3) Floor Construction & Insulation

This section looks at the different types of flooring and the insulation that is used with them.

Screeded Floor


  • Screed can be either traditional 4:1 sand cement with additive (75mm depth recommended) or freeflowing liquid screed (55mm depth recommended). 
  • All insulation joints must be thoroughly taped when using freeflowing screed. 
  • Floor insulation has the dual purpose of preventing the downward loss of heat and securing the pipe clips. 
  • Insulation boards should be close butted with staggered joints. 
  • The thickness of the floor insulation will be determined by building regulations and responsibility for meeting these rests with others. When using EPS Tackerboard a rule of thumb is for 75mm thick insulation on Ground Floors and for floors above unheated areas such as car parks; and 25mm on upper floors. 
  • The density of the insulation will be determined by the type of building e.g. a warehouse that will have heavily laden fork lift trucks running over the floor will require a dense insulation to reduce the risk of the screed cracking. 
  • Screeded floors must be allowed to dry and reach their maximum strength - 28 days - before heavy plant such as cherry pickers and scissor lifts are driven over them. 
  • Assuming the appropriate insulation has been used, and the screed has dried, the best way to avoid cracking of screed when using heavy plant is to lay 2 x 12mm ply boards at opposite angles on top of each other. 
  • Fast drying screeds such as Ardex, Flexidry, K-screed and Truscreed use super-plasticisers to reduce the amount of water, which in turn accelerates drying.
  • Edge insulation will be required around the floor perimeter to allow for the expansion and contraction of the screed and to prevent the loss of heat through the wall. 
  • Heat output from a screeded floor is 100W/sm at a room temperature of 20 deg C and a floor temperature of 29 deg C. When screeding is in progress, the pressure gauge on the manifold should be regularly checked. There are different types of floor insulation – expanded polystyrene (EPS), polyisocyanurate, polyurethane, XPS and mineral wool.




  • Can be used for residential and commercial projects.
  • Has a BRE rating of A+.
  • The polystyrene is covered with a woven cover with a 50mm grid pattern that allows for straight pipe runs and protects the insulation from the screed.
  • Completely waterproof – even if completely immersed in water, once dried out, no harm is done to the insulation.
  • Comes in different densities – EPS 70; EPS 100; EPS 150 and EPS 200.
  • EPS 100 gives excellent grip to clips, so when screed is in progress, it is more difficult for the snaking screed pipe to knock the clips and underfloor heating pipe out of place.
  • EPS is 98% air and 2% cellular matrix – it is consequently light and Health & Safety friendly.
  • High compressive and compression strengths – strength tests over 25 years confirm this.
  • Thermal qualities are preserved over the lifetime of the insulation.
  • A more economic option compared to other types of floor insulation.
  • EPS does not contain HCFC’s or CFC’s.
  • EPS has no nutritional value and does not provide food for rodents or insects.
  • Can be used with all screeds and cement, lime, Gypsum and anhydrite screeds.
  • Tested and manufactured in accordance with BS 13163.
  • Carries the CE Mark.
  • Manufacturer operates ISO 9001 – 2008 quality system.
  • Bespoke thicknesses can be supplied between 20mm and 200mm.
  • 50mm overhang on two sides of each board allowing easier taping of joints.
  • Manufactured using a steam process which allows the process to use re-useable energy.
  • All EPS waste can be recycled back into production.
  • EPS has zero depletion potential and zero global warming potential.
  • EPS reduces CO2 emissions up to 50%.


EPS 70

EPS 100

EPS 150

EPS 200

Thermal Conductivity





Compression @ 1% kPa





Compression @ 10% kPa






  • Good thermal conductivity – Kingspan K3 - 15mm – 24mm = 0.024W/mk; 25mm – 44mm = 0.023W/mk; 45mm + = 0.021W/mk.
  • CFC and HCFC free.
  • ISO 9001 quality systems in place.
  • Kingspan K3 is a phenolic insulation with a compressive strength @ 10% compression of 150 kPa.
  • Resistant to mould and does not provide food for vermin.
  • Has a BRE rating of A+.
  • Kingspan recommends 500 gauge polythene sheet to be laid over the K3 insulation before the pipe is installed and Screed laid.
  • Kingspan states that boards that have been allowed to get wet should not be used.
  • Details about the above products are available on the respective websites.

Site conditions for the storage of insulation vary considerably.


  • Edge insulation is used to insulate the perimeter of each room.
  • It must be installed for the full depth of the screed to avoid cold bridging.
  • In addition to preventing heat loss through the wall it allows expansion and contraction of the screed and helps to prevent cracking.
  • We recommend the use of a specially designed perimeter strip – cutting thin strips of insulation board creates on site health and safety risks.
  • The strip we use is made from closed-cell expanded polyethylene.
  • It has an adhesive strip for fixing to the wall.
  • It has a polyethylene skirt on the panel side, which prevents screed from getting down between the edge insulation and the floor insulation – especially desirable where liquid screeds are being used.
  • The edge insulation we use is 7mm thick and 150mm deep.
  • Edge insulation can also be used to diffuse heat where there are a large number of underfloor heating pipes close together e.g. in a narrow corridor.



The most economic floor insulation option is for plain EPS insulation covered with polythene sheets.

In order to get a neat installation it is essential that, after laying the insulation floor panels and polythene, it is essential that the floor is measured and marked out.

The neat installations in the above photographs were achieved by marking out and following chalk ‘ping’ lines on the polythene.

Timber Suspended Floor

In this type of floor structure, mineral wool insulation is laid between the joists.

Aluminium heat emission plates are fixed to the joists.

The underfloor heating pipe is fixed into the grooves in the aluminium plates which have the effect of making the whole of the plated area the radiant surface.

After the underfloor heating system has been pressure tested, the wooden sub floor can be installed.

With a room temperature of 20 deg C and a floor temperature of 27 deg C, the maximum heat output from an aluminium plated system is 70 W/m.


  • Rockwool is manufactured from volcanic rock which is blended with coke and limestone.
  • The materials are heated and melted in a furnace, then runs on to a series of rotating wheels which spin the drops into fibres.
  • The fibres are then coated with resin and water repellent mineral oil.
  • The loose material is then compressed, oven cured, then cut into rolls.
  • Rockwool is denser than glass mineral wool and it is made up of short strands which give it a high compressive strength. It is also non-combustible.
  • The thermal conductivity of mineral wool ranges between 0.039 W/m and 0.031 W/m.

Floating Floor System

A floating floor system can be used on almost any floor surface. We can supply two different floating floor systems:

  • Castellated floor panels with aluminium plates.
  • Foil faced grooved insulation panels.



  • The panels come in three thicknesses – 32mm; 48mm and 63mm. Thermal conductivity is 0.034W/mk; 0.35W/mk and 0.035W/mk respectively.
  • The panels are made from extruded polystyrene (EPS) and they are strengthened by a blue film of rigid polystyrene.
  • The aluminium plates are at 200mm centres.
  • The panels interlock and they are laid over the entire floor.
  • The aluminium plates fit onto the castellated floor panels.
  • Once the underfloor heating pipes have been installed and tested, the finished floor can be laid.
  • The heat output is the same as the aluminium plated system – 70W/sm with a room temperature of 20 deg C and a floor temperature of 27 deg C. Please note that if a wooden floor is to be laid over a floating floor system, the maximum floor temperature is 27 deg C.



  • The panels which are made from extruded polystyrene (EPS) are grooved, with aluminium foil factory fitted to the grooved surface.
  • The polystyrene panels have grooves at 200mm centres.
  • These panels can be supplied in any thickness.
  • Special panels are supplied that allow for pipe turns at the ends of the room.
  • Once the underfloor heating pipes have been installed and tested the finished floor can be laid.
  • With a room temperature of 20deg C and a floor temperature of 27deg C, the heat output from this system is 60W/sm.
  • If a wooden floor is to be laid over this system the maximum floor temperature is 27deg C.



  • Acoustic insulation is laid on upper floors in apartments, schools, hospitals, nursing homes etc.
  • It consists of (usually) 10mm insulation laid on the floor before the floor insulation is put down. Where floors are to be screeded, acoustic edge insulation is installed around the perimeter of the room.
  • Acoustic insulation can be used with screeded and floating floor systems.
  • There is a difference in the method of laying this insulation between a screeded floor and a floating floor. With a screeded floor the acoustic insulation can be butted together or overlapped to preserve the acoustic bridge.
  • With a floating floor the acoustic insulation sheets are butted together and special acoustic tape must be used to join the acoustic insulation to preserve the acoustic bridge.
Photos below show Acoustic Insulation on a Floating Floor:-

... and on a Screeded Floor:-

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