Half-Round Gutter Installation
Complete guide to installing 112mm half-round guttering with fascia-mounted brackets, running outlets, and downpipe connections.
Safety Warning — Working at Height
Gutter installation involves working at height. Use a properly secured ladder or scaffold tower in accordance with the Work at Height Regulations 2005. Always have a second person on site. Do not overreach — reposition the ladder instead. Wear non-slip footwear and check weather conditions before starting.
What You'll Need
Tools
- Tape measure (minimum 5m)
- Spirit level or laser level
- String line and chalk
- Hacksaw or fine-tooth panel saw
- Drill/driver with 4mm pilot bit
- File or deburring tool
- Scaffold tower or secured ladder
- Pencil and marker
Materials
- 112mm half-round gutter lengths (4m)
- Fascia brackets
- Running outlets
- Union clips / joint brackets
- Stop ends (internal / external)
- 68mm round downpipe and fittings
- Downpipe clips (pipe brackets)
- Stainless steel screws (4.0 × 30mm)
Technical Specifications
Step-by-Step Installation
1 Plan the Layout & Outlet Position
Identify where each downpipe will discharge — typically at the corners of the building or near existing drainage. For runs up to 9 metres, a single running outlet at the low end is sufficient. For longer elevations, position a central outlet and fall the gutter in both directions towards it. Mark the outlet position on the fascia board.
2 Establish the Fall
The gutter must fall towards the outlet at a gradient of 3mm per metre. Fix a string line from the highest point (far end) to the outlet position. For a 6m run, the outlet end should be 18mm lower than the high end. Use a spirit level and tape measure to mark the fascia. The top edge of the gutter should sit approximately 25mm below the roof tile line to catch water while allowing tile overshoot.
3 Fix the Running Outlet
The running outlet acts as a bracket and connects gutter to downpipe. Position it at the marked outlet point, aligning the top edge with your string line. Pre-drill pilot holes and fix to the fascia using stainless steel screws. Ensure it is level across its width — the outlet spigot should point straight down.
4 Install Fascia Brackets
Starting from the running outlet, fix fascia brackets at maximum 1-metre centres along the string line. Ensure each bracket aligns precisely with the string line — even small deviations can pool water. Always position a bracket within 150mm of each joint and within 150mm of any stop end. Pre-drill pilot holes to prevent splitting on timber fascias.
5 Cut & Fit Gutter Lengths
Measure and cut gutter lengths as needed using a hacksaw. Deburr cut ends thoroughly with a file — burrs prevent proper seating in union clips and can cause leaks. Clip gutter lengths into brackets by hooking the back edge first, then pressing the front edge down until it snaps into the bracket clips. Leave a 6mm expansion gap at each union joint (marked on the fitting).
6 Join Gutter Lengths
Use union clips to join gutter lengths. Each union clip has a built-in rubber seal — check the seal is present and correctly seated before assembly. Position the gutter ends so they meet in the centre of the union clip with an expansion gap at each end. Engage the back edge first, then clip the front. Ensure the joint sits level within the run.
7 Fit Stop Ends
Push-fit stop ends onto each open end of the gutter run. Ensure the rubber seal is in place and the stop end is fully engaged — it should snap firmly into position. For additional security on exposed elevations, a small bead of silicone on the seal can provide extra weather resistance, though this is not typically required.
8 Install Downpipe
Connect 68mm round downpipe to the running outlet spigot. Where the fascia overhangs the wall, use an offset bend (112.5° bends back-to-back) to bring the pipe into the wall line. Fix downpipe clips at maximum 1.8m centres, with a clip within 150mm of each fitting. At the base, connect to a back inlet gully, shoe, or underground drainage system.
9 Test the System
Run water through the completed system using a hosepipe at the high end. Check every joint for leaks. Verify the fall is correct — water should flow steadily towards the outlet with no pooling anywhere in the run. Check that the downpipe discharges cleanly into the gully or drain below. Rectify any issues before leaving site.
Common Mistakes to Avoid
- Insufficient fall — 3mm per metre is the minimum. Less than this and water pools in the gutter, leading to overflow, algae growth, and premature joint failure.
- Ignoring expansion gaps — PVC-U expands and contracts with temperature changes. Failing to leave the marked expansion gap at unions will cause buckling in warm weather.
- Bracket spacing too wide — Exceeding 1m bracket centres causes sagging under rainwater load. Sagging creates low spots that hold standing water.
- Gutter positioned too low — If the gutter sits too far below the tile line, heavy rain will overshoot. Keep the rear edge tucked just under the tile course.
- Not deburring cut ends — Rough cut edges prevent union seals from seating properly, causing leaks at joints.
- Gluing joints — Half-round gutter systems use push-fit rubber seals, not adhesive. Gluing joints prevents expansion movement and causes damage.
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