Just found out my house is of non-standard construction -- liability of seller/agent?

D00gie72

You mention yourself that you haven't read the original valuation report. Makes me wonder how engaged you were with the purchase process? You don't know if the original valuation identified the non standard construction or not - it's possible they did mention it, in which case you were informed at the time you bought.
The previous owners may have known about the construction - what they may not have realised is the implications in terms of getting a mortgage - perhaps they'd never had difficulty themselves, In which case they may not have seen the importance of mentioning it to potential buys. (this may be a bit tongue in cheek - but you would have to prove their liability) After all - you don't see sellers telling everyone their house is brick construction do you? It's just possible the previous owners didn't think it relevant to mention.
I live in a property of non-standard construction - and agree it can be more tricky to get a mortgage - however there are lenders out there that will lend (some of the high st lenders even) so don't be too disheartened that one has refused - you may be able to get a good deal elsewhere.

Pa_Ja

From my experience, Halifax was the only lender on this property type.