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Mastic Asphalt Warm Roof on Concrete Decks

Asphalt Warm Roof on Concrete Decks | RJ Evans Specification

Laid upon Cork, Mineral Wood, Cellular Glass, Perlite Rigid Urethane (PIR), Phenolic or Composite Insulations

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.

Deck

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.

Vapour Control Layer

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

U- Values

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.

 

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