Sharp Pencil › Guides
Should You Ask the GC for the BIM Model on a Roofing Bid?
Disclosure: Sharp Pencil sells commercial roofing takeoffs, so we have a stake in this topic.
Yes. If a BIM model exists, ask your GC for it. A model is the database the drawings were printed from, so roof planes, walls, drains and curbs are dimensioned in it, not scaled off a PDF. Use it with the plan set and spec book, not instead of them. Models usually come with a disclaimer that they cannot be relied on, and the contract normally names the drawings and specs. If the model and the sheets disagree, put it on the Questions tab with the sheet value as the stated default.
Should you ask the GC for the BIM model?
Yes. Asking costs nothing. Ask your GC for the model so you can check geometry on your side. A model is often the database the drawings were printed from, so roof planes, walls, drains and curbs can be dimensioned in it rather than scaled off a PDF. Drawings and specs usually govern as the contract documents. The model helps with geometry. For Sharp Pencil, send the plan set and, when useful, PDF sheets exported from the model. Most GCs can share the model on request.
The same applies to standing seam and shingle planes, where slopes, hips and valleys are modeled geometry. See standing seam metal roof takeoff. We take off standing seam and shingle in full, not as an afterthought.
What a Revit model gives a roofing takeoff
Geometry. A design model carries the roof planes, slopes, openings and the locations of drains, curbs and walls as modeled objects, so lengths and areas can come from the model rather than from scaling a printed sheet. Use the model on your side to check geometry against the set. Package quantities still cite the issued sheets and specs (source sheet and basis). The package does not cite the model as the quantity source.
| Takeoff item | What the model can help with | Where the bid answer still comes from |
|---|---|---|
| Roof area by plane | Modeled roof element areas and slopes | Roof plan and sections, plus the spec for the system |
| Perimeter and edge lengths | Modeled edges and wall lines | Roof plan, edge and coping details |
| Parapet and wall heights | Modeled walls and parapets | Elevations and wall sections (see drawing sheets) |
| Drains and overflow drains | Modeled locations if the plumbing model is included | Plumbing sheets and drain schedule |
| Curbs, units, penetrations | Modeled locations if MEP models are included | Mechanical, plumbing and electrical sheets, plus curb details |
| Steep slope planes, hips, valleys, rakes, eaves | Modeled geometry and slopes | Roof plan, elevations, details and spec (see standing seam and mixed-system) |
| Tapered insulation | A sloped top surface may be modeled | Tapered insulation plan and spec (see the next section) |
| Assembly, attachment, warranty, flashing heights | Often not carried, or carried as generic layers | Spec book (Division 07) and details |
The Penn State BIM Project Execution Planning Guide v2.2, Appendix B-23 on Cost Estimation (Quantity Take-Off), lists "Precisely quantify modeled materials" as potential value and "An accurately built design model" as a required resource. The value depends on how the model was built, and only modeled items can be counted.
Autodesk Revit help on Material Takeoff Schedules says Revit can schedule any material that is placed in a component, and notes that minor discrepancies might appear between the volumes visible in the model and those shown in the material takeoff schedule. A schedule pulled from the model is a starting quantity, not a checked takeoff.
What the model may not tell you
The model is design geometry. It may not carry the specified roof assembly, attachment, warranty, flashing heights, or a tapered layout you can measure, and it may be at a level of development that was never meant for quantities.
Level of development. The AIA Digital Practice Documents Guide says that using LOD designations, Model Authors can convey the specificity and exactness of their Model Elements and, in turn, other Project Participants with access to the Model can determine an appropriate amount of reliance on those elements. Ask whether the BIM execution plan states LOD for roofing elements. If no one can say, treat model numbers as a check, not the source.
Tapered insulation. Autodesk About Shape Editing says shape editing can model a variable thickness material used to slope the surface of a horizontal plane (for example, tapered insulation), and also says shape edited elements will not report a true thickness. A modeled taper shows intent. Board counts, panel sizes and crickets still come from the tapered plan and spec. If the set has no tapered plan, put this on the Questions tab: no tapered quantities carried until the tapered plan is issued.
Missing disciplines. If the GC sends only the architectural model, drains, curbs and penetrations from MEP may be absent. Ask for every model they can share.
Version. The model keeps changing during design. Ask which issue or date of the drawings it matches. If it is newer or older than your set, the set you were issued to bid governs.
The drawings and specs are still the contract documents
Unless the agreement says otherwise, the contract names the drawings and specs, and models are usually shared with a disclaimer that they cannot be relied upon. Use the model to measure faster and check your numbers. Bid to the documents.
The AIA Digital Practice Documents Guide (2022 documents), under BIM as a Contract Document, says the common practice is for design teams to use models internally to meet their contractual obligation to generate 2-D drawings. Models might be shared with other project participants, such as the contractor, but the models are usually accompanied by a disclaimer stating that the model cannot be relied upon. The Guide also says the owner and contractor typically enumerate the documents that will be considered Contract Documents in their agreement, citing A201-2017 Section 1.1.1.
AIA E202-2022 instructions say E202-2022 is intended to be used when Project Participants agree that no Model Versions will be enumerated as a Contract Document. E201-2022 is the AIA exhibit that permits a model version to be a Contract Document. It is possible for a model version to be a contract document, but only when the agreement says so. Check the bid documents and any BIM exhibit.
If your subcontract or the bid documents list a model version as a contract document, read that language before you rely on it.
The model complements, it does not replace, the sheets, details and specs. See the sheets a roofing takeoff has to read.
What to ask the GC for (a short request list)
Ask for the current model from every discipline they can share, which drawing issue it matches, and the BIM execution plan if there is one.
- The architectural model (and structural and MEP models if available)
- The drawing issue or date the model matches
- Any BIM execution plan or model element table that states level of development
- Any disclaimer or exhibit that comes with the model
- The full plan set and the spec book (the model does not replace them)
We do not contact the GC for you. You ask, and you send what you get.
See a sample takeoff to check what a plan set takeoff hands back.
When the model and the drawings disagree
Do not pick the number you like. Note both, cite the sheet, and put it on the Questions tab. See roof plan and details conflict and the roofing RFI register for the conflict habit.
Default: the quantity follows the issued sheets and specs. The model difference becomes a Questions tab item with the sheet value as the stated default.
Worked example: model area vs PDF-scaled area (made up, not a real job)
These numbers are invented. No real project. No dollar totals. No waste percent.
Assumptions (invented): One low-slope roof with plan dimensions of 240 ft by 172 ft on the dimensioned roof plan. A 30 ft by 40 ft mechanical penthouse with its own roof sits inside that footprint. Parapet height from a wall section is 3 ft all around. The estimator also scales the PDF roof plan.
| Step | Calculation | Result |
|---|---|---|
| 1. Dimensioned plan area | 240 × 172 | 41,280 SF gross footprint |
| 2. PDF scaled | 240.5 × 172.5 | 41,486.25 SF |
| 2a. Difference vs dimensioned | 41,486.25 − 41,280 | 206.25 SF (~0.50 percent) |
| 3. Model main roof element | Model reports | 40,080 SF |
| 3a. Opening check | 41,280 − 40,080 | 1,200 SF (= 30 × 40 penthouse) |
| 3b. Penthouse roof element | Separate modeled element | 1,200 SF |
| 3c. Roof total | 40,080 + 1,200 | 41,280 SF of roof |
| 4. Parapet face (not in roof element) | 2 × (240 + 172) = 824 LF, then 824 × 3 ft | 2,472 SF of parapet face before wrap |
Scaling a printed sheet drifts. Half a foot on each side adds about 200 SF here. Use written dimensions or the model when you have them.
The model number is right for what was modeled, but it is not your scope until you check what each element includes. Main roof plus penthouse roof equals the footprint of roof, plus the penthouse walls and curb flashings from details. Parapet face membrane comes from the wall section, not the roof element. See parapet membrane takeoff for the wrap method.
Questions tab (example): The model shows a sloped insulation surface, but the set has no tapered insulation plan. Default: no tapered quantities carried until the tapered plan is issued.
Get your first takeoff free
One per contractor, on a job you're bidding or quoting. Upload the plan set (include PDF sheets exported from the model when you have them) and you get quantities you can check against the sheets.
Usually within one business day. Delivered within 48 hours*.
*Clock starts once any questions we send you are answered.
FAQ
Should a roofing contractor ask the GC for the BIM model?
Yes. Ask your GC for it. It costs nothing to ask. Use the model with the plan set and the spec book, not instead of them.
Can I take roofing quantities straight from a Revit model?
Geometry, yes, as a starting point. Assembly, attachment, warranty, flashing heights, and tapered layout still come from the specs and details. Autodesk notes that minor discrepancies can appear between model volumes and a material takeoff schedule, and that shape edited elements will not report a true thickness.
Is the BIM model a contract document?
Usually not. The AIA Digital Practice Documents Guide says models are usually shared with a disclaimer that the model cannot be relied upon, and that the owner and contractor typically enumerate the contract documents in their agreement. A model version can be a contract document only when the agreement says so.
Does a Revit model show tapered insulation?
It can show a sloped top surface. Autodesk says shape edited elements will not report a true thickness. Take tapered board counts, panel sizes, and crickets from the tapered plan and spec. If the set has no tapered plan, put it on the Questions tab with this default: no tapered quantities carried until the tapered plan is issued.
What if the model and the drawings disagree?
Do not pick the number you like. Note both, cite the sheet, and put it on the Questions tab with the sheet value as the stated default.
What should I upload when I have a BIM model?
Send the full plan set and the spec book. If you have a BIM model, export PDF sheets from it and upload those with the set (the picker accepts PDF or ZIP only). We do not take quantities from model files. If a file will not fit the upload caps (20 files, 2 GB each), email [email protected].
Why send your takeoffs to Sharp Pencil
A model helps you check geometry against the set. The bid still comes from the drawings and the spec book, and every page of them has to be read.
- Usually within one business day. Delivered within 48 hours*. A takeoff stuck in a week-long queue does you no good when the bid is due sooner.
- Every page gets read. Send the full set: architectural, structural, mechanical, plumbing, and the spec book if you have it.
- Every quantity names its sheet. Every quantity carries its source sheet and its basis, so you can check it against the drawings.
- Questions instead of guesses. If the set leaves something open, it goes on the Questions tab in Takeoff.xlsx, not into the number as a guess.
- Checked before it goes out. Every paid takeoff is checked before delivery.
- Four files, one package. START HERE, marked-up drawings PDF, Takeoff.xlsx with a Questions tab, and the material order list.
- Your plans stay yours. A plan set you send us will never be used to compete with you, and plan sets are deleted whenever you ask. See what happens to your plans.
- First takeoff free, one per contractor, on a job you're bidding or quoting. After that, $395 per new set of drawings, or monthly Shop plans. See what a takeoff costs and how it works.
Commercial roofing takeoffs for low-slope (TPO, EPDM, PVC, mod bit and BUR), standing seam and shingle roofs. Residential is not our focus today, but ask if you have a job in mind. See our commercial roofing takeoff services and where every number comes from.
Get your first takeoff free · See full pricing and plan terms · Or email [email protected]
*Clock starts once any questions we send you are answered.
The Sharp Pencil team
Sources
- Sharp Pencil home FAQ (BIM model), getsharppencil.com, /upload (PDF or ZIP picker), standing seam Why send, /your-data
- AIA Contract Documents, Digital Practice Documents Guide (2022 documents): assets.aiacontracts.com PDF
- AIA Contract Documents, Instructions: E202-2022 BIM Exhibit: help.aiacontracts.com
- Penn State CIC, BIM Project Execution Planning Guide Version 2.2, Appendix B-23 Cost Estimation (Quantity Take-Off)
- Autodesk Revit 2026 help: Material Takeoff Schedules and About Shape Editing