Plumbers and Heating Contractors
There is often an overlap in expertise between plumbers and heating contractors. When installing, servicing, or maintaining a gas- or oil-fired furnace, they must have the relevant county and state certification/licensing. If you do not have experience in working with gas or propane piping, hire a professional. For general plumbing work such as installing tubs or toilets, the law is less exacting but most often also requires state or local licensing. Always find out what is required by your area before you hire one of these specialty trades.
A general contractor may be the best choice for project management. He can schedule the job, coordinate the various trades, and communicate on your behalf with everyone involved in the project. If you are employing an architect on new building work, it may be best for them to project-manage. If the size of job warrants a professional project manager, be certain of their credentials based on proven experience.
Usually, roofers only deal with roof coverings, such as tiles, shingles, felt, and finishing and any mortar work on the roof. A carpenter will deal with any structural elements. Large companies have carpenters working with the roofers. Smaller firms subcontract out structural carpentry. Roofing bids or prices can be complicated. If weather delays work, this can have effects such as increasing the price of scaffolding rental. On large jobs, a roofer may actually scaffold over the top of the house and provide a waterproof "tent" so that work can continue in most weather. This increases cost and is only worthwhile on larger jobs. Check samples of materials, such as tiles and felts, before they are bought and make sure your choices are specified in writing.
Excerpted from Do It Yourself Home Improvement
© Dorling Kindersley Limited 2009