National Conference Emerging trends of Energy Conservation in

In over-deck insulation, a thermal insulation with waterproofing is provided over the RCC as
a barrier against direct solar heat on RCC roof slab. This prevents the RCC slab from heating
up. The conventional method is under-deck thermal insulation by using methods like false
ceiling or extruded polystyrene. However its effectiveness is always a question since the
thermal barrier is provided under the RCC roof slab. Some heat passes through the underdeck
insulation and decreases the comfort level of the room. If the building is air-conditioned,
this heat leakage increases the AC load. Hence it can safely be concluded that over deck
insulation has its own advantages against under deck.
2. Building envelope insulation – a holistic approach
2.1 Roof insulation (over-deck)
This type of insulation has to take a composite approach to provide –
Thermal insulation
Waterproofing and
Slope built-up.
The traditional and conventional systems of waterproofing and thermal insulation in India
worked well for ages to suit the Indian construction and economics. However, these systems
do not have a long life and require frequent maintenance. These systems also do not suit the
complicated site dynamics of today’s construction and do not offer insulation values to
comply to ECBC norms.
2.1.1 Mud Phuska
In this conventional system of providing thermal insulation, a 10 cm layer of puddled clay
mixed with grass straw is applied in slope on a sand-bitumen waterproofing layer. This layer
is consolidated and plastered with 13 mm of cow-dung mortar. Tile bricks are laid flat on
plastered surface and the joints are grouted with cement mortar.
The Thermal and surface properties of mud phuska are as below;
Density = 1622 kg/m 3
Thermal conductivity = 0.750 W/mK
Specific heat capacity = 0.88 kJ/kg-K
[Reference: SP 41, Handbook on functional requirements of building (Other than industrial
buildings), Part 1-4, Bureau of Indian Standard (1988)]
2.1.2 Brick bat coba
The love of the Indian construction industry is the use of brick
bat coba for roofs. This system consists of putting brickbat on
flat roofs to give a slope and then grouting the same with
cement mortar admixed with some water proofing compounds.
This is mostly finished with IPS topping with a tile pattern cut
into the top to form crack inducer joints to prevent cracks from
appearing; alternatively China mosaic is done as the top
wearing course. There is a myth that brick bat coba offers