Mastic Asphalt Warm Roof on Timber Decks

On Cork, Mineral Wool, Cellular Glass, Perlite, Rigid Urethane (PIR), Phenolic Or Composite Insulations

Two coats of mastic asphalt R988 T25 on sheathing felt to a thickness of 20mm. Surface should be covered in solar reflective paint or stone chippings bedded in bitumen based adhesive.

Or:

Two coats of polymer modified asphalt on sheathing felt to a thickness of 20mm. Surface should be covered in solar reflective paint or stone chippings bedded in bitumen based adhesive.

Decks

Plywood

Plywood should be exterior grade type WBP bonded in accordance with BS 6566: Part 8:1985. Panels should be well nailed to timer joists and noggins.

Particleboard

Chipboards should conform to BS 5669: Part 2:1989 types C3, C4 or C5. Panels should be well nailed to timber joists and noggins. The boards should be prefelted, and the joints taped to give a temporary waterproof covering.

Oriented strand board should confirm to BS 5669: Part 3: 1992 type F1 or F2. Panels should be well nailed to timber joists and noggins.

Timber Boards

Timber Boards should be well seasoned and have a nominal thickness of at least 19mm. Tongued and grooved boards are essential. The boards must be closely clamped and securely nailed.

Vapour Control Layer

The requirement for a vapour control layer should be assessed by conforming to BS 6229:1982.

Particleboard

Vapour Barrier

Particleboards are not recommended for the high humidity applications which require a vapour barrier.

Vapour Check

One layer type 3B or 5U or polyester 180 bonded.

Plywood

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

Timber

Vapour Barrier

First Layer: Type 5U or polyester 180 nailed to deck.

Second Layer: Type 3B fully bonded.

Vapour Check

Type 5U or Polyester 180 nailed to deck.

U-Values

19mm Plywood, particleboard or timber

1For composites thickness shown is 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