Dormer window? Choose the right scaffold.

The wide Altrex RS52, 135 cm between the uprights, is the model you want at a dormer. You rarely work straight ahead of you here: you lean out over the guard rail towards a point that lies a good way off, and then a wide deck under your feet is literally the difference between comfortable and standing on your toes. Which other sizes are in the range you compare on the page for mobile scaffolds to hire.

Dormer work also means carrying things up. A panel or a length of fascia timber, a sealant gun, sanding kit, paint or zinc tools, and usually a second person to pass things across. On a deck of 245 by 135 cm those items lie beside each other rather than on top of each other, which saves searching at the moment you are holding a panel in place with one hand. The second person then still has somewhere to stand without stepping over your tools.

The narrow RS51 comes into play if the dormer sits above a narrow alley or an extension where 135 cm simply will not pass. You give up working room then, so measure that passage first. A room scaffold or a MiTower is out here: they reach four and 6.2 metres respectively, which is too low as soon as the dormer sits on a second floor. In this comparison for dormers the options stand side by side.

The first measurement is the ordinary one: how high does the point sit that you need to reach. Measure from the ground the castors will rest on up to the top of the dormer, so to its little roof and not to the bottom sill. On a house of two storeys you usually land between 6.2 and 9.2 metres of working height. The deck then hangs between 4.2 and 7.2 metres, because a good two metres of your own reach comes on top of the platform height.

The second measurement is the one most people forget. A dormer does not begin at the gutter but a metre or a metre and a half higher up the sloping roof, and you cover that distance horizontally as well. Stand level with the front of the dormer and there is still a stretch of roof between you and your work. So measure how far back the front sits from the eaves and count that in when you choose your level.

In practice that means you nearly always pick a level higher than the height alone would suggest. From a deck that comes out a little above the dormer you look and reach across to it at an angle instead of pressing against it. What that means for a dormer on the second floor is set out on the page about work on the second living floor. Choose too tight and you stand too far off and never make the top edge.

The standing position follows from where the dormer sits, and that is as often at the back as at the front. At the rear you are dealing with a garden, a terrace, a shed hard against the boundary and a fence that narrows the delivery route. Walk that route first with the parts in mind: will the longest components pass through the gate, or do they have to go over the fence. At the street side the carrying is easier, but you have parking and the pavement to deal with.

Under the build you want flat, firm ground. Terrace slabs on sand sink under an extended stabiliser, and a border turns to mud after a shower. Put down spreader plates or thick boards under the feet if you have to. Bear in mind too that a dormer usually needs two or three places along the same elevation, so that flat strip has to run on. For soft or falling ground the approach is in this guidance on the ground.

When you set out, look at exactly where the dormer comes out above. You do not want the build straight under its middle but slightly off centre, so that you can take the front and one of the sides without moving straight away. A downpipe, an extension or a low outbuilding sometimes forces you a metre to one side, and then the point you reach across the roof from shifts as well. Walk it through with a broom in your hand and you see at once how far you will get.

All sorts of things fall under dormer work, which makes the number of hire days mainly a question of how many part jobs you stack up. Just checking the front over and touching it up is a day. Add the sanding, the zinc at the junction or a rotten section in a cheek, and you are soon at three or four days. Count in as well that every part job means moving from front to cheek, and that costs half an hour each time.

Waiting time comes with the territory and you cannot make it up. Sealant and paint have to cure before the next coat goes on, and on a dormer in full sun that happens faster than on a north wall. Rain stops the work, because you cannot reach the top edge across a wet sloping roof. So book your period with the slowest step as your starting point rather than the quickest, certainly if you are starting in autumn.

Margin like that costs little when you hire. The first twenty four hours is charged at the whole rate; from day two a 95 per cent discount applies, which leaves a twentieth per day. A day of waiting for dry weather therefore hardly counts. Booking a second hire period, by contrast, costs you a whole build and an extra journey. So reckon a day too many rather than too few. What others allow on jobs like these is in this overview of hire days.

An average dormer is two to three metres wide, so a deck of 245 cm has the front covered in one position. The cheeks are another story. They stand at right angles to your platform, and to get at them properly you move the build a good way to one side and work in towards the flank at an angle. So do not count on a single position but on two to three places around the same dormer.

You move with an empty deck. Take the material off, release the brake, roll a few metres along and set the stabilisers out again before anything goes back up. That looks laborious for three metres sideways, but with a sloping roof above your head you particularly do not want to push a half loaded deck. On a terraced house with the dormer at the back this is usually the only moving of the whole job.

What people misjudge is the top edge of the little roof. From a level measured out on the front you just fail to make the roof trim, and then you are working with outstretched arms exactly where you need force. So take that top edge into account as soon as you take your measurements, even if you are not going to touch it. If it is purely about the roof of the dormer, you hire a level higher still.

The set reaches your door as loose parts, counted and complete, and building it is your own job, with the supplied manual and an instruction video beside you. For a build of this height two people set aside half a day. If the dormer is on the rear roof, agree where the van may unload and how you get the parts round the back, because carrying through a narrow gate is invariably the first thing to disappoint on jobs like these.

The arrival date and the departure date are both yours to name. Get an order in before 15:00 on any working day and the parts can be standing with you by the next working day. On dormer work, let the delivery preferably coincide with the start of a dry run of days, so that you build straight away and can start the next morning. What the journey to your province costs is set out clearly under the charges for dropping off and collecting.

After your last day we come and collect the set. You make sure everything is dismantled and complete at the spot you gave us. Take it down while it is light and while you are still sharp: the parts of the top layer are better passed down with attention than at the end of a long day. So do not put the stack at the bottom of the garden where the van has no chance of reaching it.

The build follows the EN 1004 standard in load class 3, which puts the limit at 200 kg for a square metre of decking. On dormer work, with two of you up there plus panels, tools and a bucket, you get closer to that than you think, so spread the weight and leave spare material below. Put the castors on the brake before you step up, never wheel it with anyone or anything still aboard, and stop once the wind starts pulling at the decks.

The risk that heads the list here is reaching. Because the dormer lies further off than a wall does, it tempts you into hanging far over the guard rail or putting a foot on the top rail. Do not do it: move the build one more time instead. Nor should you step onto the sloping roof to finish a last patch, because tiles are slippery and they break, and there is nothing up there to hold on to.

Keep the space under the build clear as well. At a dormer you often work above a terrace or a garden path where children and pets simply walk past, and anything that slips out of your hands lands exactly there. Do not work with tools lying loose along the edge, fence the zone off with what you have and say indoors that nobody should walk underneath. The further rules are with the guidelines for working at height.