Hybrid roofs explained

Hybrid roofs explained

Hybrid roof explained

I explain what a hybrid roof is and how to make one

I’m frequently asked if I install hybrid roofs and do they work.

In this video, I try to explain:

  • what makes a hybrid roof
  • how a hybrid roof differs from the standard cold roof or warm roof constructions, which are widely used in the building industry
  • the different ways you can form a hybrid roof.

A hybrid roof is a mixture of a cold roof and a warm roof construction.


If you are constructing a  cold roof –

  • If you totally fill the void between the joists with insulation, it’s a hybrid roof. 
  • You don’t vent the roof, it’s a hybrid roof. 
  • Or you don’t use any insulation at all, it’s a hybrid roof.

Or a warm roof –

  • I’m often asked if some insulation can be put inside the roof and some outside the roof. If you do, it’s a hybrid roof. However, if you only place a small amount inside and have at least 3/4 outside this will probably work, but it’s still a hybrid roof! You definitely can’t have more insulation inside, and less outside that just won’t work. 
  • Having different layers of insulation with air gaps under a warm roof will be a hybrid roof, and it may or may not work.


The problem with changing the known buildup of a warm roof or cold roof, is that you need to get it designed. If the design team come back with calculations showing that it will work, who is to say that it won’t. But bear in mind that you only get the answers from the data that you enter! 


It’s easier to think of it like this:

If you stand too close to a cliff edge, you could fall over, so you should always stand well back, in the safe zone.

So why would you design a roof in a way that if the internal humidity or the external temperature were to be just off normal, it could have problems? You always design to stay in the safe zone, because the surrounding elements can change. So don’t use a hybrid roof and don’t use a cold roof, stay in the safe zone. Always try to build a warm flat roof.


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Comments (2)

  • Chris Reply


    Excellent blog and video thank you!

    I have had an acoustic engineer recommend 100mm dense wool insulation inside the air gap of a warm roof, against the plasterboard though and 100mm air gap up to the warm deck (200mm joists). I wonder what your thoughts are on this design?

    So it would be from top to bottom (note 200×50 joists):

    100mm insulation
    (Vapour barrier)
    100mm air gap
    100mm RWA45 dense mineral insulation

    Interested what you think about this hybrid construction?

    Thank you

    27th April 2023 at 10:49 am
    • Steven Dickinson Reply

      sorry for the late reply I get so much spam on this that is really hard to find the real people who need help. However I’m here now if you need help still please just email email me speak soon

      19th August 2023 at 8:54 pm

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