What size fascia board do I need?

How do I measure the fascia I have?

Measure the timber board face from top edge to bottom edge, at three points along the run, and take the largest figure. Then measure the total length of every elevation.

Take the measurement from behind the gutter, not from the gutter itself. Lift a bracket if you have to. The top edge usually sits under the felt and the first tile batten, so hook your tape over the top and read down. Write each elevation down separately, because a bay or a dormer will not match the main run.

Cover board or replacement board?

Cover board goes over sound timber and is 8mm thick. Replacement board replaces rotten timber outright and is 16mm thick.

The test is a screwdriver. Push it into the timber at several points, especially at the rafter ends and behind the gutter. If it sinks in, the timber has gone and capping it only hides the rot. Cover board is faster and cheaper, but it relies on the timber behind it to hold the gutter brackets. Replacement board is stiff enough to carry brackets itself once fixed back to the rafter feet.

What width fascia board do I need?

Take your measured timber width and go to the next size up. Never go down.

Boards are stocked at 150, 175, 200, 225, 250, 300 and 405mm, in 5m lengths. Old timber fascia is usually nominal imperial: 6×1 is around 150mm, 8×1 around 200mm, 9×1 around 225mm. Sawn timber varies by several millimetres and may have been planed, so measure rather than assume. On a cover board, allow 10 to 25mm hanging below the timber edge to hide it cleanly.

What thickness should the board be?

8mm for a cover board, 16mm for a replacement. There is no useful middle ground.

16mm is the structural one. It takes gutter brackets, holds a straight line over a 5m run and does not dish between rafters. 8mm is cladding. It looks the same from the ground but it follows every hollow in the timber behind it, so pack the low spots before you fix.

Fascia board sizes and fixing figures

Item	Figure	Note
Cover board thickness	8mm	Over sound timber only
Replacement board thickness	16mm	Carries gutter brackets itself
Widths stocked	150, 175, 200, 225, 250, 300, 405mm	Both types, 5m lengths
Common existing timber sizes	150mm, 200mm, 225mm	6×1, 8×1 and 9×1 nominal
Board width to choose	Next size up from the measured timber	Never a size down
Cover board drop below the timber	10 to 25mm	Hides the old bottom edge
Fixing centres	Every rafter, 400 to 600mm	Two fixings per rafter on 16mm board
Nail length	50mm cover board, 65mm replacement	Stainless colour-head only
Expansion gap	10mm per 5m length	Hidden by the joint trim
Gutter bracket spacing	1m maximum	150mm each side of a joint or outlet
Gutter fall	3mm per metre	Towards the outlet
Wastage to order	5 to 10 per cent	Higher on hips and dormers

What happens if the fascia is too narrow?

You get a gap behind the gutter, open straight into the eaves. Wasps, birds and rain all find it.

The fascia has to reach up under the felt and tile batten. Too narrow and the top edge stops short, leaving a slot along the whole run. It also leaves the old timber edge showing above the new board, which is the giveaway of a rushed job. Going one size wider costs a few pounds a length and is always the cheaper mistake.

How many boards, joints and corners do I order?

Divide each run by 5m and round up. Add one joint trim per butt joint, and one corner trim per external or internal corner.

Add 5 to 10 per cent for wastage, taking the higher figure on a roof with dormers or hips. Leave a 10mm expansion gap at every 5m length and let the joint trim cover it. If you are refitting gutter at the same time, brackets go at 1m maximum centres, 150mm each side of a joint or outlet, with a fall of 3mm per metre to the outlet.

Do I need scaffolding to fit fascia?

Above single storey, yes. Fascia work puts you at the roof edge holding a 5m board with both hands.

Ladders and roof edges are where people get badly hurt in this trade. Hire a tower or a scaffold, and work in pairs on full lengths. Every roof is different, and gable ends, bays and conservatory abutments all change the answer. Ring us with the measurements and we will tell you straight what the job needs.