What to include when costing a new roof

Prepare a roof plan, its cross-sections and a description of the layers. The lengths of eaves, ridges, roof valleys and side edges are needed. Mark chimneys, roof windows and service penetrations. The floor area of the house is not the roof area. For a quote, the developed area of the roof slopes counts, and for an order also the way the sheets are divided and their laps.

For a renovation, an assessment of the existing roof structure is added. Bent battens, damaged timber or the need to correct the eaves can change the cost more than the choice of coating colour. An inspection before the quote allows these works to be named. An offer based only on a photo of the building should clearly state what has not yet been checked and what the contractor may charge extra for.

Check whether the price refers to a square metre of total sheet or of covering area. These quantities are not interchangeable. Part of the sheet disappears under the lap, and offcuts arise at valleys and corners. For tile-effect metal roofing cut to size, ask for the sheet layout. For the modular version, the number of panels and the area they actually cover are needed.

Two T18 sheets may have a different effective width, thickness and coating. Comparing profile names alone therefore leads to wrong conclusions. In the comparison, record the designation, nominal steel thickness, type of protection and colour. List separately the surcharges for non-standard lengths, minimum order, transport and unloading on site.

For the covering you need components at the eaves, ridge, gables and roof penetrations. Appropriate fasteners, seals and ventilation accessories are added. Price the gutters as a complete system with brackets, outlets, pipes and clamps. The length of the gutter alone does not say how much draining water from the building will cost.

If the attic is heated, include insulation and the layers responsible for airtightness and protection against moisture. PIR boards can reduce the required insulation thickness, but they do not replace a correct detail design. In an outbuilding, a roof sandwich panel may be the solution. Compare its cost with the entire system it is to replace.

Ask for the labour to be broken down by scope. Installing the sheet metal alone is a different service from demolition, substrate repair, making flashings and installing drainage. Establish who provides the scaffolding, equipment for lifting the sheets and waste removal. The quote should also indicate how works that could not be determined before exposing the structure will be settled.

The price per square metre for installation is only useful when roofs have a similar geometry. A simple roof slope requires less cutting than a roof with dormers. Roof valleys and chimney flashings also take more time. In the contract, record the acceptance standard, payment deadlines and the documents handed over after completion. This lets you compare specific services.

Simple geometry and good order planning help most. One correct measurement reduces the need to reorder small items with separate transport. On a regular roof slope, cut tile-effect metal roofing can give a favourable sheet layout. With many breaks, it is worth comparing modules. The result depends on the project, not on a general opinion about a given material.

Do not reduce the sheet thickness, the number of fixings or the scope of flashings on your own. Such changes can impair load-bearing capacity or tightness. It is better to compare two complete variants with the required parameters. Choosing a different colour while maintaining the required protection is a different decision from omitting an element responsible for roof safety.

Create a single table covering material, accessories, transport, equipment, labour and disposal. For each item, record the quantity, unit and price. Check whether the values are net or gross and how long the offer is valid. In a renovation, leave a reserve based on identified risks. Set its amount after inspection, not according to an arbitrary percentage.

Before paying a deposit, confirm the full specification and the delivery date. Attach the agreed sheet layout and the list of flashings to the order. When comparing offers, clarify every missing item. A cheaper estimate is advantageous when, for that amount, you receive a complete roof with the assumed properties, not just its visible layer.