A vital element of any construction contract is a clearly defined scope of work.
In house building, scopes of work are not commonly used and there is a heavy reliance on quotes to establish the extent of the work. Good contractors (and suppliers) will include a list of exclusions with the quote and rely on terms of trade to carry the legal aspects of a contract. This is lazy and always leads to arguments when work or goods are not executed to the expected standard.
A good Scope of Work document will reinforce to your contractors that your company is also a professional business and clearly understands its quality standards. It will also ensure there is consistency across multiple contractors carrying out the same work.
It also serves as a legal document once the terms have been agreed upon.
Once completed, a scope of works reduces the amount of time spent by estimators explaining the extent of work required when chasing quotes from multiple contractors. It also assists when disputes arise with contractors regarding workmanship, extent of the work and variations to the contract.
Engaging any sub-contractor without a scope of works is like jumping in a cab and then not telling the driver where you want to go. He can choose whatever he wants.