The Re-Use Of Second-hand Roof Slates & Tiles

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As a leading commercial roofing contractor we are often asked about the viability of stripping off the existing roof coverings, salvaging those which are in good condition, making up any shortfall with second-hand roof slates or tiles and then reinstating them.

This may be for budgetary reasons but often it is because we are working on buildings of architectural merit such as churches or listed buildings. It is hoped by reusing the old slates or tiles the character of the building will be maintained.

Challenges and Considerations in Salvaging Roof Tiles and Slates

When roof tiles/slates are suitable for re-use it is usual to be able to salvage around 50% of them. This is because tiles/slates which have been cut to the various roof details, cannot usually be reused. On top of that, a large number of tiles/slates are inevitably broken during the process of stripping them, moving them to the scaffold or onto the ground for storage and then reloading and reinstating them. If the roof has a complex design, with lots of dormers, windows, hips and valleys, there will be a much higher than normal number of cut tiles/slates and therefore the likely number of tiles/slates which can be salvaged will be lower.

A further difficulty with re-using the existing tiles/slates, will be making up any shortfall, which for the reasons we have described above, could be more than 50% of the overall requirement.

Matching and Sourcing Replacement Tiles and Slates

It is important that any tiles/slates brought in to make up the shortfall, should match the existing, particularly on listed buildings, period buildings or on buildings of architectural significance or merit. This is usually done by obtaining second hand tiles/slates from an architectural salvage yard. However, the chances of finding a sufficient quantity of tiles/slates of the same manufacture/quarry, colour and weathering, is all but impossible. More likely is that the tiles/slates will come from a number of different sources and rather than blending in seamlessly, will create an unsightly patchwork. A further complication in this regard is that the tiles/slates used to form the roof perimeters are usually mechanically fixed or bedded in mortar which makes them much harder to salvage. This means that more of these tiles/slates are broken when they are stripped off. Consequently when it comes to finding matching salvaged tiles/slates there are less of these particular specialist tile/slates available in salvage yards. Often the only option is to use brand new tiles/slates which will stand out and be even more unsightly.

Re-holing Second Hand Roof Slates

A further complication with second hand slates is that they will all need to be re-holed before they can be re-used. The original slate holes should have been 25 – 30mm from the edge of the slate to give enough strength. The new fixing holes must be brought inside the original fixing by the same amount, towards the centre of the slate. This is a total of 50 to 60mm from the slate edge on either side of the slate. This brings the new fixing holes closer to the ‘angle of creep’. If the fixing holes enter into this area the roof will leak. As a general rule, slates narrower than 10 inches or 250mm, cannot be re-used. Slates which have been re-used already cannot be re-used again.

Assessing Existing Roof Tile and Slate Lifespan

In most cases, the existing roof tiles/slates are very old and they have often already exceeded their life expectancy. It is often stated that slate and clay are natural materials which take millions of years to form and that therefore they should easily be able to last the life of the building. What this fails to address is that the slates and tiles have been quarried and processed and then left exposed to the elements, experiencing thousands of freeze thaw cycles, gales and hail storms, acid rain and other pollutants for many decades and sometimes a hundred years or more.

Some materials, like Burlington grey and green Westmoreland slates may occasionally provide the exception that proves the rule. But in general, in our view, it would be a false economy to try and re-use second hand slates and tiles.

Guarantees and Value of Second-Hand Slates/Tiles

Finally, second-hand roof slates and tiles cannot be guaranteed, whereas new tiles/slates, which will overcome all of the above issues, will come with a manufacturer’s/quarry product guarantee, guaranteeing their performance for years to come.

Second hand tiles and slates do have a value and they can still be used for repairs or small extensions. Therefore we would suggest that the client states that an allowance must be shown in the tender return for the cost of selling any salvaged slates/tiles or other materials.

This article, as with all other articles we produce, is for guidance purposes only. It does not constitute formal advice and should not be relied upon as such. For bespoke, unbiased advice relating to your commercial roofing project please contact us and we would be pleased to assist.

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