How to Field-Verify Existing Conditions Before You Order

Why this matters

Renovation drawings are drawn from what someone believed was there: an old as-built, a quick survey, a guess. Where the designer was not sure, the sheet says so with a note such as V.I.F. (verify in field) or "field verify existing." That note moves the measuring onto you. Order a unit, a fixture or a fabricated part to the drawing's number without checking it, and the mismatch you find on delivery day is usually yours to absorb: the restocking charge, the adapter nobody priced, the crane booked twice. Checking first costs an hour on site and a written note.

What the note means and who owns the number

A V.I.F. note says the dimension or condition shown is approximate and the contractor is to confirm it before proceeding. Many general conditions separately require the contractor to compare the documents with field conditions and report discrepancies before starting the affected work; under AIA A201, in the edition the contract incorporates, that duty sits in Section 3.2. What that duty means legally if something goes wrong, and how it splits responsibility with the designer, is a question for your contract and your attorney; this is not legal advice. Operationally the answer is simpler: once the note is on the sheet and you place the order, nobody else is going to check that number. Treat it as yours.

The example

A tenant improvement replaces a rooftop unit. Sheet M-301, note 4: "RTU-2, new, set on existing curb. V.I.F. curb dimensions. Provide curb adapter if required." The new unit's approved submittal shows its own matching curb footprint and the positions of its supply and return openings, its gas connection, its electrical data and its service clearances. The old unit is still in place and running.

Before you go up

The work is on a roof. For construction work, fall protection is required at 6 ft above a lower level under 29 CFR 1926.501, and for general-industry work (routine maintenance on an existing building) the trigger is 4 ft under 29 CFR 1910.28. Which applies depends on the activity, not on the building. Know where the unprotected edges, skylights and roof hatches are before you start measuring, and do not walk backward with a tape toward an edge. Skylights are holes; cover or guard them or stay clear. A portable ladder to the roof extends at least 3 ft above the landing (29 CFR 1926.1053 for construction).

Everything below is measured from outside the running unit. If any measurement needs a panel off, the unit is shut off and locked out at its disconnect, and the electrical side of that isolation is work for a qualified person. When the panel is back on, that person removes the lock, restores power and confirms the unit starts and runs normally before anyone leaves the roof. Most of what you need can be had without opening anything.

The steps

1. Read the note, the submittal and the drawing together, and list what has to match. Before you climb, write a list of every interface between the new thing and the existing building: footprint, height, opening locations, connection points (gas, power, condensate, controls), service clearances, the path in. The submittal tells you what the new unit needs; the drawing tells you what the designer believed exists. What breaks if you skip it: you measure what is easy to measure, the curb, and miss the clearance that decides whether the unit can be serviced.

2. Measure the opening or footprint, with the method stated. For a curb, measure outside length and width at the top, both diagonals (equal diagonals mean the curb is square), and the height above the finished roof surface on more than one side. Record to the 1/8 in. Note whether you measured outside or inside the curb, because the submittal will be one or the other. What breaks if you skip it: an outside measurement compared against an inside dimension, an error of twice the curb wall.

3. Measure clearances to everything that cannot move. Distance from the curb to the parapet or roof edge, to other units, to vents and exhausts, to roof drains. Compare with the service clearances in the submittal's installation section and with any clearance the drawings or the adopted code require. What breaks if you skip it: a unit that fits on its curb and cannot have its access panel opened.

4. Locate every connection point. Where the gas stub is and its size; where the electrical disconnect is and its rating (read off the outside of the disconnect's label, or the existing drawings; do not open it); where the condensate goes; where the existing supply and return openings sit inside the curb, viewed from below through the ceiling where possible. What breaks if you skip it: a new unit whose openings sit at its end, over a curb whose openings sit at its center.

5. Record the ceiling space and anything in the way below. From inside, measure from the underside of the roof structure or curb to the ceiling, and note what else lives there: sprinkler lines, conduit, structure. An adapter curb that transitions openings may need room below the roof too. What breaks if you skip it: the adapter fits on the roof and its duct connection does not fit in the ceiling.

6. Photograph with a tape in frame. One overall photo for location, then one per measurement with the tape visible and readable, labeled in the log. A photo of a curb without a tape proves a curb exists. What breaks if you skip it: the reviewer has your word against the drawing.

7. Compare, and send every discrepancy in writing before you order. Put the drawing or submittal figure beside your field figure for every item on your step 1 list. Each difference goes on an RFI, with the photos, and the purchase order waits for the answer. See related: How to Write an RFI That Gets a Usable Answer.

The record from the example

 FIELD VERIFY: RTU-2 curb, M-301 note 4
 Date Mar 3, by [tech], photos FV-01 to FV-07

 ITEM            SUBMITTAL        FIELD
 Curb out L x W  92 1/8 x 59 3/4  88 1/4 x 51 3/4
 Curb diagonals  -                equal, square
 Supply opening  at unit end      at curb center
 Gas stub        size per fitter  3/4 in, E side
 Disconnect      MOCP 50 A        60 A fused, N
 Svc clearance   36 in, access    30 in to parapet
 Below roof      -                30 in to ceiling
 RESULT: 4 discrepancies, 1 open question.
 RFI 011 sent Mar 3. PO held.

Reading the record:

• Footprint. The new curb is 92 1/8 - 88 1/4 = 3 7/8 in longer and 59 3/4 - 51 3/4 = 8 in wider than the existing one. An adapter curb is required, which the drawing allowed for but nobody had priced or scheduled. Adapters are commonly fabricated to order, so the lead time starts at the RFI answer, not at delivery of the unit.
• Openings. The existing supply opening is at the curb center; the new unit's is at its end. The adapter has to transition the openings as well as the footprint, which makes it a more complex fabrication and needs the ceiling-space figure from step 5.
• Service clearance. The submittal shows 36 in on the access side (that figure is this example's; read your own unit's installation manual), and the field has 30 in to the parapet. 36 - 30 = 6 in short. Either the unit is rotated on the adapter, which changes the opening transition again, or the designer accepts it. That is their call.
• Disconnect. The unit's maximum overcurrent protection is 50 A on the submittal. The existing disconnect's label reads 60 A, and sheet E-301 says the existing disconnect and its 60 A fuses remain. Fuses larger than the nameplate's maximum are not acceptable, so either the fuses come down or the disconnect is replaced. Confirming what is inside and changing it is the electrician's scope, and the drawing as written gets it wrong, so it goes on the RFI.
• Gas. The open question. A 3/4 in stub may or may not carry the new unit's input at the length and pressure of the existing piping. Gas pipe sizing is the gas fitter's work (licensed where your state or locality licenses it), from the code tables as adopted; the field record just captures the size and location for them.

Count check: footprint, openings, clearance and disconnect are the four discrepancies; gas is the one open question.

What would change the approach

• The old unit is gone or the space is gutted. Measure what remains, and record what you could not see because it was removed. A missing piece of information is a line in the record, not a blank.
• The existing condition is hidden. A pipe in a wall or a duct above a hard ceiling cannot be measured without opening something. Say so in the RFI and ask whether a selective demolition probe is authorized, rather than guessing. Any opening into an older building's finishes can disturb lead paint or asbestos-containing material, so it waits until someone has checked whether those are present.
• The item is not custom. A standard part that can be returned cheaply changes the risk, not the method. Verify anyway when the verification is short; skip only when the record says why.

How to check you did it

Every item on the step 1 list has a figure in both columns or a reason it does not. Every field figure has a photo with a readable tape. Every difference is in an RFI, and the PO is held until the RFI is answered. Then give the record to someone in the office and ask them to explain, without calling you, why the order is on hold. If they can, the record will also make sense to the engineer.

References

• AIA A201 General Conditions, in the edition your contract incorporates: Section 3.2, review of contract documents and field conditions by contractor
• 29 CFR 1926.501 and 29 CFR 1910.28 (fall protection triggers), 29 CFR 1926.1053 (ladders)
• The equipment manufacturer's installation manual and submittal, for curb, clearance and electrical data
• See related: How to Read a Submittal Package
• See related: As-Builts and What Happens When Nobody Updates Them