Firstly what do you currently have? Polycarbonate is a clear or tinted sheet, usually thin enough to bend easily by hand. The tints come in a  variety of colours such as dark tint, grey and even yellow depending on what brand you are buying.

If you have a thicker ‘milky’ sheet (either in a flatter style trimdeck or corrugated sheet then this is more likely to be fiberglass gel coat style. Other telltale signs are thicker construction so it’s harder to bend by hand as well as as it ages you can see the fiberglass strands even sometimes to the extent of finding fiberglass in your gutters. These are very popular on commercial buildings or where a stronger application is necessary.

Now you know what sheeting you have or want, let’s look at whether it is appropriate. Do you have an existing structure? What is the slope of where the sheets are to go. For any polycarb sheeting 5 degrees is the recommended minimum. That works out to around 90mm fall over a 1 metre length.

Longest spans for polycarb sheeting

Like most roof structures, polycarb sheeting needs to be attached to purlins. These can take the form of wood battens or metal tophat. For a standard situation (non storm area) N3 rating the following spans are fine.

Corrugated 800 mm End Spans and  1000 mm Mid Spans

Greca 900 mm End Spans and 1200 mm  Mid Spans

Trimdek 900 mm End Spans and 1200 mm  Mid Spans

Cutting

We can cut sheets to length for you free of charge.  Otherwise, sheets can be cut using a fine tooth circular saw, a jigsaw, or even with a good pair of scissors.  When using power tools you will need to clamp the sheet as close to the end as possible to stop vibration. Remember to allow for some overhang to ensure that water from the sheet will fall into the gutter and not onto your structure.

Movement

All materials expand and contract when they heat up and cool down, and polycarbonates move more than most roofing materials. This means that it is important to allow the sheet room to move a little after it has been installed.  This is easily done by following a few rules.

Firstly, drill an over-sized hole in the sheet for the screw fixing. Both Clearfix and OneShot branded screws have cutters embedded on the screw to save you time in completing this step – they cut the hole when you put the screw in.

Secondly, by allowing a small gap between the ends of sheets and where they might come up against another object – like a wall fascia. This isn’t as important on the barge sides as the majority of the expansion will occur along the length of the sheet.

Silicons

As a rule – they are not recommended.  Silicons can act as an adhesive which can stop the sheet from moving (see above).  Some silicons can also affect the chemicals in the sheet which protect it from UV radiation.  If you can’t avoid it use a neutral cure or non-acidic silicon sparingly.  Be sure not to put it along the length of the sheet where you will see the most expansions and contraction.

Accessories

Purlin tape can be used to stop creaking of the sheet with expansion and contraction. As the name suggests it is applied to the purlin prior to installing the sheet, and acts as  buffer.  It is particularly useful with painted purlins, where in hot weather the paint can become tacky and cause the sheet to stick and make more noise as it expands and contracts.

Flashings are used to seal the edges of the sheet.. There are a few different types that are common. Ridge capping is used to flash a gable at the peak of the roof. Barge Flashing is used on the sides of the structure to cover the edges of the sheet and sometimes protect the timber structure underneath. And Apron Flashing is used to seal between a vertical wall or fascia and the roof itself.  You can get a number of these flashings in polycarbonate or have them manufactured in metal.

That’s it. Just about everything you need to make an informed decision. If you have any questions or you are interested in a specific product let us know. We’ve been installing patios for nearly 20 years so there’s not much you can ask that’ll make us scratch our heads.