How to fit composite fencing

Do I need aluminium posts, or can I reuse my concrete posts?

Both work. A new run goes on Nova aluminium posts. Existing concrete posts are kept by screwing a U-channel adaptor to the face of each one, which gives the boards a slot to drop into.

Reusing concrete posts saves the digging, and the digging is most of the labour. It only works if the posts are sound, upright and close enough together for the boards to reach. Measure the clear gap between post faces before you order anything, and measure every bay, not one. Old 6ft timber panels sat at 1.83m centres, which is close to right. Posts set wherever the ground allowed are the problem: one bay at 1.9m and the boards will not span it. Concrete posts that rock, or have blown at the base, come out. No adaptor fixes a bad post.

How far apart do the posts go?

Set the posts so the clear gap between them is roughly 60mm less than the board length. A 1.8m board wants about 1.74m of clear gap, leaving around 30mm of board held in each channel.

Confirm the board length on the product page and work from that figure, not from the fence you took down. Run a string line first, get the two end posts and any corner posts in, then divide the run into equal bays. Take the shortfall on the last bay and cut one board down. Do not stretch every gap by 20mm to make the maths work. Composite does not flex to cover a mistake, and a board that only sits 10mm into a channel will drop out in the first gale.

How deep do the posts need setting?

For a 1.8m fence, dig 600mm deep and about 300mm across. Put 100mm of gravel or hardcore in the bottom for drainage, then set with fast-set post mix, one to two 20kg bags per hole.

Posts must be plumb on two faces and dead in line with the string. Brace them while the mix goes off. Fast-set is hard in 20 to 40 minutes, but do not start hanging boards the same hour. Leave it overnight. A composite fence weighs considerably more than timber panels and it takes wind like a solid wall rather than a lapped panel, so the posts and the concrete are doing real work.

Two planning figures worth knowing: a fence is limited to 2m without planning permission, and 1m where it adjoins a highway. Ground levels vary along most runs, so if your garden falls away, ring us before ordering post lengths.

How do the boards go in?

Boards slide down the channels from the top, one at a time, working upward from the bottom. Each board interlocks with the one below it.

Start the bottom board first and check it is level, because every board above copies it. Leave a few millimetres of end play so the board is not jammed hard against the back of both channels; composite expands and contracts along its length with temperature. Once you are three or four boards up, a full bay is heavy and awkward to lift over the top of a post. This is a two-person job from that point on, and it is where people trap fingers.

Count the boards on the first bay before you order the rest. Twelve 150mm boards give roughly 1.8m of height, but the interlock loses a few millimetres per joint and the starting section takes up some of the drop.

What are the starting and finishing sections for?

They close a run where there is no post, typically against a house wall, a garage or an existing brick pier. The board ends slot into the section and the cut edges are hidden.

Fix the section plumb to the wall with suitable masonry fixings before any boards go in, because the boards feed into it. Where a run meets a building at an angle, or steps down a slope, this is where the job stops being standard. Measure it, photograph it and ring us rather than cutting boards to a guess.

What figures should I work to?

Nova composite fencing: working figures. Confirm sizes on the product page before ordering.

Item	Figure	Note
Board size	1.8m long x 150mm high	Check the listing for the run you are buying
Clear gap between posts	Board length less approx. 60mm	About 30mm of board in each channel
Boards per 1.8m high bay	11 to 12	Count the first bay before ordering the rest
Post hole	600mm deep x 300mm across	For a 1.8m finished height
Gravel at hole base	100mm	Drainage
Fast-set post mix	1 to 2 x 20kg bags per hole	Brace until set
Cure before loading boards	Overnight	Not the 30 minutes on the bag
End play per board	5mm total	Do not jam boards tight
Maximum height without planning permission	2m (1m next to a highway)	Measured from ground level
Wastage	5%	More on a stepped or angled run

What usually goes wrong?

Three things: posts set out of line, the bottom board not level, and boards ordered before the first bay was built. All three are measuring faults, not fitting faults.

Set out the whole run with a string line and a tape before the first hole is dug. Build one complete bay, count what it took, then order the balance. If your ground slopes, steps down, or the existing concrete posts are at odd spacings, that is a job worth talking through with us on the phone. Bring your measurements to the counter and we will work the quantities with you.