Managing material price risk in fixed-price construction contracts

We signed a fixed-price contract for a school extension eight months before construction started. Since then, prices for reinforcement steel, insulation and electrical cable have risen sharply, eating most of our margin.

For future bids we are considering price adjustment clauses linked to published indices, early procurement of critical materials and shorter validity periods for quotations. Clients in the public sector have limited flexibility. How do contractors in your market protect themselves against material price volatility?