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Deck Penetrations

28 November 2011 No Comment

Penetrations through decks affect the structural integrity, and therefore must be suitably braced, dependent on opening size.

1. Small penetrations, through the bottom trough, can be accommodated without any additional support.

Multiple penetrations must be spaced at 1500 mm minimum centres. Note: No part of the web, or crown, can be removed without additional support.


Trough Widths



27 mm

200 mm


35 mm

150 mm


67 mm

225 mm


100 mm

610 mm


64 mm

200 mm


63 mm

233.3 mm


43 mm

310 mm


38 mm

250 mm


75 mm

375 mm

2. Medium openings, up to one profile pitch, require a stiffening plate.

The stiffening plate is generally installed above the deck, however for retro fitting of penetrations, where the roof build is installed, the stiffening plate can be installed under the deck.

Stiffening plate length must span over one full web each side of the penetration, with the plate width twice the penetration dimension, ensuring that the cut out is central to the plate.

D159 and deeper decks require a plate thickness of 3 mm, all other decks to be 2 mm.

Stiffening plates require fixing with Tec screws or rivets to fastener manufacturers recommendations.

Support plate for penetrations up to one pitch

3. Larger openings, greater than one profile pitch, require full structural support.

Deeper decks are capable of wider spans. A full structural frame support below the deck can be visually obtrusive. An alternative proposal would be to install a structural frame above the deck, ensuring that the support frame legs extend over two full webs either side. This however adds to cold bridging through the build construction, which must be considered.

Support frame positioned above the deck

Options 2 and 3 effectively distribute the load away from the opening into the surrounding deck. Unless the framing around the opening is actually connected directly to the support structure, the deck must have sufficient reserve capacity to carry the extra load; if there is any doubt about this consult Tata Steel RoofDek Technical Department.

All penetrations must be sealed to ensure that the integrity of a vapour check and / or an air barrier layer is maintained. The metal deck / vapour control membrane must be reasonably airtight so that the air permeability does not exceed 5 M³/Hr/M² at an applied pressure of 50 pa in accordance with the Building Regulations 2000, Approved Document ADL2 2010. Under laboratory testing sealed decks can achieve an air leakage as low as 0.5 M³/Hr/M². A reasonable practical expectation for a finished system would be 3 to 5 M³/Hr/M².

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