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 problems 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.
Shingles must be installed according to the slope of the roof
There is a category called “Low Sloped” roofs where wider shingles are used to help to shed water. Low Sloped shingles are no longer sold in Canada because with our snow and ice, they always allowed water in under the shingles.
Most Standard and Steep sloped roofs require 4 nails per shingle, properly placed. The manufacturer’s warranties also requires that the shingles are installed in a manner and under conditions that allow the self-adhesive strip of adhesive that comes on the shingle to effectively adhere to the loose end of the shingle tab above. If conditions do not allow that to happen, then there is no warranty on the shingles. It takes about 60deg C from the sun for the adhesive to melt and adhere – hence cold weather installation usually requires manual tabbing; applying a dab of glue under each corner of each tab. Most roofers avoid working in cold weather as they need to charge extra for the “tabbing”. Extremely dusty conditions could also prevent the self-adhesive from working and roofers should return to check if tabbing is necessary. Roofers rarely do that as it is a lot of work, but if it can be shown that the tabs were not adhered to the underlying shingle, there is no warranty. See this entry on the Self-Adhesive Strip.
When we get to the very steep or Mansard roofs, gravity will not work in allowing the self-adhesive to stick. On these roofs the manufacturers require for their warranty, 6 nails per shingle, and manually glue every tab under all conditions. This is rarely done, and hence manufacturers rarely pay out on warranty for Mansard roofs. All they have to prove is that the loose edges and corners of the tabs were not adhered to the shingle below; it is no longer the manufacturer's problem -- the warranty installation criteria was not followed. For a detailed research report on gluing down tabs, which includes the Mansard problems, click here.
Most shingles can be subject to problems -- there is no one bad manufacturer in the business
Even after you get the whole attic perfect, there have been many shingle failures over the years and several class action suits. This industry wide, but little talked about problem seems to be related to the extremely unstable supply of bitumen that all companies face. The bitumen used to make shingles is a by-product of the petroleum refining process. The shingle manufacturers have to test and adjust every truckload of their raw materials. That is a tough task for a mass production facility -- but that is the reality for our most popular roof covering, asphalt shingles.
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, 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.