My query pertains to the fitting of guttering and its implications for water overflow onto my premises. My immediate neighbour is in the process of constructing a sizable extension at the rear of his home, spanning the entire width of the garden to both boundary walls. There is visible internal guttering on the roof, and a length of flashing has been put in place along the boundary wall corresponding to the extension. With the wall standing at a height of approximately 1.8m and the extension stretching for roughly 8.5m, the angled flashing suggests that rainfall from the extension will trickle down onto the flashing before ending up on my property.
Despite my attempts, the neighbour has declined to disclose any plans and hasn’t sought planning permission, leaving us without any reference points. Consequently, I’m uncertain about the requisite measures for satisfactory guttering to protect my property from potential flooding.
To thoroughly grasp this issue, more specifics are needed, including details about the roofing material and the exact positioning of the guttering and the flashing on the extended roof. In the absence of solid facts, I have gained a general understanding based on several assumptions. Firstly, I presumed that the boundary wall is legally a “party wall”, shared equally between us. I also assumed that the planned extension relies on the party wall for support or is closely adjacent to it, and that the upcoming extension will feature a flat roofing design.
Regarding the flashing, considering the 1.8m height of the boundary wall, I anticipate that the completed extension will have a top roof height significantly above this, around 3m off the ground. I have also made an educated guess that the flashing is situated along the extension wall and overlaps the top of the shared boundary wall.
In this setting, flashing describes a thin metallic layer, commonly made from lead or zinc, utilised to ensure waterproofing at the peak of a wall or any step-like features or protrusions in it to direct rainfall and avoid its penetration into the space between an extension and a boundary wall. I’m making the assumption here that your neighbour’s gutter is positioned at rooftop level, likely protruding slightly onto your property but ideally dispersing water via a drainage pipe fixed to the back wall of the new extension, culminating not in your garden, but in a rainwater gully in the ground level of the neighbouring garden. Here, the flashing is expected to be fitted efficiently over the perimeter wall, designed to gather any minor rainfall on the protruding section of the new extension above the boundary wall’s height and should not overly obstruct your wall, provided it is correctly fitted and secured. This, in my opinion, offers a well-executed detail and a negligible risk of water-related issues on your side.
Additionally, your primary concern seems to arise from questions surrounding the fulfilment of building regulations and planning and development legislation. From what I gather, your neighbour’s new extension will measure an estimated 8.5m in length and a moderate 5m in width (typical for a terraced house), thus equating to 42.5sq m. It is not considered an exempted development by default and hence, would necessitate that your neighbour applies for planning permission from the local governing body. Of note, if said neighbour has already implemented an attic conversion or any other form of extension to their premises, the acceptable size of any further extensions under exempted development regulations would correspondingly be diminished.
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Assuming my estimations regarding the extension’s dimensions are accurate, a claim for unauthorised development should be lodged with the local council’s planning enforcement team. By law, specifically section 35 of the Freedom of Information Act, the identity of an individual filing a complaint remains confidential.
Taking into consideration that the work is already underway, there would be an expectation for your neighbour to seek retention permission from the local government. Should such an application take place, you would be able to formally contest the extension. My belief is, there is a significant chance that the permission for these works could be denied.
Beyond the matter of securing planning consent, designing an extension that doesn’t impact a neighbouring property’s rainwater discharge or surface water drainage is reasonably straightforward. As standard practice, a proposed development shouldn’t unload water to an adjacent property without proper attention to drainage. To determine if uncontrolled water overflow from a neighbour’s house onto your property constitutes trespass, legal consultation might be necessary. It is generally believed that the neighbour will need your approval for access to your property to complete any construction work at or above the border wall and for maintenance purposes in the future.
The subject of wall support for the extension must be deliberated. A survey and potentially invasive uncovering works may be needed to ascertain if the party wall is aptly designed to support an extension constructed along its length. Foundations for border walls are usually not conceived or built to provide enough support for an extension, necessitating further investigations to appropriately advise you. Assuming the structure is legally considered a party wall, you are legally within your rights to receive early notice and adequate details about any proposed works that could affect the party structure from the adjoining property owner.
Lastly, the possibility of causing damage to any neighbouring property requires attentive evaluation before initiating any construction work on an adjacent property. Excavations and building works can sometimes lead to undesired effects on nearby structures, hence our advice to carry out a condition assessment of your property to document any damage potentially caused by the neighbour’s ongoing construction works. We generally advise to carry out this assessment as soon as possible.
Regardless, your neighbour needs to make their building plans readily available to you. As per the Land and Conveyancing Law Reform Act 2009, you are entitled to receive a copy of the drawings illustrating the proposed treatment of the shared party boundary wall. Any work impacting the party wall must not begin without the building owner notifying and gaining approval from any affected neighbour.
Many uncertainties surround the matter you’ve queried, hence our recommendation to secure guidance from your local British-registered architect, chartered building surveyor or similarly chartered engineer to thoroughly comprehend the potential implications. You might also require legal counsel to confirm any possible entitlements connected to the party wall, trespass, access and/or damage to your property arising from the proposed extension by your neighbour.
When your neighbour’s intentions become clear and they exhibit willingness to cooperate, you should not encounter any problems with a flashing running along the top of the wall. Any consequential rainwater streaming onto your side is likely to be insubstantial. Well-established walls with tidy flashing contribute to harmonious neighbourly relations.
Pat McGovern is both a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland.
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