Fitting a dormer window? Choose the right scaffold.

The wide Altrex RS52, 135 cm across the uprights, is the obvious pick here. On this work you are forever taking material up that will not go in a pocket: a roll of lead, strips of zinc, a two metre fascia board, a box of screws and a sealant gun. All of it has to lie somewhere without being in the way and without rolling off the edge. A broad working surface is then the difference between getting on with it and climbing up and down all day.

If you are working in a back garden reachable only through a narrow gate, the 75 cm RS51 may be the only option. Reckon on going down more often in that case, because you can set almost nothing beside you. For a short fixing job on a small box that can work out perfectly well; on a wide dormer with a lot of zinc you would rather have the room. Both widths appear where you hire a mobile scaffold for outdoor work.

Think about who is going up with you as well. Laying lead is a two person job more often than not: one holds the soaker in place while the other dresses it and fixes it. Two people shoulder to shoulder on a 75 cm floor is unpleasant once tools are lying there too. The exact figures per model are set out in the size comparison of the towers, so you know beforehand what will fit.

The highest point you have to reach is not the ridge of the box but the top of the fascia board and the corners where the cheeks meet the roof slope. Over two storeys that point sits somewhere near 7 to 9 metres above ground level, and on a property with a floor more it is nearer 11. That is exactly why you pick inside a band of 8 to 12 metres for this job and tune the build to your own tape measure rather than to a rule of thumb.

Remember when you book that the working height quoted is where your hands come, not the level of the floor you stand on. Between the two sits about 2 metres of reach. If you want to drive the top screw into the fascia at 9 metres, the deck that belongs with it is around seven. Where the box sits in the roof of a second floor, that sum lands you in the upper half of the range on its own.

Choose too low and you finish the seam with your arms stretched above your head, which is the worst thing you can do with lead and sealant: you cannot see what you are doing and your strength has gone. Stand too high and you spend the day bent over work at your feet. The deck sits best just under the bottom rail of the box, so the junction lies at hand height and you can also judge what you have made.

A dormer has three sides that want attention, and you notice that in where the tower ends up. Most people start square in front of the box, do the face and the bottom junction there, then move left or right for a cheek. So choose your pitch such that at least two of those positions are reachable without a fuss. A garden with a terrace across the full width is ideal; a garden with a pond exactly under the right hand cheek is not.

Under the wheels you want something flat and load bearing: patio slabs, block paving or a concrete path. Fresh grass, bark chippings and loose gravel settle unevenly the moment the weight of the build comes on to them. Allow as well for the spread of the stabilisers, which you set out at all four corners and which reach a little further than you judge by eye. How you make that firm in an awkward spot is covered in the guidance on stabilising and anchoring.

The obstacles on this job are usually low ones. A downpipe along the wall, an outside tap, a shed on the boundary or a kitchen extension holds the tower half a metre off the brickwork, and up top you feel that half metre straight away in your reach. So walk the route and the pitch once before you rent, with a tape in your hand and your head up. Round the back of a house there is more in the way than you remember from last year.

Bolting the box down is usually a matter of hours. The days go into what follows: dressing the lead soakers in, bringing the tiles back up to it, setting the zinc, mounting the fascia boards and trimming and sealing the joints. For an ordinary dormer on a pitched roof, reckon on two to three days with the scaffold standing. Work alone, or add a gutter or a rebuilt cheek to the list, and that soon becomes one more.

Inside that period sits time you cannot speed up. Sealant and adhesive keep their own pace, and while a joint is still wet you put nothing over it. The work is weather sensitive on top of that: you would rather not dress lead in pouring rain, and a roof slope shining with wet is not one to lean on anyway. So build a day of slack in and watch the forecast before you fix your final dates.

That slack costs very little. Only the first 24 hours go at the full rate; every day you book behind it carries a discount of 95 per cent. Two extra days therefore cost you some space on the drive and almost no money, while they buy the certainty that you need not stop halfway through the zinc because the van is on its way. How that works out over a longer stretch is set out in the comparison of hiring by day or by week.

A deck measures 245 cm along its length, which puts you in front of the whole face of a standard box of two and a half metres. If the dormer is wider, you do it in two pitches: the left half with its cheek first, then the right. Mark that second spot out beforehand with a slab or a line of chalk, so you are not shuffling about after you roll. That keeps the number of moves down to what is genuinely necessary.

What you take up per trip matters more here than on most jobs, because lead is heavy and zinc is awkwardly long. Do not carry a roll of lead up the ladder in your hand; haul it up the outside on a rope and lay it flat on the floor. Three metre strips of zinc get passed up rather than wrestled vertically past the rails. Work out beforehand what fits in one round and lay it ready at the foot.

Repositioning is done with nothing left on the floor. Anything loose goes down first or is clamped, because a roll of lead that starts rolling while you push changes the balance of the whole build. After the move, walk the brakes and the stabilisers again. A tidy floor works better anyway, since you are not tripping over offcuts of zinc. If you go straight on to painting the dormer, you can use these same positions a second time.

What turns up at your door is a complete set of parts, counted and checked: uprights, decks with a hatch, braces, guard rails, toe boards and stabilisers. Book before three in the afternoon on a working day and that set can be with you the next working day. Find a spot beforehand where the parts can lie dry and out of the walking route, because while a dormer is being fitted more people cross that path than you would think.

When the set comes and when it leaves again you fill in yourself while booking. On this job you have it delivered on the day before the box goes up or just after, so you can start on the junction the moment the crane has gone. If the installation slips a day, simply move the delivery with it: a finished tower waiting for a box that is not there yet earns you nothing and stands in the way.

When you have done, our van comes back for the gear. You make sure the build is apart and that the parts lie somewhere the driver can reach. Do that only once the lead is dressed, the sealant has cured and you have checked the joints, because putting it all back up for one small touch up is a waste of your time. The practical points around that are gathered under the common questions about hiring.

Think about the weight of your material on this job. The floor you stand on takes 200 kilos to the square metre, which is what load class 3 under EN 1004 means, and with two people plus a roll of lead and a toolbox you come closer to it than on most work. Spread the weight over the deck instead of stacking everything in one corner, and leave material you no longer need today standing at the bottom.

Beyond that the ordinary agreements hold, and they weigh a little heavier here because you often hang over the rail with your upper body to reach the seam. Put the wheels on the brake before the first person goes up, never roll the build with anyone on it, and step off when the wind really picks up. A sheet of zinc or a length of fascia acts like a sail at height, and you feel that up there long before they do on the grass.

The risks that belong specifically to closing a dormer up are sharp material and falling objects. Zinc strips have edges that cut, and a hammer that bounces off the floor lands seven metres below. Work with tools on a lanyard, keep the zone underneath empty and rope the path off where the tower stands on a route that people walk along. The full set of agreements is in the overview of rules for work at height.