Insulation is an important component of a floor design and there are a number of factors which need to be taken into account.
- The position of the insulation within the floor structure
- Thermal Performance; k and R values
- Applied floor loading
- Thermal bridging
- Air leakage
- 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.
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 minimum standard for new dwellings is calculated as a notional building using the limiting values in Table 4 of Approved Documents L1A, L1B, L2A and L2B. Assessing the performance of the dwelling by calculation of TER and TFEE.
TER – The Target CO2 Emission Rate is calculated and expressed as the mass of CO2 emitted in kilograms per square metre of floor area per year
TFEE – Target Fabric Energy Efficiency Rate is calculated and expressed as the amount of energy demand in kilowatt-hours per square metre of floor area per year.
If the building is constructed using the notional building specification the CO2 target will be met. It is allowable for the builder/designer to vary the specification provided the same overall TER and TFEE are achieved in the calculation of the actual or as-built performance.
If the building is constructed to the notional building specification the CO2 target will be met. It is allowable for the builder/designer to vary the specification provided the same overall TER and TFEE are achieved in the calculation of the actual rates.
The table below shows the target U values as given in the relevant Tables of the Building Regulation Approved Documents.
Whilst these give the optimum U values for target CO2 emissions there is a statement for refurbishment and extensions that “consequential improvements should only be carried out to the extent that they are technically, functionally and economically feasible”, allowance will be made where the thickness of floor insulation in an extension or refurbishment creates issues with existing floor levels.
||Target U value
|New build domestic (L1A – Table 2)
|New build non-domestic (L2A – Table 3)
|Existing domestic (L1B – Table 2)
|Existing non-domestic (L2B – Table 4)
The table below shows the thermal resistance or U values that can be achieved with varying thicknesses of Jablite floor insulation.
||Jabfloor 70 and 100 HP
||Jabfloor 200 and 250
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 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
||Design Load at 1% compression (kPa)
||Design load at 10% nominal compression (kPa)
|Jabfloor HP 70
|Jabfloor HP 100
|Jabfloor HP 150
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.
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 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.
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 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
Thermal Floor System
Jablite TFS All-In-One and Structural Board are lightweight, easy-to-install expanded polystyrene panels installed within the Jablite suspended concrete beam floors.
An important benefit of Jablite Thermal Floor Systems are the speed of installation.
In addition, TFS 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 TFS All-In-One and Structural Board provide a high thermal performance, meeting the requirements of Part L of the Building Regulations, with U-values as low as 0.10 (W/m²K).
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.
Below ground supported 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 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
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 below 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 below 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.
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.