The biggest challenge when you need to repair some of the roofing material on an old roof, is matching new material to what is already up there. What do I mean? Well, suppose you have a beautiful old clay tile roof, with a number of tiles having been broken or torn off in a storm recently. The old tiles will have acquired a certain weathered look, both from exposure to the elements, but also from algae, dirt and other discolorations. It can be hard enough to match brand new tiles to that look. On top of that, there is another, bigger problem – if you care about the visual match of the tiles: Burnt clay tiles tend to look different from batch to batch. This is due to slight differences in the composition of the clay used, tiny differences in oven temperature and moisture in the clay, etc, etc. The clay tiles simply come out looking a little bit differently between batches. This might not be a problem, if you could just buy an entire batch and do your whole roof with that, but mostly the batches are broken down into smaller portions, packaged separately and often shipped to different buyers. What is normally done then, to get an even look across a roof, with only slight deviations in color and texture, is to mix and match between several packs of tiles, when installing them. The tiles will still differ, but the difference will be evened out over a large area, making it seem less obvious. Obviously, if you want to retain that look using new tiles on an old roof, you may need to go through a couple of packs of tiles to finds the best match. Sometimes it is even harder than that, if the tiles you have on your roof are no longer made in the exact same way. You will have to either go hunting on the second hand market, or accept a slight mismatch with a new tile. A good tip to avoid this situation, is to keep a pack or two of tiles, when you replace the entire roof or put up a new garage with a new roof. Then you will always have a stash of the original tiles handy in case of repairs.
The problem of matching is probably most prominent with clay tiles, although slate can also differ in looks, depending on what quarry it comes from. Again, keep some shingles in store for later use. If you need to replace old corrugated steel sheets or plastic ditto, then perhaps you may want to simply replace the whole roof at once. Certainly with plastic, once you start seeing breakage and brittleness, it is a good sign that all of the sheets are near the end of their lifespan. Steel sheets may be a different story. I have seen cases more than once, where zinc-plated steel sheets were rusted to bits in a single corner of the roof, due to a tree close by dripping water on that spot and preventing drying. The rest of the roof was fine. Rust can also occur if the roof has been dented or scratched deeply, as the zinc-plating may have been removed, leaving the raw steel exposed. You may get away with replacing a sheet or two, but if the roof is very old, you may again have a hard time finding matching sheets.
For new roofs or complete replacements, there is more freedom. Of course, what you put on the roof depends on the strength of the trusses and rafters that are to carry it. A construction designed to carry plastic roofing sheets will not take kindly to being loaded with slate shingles – in fact, it will probably collapse. However, you may get away with replacing one heavy material with another – such as replacing slate with clay tiles, or vice versa. Just make sure the weight per square foot ends up being approximately the same. Always consult a trained construction engineer if in doubt at all. A foolproof thing to do, would be to replace heavy roofing materials with lighter ones, such as plastic roofing sheets instead of fiber cement shingles.
This was part 2 in out little series about garage roofing. In part 3, we will look into the roofing itself – some do’s and dont’s. See you next time!