How to fix Warm Roof Fixings for Pitched Roofing

What is a warm roof?

A warm roof is a roofing structure with an insulation layer above the rafters. It is usually part of a building's complete insulating envelope. The envelope minimises heat loss.

Why insulate above rafters?

Fixing over-rafter insulation brings the pitched rafters into the building's insulated coat. It reduces cold bridging through the timbers and forms a well-insulated loft space with low U-values. The lower the U-value, the better insulated the attic. The lower thermal conductivity reduces heating costs and emissions.

What are the benefits of warm roofing?

Fully insulated lofts increase the habitable space in a building without increasing its footprint. The warm attic room stops condensation from forming and pipes from freezing.

How is insulation fixed on a pitched warm roof?

A counter-batten runs above each rafter to sandwich the insulation later. We recommend the use of Super-7™ warm roof fixings to fix the counter-battens to the rafters. Unlike standard nails, the helix shape induces rotation as the fixing hammers into the wood. The helical fasteners self-tap into both timber elements. They secure the timbers and maintain the gap between them to avoid squashing the insulation. Thor Helical Super-7™ nails have precision threads that ease driving and reduce the chance of buckling. The stainless steel fasteners are quick and reliable for fixing warm roof applications.

The Super-7™ Guide Tool overcomes problems skew fastening problems to improve build quality. The device guides the helix through the counter-batten and insulation into the centre of the rafter. Using the alignment jig avoids timbers splitting and gives a highly professional result.

How many fixings will ensure all loads are safely carried?

The number of warm roof nails necessary depends on the building's specifics. It rests on factors such as wind loads and sliding loads. These forces are a function of the building location and roof design.

There are a variety of factors to consider, including the following.

  • Compressive loads from the weight of the roof covering and snow.
  • Tension loads as a result of wind suction.
  • Bending moments from sliding forces. The load combines compressive load, roof angle and insulation depth. 

Working out the correct number of fixings can be quickly done with the HeliCalc™. The program is free to use on our website.

The software selects the fixing length and density using BRE-approved design methods. It calculates wind and snow loads per BS6399 Part 2 & Part 3. National Annexes to Eurocodes 0 and 5 apply partial safety factors for timber connections, dead loads, wind and snow. The results apply only to Thor Helical Super-7 fixings. Up to 66% less nailing is necessary when using our 7 mm warm roof nails, compared to 6 mm.

How do I fix Warm Roof Fixings?

Lay each counter-batten above the rafter and hold it tightly against the insulation. Position the alignment tool on the batten. Feed the helical fixing directly into the bore. Use the inbuilt spirit level to align the nail at right angles to the timber. Now, hammer the fixing through the batten. Remove the tool and drive the nail home.

We stock warm roof fixings in various lengths. We offer trade prices and fast delivery across the UK. Don't hesitate to contact us for advice on fixing specifications. Our expert team are always happy to help.

Warm Roof Fixing - Product specifi­cati­on


Super-7™ Warm Roof Batten Fixing


130mm - 240mm in 10mm increments



Cross Sectional Area:


Ultimate Tensile Strength:



Austenitic Stainless steel - (304)

Pitch Deviation on Tie:

< 0.5%*

Related documents:

How to fix warm roof insulation brochure How to fix warm roof insulation

How to fix insulated decks to flat roofs brochure How to fix insulated decks to flat roofs

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