Polymer Warm Roofs

Before - the flooded United Reformed Church flat roof in Colindale, North London
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The water had nowhere to run off so just pooled
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The top coat of liquid polymer roofing system being applied
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The tapered warm roof insulation being laid
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'Warm Roofs' Explained:

What is a 'warm roof' and what's the difference between a 'warm roof' and a 'cold roof'?

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Government guidelines state that ALL roofs should be insulated - but the thickness of insulation required depends upon insulant used and whether you're creating a cold or warm roof:-

Warm roof refurbishment diagram comparison cold roof

'Warm roofs':

  • Warm roofs are insulated roofs with a very low "U-value": 'U-value' measures the rate at which heat transfers over time through a building element (e.g., the roof). The better your roof retains heat, the lower your roof's U-value.
  • Warm roofs have low U-values, are high performing and give better insulation
  • Insulation is either placed between the roof deck and the weatherproofing (above, not below, the roof deck) or laid using decking with insulation pre-bonded to it.
  • No ventilation is required although to prevent cold-bridging, the external wall insulation has to be extended upwards to the bottom of the roof insulation.
  • Warm roofs help to prevent thermal movement
  • Warm roofs require extra height for additional insulation above the joists
  • Tapered warm roofs ensure proper rainwater drainage from flat roofs



Cold roof diagram, compare to warm roof

'Cold roofs':

  • Cold roofs, where insulation is placed between the flat roof joists with gaps left for ventilation, simply have higher U-values so are less heat efficient  (unless joists are constructed super-deep and topped with a concrete roof). They are suitable for outside buildings such as garages.
  • Cold roofs have poorer ventilation as air flow is restricted.
  • Cold roofs are more prone to condensation.
  • As with warm roofs, external walls need to be extended up to the bottom of the roof insulation to prevent cold-bridging.
  • Cold roofs are lower as the roof sits directly on top of the joists.

Look at more detailed cold roof diagrams

Note: A warm roof can be insisted upon by building control, particularly in cases where the joists in a new extension won't ventilate adequately because they are against 'a second abatement' (e.g., a wall). Tapered insulation is usually a necessity for flat roofs, ensuring proper rainwater run-off from the surface.


One Church's Warm Roof Refurbishment in action:

The United Reformed Church in Colindale needed urgent repairs to their flooded single storey roof in North London NW9 (see slideshow above). The liquid plastic polymer roofing system rendered the church warm, dry, and leak-free in a matter of hours! 

To find out more about warm roof refurbishment and roof insulation, call us on 01970 610047 or drop us an email. We offer free, no-obligation on-site assessment and no-obligation estimates. We never chase, never hassle and never pass on your details to anyone else!