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Insulated Roof On Metal Decks

Please contact us if you would like to receive a quote from one of our Approved Contractors.Insulated Roof On Metal Deck Diagram


Ensure that the joists supporting the metal deck are sufficiently strong to maintain an adequate fall and thus avoid ponding. If the deck abuts against a concrete or brick wall an upstand should be attached to the deck so as to allow movement between the deck and the wall thus avoiding stress on the felt.

Vapour Check/Barrier

A vapour check or barrier (C) should be laid directly on top of the deck (A) and all laps fully sealed. The decision as to whether to use a Check or a Barrier depends on the degree of humidity there is likely to be under the roof. In a properly ventilated building a membrane such as Casali 20050 should be adequate as a Vapour Check but in extreme conditions such as an indoor swimming pool one should use a Vapour Barrier (C) such as Vaporex 4 AL+VV.


If polyurethane heat-sensitive board (D) is being used it is essential that they are faced with a glass-fibre reinforced felt to protect the insulation from excessive heat hen torching. If in doubt consult the manufacturer of the board.

Waterproofing Membranes

  1. The Deck should be painted with Bitumen Primer (B).
  2. Roll out the vapour check or barrier (C) which may be lightly torched to hold it in place on the deck. Seal all laps by torching.
  3. Lay the insulation board (D) preferably in a diagonal direction across the troughs in the deck (A) and fix through to the deck with mechanical fasteners (E) according to the manufacturer's instructions.
  4. Loose lay a layer of Gruver* (F) perforated felt butt-jointing in preference to lapping.
  5. Torch on a layer of Dermabit 30160 (G) ith 80mm longitudinal laps and 150mm transverse laps. While ensuring a good flow of bitumen don't use excessive heat which could damage the insulation board (D). I fthe roof is exposed to high winds it is advisable to run a line of mechanical fasteners 40mm in form the edge of the sheet to be covered by the laps.
  6. The cap sheet should be Casali Dermabit Extra 4170 (H) and this is fully torched to the underlay (G) making sure to stagger the laps between the underlay and the cap sheet.
  7. The cap sheet (H) should be painted with 2 coats of Reflective Roof Paint (I) preferably 4 to 6 weeks after the felt is laid.

Please contact us if you would like to receive a quote from one of our Approved Contractors.

* In case of roofs exposed to high winds, we suggest to mechanically fix the underlay (G) to the deck (A) avoiding the use of Gruver (F).


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