If the puddle is against the house it could give you issues with damp walls but from what you say this problem has existed for at least 7 years since you moved in.
You must either stop the puddle forming by raising the patio (but not above the damp course of course) or by building a barrier between the garden and the patio (but rain will still fall and make puddles) - or - change things so that the water may drain away - a builder might find the low point in the patio and install a small drain connecting to the house drains - this may contravene the building regs though. You may wish to drill your own drain away holes in the patio at least 12mm and through to the substrate - fill with pea grit. Could drill a hole through the built up part of the drain but this too may be against regulations.
The elegant way is to excavate a soakaway at the lowest point 600mm square and about the same deep - fill with rubble and gravel and put a drain in the middle - make good around the drain hole.
I would start with drilling a few holes at the lowest point - much easier and it may be a solution. Then dig a small trench at the edge of the patio and fill with gravel to act as a gutter.
Alternatively - lay a new patio that slopes towards the garden - at the junction, plant water-loving plants.
Richard Buxton
September 2008
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