Fitting a chimney cap? Choose the right scaffold.

On this job the cap is the largest object travelling upward, and that settles the choice. A plate of sixty by sixty centimetres or more wants to lie down beside you, together with the drill, a box of stainless anchors, a spirit level and a socket set. So the pick is the Altrex RS52, a deck 135 cm across and 245 cm long. Hiring a tower for a cap comes down to that floor area: the plate lies next to you rather than against your shins.

The narrow RS51 at 75 cm reaches identical heights, yet a large plate will not lie flat beside your boots on it. You end up standing the cap on edge against the guardrail, which is precisely what you want to avoid once the breeze picks up. Only go narrow when the route to the back garden leaves no other option, and pace out that route between the boundary and the wall first. Both widths sit together in the choice of towers available to hire.

The rest of the range falls short here. An RS44 room scaffold tops out between 3 and 4 metres and slips through an interior door from roughly 70 cm, which makes it a model for indoor jobs. The MiTower is a one person build topping out at 6.2 metres, and with a heavy plate in your arms you would not want to be alone on a deck anyway. The RS52 carries on to 14.2 metres and gives you the surface the cap can lie on while you line it up.

With a cap you do not want to be just level with the top edge; you want to look comfortably over it. The plate gets laid down, nudged square and lifted again a few times before it sits right. So the top of the head belongs somewhere between your hip and your waist, and certainly not up at your chin. On a house of two storeys the answer sits in the 8 to 12 metre working height band, so the deck lands at 6 to 10 metres.

The gap between those two figures is the reach you get above the boards: add roughly 2 metres to the platform height and you have the working height. On this job the rule bites differently than it does for painting, because you are reaching down onto the head rather than up at a wall. Measure to the topmost brick and then add half a lift, so the plate can be lowered rather than heaved. The matching build sits on the page about a twelve metre working height.

Your tape starts on the ground beneath the castors. Where the drive falls away towards the pavement, or the back garden lies below street level, you book one lift more than the arithmetic suggests. Come out short and you are standing on tiptoe with a plate in your arms, which is exactly when a cap slips off square or scrapes down the brickwork. If you are hesitating between two builds above a room on the second floor, take the taller one without debate.

Set the build along whichever elevation the chimney breaks through closest to the roof edge. On an end of terrace that is the flank wall; on a mid terrace it is usually the back garden. Where the head rises out of the middle of a pitched slope, nothing on castors gets sensibly near it and ordering a tower for the job achieves little. Take a look from the opposite pavement before anything else, because the position of the head governs the entire approach and the width you hire with it.

Beneath the tower belongs level ground that carries weight, with clearance all round for the stabilisers that angle outwards. Reserve extra width on one side as well, because the cap rides up most comfortably on a line run down the outside of the tower rather than under your arm on the ladder. A shed, a thick hedge or a carport hard against the wall makes that manoeuvre impossible and pushes your whole build round to another face of the house.

Think about the paving underneath you too. Drilling into brickwork sends dust drifting down, and a plug or a washer does now and then slip out of your fingers at ten metres. Keep that strip empty, park no car on it and tell the neighbours if a path is shared. Should part of the build stand on the footway, ask the council in advance what your street allows, so nothing has to be shifted on the morning of delivery.

This job splits into two visits to the head. First you go up to take the outside dimensions and to see how the brickwork is lying; then you order the cap; and only once it has arrived do you bolt it down. The measuring costs an hour and the fitting a half day, but the lead time on the cap sits between those two moments. So do not reserve a day, reserve the stretch you need in order to make both visits.

Anyone taking a cap off the shelf can do the lot in one go: measure it, collect it and fit it the same afternoon. Where the plate is made to the dimensions you supplied, days pass between the two visits. You are free to leave the tower standing through that gap, which usually works out cheaper and safer than having it brought twice and building it twice. What each height and model comes to, VAT included, is listed with the current rental prices, so the comparison can be made with figures.

That choice is open to you because the charge drops away after the first twenty four hours, with 95 per cent off from the second date onwards. Waiting days between measuring and fitting therefore add very little to the bill, while a second delivery and a second assembly cost you real time. Put your end date behind the day the cap is due, not in front of it. If the cap slips, the collection date simply moves further out.

Measuring is done to the outside: across the four faces of the head, outer edge to outer edge, and then both diagonals. Where those diagonals differ by more than a centimetre the head is not square, and you allow for that when ordering. Note the height of the projecting section as well, and where the flues sit inside it. On 245 cm of decking your tape and your notebook can be set down while you copy the figures out, with nothing rolling off the edge.

The cap itself you haul up on a line outside the tower, and not tucked under one arm while you climb. Up top you lay it flat, check the fit and mark the holes. Drill into the brick rather than into the joint, drive stainless anchors and use stainless nuts and washers, because ordinary steel is rusted solid into the brickwork after two winters. Lay the level on before you tighten, since a cap sitting off true is not corrected later.

Moving the tower is rarely necessary on this job. A chimney head is narrower than your platform, so one position generally serves two faces and half a turn often reaches the third. If you want a proper look at the fourth, roll the build round once over the paving. Carry your mesh or bird guard up on the same trip, so that fitting a chimney cap is finished in a single visit to the head rather than two.

The scaffold arrives as a counted set of separate components, never as a finished structure. Choose a spot for that pile beforehand where it is in nobody's way, the drive for instance, and keep the route to the wall clear for the cap itself. Book on a weekday and beat 15:00, and the parts land on your drive the working day after that. Ideally, pick a delivery date that falls before the cap is due to turn up.

Putting it together is your work and not the driver's. With the manual supplied and the video to hand, two people stand the build up in a half day, stabilisers and guardrails included. Keep that half day to itself, because erecting the tower and then bolting a cap down the same afternoon nearly always runs over. Collection we arrange again once you have taken the components apart and set them out complete, in the place where they were dropped off.

Look at the forecast for your fitting day before you book anything. Putting a plate up in a force five is not a matter of pressing on but of waiting, and it helps enormously if the tower is already standing and only the collection date has to shift. That is allowed, so long as the build is not down for the next hirer, and you know within a day. The run itself is a fixed provincial figure, listed under delivery charges by region with VAT.

These decks sit in load class 3, the EN 1004 category that allows 200 kg on each square metre. A concrete cap weighs a good deal, and together with two people, a cordless drill and a case of anchors you reach that limit sooner than on most work at height. Lay the plate down in the middle of the boards rather than against a guardrail, and leave it there until the moment it goes onto the head.

Wind is the biggest risk on this job, because a flat plate catches like a sail. Lift it while it is blowing and it tugs at your arms at exactly the moment you are leaning out over the edge of the head. Postpone the fitting in a strong wind and keep the cap lying flat until then. Beyond that, lock the castors before anybody climbs, never roll the build along with a person or tools still up on the boards, and put the stabilisers back out after every move.

Finally, pay attention to the head itself. A chimney that has never carried a cap has stood open for years, so the top courses of brickwork may well have worked loose. Push against them before you drive any anchors in, or you are fixing a heavy plate onto bricks that were never going to hold it. The order of assembly and the checks that go with it are covered under safe assembly of a mobile tower.