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Property Surveying Blog
February 19, 2018

Overflowing Gutters

Written by Tughan Musa

In this blog post, I will be looking into overflowing gutters and hopefully clarifying how you can avoid this common issue. Rainwater fittings may not be exciting, but are one of the most important functions to any house.

The gutters are designed to channel rainwater water from the roof, towards the downpipes where it is eventually discharged into the drain. Generally speaking within the UK, gutters are plastic of metal “half-round” and are positioned around the perimeter of the roof in order to collect run-off rainwater.

If the gutters don’t function correctly, aren’t the correct fall or are blocked, rainwater could quickly fil and spill over the sides saturating the walls beneath. In my experience this is one of the most common forms of penetrating damp leading to damp and wet rot issues. The saturation of an external wall can cause frost damage, spalling, erode the pointing and ultimately increase the porosity of the wall.

Furthermore, over time wetter ground caused by overflowing gutters could mean the ground becomes so saturated, that it undermines the existing foundations of the property, potentially leading to structural movement.

In my experience, the splash marks caused to lower walls by overflowing gutters can often be misdiagnosed as rising damp. However the two forms of damp are distinctively different, with rising damp being moisture that emanates from the ground, rising up the wall by approximately a metre.

Misdiagnosing this issue can often see unnecessary repairs such as a retrofit injection damp proof course being installed which can be both costly and often ineffective.


Generally speaking, there are three main types of Gutters used widely within the UK.

Cast-Iron Gutters

If you live in an older property, usually up to the turn of the century it is likely that your gutters and downpipes are made of cast-iron and painted for additional weather protection and are relatively heavy in comparison to other property materials.

PVC Gutters

PVC is the most common type of guttering found on modern buildings and usually replace older cast-iron gutters. They are cheaper, lighter and easier to install and do not require painting. Generally speaking, they are black or dark grey and made from un-plasticised polyvinyl chloride.

Aluminium Gutters

Alumnium gutters are lighter than cast-iron and do not suffer from rust, instead as the metal corrodes it actually creates a hard finish to the alumnium adding further protection. These types of gutters can also be designed to replicate traditional styles, but as with cast-iron, it is not the cheapest option which is why it is quite rare to see them.

So, what causes Gutters to overflow?

With any property defect, there are a multitude of issues that can lead to the gutter becoming defective, I have focused on the most common in my experience.

Blocked Gutters

When a gutter becomes blocked the water builds up and overflows onto your external wall.

A common cause of overflowing gutters is due to organic debris, such as fallen leaves, moss growth, vegetation growth and even birds nests blocking the gutters and preventing rainwater traveling to the downpipes.

One simple way to tell if the gutters are blocked is to check them on a rainy day, if there is water running down the external wall of the house it most likely means there is a blockage.

In order to rectify this issue before the debris completely blocks your gutters, it would need to be scooped out with a trowel that can normally be done with ladder access. If your downpipes are blocked, you will need to use drainage rods to push trough the blockage to dispense at the bottom of the pipe.

To prevent leaves falling into your gutters and subsequently blocking the downpipe, a wire or plastic balloon can be retrofitted into the outlet. In the event of leaves blocking your gutters, this will allow you to clear it before it invades your downpipe.

Generally speaking, the rainwater goods and gullies should be cleaned after the leaves have fallen in the autumn. Perhaps every couple month check the hoppers, as they are prone to blockage from leaves etc. The hopper is effectively a box on the top of the downpipe, which receives rainwater and channels it down the pipe.

Defective Underfelt

Victorian roofs, constructed mainly in the 19th century, did not have any form of underlay beneath the tiles surface and roof void. The felt effectively acts as a water-resistant barrier from the weather.

Many Victorian properties have since had felt being installed and laid between the roof timbers and roof covering. This underfelt should lap into the gutters, by approximately 50mm, thereby preventing rainwater running down your wall.

If your roof is one of the ones that doesn’t have felt installed, it goes without saying that it is an investment you should look into having done.

Sagging Gutters or damaged Gutters

Modern gutters made of PVC are prone to sagging and twisting due to their age, lack of support from broken brackets or loose screws or poor installation. Unbeknown to most Surveyors, Surveyor’s ladders leaning against the gutters can also cause damage! Boiler flues extracting hot air or steam can also cause the gutters to warp.

When the lifespan of the PVC gutter is coming to an end, you may notice signs of cracks and leaks. To determine if your rainwater gutters are sagging, check for signs of standing water or water marks along the inner sides of the gutter, just make sure you don’t lean the ladder against the gutter when checking!

In order to rectify this issue, support for sagging gutters will need to be improved by replacing broken brackets or fixing any loose screws. The brackets need to secure before replacing any defective sections of the guttering.

If a section of the PVC gutter is damaged, you can remove that part by squeezing the top edges of the gutter together, so that it comes away from the clips that are holding it to the wall.

To prevent plastic gutters from deforming due to the hot gas coming out of the boiler flue, you could fit a protective metal deflector to the underside of the gutter.

Insufficient Downpipes and Gutters

If the gutters are firmly fixed and well maintained, overflowing could be due to an inherent defect or poor design. Having too few downpipes for the amount of guttering can cause overflow.

Victorian terraced properties tend to have one or two downpipes serving the, which is insufficient.

Occasionally, heavy rain can result in more rainwater than the gutters can handle. Unfortunately, storms hitting the UK will increase due to climate change, leading to more problems with existing gutters unable to cope with roof rainwater runoff, therefore this isn’t a property defect to hope will go away!

In order to rectify this issues, as a rule of thumb, one downpipe should not serve more than three terrace properties, as this can cause discharge problems and overflowing of rainwater.

When installing additional downpipes, the position should be considered on how it will visually impact the house and plan a straight run that avoids the windows and doors.

Corroded Iron Gutters

Cast–iron rainwater fittings often still survive on most Victorian houses. Although cast-iron gutters are durable, they are prone to rust due to lack of maintenance.

The two main types of Victorian iron gutters are ‘half-round’ and ‘ogee’. Ogee has a curved finish and is fixed to the fascia board, rather than being supported on brackets.

These types of gutters are susceptible to rust and where it’s fixed against the fascia board will cause dampness to the wall and eaves timber (edge of the roof).

Gutters should be checked at least yearly and when issues such as rusting is found the portion should be replaced.

Insufficient fall to the Gutters

If your gutters are not sloped sufficiently towards the downpipe, this will cause rainwater to inevitably build up and overflow. To determine the slope of the gutter, you can check with a spirit level to see if it’s sloping towards your downpipe.

If you find yourself suffering from a gutter with an insufficient fall, the guttering may need realigning, so it forms a slight constant slope to the nearest outlet.

Some metal brackets are adjustable and can be altered manually, however, most are not and will need to be fit correctly from the outset. In such situations the most effective solution is to replace the entire system.

Ultimately, gutters serve a valuable function and are not a part of your house in which you can afford to neglect. Regular maintenance can prevent your gutters from overflowing and potentially save thousands in replacement and repair costs.

At the very least I would recommend checking the gutters yearly for issue and defect and be sure that when issue is noted it is addressed at the first instance. Ignoring a gutter defect could quickly lead to expensive internal decoration repairs.