A) Additional insulation

For additional thermal insulation, use grooved sub-layer insulation in order to gradually drain any moisture from the old waterproof layer. Leave the old waterproof layer intact so it can function as an air barrier against any air leakage. To obtain the present thermal performance requirement, make sure that the additional insulation thickness is at least the same as in the old structure. Additional insulation increases temperature in the old structure and promotes drying.

The additional insulation layer functions as a sub-structure for the new waterproof layer. If the old structure is soft, use more rigid insulation types for additional insulation. Try PAROC ROS 30g and the surface layer insulation PAROC ROB 80.

Use long fixing screws for mechanically fixing the additional insulation and the new waterproof layer. When fixing the screws to the concrete sub-structure, the clay pellets under the insulation slabs may fall into the pre-drilled screw holes and make installation more difficult. For profile steel sheets, special accuracy is also required when directing the fixing screw in the profile steel sheet ridges.

Place the additional layer as low in the old structure as possible to obtain the optimal energy savings. 

 

Flat roof, concrete 2
New additional structure:
  • New waterproof roof membrane
  • Mechanical fasteners
  • PAROC ROB 80(t) (or ROB 50 or ROB 60)
  • PAROC ROS 30g (grooved)
  • Additional inclination layer: dry expanded clay pellets
Existing structure:
  • Roof membrane 
  • Old thermal insulation 50 + 70mm mineral wool
  • Supporting structure: Double-T slab
 

B) New roof membrane

If the old roof structure only needs a renewed waterproof layer and the sub-structure is adequately stiff, you only need new bearing layer of insulation. To drain moisture in the old roof structure and that collected during the installation phase, make grooving by placing double layers of insulation as described below.

When putting a bearing layer on an old roof the existing roof membrane must be dry. Otherwise the insulation between tight layers gets and stays wet. To avoid problems, use two layers of roof slabs or board. 
 
Flat roof, concrete 3
New additional structure:
  • New waterproof roof membrane
  • Mechanical fasteners
  • New bearing layer: PAROC ROB 40gtj, 30mm

Existing structure:
  • Old roof membrane 
  • Old thermal insulation: mineral wool
  • Supporting structure: Double-T slab 
 

If the old roof also needs surface reinforcement, use two layers of top layer insulation slabs. In the longitudinal seams, install the lower slab layer with a gap of about 60 mm. Install the second slab layer so that is forms a continuous substructure with the waterproof layer. Thus the new waterproof layer has a reinforced and ventilated substructure. Lead the insulation layer grooves to a connecting channel at the ridge and in the elevations.

Fix the bearing layer, together with the waterproof layer, to the substructure through the insulation layer. If you are mechanically fixing the bearing layer, use fixing screws that penetrate through the old waterproof layer to the insulation layer. In this case no additional holes are made in the vapour barrier.

Flat roof, concrete 4 
New additional structure:
  • New waterproof roof membrane
  • Mechanical fasteners
  • New bearing layer: 2 x PAROC ROB 50t, 20mm

Existing structure:
  • Old roof membrane 
  • Old thermal insulation: mineral wool
  • Supporting structure: Double-T slab