VERB
给（屋顶、水管或水箱）装绝热层
If you lag the inside of a roof, a pipe, or a water tank, you cover it with a special material in order to prevent heat escaping from it or to prevent it from freezing.
例句
If you have to take the floorboards up, take the opportunity to lag any pipes at the same time...
如果一定要把地板掀开，不妨趁此机会给各个管道加一层隔热保护。
Water tanks should be well lagged and the roof well insulated.
水箱和屋顶都需要敷设严密的保温层。