Metal ridge caps: calculating quantities and comparing costs

It is worth comparing the measurement from the design with the state of the prepared structure. A small change in the width of the eaves or the position of the gable affects the final cuts. For a roof that is already covered, the line of the outermost sheets must also be checked. The ridge caps are to protect the actual junction, not merely reproduce a dimension from the old drawing.

Part of the ridge cap may be hidden under the next element. Therefore the total length does not always correspond to the section that the flashing will cover after installation. Catalogues sometimes give a separate effective length. It is this that helps compare consumption and cost. The overlap should not be reduced independently in order to limit material consumption.

For example, a section priced at €13.89 with a usable length of 1.90 m costs about €7.31 per usable metre. These figures illustrate the calculation. For an order, work out the number of sections using the joint specified for that profile. Allow for any cuts or end pieces needed at the ends of the run.

Straight, angled and rounded ridge caps differ in geometry and appearance. The choice should not be based on a photograph alone. The width of the cover, the pitch of the roof slope and the height of the covering profile are important. A wing that is too narrow may not properly cover the junction zone. One that is too wide can make correct fixing difficult.

Popular tile-effect metal roofing and high trapezoidal steel sheet do not create an identical space beneath the ridge. They need matched details. Do not force a finished ridge cap into shape if the cross-section clearly does not fit. An agreed change of angle or bespoke sheet metal flashings are more sensible than stressing thin sheet metal during installation.

In a roof with a ventilated space beneath the covering, the air must have a path from inlet to outlet. Ridge caps do not create such a path by their presence alone. Suitable battens, ventilation seals or other accessories intended for the covering may be needed. Their selection should be included in the ridge cost estimate.

Completely filling the gap with random foam may block the planned flow. On the other hand, leaving the junction entirely open is not a solution for protection against wind-driven precipitation. Ask how the detail combines air discharge with protection against water. This is decided by the documentation for the roof system, not by the lowest price of the accessory.

Ridge caps are made from galvanised, aluzinc and coated sheet metals. In every case the basis is steel, and protection is provided by the appropriate layer system. Aluzinc sheets have a metallic coating containing aluminium and zinc. Coloured coated sheets add an organic layer that is also responsible for the appearance of the surface.

Do not compare these variants by colour alone. Check the sheet thickness, the type of protection, the conditions of use and compatibility with the roof material. The same colour designations do not guarantee an identical gloss or texture. Ordering the covering and ridge caps together makes it easier to check consistency, especially with a large, visible ridge.

Terminations, fasteners, supporting elements and sealing materials may be added to the calculation. Transport and cuts must also be taken into account. A long section reduces the number of joints but is more difficult to transport and lift. Shorter ridge caps can be convenient on a complex roof, although they require more joints.

It is worth including verge flashings, gutter aprons and starter profiles in the same schedule. Chimney flashings are recorded as a separate detail. This makes it possible to notice missing parts before delivery. An apparent saving on a single profile quickly disappears if installation stops because one final flashing is missing.

Ask for a description of the cross-section, length, material, coating and number of pieces. Establish whether the price refers to a piece, a linear metre or the developed area. Two offers can only be compared once they have been brought to the same scope. The name ‘ridge cap’ alone leaves too much room for technical differences.

Before approving the order, check that the ridge caps are consistent with the covering documentation. Also confirm the method of delivery and protection of the surface. A well-calculated purchase ends with a complete set of components of the correct shape. The saving then results from fewer mistakes and corrections, not from limiting the required protection of the roof.