Plastic soffits and fascias are moulded uPVC lengths that are installed over the rafter ends of a roof assembly to create a finished aesthetic look. For typical lengths off the shelf, they are 10mm thick, and come in a variety of different widths and finishes.  

The drawings display the end of the rafter as we left it having framed the roof. The timber was installed, level with an appropriate upstand above the top of the rafters in relation to the tile. A seat cut was then made to remove the waste of the rafter on the underside of the timber backer. The bottom of the backer board has been installed so that it is 10mm above the top of the external masonry. For our plastic, the first step is to install the soffit on the underside of the backer board. Due to the 10mm upstand, the 10mm thick plastic will sit flush on the underside of the backer, and hard down on the external masonry. It is then pegged down onto the masonry with a small batten fixed to the rafters. Alternatively, a soffit ladder may be installed as previously discussed to take the soffit. This ladder is level with the bottom of the backer and sits against the external masonry. In this instance, a starter trim is installed onto the batten that receives the end of the soffit. The soffit itself may be a length of flat, or multiple sections of hollow T+G soffit. Flat soffit is good for straight runs, and is joined by a small piece of H trim. Hollow soffit can also be used for straight runs, but is also very good for framing out soffits around angles such as bay windows.  

With the soffit installed, the fascia can be installed. The soffit must be installed first, as the fascia features a 1” lip that hooks over the underside of the edge of the soffit, creating an aesthetic edge, as well as covering the fixings that hold the soffit in place. The lip also supports the soffit in place over time. The fascia is pinned to the timber backer with polytop nails. The fascia typically comes in 5m lengths, and I find that 500mm even spacings for the fixings work. Depending on the overall width of the fascia, 2 fixings are placed at the outermost quarter points. I've seen many people overlook this detail - as its not really seen. Its hidden by the gutter. I like to be thorough though. When the roof is tiled in, a tile vent is installed on the top of the timber backer. The internal width of the soffit should be no more than around 10mm less than the distance from the underside of the backer to the bottom of the tile vent- as you might see the gap from the ground. A 10mm gap should be left between two lengths of fascia, to allow for expansion. The gap is covered by a straight joiner trim that is cut down to length and fitted. 2 nails on 1 side of the joiner hold it in place with silicone behind 1 side. If nailed both sides, or stuck both sides, expansion can cause the fitting to snap. A corner trim is fitted at the corners in the same manor. 135 degree fittings are available when trimming around bay windows. The timber backer and soffit ladder should be straightened before plastic installation to give the plastic a flat finish. With the plastic installed, the gutters are ready for installation.  

The same materials are used to clad barge ladders. The soffit is installed up the barge ladder, fixed to the ladder rungs and outer timber. A length of fascia capping is then installed over the face of the barge timber. For slate roofs, the plastic should extend a few millimetres above the top batten on the roof, to enable the slate to slit flat down on top of the plastic. For regular tiled roofs that feature muckwork, the plastic sits a few mm above the timber barge, so that the cement board cloaking sits on the plastic. As such, barge plastic is typically installed before the tiles. That being said, we may choose to leave off the regular fascia and soffit to prevent damage occurring during the tiling stage.