The construction of pitched and flat roofs can be categorised as warm and cold, but what does this actually mean, what are the benefits of each construction method and when is best to use one over the other?
In warm roof construction, the entire structure of the roof is kept warm with insulation installed above the structural deck in the case of a flat roof or on top of and between rafters for pitched roofs. Conversely, in cold roof construction, insulation is installed below the roof structure leaving an uninsulated cold void between the insulation and the roof structure.
Warm roofs offer better thermal efficiency than their cold counterparts and are particularly well suited to the UK climate. The reason for the increased efficiency is the reduction of thermal bridging.
Warm roofs eliminate the cold briding issues associated with cold roofs to deliver thermal efficiencies.
Thermal briding occurs in cold roof structures because the rafter is not insulated. Because wood conducts heat, cold areas will be present on the underside of the rafters which can encourage the formation of condensation if dew point is reached. This condition can be diagnosed with the aid of thermal imaging cameras which will clearly show cooler areas consistent with the location of rafters.
So given the thermal benefits of a warm roof structure, why would you want to install a cold roof?
For the construction of new roofs in the UK, warm roofs are almost always the answer. The exception is where there are restrictions on the depth of the roof build up. This is of particular importance when considering balconies and terraces with openings to take into account. Warm roofs commonly require insulation of around 150mm which significantly adds to the overall height of the roof. In contrast, insulation adds not additional height to the structure of a cold roof when installed between rafters.
If you're considering a roof rennovation or installation and would like some advice, please get in touch on 0208 132 8112 or email roofing@djcs.co.uk
