Cleaning a roof? Choose the right scaffold.

For this job the Altrex RS52 is the obvious model, the wide version with a working deck of 135 cm. When you clean a roof there is always more on the platform than you allowed for: a bucket of suds, a brush on a long handle, a coiled hose that goes everywhere at once and a sack for the moss you brush off. On a narrow deck you trip over that lot, and with wet soles you want half a metre of clear walking room past your kit.

Those 135 cm also help with the posture the job forces on you. You lean towards the tiles, push away from yourself and pull back, and then a deeper deck beats a plank you only just fit on. Working with two people, one rinses while the other keeps up with the gutter that silts up again during the clean. Which sizes are otherwise ready to go you can see in the range of mobile scaffolds for hire.

The slim RS51 at 75 cm stays in the picture when the only way round the back is a tight garden gate, because a tower that cannot reach its position is no use however wide it is. Reckon then on climbing down more often for materials, and on less room beside your bucket. The one person MiTower reaches 6.2 metres of working height and falls short at a two storey roof, while the RS44 room scaffold is an indoor model you would not hire for this.

For roof cleaning your measuring point is not the gutter but the highest place you still want to touch with your brush or lance. On most two storey houses that sits around the third or fourth row of tiles, which puts you at 8 to 12 metres. If you want to get further up the surface, you do not move the tower but use a longer handle, because walking over the tiles to shift growth is not a serious plan.

The sum is simple: take the height of your platform and add roughly 2 metres of reach, and you have the working height you state when you hire. For this work it pays to sit at the top of your range rather than land exactly on it, because cleaning with your arms stretched above your head is heavy and the rinse water then runs down your sleeves. The page on 12 metres of working height shows that build.

What goes wrong with a height chosen too low only shows once you are up. You get the bottom rows clean, but the row above them stays just out of reach and keeps standing out green against the rest of the roof. For that single strip you then rebuild the whole thing, or you hire a second time. Measure therefore from the paving or the terrace where your tower will actually stand, and not from the threshold of the back door.

On this job you choose the standing position twice: once for yourself and once for everything that comes down. Under the edge you are working on lands a mixture of water, moss and sand, and that looks for the lowest spot. A terrace with open joints, a border of perennials or the drive where the neighbour parks are therefore poor choices. Put down sheeting or an old dust sheet before you build the mobile scaffold.

Under the wheels you want ground that stays wet and still carries. Bricks and paving slabs are fine; grass that your own rinse water turns to mud within the hour is not. Think about the level difference between garden and terrace, about the room the four stabilisers need and about the hose running from the tap up to you. For ground that slopes or has settled, the explanation of levelling on an uneven surface helps.

Think about the surroundings too. Dirty water splashes further than you expect and growth off a roof leaves green streaks on white paintwork, on windows and on a fence. Warn the neighbours before you start, take the washing off the line and shut any open roof lights. Working on the street side, keep the pavement passable and sweep the grit up before it disappears into the drain. A bucket of clean water within reach saves you cleaning the elevation later.

Cleaning takes more days than people estimate, because the work goes in rounds. First you take the thick layer of moss off, then you rinse, then the gutter turns out to be blocked with everything you brushed into it, and then you go along once more to the spots that only show their state once dry. For an average pitched roof on two storeys that comes to three or four rental days, moving round the house and clearing up included.

There is a waiting day in the schedule as well. A treated surface usually has to dry before you can judge whether green is still sitting in the laps, and if you put a product on later you want a dry spell behind it. Set autumn weather beside that and you know a lost day simply happens now and then. So plan your rental period around a run of dry days and not tight against the weekend.

On this hire your first 24 hours carry the whole tariff, while each rental day you set behind them is discounted by 95 per cent, so an extra day of slack is cheap insurance against a shower. What you certainly do not want is to stop halfway up the roof, because a half cleaned surface reads visibly different from the rest and the whole street can see it. Working that out for a job that runs in rounds is covered in the length of your rental period.

Per position you have a working strip the width of your platform, so 245 cm of roof edge with the rows of tiles you can still reach above it. Finish that strip completely before you move: brush or rinse from top to bottom first, then scoop out the gutter below you, then check whether growth is still sitting in the laps. That way you never return to a spot you have already done, which saves you half a rental day.

What you take up with you decides how often you climb down. A hose with a coupling you can open and close from ground level saves climbing, and so does a bucket the loose moss goes into instead of the gutter. Lay the hose in a wide loop over the guard rail, because pulled tight along a standard it tugs at your arm with every move and across the deck it becomes a trip wire.

What people underestimate is the pace. The first two metres go quickly, and only then do you notice how much is really stuck to the tiles. The north side carries the thickest layer and costs you double what the sunny side does. So do not reckon with an average but with the heaviest side, and remember that the rinse water fills the gutter you then have to empty again, just as with clearing out a roof gutter.

The set arrives as loose, counted parts that you put together yourself. Decide in advance where on your plot that stack may lie and keep the spot clear of the strip where the rinse water will run, because parts lying in mud have to be cleaned twice. Anything booked on a working day ahead of 15:00 goes out for the following working day. Delivery and collection are arranged as one movement, on the dates you name yourself.

Putting it up is your task, with the supplied manual to hand and a video that shows the order step by step. Reckon on half a day of building work with a second pair of hands beside you. Because you choose both the delivery day and the collection day, you can line that choice up with the forecast: you clean a roof on a dry, still day, and you want the scaffold standing there the day before.

When you are done you take the build down and set everything out complete, after which we come and collect the mobile scaffold. Rinse the parts off before you stack them, because dried moss and sand on the decks are harder to shift later than now, with the hose already in your hand. Book that collection a day past the point where you expect to finish. What bringing and fetching costs you can see under the rates for delivery per province.

The decks of these mobile scaffolds sit in load class 3 under EN 1004 and carry 200 kg per square metre. On a clean you fill that faster than you think: two people, a bucket of water, a charged hose and a sack of wet moss add up nicely. Wet material weighs a multiple of dry material, so do not leave the sack of growth up there all day but lower it on a rope in between.

The ordinary rules stand and matter more here. Brake both pairs of wheels before you climb on, never move a build with a person or materials on it, and stop as soon as the wind picks up, because the mist off your lance then goes everywhere and you end up standing awkwardly yourself. After every reposition along the wall, check that the stabilisers make firm contact with the ground again, even if you only shifted two metres.

The real risk on this job is the slipperiness. A deck with a film of water, algae and grit on it is treacherous, so sweep it clean at the end of every strip and work in shoes that keep their grip on wet aluminium. Watch what happens below you as well, because grit and water come down and nobody should be standing there. The rest is set out in working at height without needless risk.