How to compare the cost of a metal roof with other coverings

Prepare a single roof drawing with dimensions of the roof slopes, chimneys, windows, roof valleys and ridges. Give every contractor the same scope of work. If one offer includes flashings and guttering, while another only covers laying the roofing, the totals are not comparable. A missing item does not disappear from the build. It usually comes back later as an additional cost.

Separate the work necessary in every variant from that which results from a specific material. Repairing damaged roof trusses may be needed regardless of the roofing chosen. A different batten spacing or required sheathing is a feature of the given system. A well-detailed cost estimate shows this difference and allows you to understand where the price change comes from.

For metal sheeting, a distinction is made between the total and the effective area. Part of the sheet is taken up by overlaps. The price per total square metre may look favourable, even though a square metre of finished roof slope costs more. For the module, check the coverage area of one piece. For roof tiles, the number of elements per metre required by the given model and batten spacing is needed.

Offcuts are added to the roof slope area itself. Their size depends on the roof geometry and the way the material is laid out. Do not assume a single waste percentage for all variants. A simple roof slope can be efficiently covered with sheets cut to length. On a roof with numerous hips, a modular tile-effect metal roofing layout may be more advantageous. The cutting plan decides, not the product name alone.

Metal roofing is usually significantly lighter than roofing made of concrete or clay tiles. During renovation, this may matter for the existing structure. However, it does not by itself allow the roof trusses to be considered sufficient. Snow, wind, insulation, installations and the condition of the timber and connections must also be taken into account.

The cost of any reinforcement should result from the structural engineer’s assessment. Do not add it in advance only to the heavier material if there is no such need. Nor omit it for lightweight metal sheet when the roof trusses are damaged. The comparison should concern two safe, complete solutions. The weight of a single square metre alone is not a full calculation.

Ridges, corners, roof valleys, chimney flashings and eaves strips can form a significant item. Ventilation elements, roof access and snow guards are added if needed. A roof with a small area but many folds may require more work than an extensive simple roof slope. That is why the installation price per metre does not describe everything.

In every quote, check the fixings, seals and the method used for roof penetrations. For modular tile-effect metal roofing, components matching its geometry are required. For trapezoidal steel sheet, flashings and fixings must be matched to the profile. A random substitute may reduce the amount on paper but make detailing and subsequent servicing more difficult.

Long sheets require planned access, unloading and safe lifting. Smaller modules are easier to carry individually but have a different method of packaging and laying. With heavier materials, the organisation of deliveries onto the roof slope can be important. Ask who provides the scaffolding, the lift and the securing of the area around the building.

When replacing a roof, add dismantling, disposal and temporary protection of the interior. Establish how the contractor accounts for damage revealed beneath the covering. If the old material contains asbestos, its removal requires the proper procedure and a suitable contractor. These costs should not be hidden in the general rate per square metre of the new roof.

Set the net or gross price consistently throughout the table. Check the date of the offer, the delivery conditions and its validity period. Record works excluded from the scope separately. If you use a price list, confirm the unit as well as the coating and thickness of the material. A catalogue price need not be the selling price nor cover the same services as a contractor’s offer.

Finally, compare the conditions of use: inspections, availability of parts and the possibility of local repair. Do not attempt to predict one certain number of years of durability without knowledge of the environment and the workmanship. The choice should combine the cost of the complete roof, the appearance and the technical requirements. Such a calculation is more useful than a ranking of the cheapest coverings based solely on the price of the sheet.