Flat Roofs: Double T-slabs

Paroc Air is a simple and safe solution for making dry flat roofs. PAROC Air keeps the roof structure dry without any mechanical systems. The basis for this simple but effective solution is natural air pressure.

Effective roof insulation has three or four insulation layers. The lowest insulation layer forms a uniform base for the vapour barrier. The vapour barrier prevents moist air from leaking into the insulation layer. Due to the continuous stone wool base, the vapour barrier remains intact even during small structural movements, such as those caused by profiled sheet metal.

The top of the intermediate insulation layer has a series of grooves which forms a network of ventilation channels. Porous stone wool with high vapour permeability doesn’t absorb the moisture into the insulation but allows moisture to move to the ventilation grooves where it is led out from the construction through ventilation hoods.

On the top of the grooved insulation layer there is a thin and rigid stone wool board. It covers the ventilation channels and carries the load from human traffic during installation and maintenance.

Here are some examples of effective roof structures:

Flat roof, concrete, grooves 
  • Roof membrane 
  • Mechanical fasteners 
  • PAROC ROB 80(t) 
  • PAROC ROS 30g (or ROS 40g) 
  • PAROC ROS 50 
  • Vapour barrier 
  • Supporting structure; Double T-slab 
 Insulation solution with U value
PAROC ROB 80t 20 mm   20 mm
PAROC ROS 30g 180 mm 100 mm
PAROC ROS 30 180 mm 130 mm
U value, W/m2K 0.09 0.14
Calculation parameters (According to EN 6946):
Bitumen roof membrane  λU = 0.23 W/mK d = 6 mm  R = 0.026 m2K/W  
Vapour barrier λU = 0.33 W/mK d = 0.25 mm R = 0.001 m2K/W
Double T-slab λU = 2 W/mK d = 50 mm R = 0.025 m2K/W
PAROC ROB 80t λU =0.038 W/mK    
PAROC ROS 30g, (grooved) λU = 0.036 W/mK    
PAROC ROS 30 λU = 0.036 W/mK    
Surface resistance Rsi + Rse = 0.14 m2K/W
U value corrections:
Air in the grooves R air gap = 0.130 m2K/W
Grooves have been calculated as one separate construction layer: depth 20 mm, 15% of area.
Mechanical fasteners: CROCO B-110 + KLA-concrete nail
Fasteners/m²,nf, 4
Thickness of the fastener, D, 5.00 mm
The effect of fasteners for the construction layers presented is less than 3%, so the fasteners do not need to be taken into account.