Hidden Internal Gutter Mechanics in Patios

Hidden Internal Gutter Mechanics in Patios & Sunrooms

Severe Queensland downpours and tropical storm fronts discharge massive volumes of water onto residential roofs. Traditional external gutters are prone to leaves blockages and overflow leaks. TS Aluminium solves these challenges using internal hidden drainage pockets engineered directly inside structural patio beams.

Catchment and Flow Calculations

To size hidden drainage channels properly, engineers must calculate the catchment area (A) and design rainfall intensity (I in mm/hr) based on regional return periods. The design water flow rate (Q in L/s) is determined by:

Where:

• C: Runoff coefficient (taken as 1.0 for metal/glass roofs).
• I: 1-in-20 year storm intensity for Brisbane (approx. 220 mm/hr).
• A: Catchment area (horizontal roof projection in square meters).

For a standard 6 m imes 4 m (24 m²) patio, this translates to a design flow rate of 1.46 L/s which must be drained rapidly without water backing up and overflowing into the house wall plate.

Downpipe Discharge Capacities (Under gravity flow)

Downpipe Diameter	Internal Area	Max Flow Capacity	Discharge Speed
50mm PVC Downpipe	1,960 mm²	1.10 L/s	1.2 m/s
75mm PVC Downpipe	4,415 mm²	2.90 L/s	1.5 m/s
90mm Heavy Duty Post channel	6,360 mm²	4.50 L/s	1.8 m/s

Flashing and Capillary Water Breaks

Water tightness at the joints between aluminium sections is achieved using high-grade EPDM gaskets and double-sealed silicone beads. Additionally, TS Aluminium designs all joinery with physical capillary breaks—small air chambers that prevent water from traveling upward against gravity due to surface tension.

Downpipes are routed inside the support posts. This hidden drainage configuration protects downpipes from mechanical damage and preserves clean architectural lines.