T18 or T35 on the same roof? How the profile changes the order

Record the depth, cover width, thickness and steel grade. Confirm the laying direction and suitability for roofing. Compare the two profile drawings side by side to see how geometry affects weight per unit of cover and the side lap.

Consider a T18 sheet covering 1.128 m and a 35 mm profile covering 1.050 m. These figures describe only the two example products. Across a roof 10.60 m wide, you need ten runs of the first or eleven of the second. Round up to the next full sheet.

Ten T18 runs cover 11.28 m and eleven runs of the second profile cover 11.55 m. At a sheet length of 6 m, the ordered cover areas are 67.68 m² and 69.30 m² respectively. Both options require an edge cut. Include that difference when comparing the two prices per square metre.

A deeper section often has more favourable section properties, but the full geometry and gauge determine the result. Check the exact product for the loads, support arrangement and fixings. Each load table applies to the section specified in it.

Compare load capacity and deflection. The designer also checks areas subject to higher wind loads and the connections to the frame. If the supports are already installed, verify the proposed replacement against their actual layout before changing the design.

T35 casts deeper shadows, particularly at eaves, edges and on façades. T18 gives a finer pattern, although rib width and colour also affect the result. View samples from the usual viewing distance to judge how a large roof will look.

Match flashings and seals to the actual section. Profile fillers in particular must follow its shape. Check the manufacturer’s instructions for pitch and end laps for the chosen product.

Count sheets, list lengths and establish the actual billed area. Include flashings, fasteners, seals and delivery. If the designs require different supports, price these too. The result shows whether a higher sheet price can be recovered elsewhere in the roof assembly.

Compare like coatings and gauges or identify the differences explicitly. A price premium may pay for the finish as well as the deeper profile. If the frame is already in place, a wider permissible support spacing may offer no saving on this job.

Check how the new profile height meets existing gutters and walls. A refurbishment may require different flashings. Add that cost even if the roof area and number of supports stay the same.

Select a variant that meets the structural and roof requirements. Check the cutting layout and appearance, then agree the full specification, accessories and unloading method. Keep the exact profile drawing for checking deliveries marked only with an abbreviated name.

At delivery, compare shape, markings and lengths with the approved schedule. Confirm compatibility before substituting a similar sheet for a missing one. Even a small difference can prevent the side lap from fitting and complicate future maintenance.