Jablite is the UK's largest producer of EPS products for insulation and civil engineering applications

Insulation for Ground Floors

There are a number of factors to take into account when specifying insulation for a floor design, these are covered in this article and include:

  1. The position of the insulation within the floor structure
  2. Thermal Performance; k and R values
  3. Applied floor loading
  4. Thermal bridging
  5. Air leakage
  6. Condensation
  7. Retrofitting floor insulation

Position of the insulation within the floor structure

Ground bearing floors can include insulation either below or above the concrete slab, the choice the designer makes will have an impact on the temperatures inside the building, as follows:

  • If the insulation is installed below the slab, the thermal capacity of the building is increased, helping to maintain steady internal temperatures.
  • If insulation is installed above the slab, the building will respond much more quickly to the heating system.

Suspended floors are usually insulated in such a way that they offer reduced thermal mass and respond quickly to the heating system. In the case of suspended concrete, the insulation is installed above the deck, either under a screed or timber boarding. Suspended timber floors are normally insulated between the joists.

Choosing a suspended floor allows the designer to use the same design regardless of site ground conditions. The void below the floor can be ventilated to reduce radon or methane build up. It also allows for expansion of clay soils without affecting the structure of the floor.

Thermal Performance

The thermal performance achieved by the floor is critical for the overall energy efficiency of the building. Approximately 15% of heat is lost through the floor and insulation can reduce this.

The table below shows the U values recommended in the current Building Regulations for floors in new build and target U values for floors in existing buildings. These are the optimum U values if they are ‘technically and economically feasible’.

Building Type Target U value
New build domestic (L1A – Table 2) 0.25 W/m²K
New build non-domestic (L2A – Table 3) 0.25 W/m²K
Existing domestic (L1B – Table 2) 0.22 W/m²K
Existing non-domestic (L2B – Table 4) 0.22 W/m²K


The tables below show the thermal resistance or U values that can be achieved with varying thicknesses of Jablite floor insulation.

Thickness Jabfloor 70 Jabfloor 100 Jabfloor 150 Jabfloor 200 Jabfloor 250 Jabfloor HP
25 0.6579 0.6944 0.7353 0.7576 0.7576 0.7813
40 1.0526 1.1111 1.1765 1.2121 1.2121 1.2500
50 1.3158 1.3889 1.4706 1.5152 1.5152 1.5625
60 1.5789 1.6667 1.7647 1.8182 1.8182 1.8750
75 1.9737 2.0833 2.2059 2.2727 2.2727 2.3438
100 2.6316 2.7778 2.9412 3.0303 3.0303 3.1250
125 3.2895 3.4722 3.6765 3.7879 3.7879 3.9063
150 3.9474 4.1667 4.4118 4.5455 4.5455 4.6875
200 5.2632 5.5556 5.8824 6.0606 6.0606 6.2500
250 6.5789 6.9444 7.3529 7.5758 7.5758 7.8125
300 7.8947 8.3333 8.8235 9.0909 9.0909 9.3750


Applied Floor Loading

Materials will compress when a load is placed on them. is one of the important factors to consider when designing a ground floor and specifying the insulation for it.

The insulation used must be capable of accommodating the applied loads with the minimum of compression.

If the insulation is below a slab, screed or timber boards the entire load is acting on the insulation. Point loads are spread by the layers above the insulation so that the load acting on the insulation is lower than the load applied to the floor surface.

A point load applied to a floor where the insulation is positioned below a thin screed will result in a higher applied load on the insulation than where the insulation was positioned below a thicker floor slab because the load is bearing on a smaller area of insulation under the screed.

The dead load applied by the screed and the floor slab should also be allowed for when calculating the total load applied to the insulation. This is a useful point to explain the difference between:

Active and dead loads

The actual applied floor load acting on the insulation material has two components:

  • The dead load, which is due to the weight of the materials laid on the insulation and
  • The design load associated with the use of the floor.

For specific applications the guidance and recommendations contained in BS EN 1991-1-
1:2002 and BS EN 1990:2002+A1:2005 should be followed, and this will help the designer ensure that the strength of the floor will be sufficient to support any applied loads over the loaded area.

Standardised values

Standardised values are available to the designer for the dead loads applied by building components and the estimated active loads for various types of building use. These form the structural design requirements of the floor, but are of less value when considering the compression resistance requirements of the floor as the active loads are likely to be localized for point loads, not uniformly distributed loads. Click here for more info.

Jablite Floor Insulation and Design Loads

The Jablite Flooring Range is available in Grade 70, 100, 150, 200 and 250 grades.

For a quick rule of thumb, the following guidance about use and design loads applies:

  • Jabfloor 70 is used for standard domestic loads
  • Jabfloor 100 is used in offices and schools.
  • Jabfloor 150 – 250 is used in heavy commercial, industrial where heavy loads from storage racking or fork-lift trucks are expected

The information in the tables below will help the design engineer to specify the right product for the building.

Properties for Jablite Flooring Range
Product Design Load at 1% compression (kPa)
Jabfloor 70 20
Jabfloor 100 45
Jabfloor 150 70
Jabfloor 200 90
Jabfloor 250 100
Jabcore 70 20
Jabcore 100 45

Thermal bridging

The overall heat loss from dwellings is measured using SAP 2009 or SBEM. Both require the heat loss from the total amount of linear thermal bridging to be taken into account.

Junctions of the walls with the roof and floor are non-repeating thermal bridges and the head loss can be calculated by numerical modelling in accordance with the methodology detailed in BS EN ISO 10211.

Heat loss through thermal bridging is commonly referred to as the `linear thermal transmittance value` or the psi value (Ψ-value).

Heat is lost through the edges of the floor where it meets the wall. This can lead to cold spots and potential condensation problems if the floor insulation does not overlap the wall insulation.
Accredited Construction Details provide standard details at floor/wall junctions to overcome this problem. There are also a set of enhanced construction details available on the Energy Savings Trust website.

Air leakage

Air leakage is an important factor in the overall thermal performance of the building envelope. As much as 10% of the overall heat loss of the building can be caused by air leakage.
Building Regulations incorporate target air tightness values to reduce the levels of heat lost through air leakage and balanced ventilation systems are recommended to provide appropriate air changes in a controlled manner.


Surface Condensation

In order to prevent localised surface condensation the temperature factor (known as the f-factor) should be established.

BRE Information Paper IP 1/06 (which can be obtained from the BRE – www.bre.co.uk) provides guidance and limitations on the types of buildings and the f-factor required in order to prevent surface condensation and mould growth from occurring.

Generally, an f-factor of no less than 0.75 is adequate for the internal environment in dwellings. Non residential values vary between 0.30 and 0.90 dependent on the activity within the building.

The risk of surface condensation can be reduced or eliminated by following the good practices for continuous insulation shown in the Accredited Construction Details (see website details above).

Surface condensation is expected to occur at points where the surface is less than 75% of internal air temperature (see BRE Information Paper IP17 for further information and method of calculating).

With increasing insulation performance of the building fabric this is more likely to occur where gaps in insulation are evident

Condensation within the fabric of the building is not a problem except when it occurs within or adjacent to a moisture sensitive material such as timber or mineral wool insulation.

Building fabric condensation occurs when moisture from inside the building escapes through the fabric and is trapped by a moisture resistant barrier.

The best methods to eradicate or reduce this problem are to use an appropriate vapour control layer (VCL) in the correct position or to create a ‘breathable’ construction. The VCL is always on the warm side of the insulation.

Good practice for ground floors

  • Ensure all thermal and cold bridging is eliminated around the external perimeter of the floor
  • Ground bearing slabs must have a suitable damp proof membrane which can be placed above or below the insulation
  • Suspended floors should incorporate a ventilated void below the floor with a minimum height of 150mm. A vapour control layer should be positioned above the insulation layer.


Suspended Floors

Suspended floors are specified when there is a soil contamination issue or a stability issue with the soil or land. The void under the floor can be ventilated to avoid build up of radon or methane.

Jablite has two solutions for insulating suspended floors:

  • Jablite Quickfloor
  • Jabfloor over concrete beam and block
Quickfloor Insulation

Jablite Quickfloor insulation is a lightweight, easy-to-install expanded polystyrene panel insulation for suspended floors.

Quickfloor lives up to its name, an important benefit of this product is the speed of installation. In addition, Quickfloor requires less brickwork than insulation over beam and block. A typical Quickfloor application would incorporate 150mm insulation plus 75mm screed, a total of 225mm depth.

A typical beam and block application would have beam and block 100mm depth, insulation between 150-300mm and screed 65-75, a total floor depth of between 325-475 which could require as many as three extra rows of brickwork.

Designed to be laid between pre-cast concrete beams, Jablite Quickfloor insulation provides a high thermal performance, meeting the requirements of Part L of the Building Regulations, with U-values as low as 0.10 (W/m²K).

The Jabfloor Range

Jablite floor insulation is manufactured to a range of compressive strengths, providing a solution for every type of ground floor application. See Selecting the right grade of floor insulation for your product below.

Jabfloor is unaffected by ground moisture and offers reliable performances in compressive strength and thermal conductivity in normal ground conditions. It is supplied as square-edged sheet boards sized 1200 x 2400mm.

Standard thickness available are 25, 30, 40, 50, 60, 75, 100, and 150mm. Other thicknesses are available to order in 5mm increments up to 600mm.

A damp proof membrane is required and should be placed over the insulation to prevent water and fine particles from the concrete leaching down the joints in the insulation. No other protective membrane is required above or below Jablite floor insulation.

Selecting the right grade of floor insulation for your project

For domestic floors, Jabfloor 70 and Jabfloor Premium 70 can be placed over the beam and block with an 18mm chipboard (see BS EN 312 for guidance) or a 65mm screed finish (BS8204 for guidance).

Jabfloor 70 and 70 Premium have a design load capacity of 20kN/m2 (required in BS 6399). For commercial or other non-domestic floor applications Jabfloor 100, 150, 200 or 250 provide the higher compressive strength required.

22mm chipboard or 75mm screed are typically used as the finish in non-domestic floors applied in the same way as for domestic floors and Jabfloor can be used with other floor finishes such as lightweight screed or plywood.

Note: The design loads for non-domestic buildings are given in the tables contained within BS 6399.

Insulation Above Slab

This is a ground bearing application and the land and soil of the site must be strong and stable enough to take the weight of the building or house.

For information about the soil characteristics of the site you can contact the Local Authority. In any case, it is likely you will be required to undertake a site survey to find out:

1. Contamination of the soil
2. Stability
3. Soil type

If there are any doubts about the soil or its California Bearing Ratio (CBR), the best option is a suspended floor.

Above slab with screed

The insulation is installed on the concrete which is directly on top of the ground. Then screed is installed above the insulation. This approach avoids the ‘heat sink’ of having concrete directly under the floor, as described in ground bearing floors under slab.

This building method works well with underfloor heating. The screed over the insulation gives even temperature, with no hot spots, right across the floor span and warmth is retained after the heating is turned off. A good ambient temperature can be achieved.

Above slab with chipboard

Without underfloor heating, this is a good option. The chipboard over the insulation prevents the heat sink, as described above and provides a warmer underfoot experience than concrete or screed and is faster to install as there is no drying time for the screed.

Insulation Below Slab

If the land and soil being built on is strong and stable enough to take the weight of the building or house, this is the quickest and most cost-effective option.

For information about the characteristics of the site you can contact the Local Authority. In any case, it is likely you will be required to undertake a site survey to find out:

1. Contamination of the soil
2. Stability
3. Soil type

If there are any doubts about the soil or its California Bearing Ratio (CBR), the best option is a suspended floor.

The disadvantage of this system compared against above slab with screed or above slab with chipboard is the ‘heat sink’.

The heat sink is created because the concrete is situated directly under the flooring – with no insulation above it. The result is cold floors underfoot.

Concrete Hollow Core Plank

Concrete hollow core planks are specified when there is a large open span of floor. Typically these are in large commercial buildings or possibly in blocks of flats.Hollow Core with Chipboard_HighRes

The Jabfloor insulation range can be installed over concrete hollow core planks to provide the specified u-value of the project.


Cold Store Floors

The main function of the insulation in a cold store floor is to prevent the ground and main structure from freezing due to temperatures inside the building being set as low as -32ºC.

Jabfloor 250 will stand up to the loads in a cold store and should be laid in two layers of 100mm with boards cross-laid to reduce the risk of any cold bridging.