Flat Roof Insulation

  • Glass faced PIR boards
  • Mineral wool slabs
  • PIR boards with plywood
  • Warm deck insulation
  • For single ply or built-up

KNAUF, ROCKWOOL, CELOTEX, XTRATHERM, CELLECTA


The type of insulation used in a new flat roof is dependent on the roof specification. On a new concrete slab, with a screed, semi-rigid insulation boards such as expanded polystyrene board, extruded polystyrene board, glass fibre batts, mineral fibre batts, urethane foam board or phenolic foam board are laid under the roof covering. In a new timber structure, glass fibre quilt and mineral fibre quilt can be laid between the joists. In case of an existing flat roof, insulation can be increased externally with extruded polystyrene or foamed glass, or internally with an insulated lining board such as mineral fibre or polyurethane foambacked plaster-board.

Three choices are available for insulating a flat roof depending on the roof specification:
  • Cold roof
  • Warm roof
  • inverted roof

It is essential to understand the difference between those specifications to be able to install insulation in the right place to create a vapour barrier in the right area and prevent rotting of the roof joists.

Warm roof

A warm roof is when the insulation spans across the top of all the joists; it must be continuous and span over every joist. This means that any air rising from underneath would make the void between the joists warm hence a ‘warm roof’.

Cold roof

In a cold roof the insulation is put at the bottom of the joists or below the joists. This way sufficient ventilation is maintained which allows air to circulate above the insulation (below the roof). The void above the insulation should be at least 50mm thick. In this case the decking with the roof on it, which is above the joists, would be cold hence a ‘cold roof’.

Common mistake in the roof specification is when the insulation is installed inside the joists (close to the top part of the joists). This makes the roof neither cold nor warm, creating the void below the insulation. In this case there is no ventilation which makes the whole roof ‘sweat’ and causes the joists to rot.

Inverted roof

The inverted roof concept which is also known as protected membrane or upside down roofing. This method ensures insulating both the water proofing membrane and the reinforced concrete slab from extreme thermal stress. This is achieved by placing an extruded polystyrene thermal insulation board above, instead of below the waterproofing membrane and can be used for insulating flat topped buildings or balconies, retail or office developments, flats, hospitals, airports, hotels and residential housing in areas where roof is exposed to high temperatures.

Insulationshop.co offers a wide range of high density flat roof insulation from manufacturers such as Xtratherm, Celotex, Knauf, Kay Metzeler, Cellecta and more. For more information about particular products please see product description.



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96mm Celotex TD4000 PIR Flat Roof Insulation Board with Plywood

96mm Celotex TD4000 PIR Flat Roof Insulation Board with Plywood

TD4000 - 2400 x 1200   show quantity discounts

Guide Price: £65.17 (£78.20 inc VAT)

£22.63/m2 (£27.16/m2 inc VAT)

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Celotex TD4000 comprises a polyisocyanurate rigid foam insulation core, with a thermal conductivity of 0.022 W/mK, and low emissivity aluminium foil facings on both sides bonded to a layer of 5.5mm WBP exterior grade plywood. APPLICATION Celotex TD4000 is purpose designed for use in l..

Guide Price: £65.17 (£78.20 inc VAT)

£22.63/m2 (£27.16/m2 inc VAT)

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50mm Celotex EL3000 Flat Roof Board (pack of 10)

50mm Celotex EL3000 Flat Roof Board (pack of 10)

EL3000 1200x600 - 7.20m2  show quantity discounts

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Celotex EL3000 provides a quick and easy method of achieving effective thermal insulation in flat roofing structures. With coated glass tissue facings, EL3000 is manufactured from rigid Polyisocyanurate (PIR) using a blend of blowing agents that have zero ozone depletion potential (zero ODP) and a l..

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50mm Celotex TC3000 Flat Roof Board - Torch on (pack of 10)

50mm Celotex TC3000 Flat Roof Board - Torch on (pack of 10)

1200 x 600 - 7.2m2  show quantity discountsDelivery Time: 3 - 5 days

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50mm Celotex TC3000 Flat Roof Board - Torch on (pack of 10) Size: 1200mm x 600mm Area per pack: 7.2m2 Thermal conductivity: 0.027 W/Mk R-Value: 1.85m2K/W Compressive strength: ≥150kPa Weight: 2.40kg/m2   Celotex TC3000 provides a quick and easy method of achie..

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12mm Celotex TB4000 PIR Insulation Board

12mm Celotex TB4000 PIR Insulation Board

TB4000 - 2400x1200  show quantity discountsDelivery Time: 2 - 3 days

£10.40 (£12.48 inc VAT)

£3.61/m2 (£4.33/m2 inc VAT)

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Celotex TB4012 is targeted at ‘cut-to-fit’ applications between rafters or joists and enables users to achieve lower U-values with a single layer of insulation than has previously been possible. TB4012 is also appropriate for use in floors and walls. With low emissivity foil facings, TB4012 is manuf..

£10.40 (£12.48 inc VAT)

£3.61/m2 (£4.33/m2 inc VAT)

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50mm Celotex GA4000 PIR Insulation Board

50mm Celotex GA4000 PIR Insulation Board

2400x1200mm - 2.88m2  show quantity discountsDelivery Time: 1 - 2 days

£17.05 (£20.46 inc VAT)

£5.92/m2 (£7.10/m2 inc VAT)

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50mm Celotex GA4050 is a multi-purpose insulation board that provides solution to overcome from the localized thermal bridges problem. Featuring a low emissivity foil facings, this board has been manufactured from tough polyisocyanurate (PIR) by using a perfect mix of certain blowing agent..

£17.05 (£20.46 inc VAT)

£5.92/m2 (£7.10/m2 inc VAT)

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110mm Celotex XR4000 PIR Insulation Board

110mm Celotex XR4000 PIR Insulation Board

XR4000 - 2400x1200  show quantity discountsDelivery Time: 1 - 2 days

Guide Price: £37.09 (£44.51 inc VAT)

£12.88/m2 (£15.46/m2 inc VAT)

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Celotex XR4110 is targeted at ‘cut-to-fit’ applications between rafters or joists and enables users to achieve lower U-values with a single layer of insulation than has previously been possible. XR4110 is also appropriate for use in floors and walls. With low emissivity foil facings, XR4110 is manuf..

Guide Price: £37.09 (£44.51 inc VAT)

£12.88/m2 (£15.46/m2 inc VAT)

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90mm Celotex TA4000 PIR Insulation Board (pack of 13)

90mm Celotex TA4000 PIR Insulation Board (pack of 13)

1200x2400 - 37.44m2  show quantity discounts

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90mm Celotex TA4000 PIR Insulation Board (pack of 13) Size: 1200mm x 2400mm Area per pack: 37.44m2 Thermal conductivity: 0.022 W/Mk R-Value: 4.05m2K/W Compressive strength: ≥150kPa Water vapour resistance: >150 MNs/g Weight: 3.09kg/m2   Celotex TA4000 p..

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25mm Celotex FR5000 Fire Resistant PIR Insulation Board (pack of 16)

25mm Celotex FR5000 Fire Resistant PIR Insulation Board (pack of 16)

1200x2400mm - 46.08m2  show quantity discountsDelivery Time: 3 - 5 days

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Celotex FR5025 is one of the available dimensions of the Celotex FR5000 PIR insulation boards made from polyisocyanurate rigid core and faced on both side with low emissivity aluminum foils for improved thermal performance. The product is applicable to different types of constructions incl..

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25mm Earthwool RS45 Universal Insulation Slab Knauf (pack of 20)

25mm Earthwool RS45 Universal Insulation Slab Knauf (pack of 20)

1200x600 - 14.4m2  show quantity discountsDelivery Time: 2 - 3 days

Guide Price: £30.78 (£36.94 inc VAT)

£2.14/m2 (£2.57/m2 inc VAT)

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25mm Earthwool RS45 Universal Slabs are unfaced, rock mineral wool slabs, available in a range of densities from 33 to 200 kg/m3. The standard product is supplied unfaced, but slabs can also be manufactured with a factory applied foil or tissue facing and are also available with a water repellent ad..

Guide Price: £30.78 (£36.94 inc VAT)

£2.14/m2 (£2.57/m2 inc VAT)

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50mm Earthwool RS60 Universal Insulation Slab Knauf (pack of 9)

50mm Earthwool RS60 Universal Insulation Slab Knauf (pack of 9)

1200x600 - 6.48m2  show quantity discountsDelivery Time: 1 - 2 days

Guide Price: £30.78 (£36.94 inc VAT)

£4.75/m2 (£5.70/m2 inc VAT)

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Earthwool RS60 Universal Slabs are unfaced, rock mineral wool slabs, available in a range of densities from 33 to 200 kg/m3. The standard product is supplied unfaced, but slabs can also be manufactured with a factory applied foil or tissue facing and are also available with a water repellent additiv..

Guide Price: £30.78 (£36.94 inc VAT)

£4.75/m2 (£5.70/m2 inc VAT)

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50mm Earthwool RS100 Universal Insulation Slab Knauf (pack of 6)

50mm Earthwool RS100 Universal Insulation Slab Knauf (pack of 6)

1200x600 - 4.32m²  show quantity discountsDelivery Time: 2 - 3 days

Guide Price: £26.19 (£31.43 inc VAT)

£6.06/m2 (£7.27/m2 inc VAT)

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50mm Earthwool Universal Slabs are unfaced, rock mineral wool slabs, available in a range of densities from 33 to 200 kg/m3. The standard product is supplied unfaced, but slabs can also be manufactured with a factory applied foil or tissue facing and are also available with a water repellent additiv..

Guide Price: £26.19 (£31.43 inc VAT)

£6.06/m2 (£7.27/m2 inc VAT)

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50mm Earthwool Flexible Insulation Slab Knauf (pack of 12)

50mm Earthwool Flexible Insulation Slab Knauf (pack of 12)

1200x600 - 8.64m²  show quantity discountsDelivery Time: 2 - 3 days

£35.83 (£43.00 inc VAT)

£4.15/m2 (£4.98/m2 inc VAT)

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50mm Earthwool Flexible is a non-combustible, inorganic rock mineral wool slab, used for thermal and acoustic insulation and specifically designed for installation by friction fitting. Earthwool Flexible is odourless, non-hygroscopic, rot proof, does not sustain vermin and will not encourage th..

£35.83 (£43.00 inc VAT)

£4.15/m2 (£4.98/m2 inc VAT)

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25mm Yelofoam X2i Cellecta

25mm Yelofoam X2i Cellecta

2500x600mm - 1.5m2  show quantity discountsDelivery Time: 2 - 4 days

Guide Price: £16.72 (£20.06 inc VAT)

£11.15/m2 (£13.38/m2 inc VAT)

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25mm Cellecta Yelofoam is made of extruded polystyrene (XPS) foam blown with a mix of HFA & CO2 gases, containing a yellow pigment, flame retardant additive and nucleating agent. Cellecta insulation products are manufactured to the highest possible specification. Ex All product’s’ physical prope..

Guide Price: £16.72 (£20.06 inc VAT)

£11.15/m2 (£13.38/m2 inc VAT)

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59mm Plydeck Xtratherm (PIR with OSB Board)

59mm Plydeck Xtratherm (PIR with OSB Board)

2400x1200 - 2.88m2  show quantity discountsDelivery Time: 1 - 2 days

Guide Price: £49.51 (£59.41 inc VAT)

£17.19/m2 (£20.63/m2 inc VAT)

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Xtratherm Plydeck is a composite insulated panel of Xtratherm Polyisocyanurate core with a composite foil face, bonded to 9mm OSB board. The Xtratherm Plydeck provides a high level of thermal insulation and decking in one application.APPLICATION Plydeck is designed to provide high levels of thermal..

Guide Price: £49.51 (£59.41 inc VAT)

£17.19/m2 (£20.63/m2 inc VAT)

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50mm Flat Roof Insulation Board Xtratherm FR-BGM (pack of 10)

50mm Flat Roof Insulation Board Xtratherm FR-BGM (pack of 10)

1200x600mm - 7.2m2  show quantity discountsDelivery Time: 3 - 5 days

Guide Price: £58.25 (£69.90 inc VAT)

£8.09/m2 (£9.71/m2 inc VAT)

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50mm Xtratherm FR-BGM is a PIR insulation board that is faced with a fleece finished bitumen/glass facers and is suitable for use below partially bonded bitumen based built up roofing systems. FR-BGM can also be used in mechanically fastened or loose laid ballasted bituminous roofing systems.&n..

Guide Price: £58.25 (£69.90 inc VAT)

£8.09/m2 (£9.71/m2 inc VAT)

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50mm Xtratherm Flat Roof Board FR-MG (pack of 10)

50mm Xtratherm Flat Roof Board FR-MG (pack of 10)

1200x600mm - 7.2m2  show quantity discountsDelivery Time: 1 - 2 days

Guide Price: £57.14 (£68.57 inc VAT)

£7.94/m2 (£9.53/m2 inc VAT)

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Xtratherm FR-MG is a mineral coated glass faced board. Xtratherm XT/FR MG boards should be laid over the vapour control layer in a break bonded pattern. The long edges of the boards should be laid at right angles to the direction of the substrate and all edges must be fully supported by the deck. ..

Guide Price: £57.14 (£68.57 inc VAT)

£7.94/m2 (£9.53/m2 inc VAT)

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100mm Kingspan Thermaroof TR24 - (pack of 5)

100mm Kingspan Thermaroof TR24 - (pack of 5)

100mm TR24 - 3.60m2  show quantity discountsDelivery Time: 3 - 5 days

Guide Price: £67.14 (£80.57 inc VAT)

£18.65/m2 (£22.38/m2 inc VAT)

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100mm Kingspan Thermaroof TR24 is a rigid insulation board used for flat roof insulation, consisting of a rigid thermoset insulation core, covered with a glass tissue coated with bitumen. Its upper surface is finished with a thermofusible polypropylene fleece, while the lower surface is covered with..

Guide Price: £67.14 (£80.57 inc VAT)

£18.65/m2 (£22.38/m2 inc VAT)

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25mm Kingspan Thermaroof TR26 (pack of 12)

25mm Kingspan Thermaroof TR26 (pack of 12)

2400x1200mm - 34.56m2  show quantity discountsDelivery Time: 3 - 5 days

£200.88 (£241.06 inc VAT)

£5.81/m2 (£6.97/m2 inc VAT)

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25mm Kingspan Thermaroof TR26 is a high performance, fibre free, rigid thermoset PIR insulation core faced on both sides with a low emissivity composite foil facing which is used for insulating flat roofs and is fully compatible with most mechanically fixed single–ply waterproofing systems and ..

£200.88 (£241.06 inc VAT)

£5.81/m2 (£6.97/m2 inc VAT)

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25mm Kingspan Thermaroof TR27 (pack of 12)

25mm Kingspan Thermaroof TR27 (pack of 12)

25mm TR27 - 8.64m2  show quantity discountsDelivery Time: 3 - 5 days

£45.60 (£54.72 inc VAT)

£5.28/m2 (£6.34/m2 inc VAT)

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25mm Kingspan Thermaroof TR27 is a PIR insulation board made from highly effective rigid PIR core faced with coated glass tissue on both sides added during manufacturing. The product offers substantial durability and long life span depending on the condition of the supporting structure. Th..

£45.60 (£54.72 inc VAT)

£5.28/m2 (£6.34/m2 inc VAT)

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56mm Kingspan Thermaroof TR31 PIR bonded to Plywood (pack of 20)

56mm Kingspan Thermaroof TR31 PIR bonded to Plywood (pack of 20)

1200x2400 - 57.60m2  show quantity discountsDelivery Time: 3 - 5 days

£954.74 (£1,145.69 inc VAT)

£16.58/m2 (£19.90/m2 inc VAT)

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56mm Kingspan Thermaroof  TR31 is the flat roof insulation comprising a high performance rigid PIR thermoset insulation core faced with an FSC certified 6 mm nominal thickness WBP exterior grade plywood on its upper surface and a low emissivity composite foil facing on its lower surface. T..

£954.74 (£1,145.69 inc VAT)

£16.58/m2 (£19.90/m2 inc VAT)

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25mm Kooltherm K7 Pitched Roof Board Kingspan (pack of 12)

25mm Kooltherm K7 Pitched Roof Board Kingspan (pack of 12)

K7 2400x1200 - 34.56m2  show quantity discountsDelivery Time: 3 - 5 days

£227.93 (£273.52 inc VAT)

£6.60/m2 (£7.92/m2 inc VAT)

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25mm Kingspan Kooltherm K7 Pitched Roof Board is the rafter/joist level insulation comprising a premium performance rigid thermoset phenolic insulation core faced on both sides with a low emissivity composite foil facing. This reflective, low emissivity surface improves the thermal resista..

£227.93 (£273.52 inc VAT)

£6.60/m2 (£7.92/m2 inc VAT)

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30mm Rockwool RW3 Slab (Prorox SL930) - pack of 15

30mm Rockwool RW3 Slab (Prorox SL930) - pack of 15

1200x600mm - 10.8m2  show quantity discountsDelivery Time: 3 - 5 days

Guide Price: £26.69 (£32.03 inc VAT)

£2.47/m2 (£2.96/m2 inc VAT)

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30mm Rockwool RW3 Slab (Prorox SL 930) is a semi-rigid resin bonded slab, providing great thermal, acoustic and fire resistance, designed to be used in various applications in floors, walls and roofs, including special applications in industrial buildings for insulation of  ships, offshore plat..

Guide Price: £26.69 (£32.03 inc VAT)

£2.47/m2 (£2.96/m2 inc VAT)

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50mm Rockwool RW5 Universal Insulation Slab (Prorox SL960) - pack of 4

50mm Rockwool RW5 Universal Insulation Slab (Prorox SL960) - pack of 4

RW5 50mm - 2.88m2  show quantity discountsDelivery Time: 2 - 3 days

£20.09 (£24.11 inc VAT)

£6.98/m2 (£8.38/m2 inc VAT)

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50mm Rockwool RW5 (Prorox SL960) is a high quality resin bonded Slab for a wide range of thermal, acoustic and fire insulation requirements both within buildings and for industry. They are suitable for many applications including thermal insulation for floors, walls, roofs and boiler rooms. The stru..

£20.09 (£24.11 inc VAT)

£6.98/m2 (£8.38/m2 inc VAT)

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50mm Rockwool Flexi Insulation Slab 1200mm x 600mm (pack of 12)

50mm Rockwool Flexi Insulation Slab 1200mm x 600mm (pack of 12)

1200x600mm - 8.64m2  show quantity discountsDelivery Time: 1 - 2 days

£28.05 (£33.66 inc VAT)

£3.25/m2 (£3.90/m2 inc VAT)

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50mm Rockwool Flexi Insulation Slab is a semi-rigid thermal and acoustic insulation product made from volcanic rock, thus extremely durable, fire resistant and applicable to various constructions including walls, partitions, roofs and floors. It comes with an innovative flexible edge on one s..

£28.05 (£33.66 inc VAT)

£3.25/m2 (£3.90/m2 inc VAT)

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100mm Celotex Crown-Up Flat Roof Board - pack of 6 - pallet of 12 packs

100mm Celotex Crown-Up Flat Roof Board - pack of 6 - pallet of 12 packs

1200x600mm - 51.84m2  show quantity discountsDelivery Time: 3 - 5 days

£963.36 (£1,156.03 inc VAT)

£18.58/m2 (£22.30/m2 inc VAT)

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100mm Celotex Crown-Up is a brand new product for use in flat roof systems. Representing the next phase of Celotex innovation, Crown-Up is a high performance rigid polyisocyanurate (PIR) insulation which delivers increased dimensional stability and added robustness in a built-up flat roofing system...

£963.36 (£1,156.03 inc VAT)

£18.58/m2 (£22.30/m2 inc VAT)

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25mm EcoTherm EcoVersal PIR Insulation Board

25mm EcoTherm EcoVersal PIR Insulation Board

1200x2400mm - 2.88m2  Delivery Time: 1 - 2 days

25mm Eco-Versal is a foil faced universal solution for insulating walls, floors, pitched roofs, dormer cheeks and ceilings. It is ideal for insulating timber frame walls and can also be used to insulate solid walls internally. EcoTherm Eco-Versal comprises a fibre free rigid polyisocyanurate (PIR) i..

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25mm Rockwool RWA45 Slab (Prorox SL920) - pack of 12

25mm Rockwool RWA45 Slab (Prorox SL920) - pack of 12

600x1200mm - 8.64m²  show quantity discountsDelivery Time: 1 - 2 days

£19.11 (£22.93 inc VAT)

£2.21/m2 (£2.65/m2 inc VAT)

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25mm Rockwool RWA45 is a high quality resin bonded Flexible Slabs for a wide range of thermal, acoustic and fire insulation requirements both within buildings and for industry. They are suitable for many applications including thermal insulation for floors, walls, roofs and boiler rooms. The structu..

£19.11 (£22.93 inc VAT)

£2.21/m2 (£2.65/m2 inc VAT)

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30mm Kingspan Styrozone H350R Flat Roof XPS Board (pack of 14)

30mm Kingspan Styrozone H350R Flat Roof XPS Board (pack of 14)

1250x600mm - 10.50m2  show quantity discountsDelivery Time: 3 - 5 days

£66.41 (£79.69 inc VAT)

£6.32/m2 (£7.58/m2 inc VAT)

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Kingspan Styrozone H350R Flat Roof XPS Board is highly effective rigid insulation board made from extruded polystyrene core covered with smooth skin on both sides. It is especially designed for protected membrane flat roofs, but is also used in green roofs as a popular alternative to tradi..

£66.41 (£79.69 inc VAT)

£6.32/m2 (£7.58/m2 inc VAT)

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37.5mm EcoTherm EcoLiner PIR Insulated Plasterboard

37.5mm EcoTherm EcoLiner PIR Insulated Plasterboard

2400x1200mm - 2.88m2  show quantity discountsDelivery Time: 1 - 2 days

£33.07 (£39.68 inc VAT)

£11.48/m2 (£13.78/m2 inc VAT)

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37.5mm EcoTherm EcoLiner is a range of thermal laminate boards designed for both new build and refurbishment projects, applicable for internal wall insulation and drylining, but also pitched, cold and room-in-roof applications. It is consisted of paper backed PIR insulation core bonded to ..

£33.07 (£39.68 inc VAT)

£11.48/m2 (£13.78/m2 inc VAT)

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50mm Cellecta Hexatherm XROOF 300L Thermal Roof Insulation Board

50mm Cellecta Hexatherm XROOF 300L Thermal Roof Insulation Board

600x1250 - 0.75m2  Delivery Time: 2 - 4 days

50mm Cellecta Hexatherm XROOF 300L is an extruded polystyrene thermal insulation board designed specifically for inverted roof applications where a high resistance to compression and water absorption is essential. XROOF roof insulation boards are ideal for a multitude of roofing requirements, in..

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