How to Set Up a Rotary Laser for Setting Out a Foundation

Get a foundation wrong and you don't find out until the brickwork starts telling you. A footing that's 20mm out of level across a corner means packing courses, arguing with the bricklayer, and a job that fights you all the way to the wall plate. Using a rotary laser for setting out a foundation is the simplest way to stop that happening — but only if you set it up properly. Here's how we'd do it, start to finish.

Why a rotary laser is the right tool for setting out

A line laser is brilliant indoors, but out on open ground it runs out of legs. A rotary laser throws a level plane through a full 360 degrees, so one instrument in the middle of the site serves every peg, profile and trench around it. Pair it with a receiver and you can pick the beam up in bright sunlight at serious range — our G60 rotary laser kit works out to 400m diameter with the LR1 receiver in the box, and holds 3mm at 30m. On a house footprint, that's tighter than anything else you'll get set up in five minutes.

Setting out with a laser level also means one person can do what used to take two. No holding a staff while someone squints through an optical level and waves at you. The receiver beeps, you mark, you move on.

What you need before you start

Before the laser comes out of the case, get your kit together:

• The rotary laser, a solid tripod, and a levelling staff with a receiver — the G60, G70 and G80 kits all ship with tripod, staff and receiver included
• Pegs, profile boards, a lump hammer and a sharp pencil
• Stringline — pink or yellow shows up best against spoil
• The drawings, with your datum level and foundation depths marked

You also want to know where your datum is. That might be a manhole cover, a benchmark on an existing building, or a peg the engineer left you. Everything on the job gets measured off that one level, so find it before you do anything else.

Setting up the laser

Plant the tripod on firm ground — not on backfill, not on the spoil heap — somewhere with a clear line of sight to the whole foundation. Middle of the plot is ideal. Tread the feet in properly. A tripod that settles halfway through the morning will quietly shift your levels, and you won't know until it's cost you.

Get the tripod head roughly level by eye, mount the laser, and switch it on. A self-levelling rotary like the G60 sorts itself from there and starts spinning. Give it a few seconds to settle. If it's knocked hard enough to go outside its self-levelling range, it'll alert you rather than carry on giving out a duff plane — which is exactly what you want it to do.

Now clamp the receiver to the staff, walk to your datum, and sit the staff on it. Slide the receiver up or down until it reads on-grade, then lock it and note the staff reading. That number is your site's magic number: it's the height of the laser plane above datum. Write it on a profile board, because you'll use it all day.

Transferring levels to pegs and profiles

With the plane established, the rest is legwork. Drive a peg near each corner of the foundation, hold the staff on top, and read the receiver. The difference between that reading and your datum reading tells you exactly how much higher or lower the peg is. Tap it down or mark it until every peg carries the same level — most groundworkers mark the peg and cut to the line rather than chasing the peg top itself.

Set your profile boards behind the trench lines, level the crossrails off the laser the same way, and string your lines between them to mark the trench edges and wall faces. The strings give you position; the laser gives you level. Between the two, the digger driver has everything needed to cut a trench that's right first time.

For the trench bottom, work out the dig reading: datum reading plus the depth of dig below datum. Drop the staff in the trench as the excavation comes down, and when the receiver reads that number, stop digging. Same trick for the top of concrete — one number, checked in seconds, anywhere on the footprint.

If the foundation needs a fall

Most house foundations are dead level, but drainage runs, driveways and some raft edges want a designed fall. That's where a grade laser earns its money. The G70 dual-grade rotary lets you dial a slope into the plane itself, and the G80 does dual slope on X and Y with a green beam that's noticeably easier to find in flat light. Set the grade once, and every reading on the receiver already includes the fall — no calculating offsets at every peg.

Check it before you trust it

Two minutes of checking saves a week of grief. Before you set out anything structural, do a quick two-peg check: take a reading on a peg close to the laser, then on one at the far end of the site, then swap the laser to the other end and read both pegs again. If the difference between the pegs changes between setups, the laser needs calibrating — book it in rather than hoping. And re-check your datum reading after breaks, knocks, or any time the tripod might have been clipped by a barrow.

The right kit for the job

Setting out a foundation with a rotary laser isn't complicated: solid tripod, settled laser, one datum reading, and a receiver on a staff. The method above will see you through strip footings, rafts and slabs alike. If your kit's the weak link, have a look at our rotary laser range — the G60, G70 and G80 all come as complete site-ready kits with tripod, staff and receiver, with free UK delivery over £100. Buy once, set out right first time.