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20mm to coat mastic asphalt R988 T25 on sheathing felt, surfaced with solar reflective paint or stone chippings bedded in bitumen based adhesive.
Or:
20mm two coat polymer midwifed asphalt on sheathing felt, surfaced with solar reflective paint or stone chippings bedded in bitumen adhesive.
In-Situ Cast Concrete Slab: For roofing a wood float finish will have to be applied either in the concrete or with screed. Temporary drainage holes should be created in the concrete slab. Before roofing commences the slab must be adequately drained and dry. If the surface is damp or dusty a bitumen based primer can be used.
Precast Concrete Units: Any joints between the units may be grouted or taped according to the instructions of the manufacturer. If necessary the deck can be primed. If there are any inaccuracies in the level of the precast concrete which can occur due to laying or the manufacture screed may be used. It also may be necessary to use a screed to create falls.
The requirement for a vapour control layer should be decided upon by referring to BS 6229:1982.
Concrete Deck
Vapour Barrier
First Layer: Type 5U or Polyester 180 Bonded
Second Layer: Type 3B Fully Bonded
Or:
One layer Polyester or glass based metal lined bitumen roofing.
Or:
13mm one coat mastic asphalt on glass fibre tissue
Vapour Check
One Layer Type 3B or 5U or Polyester 180 Bonded
Precast Concrete Units
Vapour Barrier
First Layer: Type 3G partially bonded
Second Layer: Type 5U or polyester 180 bonded
Or:
First Layer: Type 3G partially bonded
Second Layer: One layer polyester or glass based metal lined bitumen roofing
Vapour Check
One layer type 3B or 5U or polyester 180 bonded
The tables below show the thickness of insulation required to achieve specified U-values for the total roof construction.
150mm In-Situ Cast Concrete Slab
Insulation | U-value | W/m2K | ||||
---|---|---|---|---|---|---|
0.45 | 0.40 | 0.35 | 0.30 | 0.25 | 0.20 | |
Cork Board | 80 | 91 | 106 | 126 | 154 | 196 |
Mineral Wool Slab | 68 | 78 | 91 | 108 | 132 | 168 |
Cellular Glass | 85 | 98 | 114 | 138 | 165 | 210 |
Perlite | 95 | 109 | 127 | 150 | 184 | 234 |
Rigid Urethane Foam (PIR) | 44 | 50 | 58 | 69 | 84 | 107 |
Phenolic Foam | 38 | 43 | 51 | 60 | 73 | 93 |
20mm Cork/Urethane Composite | 53 | 59 | 67 | 78 | 94 | 117 |
12mm Fibreboard/Polystyrene Composite | 68 | 78 | 90 | 106 | 129 | 163 |
100mm Precast Lightweight Concrete Units
Insulation | U-value | W/m2K | ||||
---|---|---|---|---|---|---|
0.45 | 0.40 | 0.35 | 0.30 | 0.25 | 0.20 | |
Cork Board | 58 | 70 | 85 | 105 | 133 | 175 |
Mineral Wool Slab | 50 | 60 | 72 | 90 | 114 | 150 |
Cellular Glass | 62 | 74 | 91 | 112 | 142 | 187 |
Perlite | 69 | 83 | 101 | 124 | 158 | 208 |
Rigid Urethane Foam (PIR) | 32 | 38 | 46 | 57 | 73 | 96 |
Phenolic Foam | 28 | 33 | 40 | 50 | 63 | 83 |
20mm Cork/Urethane Composite | 41 | 47 | 55 | 66 | 82 | 105 |
12mm Fibreboard/Polystyrene Composite | 51 | 60 | 72 | 88 | 111 | 145 |
1For composites thickness is given in the total thickness of the board.
2Cellular glass slabs are mopped with hot bitumen after laying and two layers of non-bituminised paper are required between the sheathing felt and the insulation to prevent adhesion.
Please click the following link for more information: Asphalt Roofing