how to measure a flat sheet liner

hello all,
  as usual i am late with the next post,but here i am so lets move on
i have pointed out the different materials that are common in pond
construction,there are other types but for the time being we will stick
to the better known types,
pvc and butyl liners are by far the most widely
used  because of cost and reliability,when building a pond which has a
uniform style IE square or rectangular and in some cases round, it  is
possible to have a box welded liner made to fit the pond,although more
expensive it has the advantage of being virtually crease free,and can be
installed in a fraction of the time it takes to install a flat sheet liner of
the same size,when measuring for a flat sheet liner it is important to allow
for an overlap as you need to be able to anchor the top of the liner to the
finished top edge of the pond,so if we had a pond 10ftx10ftx4ft deep we
would add 2ft to the length and width this would give us a 1ft overlap on
all 4 sides of the pond,but we also must remember that what goes up must
come down,so we must remember that although the pond is 4ft deep it has
2 sides so we must double the depth so we have a liner 18ftx18ft but what
about our overlap,lets not forget the 2 ft overlap, so we now need a flat sheet
liner of 20ftx20ft this gives us a pond of 10ftx10ftx4ft but it now has a 1ft
overlap on each side,so we can now see where most people can make a
simple error that can leave them with a liner that is to small for the pond,and
as liners purchased off the roll cannot be returned,as the supplier will end up
with a liner he will struggle to sell as it could be a considerable time before
somebody needs a liner of that size,tomorrow we will go through the fitting
process,
regards Paul
teesside koi