10 Common Installation Mistakes and How to Avoid Them
Common Guttering Installation Mistakes?
The most common PVC guttering installation mistakes are inadequate fall (causing pooling water), missing expansion gaps (leading to buckling in warm weather), incorrect bracket spacing (causing sagging), and poor joint sealing (resulting in drips and leaks). These mistakes are almost always preventable with proper preparation, attention to the manufacturer’s installation instructions, and an understanding of how PVC-U behaves through seasonal temperature changes.
PVC-U rainwater, roofline, and drainage products are designed to be straightforward to install — but “straightforward” does not mean “foolproof.” Even experienced installers sometimes develop habits or shortcuts that lead to problems. This guide covers the ten most frequently encountered installation mistakes across guttering, roofline, and drainage — and explains how to avoid each one.
Mistake 1: Insufficient Gutter Fall
The Problem
Gutters installed dead level — or worse, with a reverse fall — cause water to pool rather than flow towards the outlet. Pooling water leads to overflow during rainfall, staining on fascia boards and brickwork, algae growth inside the gutter, and accelerated degradation of sealant joints.
How to Avoid It
Gutters should be installed with a consistent fall of approximately 3mm per metre of gutter run towards the nearest outlet or downpipe. For a typical 4-metre gutter length, this means the outlet end should be roughly 12mm lower than the far end.
Use a string line stretched between the highest point (far end) and the lowest point (outlet) as a guide when positioning brackets. Check with a spirit level against the string line to ensure a consistent gradient. Do not rely on the fascia board being level — older fascia boards may have sagged or been installed unevenly.
Mistake 2: Missing or Insufficient Expansion Gaps
The Problem
PVC-U has a relatively high coefficient of thermal expansion — approximately 0.06mm per metre per degree Celsius. A 4-metre length of gutter can expand by nearly 8mm between a winter temperature of 0°C and a summer temperature of 35°C. Without adequate expansion gaps, this expansion causes gutters to buckle, joints to pop apart, and bracket fixings to be stressed.
How to Avoid It
Every gutter union, running outlet, and stop end should incorporate the expansion gap specified by the manufacturer — typically shown as an insertion depth mark on the inside of the fitting. Push the gutter into the fitting only as far as this mark, leaving a gap for expansion beyond it.
As a general rule, allow a minimum expansion gap of 6mm at each end of a gutter length in normal conditions, increasing to 10mm if the gutter is being installed in cold weather (when the gutter is at its shortest and will expand as temperatures rise).
Check the manufacturer’s specific instructions — expansion gap requirements vary between product ranges and manufacturers.
Mistake 3: Incorrect Bracket Spacing
The Problem
Brackets spaced too far apart allow the gutter to sag between fixings, creating low spots where water pools. Over time, the weight of standing water increases the sag, creating a progressive failure. In heavy rain or when leaves accumulate, sagging gutters overflow at the low points.
How to Avoid It
Follow the manufacturer’s recommended bracket spacing — typically:
- Standard PVC-U gutters: Maximum 800mm between brackets (approximately 3 brackets per metre)
- Within 150mm of each union, angle, stop end, or outlet fitting
- Deepflow and hi-cap gutters: May require closer spacing — check manufacturer’s data
Do not space brackets further apart to save time or materials. The cost of an additional bracket is negligible compared to the cost of returning to fix a sagging gutter.
Mistake 4: Fascia Board Not Checked Before Installation
The Problem
PVC-U fascia boards, soffits, and guttering are only as good as the substrate they are fixed to. Installing new roofline products over rotten timber, loose fixings, or an uneven surface creates problems that will manifest months or years after the installation is complete — sagging gutters, fascia boards pulling away from the building, and water ingress behind the roofline.
How to Avoid It
Before installing any PVC-U roofline products:
- Inspect existing timber fascia and rafter feet for rot, splitting, and structural integrity. Replace any damaged timber before over-cladding or fixing new products
- Check that the fascia surface is flat and even. Use a long straight edge to identify dips and bumps. Pack behind the new fascia where necessary to create an even fixing surface
- Ensure fixings penetrate solid timber — not just the face of an old fascia board. Use screws of sufficient length (typically 40–50mm for fascia fixings into rafters) to achieve a secure connection
Mistake 5: Over-Tightening Gutter Clips and Brackets
The Problem
PVC-U needs to be able to move as it expands and contracts with temperature changes. Over-tightening clips, screws, or bracket fixings locks the gutter or fascia in place, preventing this movement. The result is buckling, cracking, and joint failure.
How to Avoid It
Fix gutter brackets securely but not excessively tight. The gutter should sit firmly in the bracket but should be able to slide slightly within it — this allows for thermal movement along the gutter run.
For fascia boards, fix with screws at the centre of any slotted fixing holes. The slots are designed to allow the board to expand and contract around the fixing point. Driving a screw at the end of a slot defeats this purpose.
Mistake 6: Cutting Without Deburring
The Problem
PVC-U pipe and profiles cut with a hacksaw or chop saw leave burrs and rough edges. On guttering, burrs can prevent the gutter from seating properly in fittings, leading to leaks. On drainage pipe, internal burrs create snag points that catch debris and contribute to blockages. On fascia boards, rough cuts look unprofessional and may prevent proper joint alignment.
How to Avoid It
Always deburr cut edges using a deburring tool, flat file, or sharp knife. For guttering and pipe, deburr both the inside and outside edges. For fascia boards, clean up the cut end with fine sandpaper or a block plane for a neat finish.
Better still, use a fine-toothed blade designed for cutting PVC-U. These produce a cleaner cut with less burring than general-purpose saw blades.
Mistake 7: Using Incorrect or Missing Sealant
The Problem
Some gutter systems and fittings require sealant to achieve a watertight joint, while others rely on rubber gaskets or O-rings and should not be sealed. Using the wrong sealant (or using sealant where none is needed) can prevent proper joint assembly, block expansion gaps, or create a mess that is difficult to clean up.
How to Avoid It
Follow the manufacturer’s instructions for each specific product range:
- Clip-together systems typically do not require sealant — the joint relies on a gasket or seal integrated into the fitting
- Solvent weld systems use solvent cement (not silicone sealant) applied to both surfaces for a permanent chemical bond
- Where sealant is specified, use a product recommended by the manufacturer — typically a non-setting gutter sealant that remains flexible and allows for movement
Never use bathroom silicone sealant on PVC-U guttering. Standard silicone does not adhere well to PVC-U and will peel away within a few months, leaving the joint unprotected.
Mistake 8: Incorrect Drainage Pipe Gradient
The Problem
Underground drainage pipes installed too steeply or too shallowly can both cause problems. Too steep and the liquid runs ahead of the solids, leaving deposits that build up into blockages. Too shallow and the flow velocity is insufficient to carry solids along the pipe, again leading to blockages.
How to Avoid It
Follow the gradient requirements in Building Regulations Approved Document H:
- 110mm pipe serving a single WC: Minimum gradient 1:80 (12.5mm fall per metre)
- 110mm pipe serving multiple appliances: Gradient between 1:40 and 1:80
- 160mm pipe: Minimum gradient 1:150
Use a laser level or digital inclinometer to set and verify the gradient before backfilling the trench. Checking gradient with a spirit level and straight edge is adequate for short runs but becomes less accurate over longer distances.
Mistake 9: Not Allowing for Thermal Movement in Soil Pipe
The Problem
Above-ground soil and waste pipe is exposed to temperature fluctuations — particularly on external walls where direct sunlight can cause significant heating. A 3-metre length of 110mm PVC-U soil pipe can expand by approximately 6mm between winter and summer temperatures. If the pipe is locked in place by tight brackets and rigid connections, it cannot accommodate this movement, leading to stress, cracking, and joint failure.
How to Avoid It
- Use push-fit (ring seal) joints rather than solvent weld joints for above-ground soil pipe wherever possible. Push-fit joints incorporate a rubber seal that allows the pipe to slide in and out as it expands and contracts
- Where solvent weld joints are used, install at least one expansion coupling in every straight run of more than 1.8 metres
- Fix pipe brackets so that the pipe can slide within them. Do not clamp the pipe rigidly at every bracket — designate one bracket as the “fixed point” and allow the pipe to slide through all others
Mistake 10: Ignoring Manufacturer’s Installation Instructions
The Problem
This is the root cause of most installation mistakes. Every manufacturer provides detailed installation instructions — specifying bracket spacing, expansion gaps, fixing methods, joint assembly procedures, and sealant requirements. These instructions are written based on the manufacturer’s knowledge of their own product’s properties and performance characteristics. Ignoring them, or assuming that “all PVC guttering is the same,” leads to avoidable failures.
How to Avoid It
Read the installation instructions before starting work. Keep them on site for reference during the installation. If the instructions are not included with the product, download them from the manufacturer’s website or request a copy.
Installation instructions are not generic — they are product-specific. Different gutter profiles, different roofline systems, and different drainage ranges all have their own specific requirements. Bracket spacing for a half round system may differ from a deepflow system. Expansion gaps for one brand may differ from another. The only reliable source of this information is the manufacturer’s own documentation.
Quick Reference Summary
| Mistake | Solution |
|---|---|
| No gutter fall | 3mm per metre towards outlet |
| No expansion gaps | Follow manufacturer’s insertion marks (6–10mm typical) |
| Wide bracket spacing | Maximum 800mm centres; within 150mm of fittings |
| Rotten fascia board | Inspect and replace timber before fixing PVC-U |
| Over-tight fixings | Allow thermal movement; fix at centre of slotted holes |
| Unfinished cuts | Deburr inside and outside edges |
| Wrong sealant | Follow manufacturer’s sealant specification |
| Wrong drain gradient | 1:40 to 1:80 for 110mm; 1:150 for 160mm |
| Rigid soil pipe fixings | Push-fit joints; expansion couplings; sliding brackets |
| Ignoring instructions | Read them. Every time. |
Frequently Asked Questions
What is the most common cause of leaking PVC gutters?
The most common cause is joints that have not been assembled correctly — either the gutter has not been pushed fully into the fitting, the expansion gap has been ignored (causing the gutter to push itself back out as it expands), or a gasket has been displaced during assembly. A properly assembled joint to the manufacturer’s specification should not leak.
How often should PVC gutters be cleaned?
Clean gutters at least twice a year — once in late autumn (after leaf fall) and once in spring. Properties surrounded by trees may need more frequent cleaning. Regular cleaning prevents blockages that cause overflow and removes organic matter that can encourage algae and moss growth.
Can I install PVC guttering in cold weather?
Yes, but take extra care. PVC-U becomes more brittle at low temperatures, so handle lengths carefully to avoid impact damage. Also, allow larger expansion gaps (up to 10mm) when installing in cold weather, because the gutter will expand significantly when temperatures rise in summer.
Do I need planning permission to replace guttering and fascia?
In most cases, no. Replacing guttering, fascia, and soffits on a residential property is considered routine maintenance and does not require planning permission. However, if your property is listed or in a conservation area, you may need consent from your local planning authority before making external changes.
Should I use screws or nails for fascia boards?
Screws. Always screws. Stainless steel or plated screws provide a more secure fixing than nails and can be removed if adjustments are needed. Nails can work loose over time due to the thermal movement of PVC-U and the natural drying and shrinkage of the timber substrate.
Related Kalsi Products
- Rainwater Systems — Complete range of PVC-U gutter and downpipe systems
- Roofline Products — Fascia, soffit, bargeboard, and installation accessories
- Underground Drainage — Pipe, fittings, and inspection chambers
- Installation Guides — Manufacturer’s installation instructions for all Kalsi product ranges
- Roofline Calculator — Calculate materials for your roofline project
