Do you suspect a leak on your ceiling under a cantilevered deck?

Leaks under and around decks are common… so where’s it coming from?

 Below is a thermal imaging photo of a gib board ceiling underneath a cantilevered deck. The home owner had noticed a very slight discolouration on the ceiling, and decided to call me to test the area for moisture ingress. Once I saw what was directly above the ceiling area (a cantilevered deck), it was almost a given as to where the leak was coming from.

Because the cantilevered joists continue from the inside of the buiding to the outside supporting the deck, the immediate area where the joists penetrate the cladding can be very hard to seal correctly. Water has a habit of finding the most minute cracks in the cladding… and simply runs along the joist and follows the path of least resistance. The end result is the water finds a low point and drips down onto your ceiling.

A thermal imaging inspection immediately below your deck (Figure 1 Below) could identify signs of ‘trouble’ well in advance of a complete failure, without needing to pull your ceiling down. There have been cases where the joists have completely rotted over time, and decks have collapsed without notice! (See Figure 2 Below)

Figure 1

Figure 2 (Photo thanks to BRANZ)

Here’ s another recent infrared photo taken below a deck that runs back over the top of a room. This leak was originating from the corner of a tiled deck which had no clearence between the tiles and the base of the external plaster cladding (Not easy to ‘get at’ without ripping the tiles up!).

This deck was also level with the internal floor, therefore very hard to create a step down to comply with the current building code. This leak has run right down the wall below… requiring further invasive testing to check the structural integrity of the timber wall frame below (Untreated timber):