'The sun did it.

The sun made my property collapse'.

The sun in question is the solar variety, not the newspaper.

And if that assertion of culpability sounds like the property-owner's answer to 'the dog ate my homework,' consider recently-reported research by Clive Richardson, structural engineer with James Consulting Engineers in London.The results could have serious implications for residential property solicitors and their clients.

Mr Richardson claims that 'many Georgian and Victorian terraces are being driven towards collapse by progressive thermal expansion.' According to his research, old terraces sway on an annual as well as daily basis, and in the course of a single year, 'they can move more than an inch, the diameter of a 50-pence coin.'Mr Richardon's findings, some details of which appear in his article in Architects' Journal (16 July 1998), reflect observations over a 20-year period of old terraces throughout London, four specific case studies, and continuous movement monitoring of a London terrace.'Shop-fronted terraces which are perched on slender columns are most at risk of this "bookend effect" and modern terraces are immune because they have been constructed differently to older terraces,' says Mr Richardson.The sun's thermal energy causes the terrace facade to expand and party walls to sway and lean progressively toward either end of the terrace.

Contraction follows expansion, but over time the two-way process is not equal.

Gravity acts on structural distortion to accelerate the process.End-terrace properties generally and generously act as bookends for the entire terrace.

But with the wholesale lateral distortion caused by the sun, the bookends collapse.

An end terrace already suffering from the bookend effect has a poor life expectancy, and the end can be sudden.

According to Mr Richardson, 'thousands of properties are at risk across the country, and simply rebuilding the end of terrace walls will not cure the problem'.Kenneth Byass, chairman of the property and commercial services committee of the Law Society, immediately notes the consequences for one category of occupier: 'Those who take full-repairing leases of terraced properties of this kind really ought to be extremely careful because, unless they exclude liability for inherent defects, obviously they can find themselves where they have to rebuild the property they are leasing.

I'm also concerned by the fact that there is no means of enforcement by one property which relies upon the other if really extensive works are required.'The difficulty arises when an owner of a property to which works are needed to create stability for the terrace simply has not got the money for it.

It's a huge problem, and I don't think it has been envisaged before.

I think solicitors must explain to buyers that there are rights of support which will have been acquired by prescription if by no other means, and those may be enforced.'Bob Hall, a solicitor with Baker McKenzie, warns against 'alarmism' while conceding that 'the bookend effect sounds like a real issue raising problems of some concern.

It is an incident of property ownership, certainly freehold and generally long-leasehold ownership, that the owner is respon sible for carrying out repairs.'Are mid-terrace owners entirely immune from the bookend-effect problems sustained by their end-terrace neighbours?' It does seem to me that there may be rights of support or help, actual or even implied, which might be capable of being used.It seems that, given that party walls are involved, there may be analogous rights to something in the nature of natural rights such that there is an obligation on people living in the mid-section of a terrace to co-operate in putting together a scheme which could be for communal benefit,' says Mr Hall.Pressure for a satisfactory resolution might derive from the fact that the individual home-owner's dilemma is potentially social in nature.

'It would need to be looked at, because if nothing is done then a not insubstantial element of our housing stock is going to deteriorate, and the economic costs will be huge.

And the capital cost of dealing with older terraced properties, if that needs to be the case, is extremely substantial,' adds Mr Hall.

Problems will be exacerbated if owners simply walk away from the problem, and write off their homes.Although many old terraces do not suffer from the bookend effect, Mr Hall suspects that 'presumably lenders will be rather more wary of lending on end-terrace properties unless they have satisfactory clearance from surveyors that this particular problem does not exist.

A local solicitor when acting for a lender on an end of terrace, or even mid-terrace property, would need to be aware that there are potential difficulties here, and he would need to be sure that any conditions attaching to the mortgage advance and the instructions issued to the solicitor are fully complied with.'But Leslie Dubow, chairman of the Solicitors Property Group, predicts: 'Surveyors will qualify their reports.

The building societies have to get a clear report.

If this bookend effect creates a scare, surveyors will protect their backsides.

The lenders won't get a report saying the wall is not buckling.

Surveyors will hedge even more than normal.

They will insert a new standard phrase, something like: "With buildings of this age, we can not ensure that there is no damage from the bookend effect".'As to communal cures, 'there probably are some remedies, but they would be cumbersome,' says Mr Dubow.

'The Party Wall Act enables you to claim against the adjacent owner, but I have reservations as to its effectiveness if they are several doors away.

It is a new Act, not tested by litigation yet.

It replaces similar legislation in London.

For example, someone in number 11 could have go at number nine and number nine at number seven, and so forth.'Some vendors conceal cracks with toothpaste.

For surveyors, solicitors and homeowners alike, extra vigilance will be required when considering old end terraces.