Many extension projects involve excavation close to a neighbouring property.
The Party Wall etc. Act 1996 contains specific provisions relating to certain excavations, but assessing whether they apply can become more difficult when nobody knows how deep the neighbour’s foundations are.
This is particularly common with older buildings.
Why does foundation depth matter?
Whether excavation falls within the relevant provisions of the Party Wall Act can depend on:
- the distance between the proposed excavation and neighbouring structure;
- the depth of the proposed excavation; and
- the depth of the neighbouring foundations.
Modern extension foundations may be significantly deeper than the original foundations of an older house.
What if there are no drawings?
For many older properties, there will be no reliable foundation drawings.
Even where historic plans exist, they may not accurately represent what was constructed.
Surveyors and engineers may therefore need to make a reasonable assessment based on the building’s age, construction and visible evidence.
Trial holes may help
In some circumstances, a trial hole can be excavated to establish the depth and configuration of an existing foundation.
This should be done carefully and in an appropriate location.
Your structural engineer or Party Wall surveyor can advise whether this would be useful.
Should notice be served if there is uncertainty?
Where proposed excavations are close enough and deep enough that the Act may apply, it is generally sensible to resolve the issue before construction starts.
Trying to establish the position after excavation has already begun can create unnecessary difficulty.
Your engineer may need the information too
Foundation depth is not only a Party Wall issue.
A structural engineer may need to understand neighbouring foundations when designing new excavation and determining whether additional safeguards are appropriate.
Simple Survey can help
If you are planning an extension and the neighbouring foundation depth is unknown, Simple Survey can review the proposals and help determine the appropriate Party Wall approach.
Send us your drawings and we can advise before excavation begins.