A properly laid felt roof will last for up to 25 years or more – or so they tell us. In all likelihood though, it will begin to show signs of wear long before that. There could be many reasons for it, but for your average flat roof, the presence of water during the year, and the buildup of ice in the winter, can slowly tear a roof apart. It doesn’t mean you got a bad deal when the roofing service company installed it, it just happens at some point.
What should you look for then? Well, the obvious places where damages (and hence leaks) could occur, is anywhere two sheets of felt are joined together. Typically, more than one layer of felt is used to lay a roof, which means ther will be overlapping sections. Sometimes the edges, or often corners, will start to lift from the layer underneath, which allows water to seep in. If any water is still there come winter, then it will freeze, which means it expands, which again could lift the felt further off the underlying layer. If this process goes on for a few years, you can probably imagine that there will be some damage.
There are also some vulnerable spots around the parapet which is often constructed around the perimeter of the roof to make it look completely flat from the outside (you often see garage roofs done this way). The felt here will often have to be laid with great care, as there are some tricky details – which always means a higher risk of errors in the work. You should check the drip edges that sometimes hang into the gutters, as these can become brittle with time, and simply break off. If that happens, some of the underlying wood in the overhang could become exposed and damaged over time.
It can be difficult – if not impossible in most cases – to tell from the outside if a felt roof is leaking. You should always do a thourough check of the underside of the roof, which means inspecting the underlayment, basically. If water leaks through the roofing felt, it will not run directly down the underlayment, as often it can’t due to the felt still being well adhered in most places. Instead, it will slowly creep around the surface of the underlayment where it can, or just stay put in a small puddle, never drying up completely. This is a bad situatin which can lead to serious damage of your roof. If your underlayment is plywood sheets, you won’t actually see the damage until the water eaches the edge of the sheet, and at that point it could have been years that the decay has been going on. I recommend to always use 1×4 inch planks of wood for underlayment, simply because any water coming in, will find the cracks between the planks faster, and will be visible soon after the leak has been created. If you are having a new roof built, be sure to ask for this in the roofing quotes you get.
