Insulating a cavity wall? Choose the right scaffold.

For a survey on a two storey cavity wall, the tower to hire is the Altrex RS51, built a mere 75 cm wide. On this job you walk the whole elevation and usually the flank and the rear as well, so the setup has to clear a shed, pass through a gate and cross a garden path without a struggle at every corner. The page listing mobile towers available for hire shows which widths exist and which of them still fit along a tight boundary strip beside a neighbour.

What travels up with you is light but plentiful: a drill with a long masonry bit, an endoscope, a tape, chalk, a small mirror and the phone that takes photographs you will certainly want again. On a 245 cm deck all of it stays within reach without rolling about underfoot. Width is not what you are short of, because you stand tight against the brickwork the whole time, looking, measuring and marking up what has to be drilled once a decision has actually been made.

Where a surveyor or a second pair of eyes walks the job with you, the 135 cm RS52 behaves more kindly: two people studying the same stretch of pointing need room to pass without the camera sliding out of the hole. For a one-person survey that never outweighs the ease of a narrow tower you can roll along on your own between one stand and the next. How the two sizes compare, and which you can still roll alone while insulating a cavity wall, sits in the table of scaffold dimensions.

The highest point of this survey is not eye level but just beneath the roof edge, since that is where the top row of holes will go and where a silted cavity is likeliest of all. Two storeys puts your working height between 6 and 8 metres. Reckon it back by taking the deck height and adding the two metres or so a standing adult still covers, and the build to order becomes obvious. The explainer on working heights ranks those builds.

Measure from the level the wheels will occupy, and allow for the plinth at the bottom. Should the garden lie lower than the pavement, or the house sit on a raised bank, your entire ladder of measuring heights travels up or down with it. On a survey you also want sight of where the cavity meets the eaves, and that sits a good deal higher than the topmost brick you believe you can pick out while standing on the lawn.

Book too low and you miss precisely the part that holds the surprises. Where the top metre has not been seen from close range, you learn only during the filling that the cavity narrows there or that a perpend holds a nest. By then a machine is waiting on your ground and standing idle costs money that the survey was meant to save. For an elevation carrying on above first floor level, hire one lift more rather than one too few, since nobody regrets spare reach when insulating a cavity wall.

A survey travels right round the house, so look at every side of the plot before you order anything. The front wall usually stands on the pavement, the flank against a narrow strip of ground, the rear behind a garden with a shed on it. Position the setup so each stand covers a decent width of wall, and mark on a rough plan where the tower goes in turn. That spares you rethinking the route halfway through the morning with a drill in one hand.

Whatever lies under the wheels must be flat and must carry weight. Garden soil that softens after a wet week, a band of gravel or a sunken slab path is no base to build several metres up from, so lay boards or sole plates. All round, keep room free for the stabilisers, which reach further out at an angle than the tower itself is wide. Where the ground falls away between terrace and lawn, look at working off a surface that is not level before the parts are dropped off.

One rule counts for more here than anywhere else: the tower is never tied to the wall you are surveying. An anchor through the outer leaf damages exactly the brickwork whose watertightness you are trying to establish. The tower stands free on its own feet, which is why the strip beside the wall has to stay clearer than people assume at the moment they hire. Reckon on a good metre beside the plinth, and on the narrow side of the house as well.

A survey on an ordinary terraced house runs to half a day or a whole one. In that time you drill test holes at several heights, look inside with the camera, measure the cavity, locate the lintels and walk the pointing for cracks and weathered joints. A detached house with four elevations and an extension soon wants a further day, simply because the tower has to be repositioned rather more often than anybody expects at the outset, and each move costs a quarter of an hour.

Season matters here in a way it does not for other facade work. Nesting birds and bat roosts decide when the cavity may be opened at all, and you check for them on that same circuit. Spot nesting material, or behaviour pointing to it, and the filling shifts to another period even though the survey is already behind you. A wall still drying out after a wet week moves the date for precisely the same reason, and neither of those is a delay you can argue with.

On the rental price it pays to glue survey and execution together. The full figure is charged across the opening twenty four hours; every following day counts with 95 per cent taken off, so letting the booking simply run on costs next to nothing at all. Prove the wall suitable and the tower already stands ready for the day the cavity is actually filled, which is the sister page to this one. Two separate periods mean two deliveries and two assemblies, and that adds up however you count it.

From a 245 cm deck you chalk a band of wall that gets finished in one visit. The pattern goes in the perpends rather than through a brick: it fills neatly later and the making good draws less attention. Use the brick course as your grid, hold the rows at a steady spacing and mark at once wherever an extra hole is wanted. Work band by band and the pattern stays in line across the whole elevation instead of drifting.

Around openings that grid always breaks down. Above every frame sits a lintel interrupting the cavity, and at the reveals of windows and doors there is frequently a closed return. Those panels need holes of their own, or a cold strip is left behind that nothing can reach afterwards. Mark up as well where the cavity is blocked with mortar, because that is what the test hole told you and it is exactly the sort of detail lost within a week.

Every test hole carries a short check for life behind the wall. Feathers, droppings or dragged-in material in an open perpend means you stop drilling and establish first what is in there. Bats squeeze through gaps barely a centimetre across and seldom show themselves at all while you happen to be standing right there on the deck. This page covers the judgement that precedes insulating a cavity wall; going hole by hole afterwards sits on the sister page about filling the cavity, where the machine and the lance take over.

Your scaffold arrives as loose parts, counted and gathered into one complete set. Choose a spot for that stack in advance where nothing leans against the wall, since that surface is the one you want to sight along and drill into unimpeded. A drive, a patch of lawn or the verge in front of the house all serve. An order wrapped up by 15:00 on a weekday puts the parts on the van for the following working day.

Arrival and collection dates are both picked by you at the booking stage. When insulating a cavity wall it pays to take delivery the day before the survey starts, since assembly is your own work: two people, a couple of hours, manual and video open beside them. Your survey morning then opens with a tower already standing over the plinth and the entire span of daylight still in front of you rather than half spent on frames and braces.

Afterwards we fetch the parts; dismantling and stacking the set complete stays with you. Wait until you are certain everything has been seen and recorded, because returning for one detail otherwise means a fresh assembly and a fresh hire day for the sake of one photograph. Count the parts as you release them and the set tallies exactly at handover. What your own province carries for the round trip appears on the page about delivery and collection charges.

Load class 3 of the EN 1004 standard covers this deck, meaning every square metre carries up to 200 kg. A drill, a camera and a handful of tools come nowhere near the limit, so what the deck bears is seldom your worry on a survey. What you do feel is the moment the long bit breaks through the outer leaf: the machine lunges forward, and that is exactly why the wheel brakes go on before you press the trigger.

You roll with an empty deck, no tools aboard and nobody standing on it, then set all four stabilisers down hard again wherever the tower comes to rest. When the wind picks up you stop; along a bare wall with no shelter you feel it sooner than in an enclosed back garden. Bear in mind as well that you are pushing a machine against the brickwork, and that the reaction keeps trying to shove the tower away from the wall.

Drilling into brick throws fine dust straight into your face whenever you are working at height above your own head, so goggles and a mask are hardly excessive on this job. Let nobody stand directly beneath you, because a bit or an endoscope slipping from your hand arrives below at a fair speed indeed. Everything else that applies aloft, even when you are inspecting for an hour and coming straight back down to the grass, sits at the safety rules that apply on a tower.