Risk assessments, part of the Health & Safety regs, are required by law, does not matter if the client is commercial or domestic, these need to be in writing if you employ 5 or more people, but it is considered good practice to have them written down regardless.
It is not enough just to have the written word as it were, you must also show that all staff adhere to the companies rules in these matters, this can take a number of forms, but the simplest is probably regular training, making sure that this is documented, then getting the staff to sign a document stating that they have recieved said training and have understood that training etc. These procedures also have to be regulary monitored, again in writing as the MD or owner carries full responsibilty in these matters under present legislation, hope this helps, regards.
Rob