Sharp Pencil › Guides
TPO or PVC over an existing metal building roof: what the retrofit takeoff has to count
What does a takeoff for TPO over a metal building roof have to count?
Flute fill by rib profile and run, insulation and cover board by layer, membrane by attachment, fastener rows on the purlin lines, perimeter nailers, edge, gutters, curbs and penetrations. Purlin spacing and pullout results change the counts, so they go on the Questions tab.
Disclosure: Sharp Pencil sells commercial roofing takeoffs, so we have a stake in this topic.
This is a takeoff checklist, not structural, wind or warranty advice. The design professional, the manufacturer and your bid documents decide the assembly.
Short answer
A single-ply retrofit over a metal building roof is a stack of separate lines. Flute fill between the ribs, insulation and cover board by layer, membrane by attachment, fastener rows on the purlin lines, perimeter wood nailers, edge, gutters and every curb. The panel profile, purlin spacing and pullout test results drive the counts, so send those questions before bid day. If the drawings do not show them, the takeoff says so.
Why a metal building retrofit is its own takeoff
The old metal roof stays, so the new roof has to sit on ribs, not a flat deck.
The panels leave open flutes between the ribs. Those get filled first so the boards above have a level base.
New insulation or cover board goes over the ribs and the flute fill, then the membrane.
Manufacturer guides prefer fastening the membrane through the panel into the purlins, so the purlin layout sets the fastener rows. Insulation may be fastened into the panel.
For the wider choice between tearing off and covering over, see tear-off vs recover takeoff.
Flute fill: count it by profile and run
Flute fill is an easy line to miss, and it is not square feet of roof.
Identify the panel profile and rib height from the existing roof survey or the drawings. Flute fill is sized to match the rib height. Count it by the length of flutes across the roof (LF by profile), or by the area of the fill board the profile needs, as your supplier quotes it.
If the rib height or profile is not on the drawings, it goes on the Questions tab. Do not guess a profile.
Insulation and cover board by layer
Once the flutes are filled, the layers above count like any low slope roof.
One line per layer, by SF, with thickness or R-value as specified. Cover board is its own line. Tapered insulation for drainage is its own line. See tapered insulation takeoff.
Thickness changes edge heights and fastener lengths, so note the total stack on the takeoff.
Attachment: purlin lines, fastener rows and the pullout questions
On a metal building retrofit, manufacturer guides prefer the membrane fasteners in the purlins, not just the panel.
Lay the purlin lines on the roof plan, then count fastener rows along each purlin line by zone (field, perimeter, corner) as the assembly calls for. Fastener length depends on the stack above the panel and the required embedment.
Manufacturer guides call for on-site pullout testing on metal building retrofits, and the results can change the attachment rate. Until results are in, the attachment rate is an assumption, and the takeoff marks it that way.
Some manufacturer guides suggest asking for a unit price for added fastening when pullout tests cannot be run before bid. See bid alternates and unit prices.
| Line | Unit | Needs before it is final |
|---|---|---|
| Purlin fastener rows, membrane | EA by zone | Purlin spacing and gauge, assembly attachment pattern |
| Insulation fasteners and plates | EA by board layer | Board size, attachment rate, pullout results |
| Seam plates or bars along purlins | EA or LF | Attachment method named in the spec |
| Fastener length | Each size by stack | Total stack height and required embedment |
| Pullout tests | EA (allowance) | Who runs them and when |
Edges, nailers, gutters and curbs
The perimeter on a metal building is where the new stack meets an edge that was never built for it.
Wood nailers at the perimeter, built up to match the new insulation height, go on their own LF line. Edge metal and gutters as LF. Each curb, pipe and penetration as EA. Ridge, eave and endwall conditions where the membrane terminates.
Existing vents, edging and wall transitions: the designer decides what is closed off before the new roof goes on. If the drawings do not say, it is a question.
See edge metal takeoff and, where the metal stays exposed next to the new membrane, mixed-system commercial roof takeoff.
The Questions tab for a metal building retrofit
A lot of the risk in a retrofit bid sits in what the drawings leave out.
| Question | Why it matters to the count |
|---|---|
| Panel profile and rib height | Sets the flute fill line |
| Purlin spacing, gauge and layout | Sets the fastener rows and lengths |
| Pullout test results, or who runs them | Can change the attachment rate |
| Structural review of the added load | The design professional confirms it, not the takeoff |
| Existing panel attachment to purlins | May need refastening before the new roof |
| Drainage, gutters and slope | Sets taper, crickets and gutter lines |
| Wet or damaged existing insulation | Sets any removal and replacement line |
The takeoff lists these questions. It does not answer structural, wind or warranty questions. See the roofing RFI register.
Worked example
Example data, not a real job.
- An example metal building roof is 200 ft by 100 ft (20,000 SF), with purlins at 5 ft on center running the 200 ft length.
- Purlin lines: 100 ft divided by 5 ft is 20 spaces, so 21 purlin lines of 200 ft, 4,200 LF of purlin line for fastener rows.
- Insulation: one layer of polyiso and one layer of cover board, 20,000 SF each, 40,000 SF of board in total.
- Perimeter: 2 times 200 ft plus 2 times 100 ft is 600 LF of edge and nailer.
Where the takeoff fits
Every quantity carries its source sheet and its basis.
Four files: START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list.
Pricing is optional. Send your cost data and we apply your prices to the quantities. Any line you have not priced comes back marked UNPRICED.
See commercial roofing takeoff services and a sample takeoff.
FAQ
What is flute fill on a metal roof retrofit?
Insulation that fills the open flutes between the ribs of the existing metal panels, so the boards above have a level base. It is sized to match the rib height.
Is the TPO fastened into the metal panels or the purlins?
Manufacturer guides prefer fastening the membrane through the panel into the purlins. Insulation may be fastened into the panel. The assembly in the spec decides.
Do I need pullout tests before I bid a metal roof retrofit?
Manufacturer guides call for on-site pullout tests on metal building retrofits, and the results can change the attachment rate. If tests cannot be run before bid, ask how added fastening will be handled.
How do I count flute fill?
By the panel profile and the length of flutes across the roof, or by the fill board area your supplier quotes. If the profile is not on the drawings, ask.
Does the takeoff confirm the building can carry the new roof?
No. The design professional confirms the structure. The takeoff lists it as a question.
What does Sharp Pencil send back on a takeoff?
Four files: START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list. Every quantity carries its source sheet and its basis. Usually within one business day. Delivered within 48 hours*.
*Clock starts once any questions we send you are answered.
Why send it to us
- We take off steep slope (standing seam, shingle) and commercial low slope (TPO, EPDM, PVC, mod bit, BUR) from the full set.
- Every quantity carries its source sheet and its basis.
- Four files: START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list.
- Pricing is optional. Send your cost data and we apply your prices to the quantities. Any line you have not priced comes back marked UNPRICED.
- Usually within one business day. Delivered within 48 hours*.
- A plan set you send us will never be used to compete with you, and plan sets are deleted whenever you ask.
- First takeoff free, one per contractor, on a job you're bidding or quoting.
Residential is not our focus today, but ask if you have a job in mind.
*Clock starts once any questions we send you are answered.
Try it on a job you are bidding
Get your first takeoff free · $395 per takeoff · See a sample takeoff
The Sharp Pencil team