Roofing materials

There are two main types of material available for roof cladding: fibre cement or steel, each with several options for finish.   Each has its advantages and disadvantages for different applications

Fibre Cement Cladding

Originally manufactured from asbestos, the fibres are now a mixture of synthetic material and natural products such as cellulose combined with portland cement and binders.   (You will hear comments that the new material "is not as good as asbestos", while it is marginally weaker it does have the benefit that the people who make it and work with it have now considerably less chance of dying in agony which makes it considerably better in our book).

The fibres and cement are mixed to a slurry with water and a sheet formed by squeezing water out as the material passes around a drum before being moulded into a corrugated profile.

What happens next determines the strength and characteristics of the product.   Semi compressed products are stacked and cured under their own weight- the initial thickness of the material is approximately 7.5mm and it finishes after curing at around 6mm.   A fully compressed sheet comes off the drum at 9mm and is subjected to massive pressure during the moulding process, removing more water and producing the final thickness of 6mm approx to give a stronger material with lower water content.

Eternit and Cembrit supply semi-compressed products, the only fully compressed roof cladding sheet suitable for the UK climate is manufactured by Landini and distributed by Briarwood.   All three of these manufacturers produce quality roofing materials with interchangeable profiles, tried and trusted in the UK, and we are proud to offer the full range: the choice is yours.

Fibre cement sheets are available in a range of colours and finishes: "Natural" is the unpainted cement grey which can also be supplied painted in a standard range of dark blue/black, green and brown supplemented by "accent" colours (depending on manufacturer) if you really want them.   Additionally a range of colour washed sheets which have pale pastel shades are available at less cost than painted sheets

The major benefit that fibre cement cladding has over steel lies in the fact that it is vapour permeable.   Water which has condensed on the inner surface is absorbed and evaporates from the top surface preventing dripping and reducing humidity inside the building.   Condensation is caused when warmer humid air comes into contact with a cooler surface and the water vapour condenses into droplets on the inside face of the roof and wall cladding.   The droplets then run down to the nearest purlin, coalesce and drip drip drip drip.   High humidity is common in farm environments such as livestock buildings and grain stores with drying floors.

Other advantages are corrosion resistance and freedom from maintenance.

The disadvantages are that installation is a little trickier (but not insurmountably, courage mon brave!) for the amateur builder, the cost is higher especially if a coloured finish is required and that they do not respond well to a knock (for example during tipping in limited headroom), instead of denting the whole sheet will shatter.

Steel Cladding

Steel cladding (aka box profile, wrinkly tin etc) has a galvanised sheet steel as a substrate which is then given a polyester base coating (usually in grey) before being top coated with either Plastisol or Polyester. Polyester is a tough heat cured paint finish (like a radiator) whereas plastisol is a much thicker vinyl coating with a textured (leathergrain or scintilla) finish. Both are available in a wide range of colours.

A guage of 0.7mm is necessary for roofing whereas 0.5mm is used for side cladding.   There is a huge range of profiles available which can be difficult to match if you wish to extend later.

Steel roofing is very susceptible to condensation so should be avoided where high humidity is expected, however it is fine for machinery stores, hay and Straw barns etc where its advantages of lower cost and easier fixing can be happily exploited.

Condensation is much less of an issue for side cladding as the water drips off the tail of the sheet outside, steel is frequently used for this purpose even in live stock buildings and crop stores as its strength and ability to dent rather than break offer important advantages over fibre cement.

You will encounter claims that a steel roof will corrode quickly when laid on steel zed purlins, however we have seen many examples of such roofing with no difficulties at all and we believe that high condensation levels are necessary before this is a problem.

A relatively new material is steel roofing with a so called anti condensation coating.   This is a slight misnomer as condensation still occurs as before but the absorbent nature of the lining holds the moisture to prevent it running and dripping.   We wouldn't recommend this product for high humidity buildings but for workshops and general storage it is an advantage.

The advantages of steel cladding are cost, smart appearance, ease of fitting and breakage resistance.   The disadvantages are condensation and the need for occasional maintenance to get the maximum lifespan.

Other materials

Other materials such as slate, tiles and even green roofs are entirely possible but more expensive, contact us if you have a particular requirement.

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Copyright Paul Richmond 2012