What Is A Cold Roof System?

Many homeowners ask us ‘What is a Cold Roof‘ as they are usually comparing them to Warm Roofs which are becoming increasingly popular for conservatory roof replacements.

A Cold roof is a flat roof system that has a layer of PIR insulation inside of the rafters, unlike a Warm roof that has insulation on top of the rafters above the top deck.

Let’s look at the components that make up a Cold Roof construction from the outside layer to the inside layer and what each part does.

Cold Roof Construction

A Cold Roof consists of the following components that make up the construction:

Waterproof Layer
OSB Board
Rafters
Insulation (Rockwool or PIR)
Vapour Barrier Membrane
Plasterboard Ceiling

 

GRP, FELT, TILES OR EPDM

Depending on the type of roof whethers its pitched or a flat roof construction, you will have a choice of waterproof layers. Pitched roofs typically have tiles or slates, whilst flat roofs either have GRP, Felt or EPDM, whichever waterproof layer is used, the basic construction remains the same.

GRP

Glass reinforced plastic (GRP) is a composite material also reffered to as  fibreglass.It is hard wearing and long lasting,  perfect for flat roofs.

Felt

Felt is used as a waterproof layer on non-habitable buildings such as garages or sheds. Not especially hard wearing.

Tiles

Tiles or slates come in numerous designs and are suited to pitched roofs over 15 degrees, different slates have different pitch tolerences.

EPDM

EPDM is an hard wearing & very durable synthetic rubber roofing membrane (ethylene propylene diene terpolymer).

THE MAIN BENEFITS OF A COLD ROOF

A Cold Roof design typically has a 50mm gap between the top of the insulation, and the roof deck above that allows air to circulate and prevent. The downside to this design is that cold air enters this space hence the name ‘Cold Roof’.

As a result, this type of roof is known as a cold roof. Because the structure, above the ceiling, is not insulated on a cold day cold air courses through the rafters, into the air flow space, and into the room below. This can lower the temperature of the room, and the rest of the property.

The main benefit to this type of build up is it doesn’t require much space, its perfect for construction where there may be height restrictions.

VENTILATION REQUIRED

A cold roof construction relies on adequate ventilation in order to work efficiently and prevent condensation, however, achieving a cross ventilation that is adequate to perform at optimum levels is very difficult to achieve in most conditions which results in condensation occuring.

COLD ROOF INSTALLATIONS ARE ON THE DECLINE

Cold roof systems in the UK used to be very popular but recent years has seen a massive decline of cold roof installations, Scottish Building Regulations do not allow cold roof design in any circumstances. Most modern builds are encouraged to install a Warm Roof build up instead,however, cold roof systems are still common within flat roof construction where there may be height restrictions.

Frequently asked questions

DO I NEED BUILDING REGULATIONS FOR A COLD ROOF?

Building Regulations specify that where a new waterproofing layer is added solely as a means of repair to an existing flat roof there is no requirement to add additional insulation. If the work involves, stripping the roof and replacing elements there is no need to add additional insulation provided:

  • The amount to be stripped and replaced is less than 50% of the total roof area, or;
  • The overall renovation is less than 25% of the building envelope, or;
  • The calculated payback of the additional investment is greater than 15 years, or;
  • It is not technically, functionally or economically feasible – for example, it may not be cost effective due to the cost of raising thresholds, parapet walls etc.

Do COLD ROOFS NEED VENTS?

A Cold Roof construction requires adequate ventilation to prevent the build up of condensation, however achieving this is very difficult in most circumstances.

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