How to fix insulation over rafters in a warm pitched roof

kingspan Kooltherm K7 pitched roof insulation board in warm pitched roof

Insulation positioned over rafters in a pitched roof is called a warm pitched roof. The weight of the tiles or slates is taken by the counter battens which are laid on top of the insulation (a non-structural element). Here’s how you fix it together…

The counter batten to which the tiles / slates are fixed effectively becomes a structural element and an extension of the rafters below. As such, it needs to be able to take the weight of the roof, wind uplift, and any snow loads. Any fixings also need to be able to resist any sliding load of the tiles or slates – particularly important as insulation thicknesses increase to meet tighter building regulations. (See Kingspan Kooltherm K7 Pitched Roof Board brochure for details)

Advice should be sought from fixing manufacturers such as Helifix orTwistfix, but generally the advice is as follows:

  • Counterbattens should be at least 25 mm thick
  • Insulation over 50 mm thick requires a stop batten at eaves level (see K7 brochure)

When contacting the fixing manufacturer, they will need to know the following to calculate the correct fixing for your job:

  1. Counter batten thickness
  2. Insulation thickness
  3. Any other thickness included in the roof build up (eg sarking board)
  4. Counterbatten / rafter centres
  5. Roof pitch (in degrees)
  6. The weight of the tiles / slates being used
  7. Location of the building (for wind uplift)
  8. Wind exposure (eg high, medium or low)
  9. Height of the roof above the ground
  10. The area of the roof


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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

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