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E2 – Roof Coverings

December 3, 2010

E2 – ROOF COVERINGS is the second element inspected during an RICS Homebuyer Survey.

The surveyor will look very closely at the roof, even using a pair of binoculars to focus in on important details. A poorly maintained roof will have serious implications for roof timbers, internal finishes and the cost of future maintenance. The lack of visibility of some parts of the roof will often result in a Condition Rating 3 – Further Investigation being given for this element.

Failure of a roof will tend to occur at roof junctions where different materials or roof slopes intersect. I would be looking at the quality of the flashings, ridge and hip tiles, valleys and around chimney stacks where the stack passes through the roof covering. The type of roof covering is also very significant as each one tends to have its own strengths and weaknesses.

The four most common pitched roof coverings in North London are natural and man-made slates, clay and concrete interlocking tiles.

Natural slates

Natural Welsh slate roofs are synonymous with the Victorian period. Primitive railways and canals were used to transport large quantities of slate cheaply to the expanding urban centres of England.

Ferrous nails have corroded and slates have slipped

There are several different types of slate so be careful. Welsh slate is regarded as the best quality and most expensive. It has a more uniform grey colour with fewer impurities. Its superior quality will allow it to last for a good 100 years, depending on thickness, orientation and roof slope.

The slope of a slate roof is important because the greater the slope the quicker the rain will discharge. Flatter roof slopes will become prone to frost damage and growth of moss and algae. Moisture ingress may also corrode the ferrous nails which secure the slates to the roof batterns. Shiny metal straps (called tingles) are a sign that the roof is in need of an overhaul.

Finally, if you do have a worn out Welsh slate roof, “push the boat out” and try and replace it with the same type of slate. It will be expensive, but the new slate roof will sell the house on its own! Splitting the roof into sections (main roof and back addition) and recovering over a number of years can help spread the cost.

Man-made slates

This roofing material is inferior in every respect to the natural slate descibed above.  Although man made slates might be a great deal less expensive, after about 10 years the roof will begin to weather and become bleached by the sun.

There is some evidence that these slates will last 30 years but their life expectancy is considerably shorter than the natural slate. As a general rule a natural slate roof will look better with age, while the man made version will deteriorate.

Clay tiles

Clay tiles found on Edwardian houses usually have the name Dreadnought, Rosemary or Acme stamped on the underside. Rosemary tiles are supposed to be the best quality. 

All the spalled tiles were quickly replaced during roofing work

In contrast to slates that are individually nailed, clay tiles are nailed every 4th row. This means tiles can be replaced individually rather than the whole roof being just chucked in the skip!

There are some people who believe it makes good economic sense just to replace an original clay tiled roof, rather than to carry out localised repairs. This is folly in the extreme. I know a roofing contractor who regularly puts 300 year old tiles back on roofs!

An original clay tiled roof should be repaired and not replaced for two reasons:

My roofing spares taken from skips

 1. Adhoc repairs can easily be carried out with secondhand tiles;

2. A well maintained old roof will retain a property’s authenticity, the very ingredient that makes the property unique and valuable.

Surveyor’s Tip:

Keep a good supply of secondhand clay tiles stored somewhere safe in the back garden. They can be used, when required to replace broken or missing ones. Once the spares are on the roof, they’ll be nicely weathered and so wont look too out of place.

Don’t buy secondhand clay tiles, all mine came from skips! Keep a look out for houses in your area that are being re-roofed, the roofer will skip perfectly good tiles for new ones.

Concrete Interlocking Tiles

I was told once that the reason why we have so many concrete interlocking tiled roofs on older properties was due to improvement grants made available by local authorities back in the 70s.

Apart from being hidious in the extreme they have lead to slender roof timbers of older houses distorting and spreading under their considerable load. Since they were part paid for by local authority grants, the workmanship and quality are often very poor.

There’s only one good thing about another house being re-roofed with concrete interlocking tiles…it makes my Welsh slate and clay tiled roof slightly more unique and slightly more valuable!

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