Colglo Blog

A Guide to Fitting a Wet Under Floor Heating System Over Solid Floors

Posted by Collister & Glover on Aug 22, 2018 10:09:21 AM
Collister & Glover

Retrofitting Solid Underfloor Heating using Polyplumbs unique red floor panels into renovations, existing buildings or just one room. What are the benefits? and How is it installed.?

Red Floor Numbered


Under floor heating has become very popular in new builds and major renovations recently and the new low profile systems have also made it possible to retrofit it into existing rooms. It is economical to run and requires little maintenance, which, over the long term, makes it relatively cheap to install.
Once fitted there is a minimal increase in floor height, it allows room by room temperature control and it also works well with renewable heat sources.

Polyplumb Underfloor Heating offers three systems for solid floors and the focus here is on installing the  Red Floor Panel system. A screed based system, it uses a lightweight plastic floor panel that is quick and easy to cut to size. As a result it is possible to fit this under floor system into any shaped room.

The Red Floor Panel system offers optimum performance alongside an easy installation for Solid/Screeded floors. The unique, lightweight floor panels are quick and easy to cut to size and lay. The panels act as a guide for laying the ultra-flexible pipe, this in turn provides optimal heat distribution over the whole of the floor.

The Red Floor Panels also offer a degree of protection for the pipes after installation. If you plan on pouring screed it allows workmen access to the site with a reduced risk of knocking the pipes out of position. 

Screed depth is measured from the bottom of the panel. The castellated points in the Red Floor Panels account for some of the volume within the finished floor slab, meaning you need approximately 15% less screed.

Features & Benefits of using the Red Floor Panel system:

  • Simpler, more accurate installation
  • Precise pipe positioning
  • Ensures minimum pipe bending radius is achieved
  • Panels are quick and easy to cut to size
  • Can be used in any size or shape room
  • Facilitates spiral configurations and 100mm pipe centres
  • Approximately 15% less screed required

A note on heat loss regulations

You should be aware that all these installations are covered by Part ‘L’ of the current Building Regulations BS EN 1264 . A suitable layer of insulation material should be included within the floor construction. It is the responsibility of the architect or builder to ensure compliance. However, in each instance, insulation must be installed beneath the underfloor heating system. 

Step 1: Fitting Insulation Materials


When laying the insulation boards beneath the red panels ensure that the joints of each board are staggered and securely taped so as to minimise any risk of movement.

Step 2: Fitting the edge expansion strips


The edge expansion strip allows movement of the floor screed. It comes with a self-adhesive strip that bonds the panel to the wall. Install the strips all around the perimeter wall and around any fixed constructions such as columns, steps, access doors etc.

The strip also comes with a plastic skirt that lays over the top of the insulation to prevent the screed seeping into the joint between the insulation panel and the strip itself. Edge expansion strips should be fitted in addition to perimeter insulation. (required by the Building Regulations)

Step 3: Fitting the floor panels

In the image below the top edge is half castellated and the bottom edge three-quarter castellated. 

Full Panel

Begin at the wall edges

  • Panels are laid over the pre-installed insulation.
  • The first panel should be laid with the half castellated edge against the wall.
  • The plastic skirt should be laid over the floor panel. (as in the image below)
  • The outside run of pipe will be pushed into the skirt and the raised castellated sections. This create a seal around the wall edge.
  • Secure the panels around the perimeter of the room using staples to prevent them lifting. 


Further floor panels should be overlapped at the edges. To do this properly the half-castellated edges should be covered by a three-quarter castellated edge

Edge to Edge

None of panels should simply ‘butt-up’. This is to stop screed from penetrating  the gap in the panels, causing them to rise up.  Further panels can be cut by simply using a saw or snip, or it can be overlapped to the nearest castellated fit. 

Floor panels should not be used at the base of the manifold. Pipes near manifolds tend to be closer together than the floor panels allow. Pipes around this area should be secured using pipe clips. These can also be used intermittently to secure the clip panel to the insulation. 

Step 4: Preparing the pipe
You will need to remove the coil from the bag, leaving the shrink wrap on, uncoiling from centre of the coil.


Step 5: Laying the pipe

Starting at the manifold position in line with the panel centres. 15 mm and 18 mm pipe can be laid at 100 mm or 200 mm centres as required, 18 mm pipe can also be laid at 300 mm centres. The minimum bend radius is achieved by encircling two castellated sections for a 90° bend or three castellated sections for a 180° bend.


Step 6: Forming Circuits

Pipe being laid at 100 mm or 200 mm centres must be laid in a spiral configuration. The first loop of pipe should be laid around the perimeter of the area to be covered by that circuit. The next loop of this circuit should be laid either 200 mm from the first loop of pipe for 100 mm centres or 400 mm from the first loop of pipe for 200 mm centres.


Continue to loop the pipe into the centre of the panels leaving enough space to form a double return (‘S’ shape in the centre of the loop).

Now work back out from the centre by filling the space between the inwardly spiralling loop of the primary circuit ensuring the pipe is laid at the correct spacing centres.


18mm pipe installation formation

Where 300mm centre spacing is required (18mm pipe systems only) a meander pattern can be used. The pipe simply crosses the room from one side to the other encapsulating 3 castellated sections at each return bend.


 Floor is now ready to be screed.

This Polypipe Underfloor Heating System can be used with the following solid floor constructions:
• Sand and cement screed (4:1 mix)
• Pumped screed systems (anhydrite etc.)
• Fine or heavy concrete
• Polymer modified screeds


Topics: underfloor heating