house doctor Peter Fall goes up on the roof to look at potential problems above our heads.
THERE is nothing like a cold snap with a coating of snow and strong winds to test the upkeep of our homes.
Many of our building materials are porous, which – contrary to popular opinion – is quite a good thing. Our bricks and stones absorb the rainwater in wet periods and dry out again in dry periods. They get a bit tested when we have a wet spell followed by a hard frost because the freezing water expands inside the material and, if it can’t cope, it snaps and breaks off.
Bricks and stones don’t often suffer from frost attacks but roof tiles can be vulnerable. Roof tiles, as opposed to slates, are made of clay or concrete. Roof slates are made from a laminate of natural rock, which is not porous.
Under normal circumstances the clay and concrete roof tiles absorb only a small amount of water. The rainwater and melting snow mostly runs off the roof into the gutters. Over the years, however, the top surface of the tiles tends to erode, so some of the water soaks into the tile. Under normal circumstances this is OK, as once the rain stops the tiles dry out again. However, the older and worn tiles don’t dry out as quickly. Therefore, if we have a hard frost, such as that of last weekend, they become vulnerable to damage.
Bricks and stone are so porous that the expansion caused by frost can usually be accommodated but roof tiles are quite thin and brittle, so they tend to snap. This snapping usually happens just at the point where they tuck up under the tile above, which makes the crack difficult to see. Indeed the damage can go un-noticed for weeks. It shows when either there is a strong blow or a coating of snow. Roof tiles, being loosely fixed, will move about in a strong wind. If a tile has snapped, the strong wind will rattle the loose tiles down the roof.
Similarly with snow, as it melts the snow slides down the roof dragging the tiles and pulling any snapped tiles away. Eventually you find the bits of tile in a heap where the snow landed when it dropped off the roof.
So does it matter if a tile snaps? Some of the more modern tiles have very little overlap, indeed they rely on each tile interlocking with its neighbours to stop water seeping through. If one of these snaps you will quickly see a hole and probably find water leaking in.
The older plain clay tiles however have significant overlaps. If one of these tiles fails it may not seem so bad. When you look up there’s no visible hole in the roof finish as the two tiles underneath butt up tightly against each other. Unfortunately water will still seep through at the gap so it’s important to keep an overlap. Don’t leave it until the spring, get it fixed now.
One broken or missing tile may also be the cause of more damage when the wind starts to blow. The wind will move the tiles about even when all of them are in position.
Once one is missing, the two adjacent tiles will be free to move. This shuffling around puts a strain on the nail fixings, which are probably part rusted, and before you know it the adjacent tiles also fall off and the domino effect starts.
If you quickly sort out one defective tile, you might have put off an inevitable big cost for a further 5-10 years.
If you are one of that small band of people looking to buy a house, you might think about the roof finishes. No doubt you will glance up at the front roof when you stand back and admire the property. But you should also take time to stand back and look at all of the other elevations. Don’t just rely on what the roof looks like, think about the age of the building. If it is more than 50 years old, the tiles and their fixings are reaching the point where regular repairs should be expected. Ask the vendor when they last did any roof repairs. If the roof is more than 80 years old then start to think re-roofing and how can we defer the inevitable. Regular repairs will help but eventually it reaches the point when you bite the bullet and re-roof. Ouch!
Peter Fall is former president of the Royal Institution of Chartered Surveyors. He is managing director of Clear Building Survey, tel: 0800 072-9003 www.clearbuildingsurvey.co.uk
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