How to do a low-voltage and AV takeoff in Bluebeam Revu

Low voltage is not one scope. Structured cabling, access control, video surveillance, fire alarm and audio-visual can each be its own bid package, its own spec section in Division 27 or 28, and its own sub. Read the spec and any responsibility matrix before you open a plan sheet, and write down which systems you are carrying.

Then find out who owns the rough-in. Back boxes, conduit stubs to the ceiling and sleeves through walls are often the electrical contractor’s work, carried under Division 26, with the low-voltage contractor pulling and terminating cable. Sometimes it is the other way round. Either answer is fine. Not knowing is how a bid ends up carrying the same back box twice, or not at all.

Fire alarm deserves its own line here. On some jobs it is a separate design-build package with its own drawings issued later. If it is in your scope, take it off as its own system. If it is not, leave it alone even when the devices are drawn on your sheets.

The legend is where a triangle with a 2 next to it becomes a two-port data outlet and a triangle with a W becomes a wireless access point. Symbol sets vary by engineer and sometimes by sheet, so read the legend on every T, TY or LV series sheet you are using, not just the first one.

The riser diagrams tell you what the plans cannot: how many IDFs there are, which floors each one serves, the backbone between the MDF and every IDF, and where the head-end gear sits for each system. Keep the riser open beside the plan for the whole takeoff. It is the sheet that turns a pile of device counts into a system you can price.

Build a Count tool for each device type in your Tool Chest, with the system in the subject: "DATA, 2-port outlet", "ACS, card reader", "CCTV, fixed dome", "AV, ceiling speaker". Box one clean instance, run Visual Search across the sheet or the set, turn the results into counts, then move to the next type. A search that mixes a single-port and a two-port outlet gives you a number you cannot cable.

For structured cabling the unit that matters is the port, because every port is its own cable back to the closet. A two-port outlet is one plate, one back box and two cables. Record both: the device count for the box and the plate, the port count for the cable and the terminations.

Then pan the sheet for what the search missed. Rotated symbols, symbols under a tag and symbols on a hatched wall are the ones that go quiet. The generic technique for that check is in How to count symbols on a drawing.

Low-voltage quantities get asked for in more ways than most trades: by system, by floor, by IDF, by room for the AV rooms, by phase for a fit-out. If the counts only carry a type, every one of those questions means counting again.

Revu’s Spaces tag a markup with the space it sits in, and the Space column in the Markups list lets you sort and filter by it. Draw spaces for the floors, the IDF zones and the AV rooms, and add a Custom Column for system so the list can be filtered any way somebody asks. Put each system on its own layer too, so you can switch one off and see the others clearly.

A cable runs from the device to its closet along the pathway, not in a straight line. Use Polylength to trace the route the cable really takes: down the corridor in the cable tray or along the J-hook path, then across to the device. Measure to the IDF that the riser says serves that area, not to the nearest closet on the sheet.

The plan length is not the cable length. Every run also climbs from the device box up to the ceiling pathway, drops at the closet down to the rack, and leaves a service loop at one or both ends. Keep those as separate allowances, written into a Custom Column or a note your shop agrees on, not buried in the traced length where nobody can check them later.

On a large floor, a common approach is to trace a fair sample of runs per IDF zone, nearest, farthest and a spread in between, take the average with the allowances added, and multiply by the port count for that zone. Whatever method you use, check the longest run against the channel limit in the cabling standard the spec calls out. A run that comes close is a sign the device belongs to a different closet.

Rough-in is the back box, the mud ring, the conduit stub to the ceiling, the sleeve through the wall and the firestop at a rated wall. Devices are what the end user touches: outlets, readers, cameras, speakers, displays, touch panels. Head-end is the gear in the room: racks, patch panels, the access control panel, the recorder, the fire alarm control panel, the AV processor and amplifiers.

They are priced differently, often installed by different people, and sometimes some of them are owner furnished. One device count can drive all three, so measure once and split the result into three named quantities rather than three separate takeoffs that drift apart.

Floor boxes and AV wall plates need extra care. A floor box in a conference room can carry power and data and AV connections in one device, and it usually needs a coring or a sleeve through the slab. Decide which scope owns each part of it, and write that into the name of the count.

Most low-voltage sets carry something to check against: a door hardware schedule that says which doors get a reader, a camera schedule, a device schedule per IDF, and on AV jobs an equipment list or a room-type sheet that says what goes in each conference room. A count that has never been held against one of those is a guess.

When the plan and the schedule disagree, that is the finding. A door shown with a reader on the plan and no electrified hardware on the schedule, or an AV room type with a mic count the plan does not show, is an RFI. Export the Markups list to CSV or Excel, set it beside the schedule, and work the differences line by line.

• Counting plates and cabling plates

  Cable follows ports, not outlets. A floor of two-port outlets cabled by plate count carries half the cable it needs.

• Taking the plan length as the cable length

  The drop from the ceiling, the rise at the closet and the service loops are real cable on every run. Leave them out and every run is short by the same amount.

• Measuring to the nearest closet instead of the right one

  The riser says which IDF serves which area. A run measured to the closest room on the sheet can be the wrong closet entirely.

• Carrying rough-in that belongs to the electrician

  Back boxes and conduit stubs are often in Division 26. Price them twice and the bid is high; assume the other trade has them when it does not and it is low.

• Mixing systems in one count

  A data outlet and an AV wall plate can look alike at plan scale. One count holding both cannot be priced or cabled.

• Counting fire alarm devices that are not in your package

  Fire alarm is drawn on many low-voltage sheets and bid as a separate package on many jobs. Read the scope before you count it.

• Never checking the AV equipment list

  AV rooms are specified by room type and equipment list as often as by symbols. The plan alone undercounts the gear in the rack.