Estimating low voltage work, part 3: doing takeoffs

The previous post covered vetting a job before committing time to it. This one covers the first real work on a job that passes: the takeoff.

A takeoff turns the drawings into quantities. Every later step in the estimate depends on it. Material is priced from the counts, labor is applied to the counts, and the proposal is checked against the counts by the general contractor and the owner's representative. A missed device or a short cable measurement does not stay small. It carries through the material, the labor, and the schedule.

The takeoff is also where most of a project's questions surface. A device on the floor plan that is missing from the riser, a detail that references a sheet that does not exist, a pathway nobody shows. Each one needs an answer before pricing starts, and the window to ask for that answer is limited.

What this post covers

The post walks through a takeoff from the moment the documents arrive to the moment pricing can begin. Along the way it covers:

• Timing. Why the takeoff has to be finished before the RFI question deadline, and why it stays open until the RFI answers are issued.
• Organizing the plan set. Finding every sheet that affects the scope, including sheets from other trades.
• Counting devices. Reading legends and notes, and counting what each symbol actually represents.
• Measuring cable and pathway. Measured runs, average lengths, slack, waste, and distance limits.
• The head end and closets. Equipment that rarely appears on a floor plan.
• Cross-checking and the question log. Comparing the drawings against each other and recording every discrepancy for the next step.

Time the takeoff around the RFI deadlines

Most bid invitations list two dates that matter as much as the bid due date: the deadline to submit requests for information (RFIs), and the date by which answers will be issued, usually through an addendum. Both are typically found in the project details or the instructions to bidders.

Finish the takeoff before the RFI question deadline. The takeoff is where the questions are found. If it is not done in time, the questions cannot be asked, and the estimator is left to resolve them in the proposal. A proposal full of add alternates covering issues that belonged in an RFI, or that were already answered in one, is likely to be thrown out.

Hold the takeoff open until the RFI answers are issued. Most plan rooms and bidding platforms allow bidders to sign up for notifications when new documents, addenda, or comments are posted. Sign up, but do not rely on notifications alone. A good rule of thumb is to treat the takeoff as unfinished until the RFI answer deadline has passed.

Review every RFI answer before starting the bid. Read all of them, including answers to questions other bidders asked, and confirm none of them change the scope. An answer to an electrical or door hardware question can add or remove low voltage devices as easily as one asked about Division 27 or Division 28.

Record what applies to the scope. Note every plan sheet and every RFI answer that pertains to the company's scope. Those references are needed later for the proposal, for submittals, and for any dispute over what was included.

In order, the sequence looks like this:

1. Receive the documents and register for notifications.
2. Complete the takeoff and log every question.
3. Submit RFIs before the question deadline.
4. Wait for the RFI answers and any addenda.
5. Review every answer, update the takeoff, and record the sheets and answers that apply.
6. Begin pricing.

Step 1: Organize the plan set

Before counting anything, find every sheet that affects the scope. The low voltage sheets are the obvious place to start, but sheet prefixes vary by design firm, and low voltage work routinely appears on other trades' drawings. Review at least:

• The sheet index. Confirm every listed sheet was received, and note which sheets each addendum replaces.
• Legends, symbol lists, and general notes. These define what each symbol means and often carry requirements that never appear on the floor plans.
• The low voltage floor plans, risers, details, and schedules.
• Architectural reflected ceiling plans. Ceiling types and heights change the labor on every drop.
• The door hardware schedule. On access control work, the hardware schedule often defines what is required at each door more precisely than the security plans do.
• Electrical drawings. Power at the head end, at panels, and at door locations, and any low voltage devices the electrical engineer placed on their own sheets.

In Bluebeam, it helps to bookmark these sheets in a single set so the takeoff moves between them without searching.

Step 2: Count devices

Count by device type, and by floor or area. Totals by area make the takeoff easier to check, easier to phase, and easier to compare against the general contractor's counts later. Using count tools with consistent subjects, as covered in part 1, lets the totals roll up automatically.

Count what the symbol represents, not the symbol alone. A data outlet symbol marked with a number may mean that many cables. A controlled door symbol may represent a reader, a lock or strike, a door contact, a request-to-exit device, and power, depending on the door detail. Read the legend and the typical details before counting, and count every component the symbol implies.

Watch for devices on other sheets. Cameras on architectural elevations, devices called out only in keyed notes, and equipment listed in a schedule but never placed on a plan are all common. Anything counted from somewhere other than the floor plan is noted with the sheet it came from.

Step 3: Measure cable and pathway

Cable can be measured run by run, or estimated with an average length. Measuring every run is the most accurate approach and is practical with a takeoff tool. On large, repetitive floors, an average length is faster and usually close enough.

The average length method. Measure the shortest and longest runs from each closet along the actual pathway, average them, then add the vertical drops and slack. An illustrative example:

Multiply that length by the number of cables served from that closet, then apply a waste factor for scrap and partial boxes. Many contractors use 10 percent as a starting point and adjust it from their own job history.

Check the distance limits. Horizontal copper cabling is limited to 90 meters (295 feet) under TIA standards. A run that measures over that limit on the drawings is a question for the log, not a problem to discover during installation.

Pathway and support. Cable needs a path. Count J-hooks or cable tray, sleeves through walls, conduit stubs and backboxes or mud rings if they are in the scope, and every penetration of a rated wall or floor that will need firestopping.

Step 4: Count the head end and closets

Floor plans show the field devices. The equipment that serves them is usually on risers, one-lines, rack elevations, and enlarged room plans, and it is easy to undercount. Work through each closet and head end location and count:

• Racks, cabinets, and wall-mount enclosures
• Patch panels, sized from the cable counts that terminate in each room
• Horizontal and vertical cable management
• Backbone cabling and fiber between closets
• Grounding and bonding to the closet busbar
• Controllers, interface boards, and power supplies for access control
• Recorders, servers, and storage for video
• Network switches and UPS units, if they are in the scope

Patch panel ports match the cables landing in each room, with spare capacity if the specification requires it. If the specification calls for a percentage of spare ports, write it down in the takeoff, not in memory.

Step 5: Cross-check the drawings

Once the counts are complete, compare them against each other. Floor plan counts agree with the risers, the risers with the schedules, and the schedules with the specification. They often do not. A riser may show twelve cameras where the floor plans show fourteen, or the specification may require a device type that never appears on a drawing.

Every discrepancy is either a question to ask or a decision to make, and none of them get resolved by quietly picking one number.

Check what the scope depends on from other trades

The questions most worth raising in an RFI are usually not about the low voltage drawings themselves. They are about the things the low voltage work depends on that are furnished by someone else, and that nobody shows.

Many of those items are in the electrical contractor's scope, so they do not appear on the low voltage sheets at all. Check the electrical plans and the other trades' drawings for each one:

• Conduit from the property line or service entrance to the demarc location
• Power at the head end, at panels and power supplies, and at controlled doors
• Conduit stubs, sleeves, and backboxes the electrical contractor is expected to install
• Door preparation and electrified hardware from the door hardware supplier
• Ceiling access, lifts, or pathway the low voltage work will rely on

If an item the work depends on is not shown anywhere, it belongs in the question log. Otherwise, the gap usually surfaces in the field, when the cost of filling it falls on whoever is standing there.

Keep a question log

Record every question, conflict, and missing item as it comes up, with the sheet or specification section where it was found. The log is what turns a takeoff into a set of RFIs, clarifications, and alternates. An example (illustrative entries):

Whether each item becomes an RFI or is handled in the proposal is a decision of its own, and the subject of the next post. For now, the goal is to make sure nothing found during the takeoff is lost.

Bringing it together

A good takeoff is complete, organized, and on time. It finds every sheet that touches the scope, counts every component each symbol represents, measures cable along the path it will actually take, and accounts for the equipment that never shows up on a floor plan. It is finished before the RFI question deadline, and it stays open until every answer has been read.

The takeoff ends with two things: a set of quantities that can be priced, and a log of questions that still need a decision. A count that is wrong carries into every number built on it. A question that is never logged becomes an assumption, and an assumption nobody wrote down is a risk nobody priced.

Next in this series: handling the questions.

Planning and device counts are numbers. Those live on the calculators. The estimating workbook that follows the method in this series is in The Kit. The rest of this series is on the estimating page.

Related on this site

• Estimating low voltage work, part 2: deciding which jobs to bid
• Estimating low voltage work, part 1: the software an estimate runs on
• Calculators