Patio Height, Fall and Drainage Explained

Roof height controls how much natural light you keep inside the house. Fall (the slope of the roof) controls drainage and water-tightness. Both decisions are made up front, before any material is ordered. Get them wrong and you end up with dark rooms or a roof that ponds. Get them right and the patio works in every weather.

Why height and fall get decided first

We're Patio Empire - a licensed crew (NSW Lic. 463700C) building outdoor rooms across the Central Coast and Newcastle. We're the ones who set the string lines, check the levels, and make sure the roof actually does what we promised it would do.

Two decisions matter more than any other in a patio build, and they both happen on day one - before we order materials, before we book the crew, sometimes before we've even finished the quote. Roof height. And fall.

Get either wrong and you'll feel it for years. Set the height too high and you've cut into the natural light reaching your kitchen or living room. Set the fall too flat and you've built a roof that ponds, leaks at the joins, and works water back up under the flashings.

This guide walks you through how we make both decisions, the numbers we use, and the drainage details that turn a roof into a dry roof.

Roof height - the trap of "just match the gutter"

The lazy answer to "what height should we set the patio?" is "match the existing house gutter". Sometimes that works. A lot of the time it doesn't - and it ends up causing one of two problems.

Problem one - the dark living room. Most existing houses have eaves, soffits, or upper windows above the gutter line. If you slot the patio fascia hard up against that gutter, you push the new roof out at full house gutter height. Looks fine from outside. But if there's a window above the gutter line - a bedroom, a bathroom, a stairwell - you've just blocked half the light coming in. The room behind it goes from "natural daylight" to "always need the lamp on".

Problem two - the awkward step-down. If the existing eave is too low, matching the gutter forces the patio to slope away aggressively to keep the right fall - and the high side gets uncomfortably tight to the windows, the door head, or the soffit. People bang their head on the beam.

The right move is to model the height before we quote. We measure -

• The existing fascia and gutter
• The soffit height (the underside of the eave)
• Any upper-storey windows that could be affected
• The door head heights coming from inside the house
• The natural ground level under the proposed patio
• The required clear ceiling height under the new roof (usually 2.4m minimum at the low side)

Then we work out the band of acceptable heights - usually a window of 100-150mm where the build still has the right fall to drain, the right clearance underneath, and doesn't block any windows. We walk you through the trade-off so you can see what we're working with.

Fall - the maths behind a watertight roof

Fall is the slope of the roof, expressed as a ratio. 1:60 means 1 unit of vertical drop for every 60 units of horizontal run. For a 6-metre patio depth, 1:60 fall is 100mm of drop from high side to low side. 1:30 fall is 200mm of drop.

The numbers that matter for an insulated or single-skin Colorbond patio -

• 1:60 minimum - the manufacturer's specified minimum for most Colorbond profiles. Below this, water can pool, capillary action can work moisture back up under flashings, and gutters struggle to clear during heavy rain.
• 1:40 to 1:30 - our target range where the design allows. Sheds water fast, gutters cope easily, no risk of standing water.
• 1:20 or steeper - sometimes needed for very deep patios or specific designs. Looks more pronounced visually and changes the way the roof reads against the house.

We don't go below 1:60. Ever. Even if it means sacrificing a bit of high-side height to get the low side where it needs to be. A patio roof has one job - to keep water out of where you don't want it. A roof that ponds is a roof that fails.

Why the height-vs-fall trade-off is the real design conversation

Here's the part that catches people out. Height and fall aren't independent. Every millimetre of fall you add to the roof has to come from somewhere - either the high side goes up (risking light) or the low side goes down (risking head clearance and ground levels).

For a 6m deep patio at 1:30 fall, the roof drops 200mm from high to low. If your maximum high side is set by an upper-storey window, and your minimum low side is set by the 2.4m ceiling clearance, the maths needs to work in the middle. Sometimes it does easily. Sometimes you need to compromise on patio depth, or step the roof, or pick a different roof system entirely.

This is why we model first and quote second. We're not trying to sell you a fixed product - we're working out what actually fits your home before putting numbers on paper.

Box gutters vs external gutters

Two main options for catching water at the low side -

External gutters - fitted to the patio fascia, exposed and easy to inspect. Cheaper to install, easier to clean, easier to repair if something goes wrong. Visually they read as a gutter on a roof - which is fine, because that's what they are.

Box gutters - concealed inside the structure, usually where the patio fascia tucks under the existing house roof or under the soffit. Tidier visually because you don't see a gutter line. But the trade-off is real - box gutters need to be sized correctly for the roof area they're catching, and any failure is hidden until water shows up inside the house.

For most residential patios in our patch, external gutters are the right call. They cost less, they last as long, and they're forgiving when leaves and gum nuts inevitably block them. Box gutters have their place - mostly on jobs where the patio sits hard against a heritage facade or where the visual line of the existing house roof can't be interrupted.

If we're going box gutter, we always upsize the cross-section, install an overflow, and use a continuous-piece liner so there's no in-line joint to fail. That's not optional - that's how box gutters need to be done if you don't want a leak in five years.

Internal vs external downpipes

Same conversation, different fitting. Downpipes either run on the outside of the patio post (external) or are concealed inside a hollow post (internal).

External downpipes - the standard. Round or square PVC, painted to match. Easy to inspect. Easy to clear if blocked. Visually obvious but neat when planned properly.

Internal downpipes - concealed inside square hollow steel posts. Looks cleaner, no visible plumbing. The catch - if a downpipe blocks inside a post, you can't see it from the outside, and clearing it means dismantling. Internal downpipes need bigger pipe diameter, smooth bends, and access points so blockages can be cleared.

We tend to recommend external as the default, with internal reserved for jobs where the visual cleanness genuinely matters and the customer is happy with the trade-off. A blocked internal downpipe in five years is a real problem - so we make sure the choice is made eyes-open, not just because it looks good in renders.

Stormwater connection - where the water actually ends up

Water leaves the roof through the gutter, runs to the downpipe, exits the downpipe at the bottom - and from there it has to go somewhere council-approved. That somewhere is almost always the existing house stormwater system, which connects to the street drainage or an absorption pit on the property.

What stormwater connection means in practice -

• We trace the existing house stormwater system to find the connection point
• We connect the new patio downpipes via underground PVC to that system
• All connections are sealed, sloped, and accessible for clearing
• The slab is finished so surface water also drains to the existing system, not back to the slab edge

What stormwater connection is not -

• Just running the downpipe onto the lawn
• Soaking into a "garden bed" against the house wall
• Discharging to the neighbour's yard
• Running surface water over a paved area without falls

Disconnected stormwater causes slab heave, undermines pavers, kills lawn, floods footings, and is non-compliant under most council DCPs. We connect every job to the existing system as part of the build, with the work documented so it's clean for any future certification.

Common DIY mistakes (we get called to fix these)

We've been called in to assess plenty of DIY or unlicensed patio jobs over the years. The same mistakes show up again and again.

• Roof too flat. Fall under 1:60 because the builder didn't want to lose head height. Result - ponding, blocked flashings, leaks in the second wet season.
• Roof set too high. No modelling of the upstairs windows. Result - the master bedroom or stairwell is dark for the rest of the home's life.
• Undersized gutter. Standard 100mm gutter on a 60sqm roof. Result - gutter overflows in any decent storm, water hits the slab edge, slab heaves.
• Downpipes terminating at the lawn. No stormwater connection. Result - waterlogged footings, undermined pavers, dead grass.
• No flashing at the existing house wall. Just butted the new roof to the wall and trusted silicone. Result - water tracks behind the patio roof and into the cavity. Damages the wall, sometimes the floor.
• Wrong screw spacing on Colorbond. Sheets lift in wind, panels rattle, fixings work loose. Result - panels need re-fixing, sometimes replacing.

None of these are exotic engineering problems. They're all decisions made on day one that compound over years. A licensed builder following the manufacturer specifications and the BCA doesn't make these calls.

Why the difference is invisible - until it rains

Here's the hard truth about a patio. The day it's finished, every patio looks the same. Beautiful steel. Tidy fixings. Clean lines. The customer is happy, the photos go on Instagram, everyone moves on.

The difference between a patio done well and one done poorly only shows up later. The first heavy rain. The first east coast low. The first wet season after the gutters fill with leaves. That's when the patio that was set too flat starts ponding. The patio with the wrong flashing starts marking the wall. The patio with the lawn-discharge downpipes starts heaving the slab.

By that point, the original builder is long gone. The customer is left ringing whoever they can find to help work out what went wrong.

This is why we obsess over height, fall, gutters and stormwater on day one. Not because they're glamorous - they're not. Because they're the part of the build that has to work in five years, ten years, twenty years. The visible finish on the day of handover is the easy part. The water management is the part that separates a real build from a flashy one.

What we do differently on every job

If you're talking to us about a patio, here's what happens with height and fall specifically -

• Site visit - we measure the existing house gutter, fascia, soffit, windows, and natural ground level. We bring a laser level and a tape, not just a clipboard.
• Modelling - we work out the acceptable height band before we quote. You'll see how much vertical room we've got to work with.
• Quote stage - the proposed roof height and fall ratio are stated explicitly. So is the gutter and downpipe spec.
• Pre-build - the licensed builder checks every measurement on site before any material is ordered. If something's tight, we adjust before tools come out.
• Build - string lines on the high and low sides. We don't eyeball the fall.
• Handover - we test the gutters and downpipes with a hose before we leave. If anything's not draining cleanly, it gets fixed.

This isn't anything fancy. It's the basic care that separates a licensed build from a knockabout job. And it's the reason our patios don't pond, don't leak, and don't need re-doing in five years.

That's the whole guide on height and fall. The numbers, the trade-offs, and the details that turn a roof into a dry roof. If you've got a specific home and you want us to come out and model the height for your block, give us a ring - it's part of the free site visit, no obligation.