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Celotex FF4000 superseded by FI5000 Range of Under Floor and Underfloor Heating Insulation Boards

Specialist Celotex Product, available in three thickness’s, but in reasonably large pack quantities. We are generally unable to split the packs to sell these boards individually. Some depots may make exceptions if pack quantity levels are exceeded. Short lead-times apply to FF4050, FF4075 and FF4100 boards. Boards of other dimensions are manufactured to order.

Product Functions Celotex FF4000 improved compressive strength underfloor heating insulation panels

Celotex FF4000 is purpose designed for use in internal underfloor, under-screed, heating applications.

FF4000 boards have a higher compressive strength than the standard GA4000 board range, (kPa) =≥ 150 and =≥ 140 respectively, making them more suitable to effectively retain the underfloor heating pipe clips in place when the screed is poured over the underfloor heating system.

Product Description

Celotex FF4000 product range is aimed specifically at the underfloor heating market where the increased compressive strength of the board provides better dimensional stability and resistance to site traffic during installation whilst the foam structure ensures better pipe clip retention.

FF4000 is manufactured using rigid polyisocyanurate foam and zero ozone depletion potential (ODP) blowing agents with low global warming potential (GWP) and low emissivity aluminium foil facings on both sides

The robust foam structure ensures better pipe clip retention than general purpose boards. FF4000's technology offers thicker boards without visible seams in the foam core.

Board size: 1200 x 2400mm, Commonly available in thickness's of 50mm, 75mm and 100mm. Manufactured to order in thickness's of 7omm, 85mm, 90mm, and 125mm Lambda: 0.022 W/mK, Low emissivity foil facers

Product Benefits

FF4000 ensures minimal downward heat loss into structure

Is easy to cut and fit into most spaces

Uses the foam structure to ensure better pipe clip retention

Provides reliable long term energy savings for buildings

Has excellent dimensional stability

Has zero ozone depletion potential (zero ODP) and low global warming potential (GWP)

Future proofs the energy performance of new and existing buildings

Product availability indicators

Excellent = Product Availability Excellent  Good = Product Availability Good  Fair = Product Availability Fair  Poor =  Product Availability Poor  Undetermined = Product Availability Undetermined
Availability relies on stock levels at closest depots and upon transport logistics to effect deliveries

Technical Data

Celotex FF4000 Underfloor Heating Insulation Boards

Product Code

Board dimensions

Thickness (mm)

λ Value (w/mK)

R-value (m²K/W)

U Value (W/m²K)

Weight (kg/m²)

Unit weight (kg)

Celotex FF4050 24 x 1.2 x 2.4 = 69.12m² 50 0.022 2.25 0.44 1.98 136.86
Celotex FF4070 17 x 1.2 x 2.4 = 48.96m² 70 0.022 3.15 0.32 2.68 131.21
Celotex FF4075 16 x 1.2 x 2.4 = 46.08m² 75 0.022 3.40 0.29 2.86 131.79
Celotex FF4085 14 x 1.2 x 2.4 = 40.32m² 85 0.022 3.85 0.26 3.21 129.43
Celotex FF4090 13 x 1.2 x 2.4 = 37.44m² 90 0.022 4.05 0.25 3.38 126.55
Celotex FF4100 12 x 1.2 x 2.4 = 34.56m² 100 0.022 4.50 0.22 3.73 128.91
Celotex FF4125 9 x 1.2 x 2.4 = 25.92m² 125 0.022 5.65 0.18 4.61 119.49

Thermal conductivity / Lambda value (W/mK) = 0.022 | Compressive strength (kPa) = ≥ 150 | Water vapour resistance (MNs/g) = > 150 | Please Note: R-Value = Thermal Resistance; U Value = Thermal Transmittance Co-efficient; Compressive strength = kiloPascals; Vapour resistance = MegaNewton seconds per gram.

Product Information and Certification

Links to manufacturer's information. Click to download in a separate browser window.
Celotex FF4000 Datasheet | Celotex Flooring Certification | Celotex Handy Guide

Alternative Products & Accessories

Underfloor Heating - Rigid PIR Boards

  • Celotex FI5000

    Celotex FI5000 is purpose designed for use in internal underfloor, under-screed, heating applications

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    Celotex FI5000 improved compressive strength underfloor heating insulation panels
  • Celotex TB & GA

    Celotex TB4000 and GA4000 branding is used to differentiate between boards thinner than the XR4000 range.

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    Celotex TB4000 and GA4000 General Application Boards thickness's ranging from 20mm to 100mm
  • Kingspan TF70

    A range of performance rigid PIR boards used for insulation of solid concrete and suspended ground floors

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    Kingspan Thermafloor TF70, Kingspan Thermapitch TP10, and Kingspan Thermawall TW55, are identical PIR boards.
  • Kingspan K3

    K3 superior performance phenolic boards for use in ground floors, or on supported or suspended concrete and timber floors.

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    Kingspan K3 high performance thermal insulation board faced on both sides with a plain (coated) glass tissue autohesively bonded to the insulation core. The board has a compressive strength that typically exceeds 150 kPa at 10% compression and 125 kPa at 5% compression

Product Installation

Celotex Tempchek FF4000 products should be installed in accordance with these instructions

Ensure that joist spacing is at no more than 600mm centres and that the dimension of the joist is sufficient to span and accept additional loads. If asphalt weathering is to be used, joists should be at no more than 400mm centres.

Install the insulation boards, ensuring that the long edges are parallel to the line of the joists. 50mm x 50mm cross noggings should be inserted between joists to support the short edges of the boards.

Where boards butt together, bed onto twin beads of vapour sealant wide enough to accommodate this arrangement. This completes the vapour control layer (VCL) when combined with each board’s foil facings.

Lay the boards with the plywood side uppermost and stagger board joints. Leave a gap of approximately 2mm between boards and ensure a minimum 20mm bearing on joists and noggings.

Fix Celotex FF4000 with corrosion-proof Suretwist Composite Panel helical fasteners at a frequency to suit the design wind load. Refer to BS 6399-2 Code of Practice for Wind Loads. As a guide, 16 fasteners per board will resist a wind load of 2.22 KN/m2 based on a design load of 0.4 KN per fastener.

Ensure that fixings are no less than 10mm in from the board edge or 50mm from each corner. They should be equally spaced along the supporting joists. Fixings should be long enough to penetrate at least 38mm into the supporting timber.

Stagger opposing fixings where two board edges share the same joist or noggin.

Provide a complete insulation envelope by extending the wall insulation board up to the underside of the roof deck.

Provide a soffit or ceiling below the joists, as the surface of the product is not designed to be used as a decorative internal finish.

Ensure that the plywood is completely dry before any weathering system is applied.

Always use a Type 3G felt to BS 747 as a vapour diffusion first layer when using BUR weathering systems. When using a single-ply membrane, additional 12mm plywood has to be applied on top of the Celotex FF4000.

Temporary protection must be provided for both the insulation and the waterproofing, if significant foot traffic is anticipated either during or after installation.


The structure should be designed so that the finished roof has a continuous, smooth and even slope towards the rainwater outlet or gutter. The minimum fall should be 1:80 to avoid ponding water.

Deck stability

Celotex FF4000 incorporates exterior grade WBP plywood to BS 1203, laminated to the surface. This gives the product excellent strength. Boards can span up to 600mm joist centres to provide a suitable substrate for a variety of weathering systems.

Vapour control layer

Celotex FF4000 has a built-in VCL due to the foil facers but this is discontinuous at the board joints. In some applications no further attention to moisture control may be necessary. Celotex would generally recommend the application of a vapour sealant between the tops of the boards at all edges. This is essential in areas of potentially high humidity.

Contact Manufacturer

Celotex Limited

Lady Lane Industrial Estate, Hadleigh, Ipswich, Suffolk, IP7 6BA

Celotex Technical Advisory Service.

Telephone: 0901 996 0100 (30p per minute) - Fax: 01473 820 889
Web sites: Celotex Home Page / Celotex U-Value Calculator.

Contact us

Insulation Online Limited

Sales Office only:

39 Normandy Road, Worthing, West Sussex, BN14 7DX, UK

Telephone: 0333 8000 828