As I look at my own database, I see that I have almost 100 answers to specific questions about roofs and roofing. Despite a good search engine, that much scattered information can get confusing. Let me make just a couple of overview statements to help guide you in getting your existing or new roof to work -- and then give you a link to the best "consumer's guide to roofing" I have found.
The roof is a whole system of elements, not just shingles or membranes
To only think about shingles as being your roof is a serious error. There are many cases where people attempt to stop a leak by repairing the roof or even changing all the shingles, only to discover that the problem was under-the-roof condensation of moisture coming up from the house through the ceiling. Yes, very large ice deposits can be found in attics that had nothing to do with leaks on the roof above.
You must not think about the roof, but the roofing system over your home. The “roofing system” actually starts with the drywall of the ceiling below, then the air and vapour barriers, then the insulation, then the ventilation, then the roof deck, then the underlayment, then the flashings and finally the roof covering like shingles or membranes. Got the point? If you only work on the top layer, you could be ignoring a lot of festering problems.
The attic must be inspected and dealt with before re-roofing
Most credible roofers will walk on a roof and test for soft spots, rotted decking, and plan to replace some of the deck before giving you an estimate for the job. Unfortunately it is rather rare that a roofer actually inspects the attic, looking for signs of problem and indications as to where there is condensation in the winter or leaks through the roof – and then if they are tracing leaks, are they coming from nail holes associated with shingles, or with flashing problems. If a roofer gives you a quote from a standing on the ground visual inspection, it is highly likely that you are going to have problems with the job, either in “unexpected overcharges” or poor performance.
An OVERVIEW CONSUMER course in roofing
Although I love to give you specific answers to specific questions, for a really comprehensible consumer course in roofing, roofing choices and hiring a roofing contractor I highly recommend that you spend several evenings reading through a web site offered by a Montreal roofing contractor but one that has done us all the great service of using his wide experience to lay out the overview without simply making a commercial for his own business. In addition he covers all roofing possibilities with great insight -- helping you to choose what is right, or not right for your roofing system. Check out www.consulting.PRSroofing.ca. I wish I had written something this good myself, but Paul has done such a great job that I have to give him the nod.