Roof Insulation

Flat roof insulation is becoming increasingly important the better the insulation in your roof the more energy you save.

Part L of building control sets out the targets that need to be reached  for insulation in roofs of new build and retrofit there are two recognised ways of insulating flat roofs [ezcol_1half id=”” class=”” style=””]

Warm roof  construction

The roof insulation is on top of the roof

Roof insulation on decking  Warm Roof construction

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Cold roof construction

The roof insulation is between the joists

Roof insulation cold roof construction


Five things to know about flat roof insulation

  1. What is a warm roof 
  2. What is a cold roof
  3. What triggers part L of the building regulation
  4. Don’t get it wrong
  5. How do I know if its a warm roof or a cold roof

So if you have been through the 5 things to know about flat roof insulation above ,you should be asking yourself the following questions.

Can my roof be insulated ?

Can my roof be insulated ?
Can I insulate over the old roof?
What’s the cost going to be?
Should I insulate now or later?

Insulating a flat roof using the warm roof construction method  means you place the roof insulation over the timber decking Insulating the roof the Cold roof method means you place the insulation between the joists with ventilation above the roof insulation.
Warm roof construction is considered to be much more efficient and is a beaser build. Cutting pieces of roof insulation between the joist is a skillful job and takes time, unfortunately if the roof insulation is not cut correctly and air can get between then cold bridging can begin.


What triggers part L of the building regulation?

  • On old flat roofs  if you strip the old covering then you trigger part L and you have to insulate the roof to the new regulations, if you already have some insulation in the roof but its poor then again this triggers part L
  • If the flat roof is part of a new build project it has to be built to part L of building control

How do you know if you have a warm roof or a cold roof?

 Generally cold roofs have ventilation and you should see the vents. 

Older cold roofs may not have vents so look to see if the roof  has been raised higher than the surrounding roofs  as the roof insulation on a warm roof is on top making it higher.

[ezcol_1half id=”” class=”” style=””]This video shows a cold roof and its vents
[/ezcol_1half] [ezcol_1half_end id=”” class=”” style=””]This video shows a warm roof and insulation

Example photos of cold roofs (roof insulation in roof)


Example photos of warm roofs


Can my flat roof be insulated?

Most old flat roofs can be insulated however sometimes the cost becomes restrictive, take an example of a flat roof that got a bedroom under it and above a balcony opens up onto the flat roof, the step of the door out onto the roof is only 50mm above the existing roof. In this instance to place roof insulation over the roof to form a warm roof would mean moving the door, and to remove the ceilings down below to add roof insulation and ventilation would devastate the room below. If building control is  involved they should be lenient and  deem the roof as “hard to insulate” and not enforce the building regulation.

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