Fibre cement, steel or plastic: how to compare roofing materials

Fibre cement sheets constitute a mineral covering, and the finished assembly may require additional layers. Likewise, the sheet metal alone is not the equivalent of an insulated sandwich panel. A comparison is only valuable when both solutions provide a comparable scope of protection and comfort. Also take into account the required service life of the building. A temporary site cover and the final roof of a house should not be given the same weights in the comparison criteria.

A lighter sheet may be easier to handle, but it does not determine the whole roof’s resistance to wind or snow. Calculations and the correct arrangement of fixings are needed. A heavier covering may require a different assessment of the existing structure during renovation. Asbestos-free fibre cement must be calculated taking into account overlaps and accessories, not solely the nominal mass of a square metre of sheet. In every material, the length of the element and site access also matter. Narrow access, lack of storage space and manual transport can change the installation cost more than a small difference in price per square metre.

Fibre cement is not subject to the corrosion characteristic of steel sheet. That does not mean the whole roof is resistant to every aggressive atmosphere. Fasteners, flashings and purlins require separate selection. Steel, in turn, may have various protection systems whose properties must be checked for the given environment. Fibre cement sheets are also not immune to impacts and support errors. Plastics differ in composition, coatings and behaviour over time. A reliable comparison concerns specific products and conditions, instead of attributing unlimited durability to an entire category.

The mineral structure of fibre cement may temporarily absorb moisture and affect the sound of precipitation. That does not guarantee a dry or quiet interior under all conditions. Fibre cement sheets work together with ventilation, insulation and the layers on the room side. Likewise, a metal roof with a suitable layer arrangement need not behave like uninsulated sheet metal over an open shelter. When comparing acoustics, ask for results for the specific assembly. When comparing condensation, define the temperature, humidity and method of air exchange. Material names alone will not replace this information.

Translucent elements can reduce the need for artificial lighting during part of the day, but they also introduce separate requirements. Their profile, support, thermal behaviour, tightness and safety in use must be checked. They are not a fibre cement sheet, even when they repeat the same corrugation. Asbestos-free fibre cement can be combined with daylighting only in a solution whose conformity has been confirmed. A large amount of light is not always an advantage if it causes glare or overheating. The arrangement of the strips should follow the function of the interior, not the wish to replace a random row with a cheaper element.

A similar profile does not justify the use of identical holes, clamping or support spacing. Different materials may react differently to temperature and point load. Fibre cement sheets require the clearance provided for in the system and correct fixing. The sheet metal instructions are not instructions for fibre cement, and the recommendations for one plastic do not cover all translucent sheets. Include these differences in the cost estimate. If the contractor proposes one method for every option, ask for a reference to the documentation. A team’s versatility does not mean the detail is universal.

For one client, the most important thing will be the absence of a metal covering surface in a difficult environment. For another, it will be mass during renovation, and for a third, daylighting of a hall. Fibre cement sheets can be a good choice with a suitable design and maintenance. There is no need, however, to declare them the winner of every comparison. Draw up a short list of requirements: function, structure, moisture, fire, light, service access and the cost of the complete set. Then check specific solutions under the same conditions. This approach allows you to choose a material for the building, instead of adapting the building description to a product chosen in advance. In the quotation table, it is worth leaving room for missing data. An unfilled box is a signal to ask a question, not a reason to enter a favourable assumption.

Ask for a comparison of complete variants for the same roof slope. Also record which requirements are met by the material alone and which only by the entire roof assembly.