Putting a Pergola on Decking

A pergola can go on a deck, but never on the boards alone. Each post has to be fixed down through the deck to the frame, or better, to its own concrete pad under it. Deck boards are 25 to 32 mm thick and are there to walk on. A roofed pergola in a gale will pull a bolt straight through them.

Three ways to do it, and the checks before you start.

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Neveronto the boards alone
3 waysto fix the posts
From the groundwhere the 3 m is measured

A pergola going up in Cork

A real job, shared by the Cork tradesman who built it.

a timber pergola frame being built over a new timber deck at the back of a pebble-dashed house in Cork — A timber pergola going up over a new deck at the back of a house in Cork. A real job, part built.

Three ways to fix the posts

A timber pergola frame being built over a new timber deck at the back of a house in Cork — A timber pergola going up over a new deck in Cork: the front posts stand on the deck frame.

Method	How	When
To its own pad	A hole cut in the deck, a concrete pad below, the post up through it	The strongest. Best for any roofed pergola
To the deck frame	Blocking added between joists, the post bolted through to it	A sound, well-built deck and an open pergola
Built with the deck	Long posts that are part of the deck's own structure	A new deck. Plan them together

Check the deck first

The joists: any soft timber, and the pergola waits.
The posts under the deck: on pads, not sitting in soil.
Composite boards: never take a fixing load. Always go through to the frame or a pad.
Height: the 3 m planning limit is measured from the ground, not from the deck.

A raised deck and planning

A pergola on a raised deck sits higher than one on a patio, and the height is measured from ground level. On a deck half a metre up, a 2.5 m pergola is at the limit. Decking has its own rules too: see pergolabuilders.ie.

What it costs

Job	Typical cost	What moves the price
Timber pergola kit, 2.4 m square to a 3.4 m corner	€428 to €733	Size and timber. Fitting and a base are extra
Aluminium louvred pergola kit, 3 × 3 m to 4 × 3 m	€1,886 to €2,998	Size and maker
Made-to-measure aluminium pergola, supplied and fitted	from €2,500	Size, roof, sides, base and fixings

Pads under an existing deck are extra, and priced after a look underneath.