How to fit uPVC fascia boards: cover or replace?

Should I cover the old fascia or replace it?

Replace the board if the timber behind is soft, damp or rotten. Cover it only if the existing timber is dry, solid and straight.

That one decision sets the cost and the life of the job. A cover board is 8mm thick and depends entirely on the timber underneath it. A full replacement board is 16mm, goes on after the old board comes off, and carries the gutter brackets itself. Some merchants quote replacement board as 18mm; ours is 16mm. Cap over rot and you hide the problem for about three years. The gutter then pulls away with your fixings still in it.

How do I tell whether the existing timber is sound?

Push a screwdriver into the board behind the gutter, at the ends and at every joint. Sound timber resists the blade. Rotten timber takes it to the handle.

Check the rafter feet, not just the fascia face. Water running behind a failed gutter rots the last 100mm of rafter first, and that is exactly what your fixings have to bite into. Black staining, spongy edges and paint flaking off a soft core all mean replacement. A cupped or twisted board is a replacement too. A cover board follows every hollow underneath it and shows every one from the pavement.

What size board do I need?

Measure the depth of the existing fascia and take the next size up. Boards run 150mm to 405mm wide in 5m lengths.

A cover board must be deeper than the timber it hides, or a strip of old board shows along the bottom edge. Measure at three points along the run. Older fascias are often two different depths on the same elevation, especially where an extension was added. Order 5 to 10 per cent over your measured length for offcuts, corners and mistakes.

What are the sizes, centres and gaps?

Item	Figure	Note
Fascia cover board	8mm thick, 5m long, 150-405mm wide	Over sound, straight timber only
Fascia replacement board	16mm thick, 5m long, 150-405mm wide	Carries the gutter brackets itself
Fixing centres	500mm maximum	Two nails per point, top and bottom
Edge distance	25mm minimum from ends and edges	Pilot within 50mm of a board end
Nail length over sound timber	50mm	Through an 8mm cover board
Nail length, replacement board	65mm	Through 16mm into the rafter end
Expansion movement	About 1mm per metre, so 5mm per 5m board	Allow it in joints, not at fixings
Joint trims	300mm, or 600mm double-ended	One at every butt joint
Corners	External 300mm, internal 300mm, external 135°	135° is for splayed bays
Wastage allowance	5-10 per cent	On top of measured run length

How are the boards pinned on?

Two nails at every fixing point, at 500mm centres maximum, 25mm in from ends and edges. Use colour-head stainless nails only.

Galvanised and bright nails rust and streak the board inside one winter. Use 50mm nails through an 8mm cover board into sound timber, 65mm through a 16mm replacement board into the rafter end. Stop driving when the head touches the face. Going further dimples the board and pins it against its own expansion, which is what causes the ripple you see on badly fitted runs. Pilot any fixing within 50mm of a board end. Where you have let in a new timber noggin, screws hold better than nails.

How do joints and corners work?

Every butt joint takes a joint trim and every change of direction takes a corner. Leave roughly 5mm of movement in each.

Joint trims come in 300mm and 600mm double-ended versions; which suits depends on your board depth and how exposed the run is, so ring us if you are unsure. Corners are external 300mm for the usual 90° return, internal 300mm where two elevations meet, and external 135° for splayed bay ends. Dry-fit the corner, then cut the boards to it. Cutting the board first and hoping the corner covers the gap does not work. A rigid angle trim tidies the abutment where a fascia dies into brickwork.

Does this job need scaffolding?

Above single storey, yes. Ladders and roof edges are where roofline fitters get hurt, and a 5m board makes a ladder considerably worse.

A 5m board catches wind like a sail. This is a two-person job at every height. Use a tower or scaffold on anything above a single-storey garage or extension, and never lean a ladder on uPVC gutter. You cannot see the state of the eaves until the gutter and old board are off. Perished felt, missing over-fascia vent support and rotten rafter feet all change the job at that point. If you find any of them, stop and ring us before ordering more board.