Fiberglass shingles without the SBS polymer may be fine in certain situations--generally they seem to perform better in warmer climates as opposed to our northern climate, and they are better suited to new construction applications as opposed to re-roofing situations.
Since the fiberglass shingle is essentially lighter weight and thinner, the shingle by its very nature is not well suited for re-roofing because it cannot hide the imperfections of the older roofing shingles beneath it, thereby creating a more irregular and less pleasing finished look to the overall roofing job.
Additionally, since it is constructed of a thin fiberglass matt, it tends to be more brittle than the fiberglass with SBS product. This allows for fracturing or cracking to take place more easily in colder climates. This can occur during installation in cold weather or due to the weight of snow and ice if the shingles lie on an irregular surface. Neither of these specific problems is covered in the manufacturer's warranty.
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