How does a roof stay waterproof, especially in the Seattle/Redmond area where there's a lot of rain?
The trick to keeping a home waterproof and protected from the elements, at least in terms of the role your roof plays, it by creating multiple redundancies. That is, when one ‘layer’ (figuratively and literally) fails, the next layer can be expected to do its job. In short, there is the outer roofing material (shake, composite, synthetics, etc.), a waterproofing layer usually made of a plastic sheeting specifically design for roofs, and a plywood layer under that.
Shakes, in particular, deteriorate with time. The constant heating, cooling, raining, drying, freezing and baking will break down almost any material on Earth. The trick is to make a roof able to withstand an optimal level of weathering. You could cover your roof with brass, and it would certainly last a long time, but it would obviously cost a fortune. What’s more, new synthetic materials are coming onto the market all the time, ones that look just like shake, but are far more durable thank natural shake, yet will take quite a beating from the elements.
Even natural shakes will benefit from a good treatment of preservatives, and today, there are excellent ‘green’ alternatives to the old heavy chemical treatments roof used to get. They will soak into the shakes and give them a far longer life than just raw, untreated shakes would get. In many respects, the treatments you apply to whatever roofing materials you choose are more important than the materials themselves. OK, so that’s the outer layer.
The waterproofing layer immediately under the outer, material layer
When you do decide to get your roofing re-done, it’s worth watching how it’s done. After all, you are living under that roof – perhaps for the rest of your life – so it’s good to know how this job if done. Right under the out layer you can see, there is a protective, waterproof plastic layer. It may not actually be plastic, as new alternatives are coming onto the mater every year, which must have some particular characteristics. Most important, it must be able to be pierced with roofing nails without its waterproof character being compromised. That means, when the nail comes from the shake, through the waterproof material and into the plywood, it must be resistant to ripping or decaying at the point of contact, while still resistant to water when it comes.
Anywhere the waterproofing material meets an edge
Did you know that those standard shipping containers all have tiny holes in them? It’s to make sure they eventually sink in the sea, should a container ship sink and leave containers floating on the open wave. Those tiny, imperceptible holes are barely big enough for a sewing needle to fit through but, over time, they can fill a container so it will sink. In the same way, the tiniest leak in a roof, if water reaches it, can draw a lot of water through it over time. That’s why every little detail on a roof’s waterproofness is critical. And where the roof meets a protrusion like a chimney, a skylight or another side of the roof must get particular attention during the re-roofing process. It’s where one ‘edge’ meets another that is often the most likely source of a leak.
North versus south-facing side of the roof
The Puget Sound brings with it different challenges for the roofer than does, for example, Albuquerque, New Mexico. The sheer level of moisture here has to be taken seriously. Moss and certain molds can eat away at a roofing material in a way that would never happen in other parts of the country. In Seattle, for example, because of its northerly latitude, it’s high levels of precipitation and often a dense copse of trees around a house, it’s not uncommon for one side of the roof to never get direct sunlight. Direct sunlight is one of the best killers of mold and other fungus, so when there is none, mold can continue to grow unabated for years. You’ve probably driven or walked past one of those houses that are completely covered in trees, and have a side of the roof eaten up with moss.
Keeping a roof moss-free, followed by treatment, will extend the life of your roof considerably. Let’s say your roof costs $25,000 to replace. Every few years, you can spend a few hundred dollars to wash and re-treat your roof. This can double the length of the life of your roof, and consequently save you a bundle. It’s also a great way to discover potential leaks that can be fixed for a fraction of the cost of waiting until your kitchen ceiling collapses in during breakfast when Aunt Mildred is here to visit her nieces and nephews.
Check back next week!