideal for sites with limited access, poor ground conditions, flood plain locations and areas with tree root issues. It also works equally well in all ground conditions whilst eliminating a sometimes difficult and expensive muck shift. A typical FastSlab house …

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Ask CDI a Question

  • Q

    What are the Lewis Deck sheet sizes?


    Q: What sheet sizes are held in stock for delivery within a few days after order? A: We stock 2500mm and 1300mm sheets.  These are all 630mm wide and 16mm deep.  Deliveries are made via the pallet network directly to site.  The smaller sheets are aimed at small bathroom renovation projects and can be supplied in small numbers via TNT. 2.5* and 1.3m sheets allow for the 100mm overlap to occur over a joist, with joist centres being either 300mm, 400mm, 600mm, 800mm*, 1200mm and 2400mm*. (*2.5m sheet only) For larger projects we are able to produce bespoke sheet sizes if required, please get in contact to discuss other options for sheet sizes.


    Lacomet – How come it has no scrap value?


    Lacomet – How come it has no scrap value? Many of the projects that we get involved in starts with a phone call or email to us from someone researching replacing stolen leadwork. Many of these are old buildings, such as schools or churches, where this isn’t the first time that the lead has been stolen and they call us fed up with having to replace it again full in the knowledge that they will more than likely go through the same problem once more in the near future if they continue to use lead. One of the big benefits that Lacomet FL brings to a project is the fact that it has no scrap value and therefore the chances of it being stolen are massively reduced. Due to the 2 thin aluminium layers, and its five layer total construction, it is of no value to thieves. Lacomet can be recycled but the polyester based coating would need to be de-laminated first and the amount of recovered aluminum is then very low, in fact it would be easier and more profitable to collect empty drinks cans than to mess about stripping Lacomet down. We can also supply stickers that can be placed in strategic locations informing people that what is now on the roof is not lead and that it has no scrap value.

  • Q

    Why don't my Lewis sheets interlock like they do in the video?


    Q: Why don't my sheets interlock like they do in the video? A: The sheets have two sides (one printed, one plain), the dovetails on either side are different widths, it is then necessary to alternate the sheets print up and then print down.


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underfloor heating on joisted floors