FEMA reimburses fixed-price and cost-reimbursement contracts, and time-and-materials contracts only in limited cases. Cost-plus-percentage-of-cost and percentage-of-construction pricing is prohibited.
You must oversee every contract to make sure the contractor performs to its terms. Time-and-materials (and time-and-equipment) contracts are used only for a reasonable period until you can define the scope of work.
For time-and-materials contracts, daily or weekly logs or records of performance meetings showing oversight. Source: PAPPG Table 15.
Convert time-and-materials work to a fixed-price or unit-price contract as soon as the scope is clear. The longer it runs, the harder it is to defend.