On a hot day our kitchen cold tap, if it hasn't been run for a while, will produce water at a temperature up to around 50-55 degrees C shortly after it is turned on. We haven't measured the exact temperature, but it's too hot to keep our hands in it.
Our house is only a few months old, so we had the plumber check the cause (in case the hot water pipes were too close, or similar) but the heat just appears to be from the ambient heat in the ceiling space, which the water pipes go through. I believe the plumber has since put some lagging around the pipe, but it hasn't prevented the problem.
Adding extra insulation around the pipe will obviously reduce the severity of the problem. What is the best type of insulation to use, and are there any techniques I can apply to get the best result? Is there anything else (within a sensible budget) that we can do?