Basement Extension Quotations

When we receive an enquiry from a property owner who wishes to undertake work, our knowledgeable team will review the project drawings and with the help of Land Registry confirm how the works are notifiable and to whom.

Where the work is straightforward, such as a loft conversion or single story rear extension, and where there are a limited number of neighbours (adjoining owners) this is typically done without visiting the property. Our team will always be keen to discuss it in more detail as there are occasionally things that are not obvious from the plans and our surveyors are particularly keen to know how you get on with your neighbours!

This has historically been the same procedure for more complicated works such as basement excavations. We have however since the beginning of 2024 offered , the option of a pre-quote site visit with the building owner and where convenient, or where there is additional value, the Architect/designer.

Basement works in particular bring about their own unique party wall challenges that my colleague Justin Burns covered in a blog post from 2016. That post is as relevant now as it was then and it’s worth a more detailed read if you have the time. I will in this post however offer a condensed list of key considerations that from this year’s experience, are far easier to convey with that pre-quote visit.

Security for Expenses.

This is a sum of money held in ESCROW to protect adjoining owners against the possibility of project abandonment and to cover “reasonably foreseeable damage”. Typical sums are in the region of £20,000 – £30,000 per neighbour but your surveyor will need a good understanding of the reasoning and calculations behind these, especially if the neighbour appoints a difficult surveyor of their own.

Special Foundations Consent

Where the party wall is being underpinned in reinforced concrete, consent must be obtained from the adjoining owner. This can lead to the building owner occasionally being held to ransom but thankfully this can be avoided by the inclusion of a section of mass concrete at the very underside of the design (nicknamed a “Bailey Rail” after the judge who presided over the relevant court case).

It is often on the pre-site visit that the building owner is first advised of this, so regardless of whether they proceed with Peter Barry, they have this information to feed back to their design team.

Advising Engineer

This involves a secondary engineer reviewing and possibly amending the proposals to minimalise the risk to the adjoining owner’s property. The handling of this part of  the process requires an advanced level of experience, especially where communications are slow and in need of pushing forward.

Managing the process

The difference between a poorly and well managed basement party wall job can be significant. A pre-site visit and a meeting with the building owner is a far more effective way to establish expectations then a quote that it is obtained remotely. A good party wall surveyor will be keen to understand your relationships with your neighbours, which will provide a greater understanding as to how they are likely to respond.

Time invested upfront can pay significant dividends in the future and encourage more favourable responses such as consents and the use of a single agreed surveyor.

Our senior party wall surveyors have numerous examples of this proactive approach and the results from completed and ongoing jobs. If you are considering a basement project of your own, contact us and we will very quickly stand out from the rest.