Under Joist
(Internal)

From simple insulation upgrades, meeting building regulations, or achieving Passivhaus standards. SuperFOIL can find you the perfect solution.

Laying Insulation on Hybrid Flat Roof

How To Install

Under Joist (Internal) Flat Roof Install

Flat Roof Conservatory With Skylight
  • Apply SuperFOIL directly from the roll, on the internal joist face, horizontally starting at the external wall.
  • Staple the start of the roll into place on to your joist and then continue to roll the product out across the joists.
  • Whilst fitting SuperFOIL, you should hold the product taut whilst stapling it into place. Staple through the product into the joists at approximately 50mm-100mm intervals using the correct size staples (see chart).
  • Once you have finished a length, simply cut to the correct size and then continue fixing the next layer with a minimum of a 50mm overlap. Ensure secure fixing by stapling the insulation onto the joists where the joint crosses.
  • Seal all joints, tears and cuts with SuperFOIL 100mm tape, paying special attention to any penetrations through the insulation to ensure an airtight finish.
  • Finish your installation by fixing counter battens on top of the insulation horizontally (maximum of 600mm centres) to allow adequate air space. Attach your internal finish to battens, following the manufacturer’s guidelines.
Product Minimum Batten Size Staple Size Required
SF19+38mm20mm
SF4050mm30mm
SF6063mm40mm

Fixing Details

Install SuperFOIL using the correct method for your application.

Roof Windows

Install SuperFOIL using the correct method for your application. To finish installation around roof windows, simply trim the SuperFOIL up to the frame and staple the insulation to the surrounding framework where possible. Finish installation by sealing all joints with SuperFOIL Butyl tape or other suitable double-sided waterproof tape.

Vents, Ducts & Penetrations

At penetrations such as vent ducting, pipework etc, SuperFOIL should be trimmed to ensure there are no gaps around the penetration.

Using SuperFOIL Butyl Tape or other suitable waterproof double-sided tape, ensure the SuperFOIL is well sealed around the penetration to create an airtight barrier. This can be achieved by using small sections of tape and working around the penetration.

Downlighters & Recessed Lighting

SuperFOIL recommends the use of an insulation guard/fire hood when insulating with recessed lighting in place.

Cut a hole in the insulation, around the insulation guard/fire hood leaving a minimum of a 25mm gap around the guard/hood. Seal around the guard/hood using SuperFOIL superior foil tape to ensure airtightness is maintained in the install.

Ideal Products For External Flat Roof Applications

SF19-3-small

SuperFOIL SF19+

SuperFOIL SF40 Roll

SuperFOIL SF40

SuperFOIL SF60 Insulation

SuperFOIL SF60

SuperFOIL SF19+

  • 2.53 R Value
    When used in a roof
  • 45mm Thick
    1.5m Wide by 10m Long

SuperFOIL SF40

  • 3.7 R Value
    When used in a roof
  • 65mm Thick
    1.5m Wide by 10m Long

SuperFOIL SF60

  • 4.48 R Value
    When used in a roof
  • 100mm Thick
    1.5m Wide by 8m Long

Choose Your Solution

Use the charts below to find the ideal combination of insulations for your project

External Flat Roof Diagram
SuperFOIL Product Internal SuperFOIL Product External
No Additional Insulation SF19BB SF40BB
No Additional Insulation N/A 0.40U 0.27U
SF19+ 0.33U 0.20U 0.15U
SF40 0.25U 0.17U 0.13U
SF60 0.20U 0.14U 0.12U
SuperFOIL Product Mineral Wool / Glass Fibre / Sheeps Wool - 0.044W/mK
No Additional Insulation 25mm 50mm 75mm 100mm 125mm 150mm 175mm 200mm 225mm 250mm 275mm 300mm
SF19+ 0.33U 0.28U 0.25U 0.22U 0.20U 0.18U 0.17U 0.16U 0.15U 0.14U 0.13U 0.12U 0.11U
SF40 0.25U 0.22U 0.20U 0.18U 0.17U 0.16U 0.15U 0.14U 0.13U 0.12U 0.11U 0.11U 0.10U
SF60 0.20U 0.18U 0.17U 0.16U 0.15U 0.14U 0.13U 0.13U 0.12U 0.11U 0.10U 0.10U 0.09U
SuperFOIL Product Mineral Wool / Glass Fibre / Sheeps Wool - 0.037W/mK
No Additional Insulation 25mm 50mm 75mm 100mm 125mm 150mm 175mm 200mm 225mm 250mm 275mm 300mm
SF19+ 0.33U 0.28U 0.24U 0.22U 0.19U 0.18U 0.16U 0.15U 0.14U 0.13U 0.12U 0.12U 0.11U
SF40 0.25U 0.22U 0.20U 0.18U 0.16U 0.15U 0.14U 0.13U 0.12U 0.12U 0.11U 0.10U 0.10U
SF60 0.20U 0.18U 0.17U 0.15U 0.14U 0.13U 0.12U 0.12U 0.11U 0.10U 0.10U 0.09U 0.09U
SuperFOIL Product Mineral Wool / Glass Fibre / Sheeps Wool - 0.032W/mK
No Additional Insulation 25mm 50mm 75mm 100mm 125mm 150mm 175mm 200mm 225mm 250mm 275mm 300mm
SF19+ 0.33U 0.27U 0.23U 0.20U 0.18U 0.16U 0.15U 0.14U 0.13U 0.12U 0.11U 0.10U 0.10U
SF40 0.25U 0.22U 0.19U 0.17U 0.15U 0.14U 0.13U 0.12U 0.11U 0.11U 0.10U 0.09U 0.09U
SF60 0.20U 0.18U 0.16U 0.15U 0.13U 0.12U 0.11U 0.11U 0.10U 0.09U 0.09U 0.09U 0.08U
SuperFOIL Product PIR Foam Board - 0.022W/mK
No Additional Insulation 25mm 50mm 75mm 100mm 125mm 150mm 175mm 200mm 225mm 250mm 275mm 300mm
SF19+ 0.33U 0.26U 0.21U 0.18U 0.16U 0.14U 0.13U 0.12U 0.11U 0.10U 0.09U 0.09U 0.08U
SF40 0.25U 0.20U 0.18U 0.15U 0.14U 0.12U 0.11U 0.10U 0.10U 0.09U 0.09U 0.08U 0.07U
SF60 0.20U 0.17U 0.15U 0.13U 0.12U 0.11U 0.10U 0.09U 0.09U 0.08U 0.08U 0.07U 0.07U
SuperFOIL Product Phenolic Foam Board - 0.019W/mK
No Additional Insulation 25mm 50mm 75mm 100mm 125mm 150mm 175mm 200mm 225mm 250mm 275mm 300mm
SF19+ 0.33U 0.25U 0.20U 0.17U 0.15U 0.13U 0.12U 0.11U 0.10U 0.09U 0.09U 0.08U 0.08U
SF40 0.25U 0.20U 0.17U 0.15U 0.13U 0.12U 0.11U 0.10U 0.09U 0.08U 0.08U 0.07U 0.07U
SF60 0.20U 0.17U 0.14U 0.13U 0.11U 0.10U 0.10U 0.09U 0.08U 0.08U 0.07U 0.07U 0.06U
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