Question

Why are exposed water pipes lagged with straw during severe winter?

Answer 1

• When water freezes it expands, as opposed to practically all other liquids. (For this reason ice fortunately forms on the TOP of ponds and lakes.) The expansion causes pressure to build up that could eventually burst the pipe.

• However, most water pipes burst because, as the ice builds up in the direction of the pipe, the water pressure continues to build up downstream from the growing volume of ice, that is between the ice and the faucet's.

• (Water pressure does not appreciably increase upstream as there is much more water on this side.) This enormous buildup of pressure can eventually cause the strongest of pipes to burst. It is a good idea to leave a faucet dripping if the pipe leading to it is in danger of freezing.

• Not only does this significantly reduce the chance of the water freezing in the pipe, but it keeps the water pressure from building up to dangerous levels that can cause bursting.