This is required to prevent Grillage Foundations being located on a neighbour's land without agreement by using the rights given by Section 1 (6) to place foundations on a neighbour's land.
Section 20 of the Party Wall Act defines 'Special Foundations' as :
"foundations in which an assemblage of beams or rods is employed for the purpose of distributing any load"
Section 7(4) States that "Special Foundations" may not be placed on a neighbour's land without the neighbour;s consent in writing.
Recently surveyors have assumed that Reinforced Concrete underpinning is a "Special Foundation". This has created a situation where neighbours can prevent the underpinning of a Party Wall with no justified reason or can 'lever' payment or other benefit from a neighbour as the price of giving consent.
David Bowden FRICS has researched and obtained meeting notes of the committee responsible for the 1939 Act (predecessor to the current Act). This document clearly show that the type of foundations envisaged were Grillage Foundations which are an assemblage of beams or rods is employed for the purpose of distributing load. David Bowden has summerised his findings in a paper.
Reinforced Concrete is not an "assemblage of beams or rods". It is interesting that the definition in Section 20 of the Act does not even mention concrete. That is because the type of 'special' foundation envisaged by the Act is a steel Grillage Foundation. The concrete encasement to a grillage foundation is just to protect the steel from corrosion, It has no structural role. Whereas, without concrete the residual reinforcement bars in a RC walls have no structural effect, they are an ingredient of the concrete to improve its ability to resist tensile loads and do not act independently as a structural element to "distribute load".
This is what a Grillage Foundation looks like. These used to be used to support the columns of steel framed buildings. These days we would use piles. Interestingly this looks like an assemblage of beams and rods and these are certainly intended to distribute load.
Watson Woods Partnership
Section 11(10) of the Act states that where consent has been given for special foundations on land of an Adjoining Owner and the Adjoining Owner erects any building or structure and its cost is found to be increased by reason of the existence of the said foundations then the owner of the building to which the said foundations belong shall repay to the Adjoining Owner so much of the cost as is due to the existence of the said foundations. This clause has often been used to claim cost for removing concrete 'over-spill'. This is wrong. Over-spill can always be recovered as a loss under the terms of Section 7(4) of the Act. The provisions of Section 11(10) were intended to address the very significant implications of grillage type foundations located on a neighbours land.