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Simon do you have a ground guy? i know you were looking into the workmans comp insurances, so I will assume you do not have someone working the ground.
There are payroll companies that you can use to handle all the payroll and it includes workmans comp. etc. BUT make sure they understand completly that your employees will be on the ground and never on the roofs or ladders. this will keep it down significantly, BUT if they are going to on the roofs, you need to carry the right insurance so your covered. It will be a big selling point as well.
Google payroll companies in your area and it should get you what you need.

In the mean time cover them with some light painters plastic sheeting, water them before covering them, during to keep the sheeting cool, and after kinda heavy.
You really need a ground guy or some serious advice from one member here Chuck Bergman out of Charlotte Fl. He works alone and has it down to a science.
I would prefer a ground guy over solo, but it can be done.

Kim R