Installing a roof fan? Choose the right scaffold.

Take the RS52 for this installation, the one whose walking surface measures 135 centimetres across. The reason is plain: something has to be put down. A roof fan is a box tens of centimetres wide with a collar on it, and beside it you carry a flashing plate, a hole saw, a cordless drill, sealant cartridges and an extension reel. On a tight floor all of that ends up in your walking line. Which versions else stand ready sits on the page about mobile scaffolds for hire, builds per type included.

On top of that you hardly ever do this work alone. One person holds the unit while the other lines the collar up or feeds the cable through, and that has to happen side by side without anyone stepping backwards. At 135 centimetres there is room for it, toolbox between you included. The slim 75 centimetre version only enters the picture when the gateway to the back garden measures under a metre, and even then you give up bench space to get through it.

Note that the model is a different thing from the build. The model says how wide and how long your floor will be, the build says what height you come out at. The same RS52 can go up low for a roof fan on a garage and high for one on a house, so tick both deliberately when you reserve. Anyone who watches only the model sometimes stands a metre short on the first morning. Each type's sizes sit side by side in the explanation of dimensions.

The measuring point here is not the spot where the fan will end up, but the edge where you yourself stand working. If the penetration sits a couple of metres up the roof plane, that changes nothing about the height you reserve: you measure to the gutter or the roof edge beside your setup. On a two storey house that comes down to a build reaching 8 to 12 metres, taken from the paving the castors come to rest on.

That working height is made of two parts: the height of the floor you stand on plus about two metres of arm's length. For this job you want the floor to come out relatively high, because you would rather lift a roof fan over the edge at hip height than above your shoulders. A unit pushed up with straight arms hangs crooked and scrapes the covering you want to keep whole. So count back from gutter height to the floor height you want, and take the stance above rather than below.

Reserving too low therefore bites at the heaviest moment of the job. Stand half a metre short and you are balancing twenty kilos above shoulder height while still having to aim. Hiring a stance higher is no more than a tick box when you reserve; a damaged tile or a torn collar costs you a fresh run to the merchant. If in doubt, look at what belongs to a roof edge on the second storey before you choose.

Unlike work that runs along the whole roof edge, here you need one standing place, and you pick it with care. Put the setup as close as you can to where the penetration comes, and on the side the cable runs in. Usually that is the back or the flank beside the extension. Stand on the wrong side and you drag the unit across the roof or pull a cable straight through the house, and neither is a small thing to put right.

For that single spot the demands are stiffer than when you move often. It has to be level, still load bearing after rain and open enough for the four stabilisers to be wound fully out. Watch for a gully, a crawl hatch, the concrete rim of the terrace or the sloping wall of an extension. If the garden falls away, a tower on a slope tells you how to take that up without setting the build askew. Half a slab as packing is no solution; it tips at the first load.

Think as well about what belongs on the ground beside your setup. You want the unit dry and sheltered until it goes up, and you need power for the reel. So reserve, next to the foot of the build, a patch where a table or a pallet fits. If the setup stands on the street side, ask the council what is allowed on the pavement. You are in the same place for a few days here, and the neighbourhood notices that sooner than a build that shifts daily.

On paper this is a job of one day. In practice you reserve two to three, and that comes from the order of things. The first half day goes on building and on laying everything ready. Only after that do you saw the opening, set the collar, finish the covering and pull the cable through. The electrical connection and the final fitting nearly always land on the second day, certainly if a circuit still has to be freed in the consumer unit.

The hard rule on this job is that you do not leave the roof plane standing open. Saw the opening and you want it shut and watertight the same day. That means laying your opening day in a dry window and not starting when showers are forecast by midday. So the date you have the tower brought matters at least as much as the number of days you keep it. Look at the forecast first and at your own diary second.

Planning roomily is cheap with us. Only the opening 24 hours are charged in full; from there on a discount of 95 per cent runs on every further hire day. Building in a spare day for poor weather or for a cable route that disappoints therefore costs you next to nothing. Book too tightly and the van is at the door while you are still finishing off. Judging that period is covered under setting your hire period, and every rental price sits on the page with rates.

You have 245 centimetres of floor length at your disposal, and here you use it as a workbench rather than as a walkway. Lay the flashing plate flat on it, stand the unit next to that and keep the last metre free as an access zone. That way you need hold nothing in your hands while climbing up or down. On this job that is the main difference from a ladder, where everything you carry has to go under one arm and nothing has a place to stay.

Take the unit up last and not first. Sealant, collar, tools, cable and the fresh pieces of covering go up before it, and only when everything lies ready does the fan follow. Lift it with two people: one below passing up and one above taking over, or use a rope with a loop if the unit is heavy. Letting go above an open roof plane is not an option. Agree in advance who releases and who holds, so no discussion starts halfway.

What you do and do not do from a mobile scaffold is a matter of expectations here too. You work from the edge and across it, but you do not use the setup as a step for walking further up the roof plane. If the penetration sits higher on the slope, other equipment belongs with it, and you sort that out before you reserve anything. For that, read the explanation about a tower at a pitched roof.

Everything arrives loose and counted, so you decide yourself where the stack lies. Do not pick the place your unit and your reel will have to stand, because you need that room at the foot of the build. If your booking comes in before 15:00 on a working day, the delivery stands for the next working day. Which date that is, and when the parts leave again, is something you indicate while reserving, so the parts land when you can use them.

Assembling the setup stays with you. The manual supplied and the accompanying video show which part comes when; with two people the first setup stands within half a day. Clear that half day separately, because on your building day you almost never get to sawing the opening, however early you begin. For an installation where the roof goes open it also helps if the delivery day falls at the start of a dry run rather than at the end of one.

Once the fan turns and the opening is shut, you break the setup down and we drive out one more time to take everything away. Set the parts down complete and within reach, and count along while dismantling so nothing stays behind in the shrubs. What a trip out and a trip back to your address comes to is listed under the rates per province, so you take that item into your budget straight away.

The floor you stand on falls in load class 3 under EN 1004, which comes down to 200 kg per square metre. On this installation you add up faster than you think: two people, a unit, a battery set, a reel and a box with sealant and tools. Spread those things over the full length, because stacking everything at the access loads the same bay every time, and the access is exactly where you stand as well. Background sits under weight on a tower.

Beyond that the familiar agreements hold: brakes on before anyone climbs, no wheeling while a person or anything else is aboard, and stop when the wind gets up. That wind limit counts double here, because a loose flashing plate or a piece of roof covering catches wind like a sail. Walk the four stabilisers after every move. And bring the setup to a standstill the moment one of you hangs half over the roof edge.

With a roof fan two dangers come along that you do not have elsewhere. The first is the electrics: take the circuit off and check that before you touch a wire, and lay the reel where nobody trips over it. The second is the open opening: tools you put down on a sloping roof plane slide off and land beside the setup. Keep that zone clear and warn whoever is working below. The full list sits under working at height.