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4 Roof types
4.1
General
There are generally three types of flat roof construction:
Warm Roof
The thermal insulation is positioned above the roof deck
immediately below the waterproofing, resulting in the structural
deck and ceiling being at a temperature close to that of the interior
of the building. A vapour control layer is placed between the roof
deck and the insulation to minimise the risk of condensation.
Ventilation of the roof void is not required. However due
consideration must be given to providing a minimum upstand
requirement of 150 mm above the finished roof level for all details.
Ventilated Roof ("cold roof")
This type of roof must be carefully designed to avoid premature
failure and should be avoided wherever possible.
Thermal Insulation is positioned beneath the structural
deck resulting in the roof covering and structural deck being
substantially colder in winter than the interior of the building.
The structural deck therefore becomes a potential point for
condensation, and so it is important to provide a minimum 50
mm void between the top of the insulation and the roof deck. This
void must be ventilated and cross ventilation must be provided
with a minimum 25 mm continuous opening at eaves on opposing
sides of the roof. A suitable sealed air-leakage barrier, or vapour
control layer installed at ceiling level is good practice, as this will
help restrict the passage of warm moisture laden air into the roof
structure.
Inverted Roof
Sometimes referred to as an 'upside down' roof, the thermal
insulation is positioned above the roof covering, resulting in the
roof covering, structural deck and ceiling being at a temperature
close to that of the interior of the building.
Since the insulation is above the waterproofing system the
insulation must be water-resistant and it must be ballasted
to prevent floatation of the insulation boards and to protect
against wind uplift. Therefore, the roof deck must be capable of
withstanding the additional loading of a ballasted roof.
4.2
Method of Attachment
The roof system must be secured to the roof structure to protect
against wind uplift. The components of the roof system can be
secured in a number of ways.
Mechanically Fastened
The membranes and insulation are secured using screw fasteners
which are fixed directly to the structural deck.
Adhered
The layers can be adhered using adhesive compounds to attach
the membranes or insulation to the substrate beneath.
Ballasted
The membranes and insulation can be secured using a selected
material, such as river-washed pebble or concrete paving slabs to
weight the layers down to protect against wind uplift or floatation.
A separation layer (PE foil) is required and an additional protection
layer may be required beneath the ballast material to protect the
underlying layers from damage.
Depending on project requirements and scheduling it is possible
to use a combination of methods, eg mechanical fastening of
insulation, and adhering of the waterproofing layers.
Monarplan
®
Installation manual
062014V1
10
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