"sarking" means: Wood, felt, or other material placed under the shingles of a roof or behind the outer leaf of a wall in order to provide support or insulati.... This is a fairly neutral word with no inherent risk attached. There is no real cause for parental concern; it is descriptive vocabulary rather than something dangerous. If your child uses it, context will usually make the meaning clear. A brief, curious question about where they heard it is generally enough to know whether to follow up.