Fitting guttering properly
Set the fall first and mark it with a line. Everything else is fixing to that line.
The fall decides everything
A gutter needs a consistent fall toward its outlet. Around 1 in 350 is the usual figure, which is roughly 3mm per metre, so a 10 metre run drops about 30mm from end to outlet. It is a smaller slope than most people expect, and it must be continuous.
Too little fall and the gutter ponds, which grows moss and overflows in heavy rain. Too much and it looks visibly crooked against the fascia, which on a long elevation is obvious from the road. Both are set at the marking stage and neither can be adjusted afterwards.
- About 3mm per metre
- Roughly 1 in 350. A 10 metre run drops around 30mm to its outlet.
- Continuous, not stepped
- A string line from end to outlet, then every bracket to the line. Bracket by bracket accumulates error.
- Outlet position first
- Decide where the downpipe goes before marking anything, because the fall runs to it.
- Long runs, two outlets
- Over about 12 metres, fall from the middle to an outlet at each end rather than one long drop.
Bracket spacing and where the load goes
Fascia brackets go at no more than 1 metre centres on most systems, and closer than that where snow is likely or where the gutter carries a long roof slope. A bracket within 150mm of each side of a joint, an outlet and a corner is also standard.
The reason is that a full gutter is heavy and plastic creeps. A run with brackets at 1.5 metres looks fine dry and sags visibly the first time it fills, and once it has sagged it holds water permanently.
- 1 metre maximum
- Closer in exposed positions. Check the manufacturer's figure, since systems differ.
- Either side of every joint
- Within about 150mm of unions, outlets, corners and stop ends. These are the weak points.
- Fix into solid timber
- The fascia, and into the rafter end where you can. A bracket in soft fascia pulls out when the gutter fills.
- Test with water
- Fill the run with a hose before you finish. A sag shows immediately and only when it is wet.
Cutting and joining plastic gutter
Cut square with a fine toothed saw in a mitre box or against a wrapped line, then file the burr off both edges. A rough edge either sits proud in the union or shaves the rubber seal as it goes in.
Plastic gutter is not glued. It clips into unions over rubber seals and it must be left short of the socket shoulder so it can expand. Every union has an expansion mark inside it, and pushing the pipe fully home is the commonest cause of a joint that pops or cracks in summer.
- Fine tooth saw, square cut
- A hacksaw at 24 to 32 TPI. Mitre box or a wrapped paper line, because freehand is not square enough.
- File both edges
- The burr shaves the seal as the pipe enters, and that is a leak that appears at the first heavy rain.
- Leave the expansion gap
- To the mark inside the union, not fully home. A gutter run moves several millimetres between summer and winter.
- Never glue it
- Solvent cement on a gutter union prevents the movement the system needs. It will crack instead.
Downpipes and where the water goes
A downpipe wants to be plumb, clipped at no more than 2 metre centres, and to discharge somewhere it can actually get away. A shoe onto a gully, a back inlet gully, or a soakaway of adequate size.
Discharging onto a path or against a wall is what causes damp and frost damage, and it is a surprisingly common shortcut. Check the fall of the ground away from the building as well as the pipe itself.
- Plumb, clipped at 2 metres
- A leaning downpipe stresses the joints and looks worse than a crooked gutter.
- Into a gully or soakaway
- Not onto a path or against a wall. That is where damp and frost damage come from.
- Leave expansion at the sockets
- Same as the gutter. A rigid run between two fixed points cracks.
- Fit an access piece
- One removable section makes clearing a future blockage a two minute job instead of an hour.
Working at the eaves
Gutter installation is done at eaves height, from a ladder or a tower, and a new run means moving along the whole elevation. That is many ladder repositions, and it is where the fall risk sits rather than in the fitting itself.
A tower is genuinely better for a full run, because you can work with both hands, keep everything on the platform, and move along without repositioning a ladder thirty times. For anything above two storeys it is not really optional.
- Tower for a full run
- Both hands free, everything on the platform, and no ladder to reposition every metre.
- Stand-off if using a ladder
- So the ladder never leans on the fascia or the new gutter you are fitting.
- Move, do not reach
- Hips inside the stiles. Overreaching sideways with a length of gutter is how ladders tip.
- Above two storeys
- Tower or scaffold. The fall distance is what changes, not the difficulty of the work.
Frequently asked questions
- What tools do I need to fit guttering?
- A spirit level, a string line and chalk line, a tape measure, a fine toothed saw and mitre box, a file, a cordless drill and driver, a ladder with a stand-off or a tower, and a hose to test with. That covers setting out, cutting and fixing a standard run.
- What fall should a gutter have?
- Around 3mm per metre, roughly 1 in 350, running toward the outlet. A 10 metre run therefore drops about 30mm end to end. It must be continuous rather than stepped, which is why a string line from end to outlet is the correct way to mark it.
- How far apart should gutter brackets be?
- No more than 1 metre centres on most systems, and closer in exposed positions or under a long roof slope. Also within about 150mm of each side of every union, outlet, corner and stop end, because those are the points that sag first.
- How do I cut plastic guttering?
- With a fine toothed saw, around 24 to 32 TPI, in a mitre box or against a line wrapped right around so it comes out square. Then file the burr off both edges, because a rough edge shaves the rubber seal in the union as the gutter goes in.
- Should I glue gutter joints?
- No. Plastic guttering clips into unions over rubber seals and is designed to move, expanding and contracting several millimetres between summer and winter. Solvent cement prevents that movement, so the joint or the gutter cracks instead of sliding.
- Why does my new gutter overflow?
- Usually not enough fall, so it ponds and cannot carry a heavy downpour, or brackets too far apart so the run has sagged once it filled. Occasionally the outlet or downpipe is undersized for the roof area draining into it.
- How do I mark the line for a gutter run?
- Fix the highest bracket first, then measure down at the outlet end by 3mm per metre of run. Pull a string line between the two, check it, then snap or mark along it and set every bracket to that line rather than measuring each one separately.
- Where should a downpipe discharge?
- Into a gully, a back inlet gully or an adequately sized soakaway, and never onto a path or against a wall. Discharging against the building is a common shortcut and it is a direct cause of damp and of frost damage to brickwork.
