A tape measure and a satellite image rarely agree. Here is the workflow PV designers use to reconcile them — without throwing the drawing set away and starting over.
Illustrative figures to explain the idea, not client data.
The Roof Never Reads the Drawing
Every residential PV layout starts as a promise: this many modules, this string split, this conduit run. Then someone climbs up with a tape, and the promise meets the shingles.
The drawing set that survives that moment is not the one drafted fastest. It is the one drafted by a team that expected the mismatch. That is the assumption behind every residential set at Microdras: the first measurement is a hypothesis, and the drawings are built to be revised.
- Satellite imagery is flat, angled, or out of date — it hides eaves, hips, and recent additions.
- Homeowner and installer sketches skip overhangs, fascia, and setback zones.
- Vent stacks, chimneys, and skylights rarely show up on aerial images.
- Pitch and azimuth read from a photo differ from the real roof plane.
- Shading details change the moment someone actually stands on the roof.
How Big Is the Mismatch? Triage Before You Redraw
Not every discrepancy deserves a new drawing set. Designers sort the gap into three levels first — it decides how much of the package has to move.
Minor drift
- Adjust offsets and setbacks on the array layout.
- Update dimensions and notes; module count stays the same.
- Reissue only the affected sheet.
Re-balance
- Trim or shift modules to fit the real roof plane.
- Re-check string sizing and MPPT allocation.
- Update BOM quantities and SLD callouts.
Re-plan
- Re-run layout, orientation, and tilt.
- Re-simulate energy yield in HelioScope or PVsyst.
- Re-route conduit, recalculate wire sizes, reissue the full set.
When Two Sources Disagree, This Is Who Wins
Designers do not average conflicting inputs — they rank them. Higher rungs overwrite lower ones, and anything still assumed is flagged on the sheet instead of hidden.
Measured on site
Tape or laser measurements with dated photos. The source of truth.
Photos with a scale reference
Dated photos where something of known size is in frame.
Installer or homeowner sketch
Good for intent; risky for overhangs and setbacks.
Satellite / Google Maps imagery
Fast for a first layout; refined later with real site data.
Assumed defaults
Placeholders, marked TBC on the sheet until confirmed.
A mismatch is not a drafting failure — an unmanaged mismatch is. The fix is a source hierarchy, a triage level, and a drawing set built to take revisions.
Four Mismatches That Reshape a Layout
The same four situations account for most of the late changes on residential roofs. Here is what the designer sees — and what changes in the drawing.
The roof is shorter than the plan
A vent stack sits where an array row was planned
Pitch and azimuth are not what the photo suggested
The inputs never arrived
What a Site Correction Actually Changes
One shorter roof edge ripples through the whole set. Here is a typical Rev A to Rev B diff.
When strings change, the single-line diagram has to follow — see electrical schematic drafting for how those sheets are built.
The Loop That Keeps the Drawing Set Honest
Capture site truth
Collect measurements, photos, and shading notes from the site visit.
Reconcile against the plan
Rank the sources, pick a triage level, and list every sheet the change touches.
QC and reissue
Multi-level checks, then a clean revision letter with updated BOM and SLD.
Re-draft what moved
Update layout, stringing, conduit, and calculations together, not one by one.
loop
This loop sits inside Microdras’s standard five-step workflow — consultation, assessment, drafting, quality review, delivery — so a revision is a loop, not a restart.
Built for the Site Visit That Changes Everything
Most drafting vendors treat the first drawing as the deliverable. Microdras treats it as the opening bid. See the full residential solar PV design & drafting service.
- Quick design modifications at any stage.
- Revision and markup support across stages.
- Editable source files with all layers.
- Multi-level quality checks for accuracy and compliance.
- Secure, NDA-bound file sharing.
- Sample available on request.
What to Send So the First Layout Lands Closer
Core inputs
- Roof dimensions
- Tilt angle
- Shading information (if any)
- Preferred inverter make
- Local code or utility requirements
Helpful extras
- Site photos, dated, with a scale reference
- Roof sketches
- Google Maps imagery
- Notes on vents, chimneys, and skylights
No measurements yet? Send what you have. Microdras starts from satellite imagery and refines with actual site data before final submission.
Input Sources Compared
Faster inputs are rarely the most accurate ones. Designers use each source for what it is good at.
| Input source | Speed | Accuracy | What the designer does with it |
|---|---|---|---|
| Measured on site | ●●○○○ | ●●●●● | Treat as the source of truth; overwrite everything else. |
| Photos + scale reference | ●●●○○ | ●●●●○ | Cross-check dimensions and spot obstructions. |
| Installer / homeowner sketch | ●●●●○ | ●●○○○ | Use for intent; verify overhangs and setbacks. |
| Satellite / Google Maps | ●●●●● | ●●●○○ | Draft the first layout; flag it for refinement. |
| Assumed defaults | ●●●●● | ●○○○○ | Mark TBC; replace as inputs arrive. |
Two Habits That Prevent Most Rework
Ask the installer for one photo of each roof plane with a tape or ladder in frame. It costs two minutes on site and often saves a full re-layout. If the mismatch is on the property side — meter location, setbacks, boundary — the site plan needs the same discipline: see site layout drafting.
Never let a late correction touch only the array sheet. A module count that is not carried into the SLD, BOM, and placards is how permit rejections and install-day surprises happen. Once the system is in, close the loop with as-built drawings.
Red Flags That the Measurements Are Off
Spot these before the permit set goes out, and the site visit becomes a confirmation instead of a surprise.
Roof framing not matching what the structural check assumed? Cover it with framing plan drafting.
Codes Don’t Move When the Roof Does
A mismatch changes the geometry, not the rulebook. Every revision stays inside the standards and is customized to local AHJ and utility requirements.
Related Drafting Services
The services that sit next to residential PV when the site and the plan disagree.
Four Things to Remember
Treat the first measurement as a hypothesis
Satellite-first layouts are fine when they are flagged and refined.
Rank sources, don’t average them
Site measurements overwrite imagery, sketches, and defaults.
Triage before you redraw
Minor drift, re-balance, or re-plan decides how much moves.
Carry every change through the whole set
Array, strings, conduit, SLD, BOM, and placards move together.
Frequently Asked Questions
What if there are no site measurements yet?
Initial layouts can be drafted from Google Maps or satellite imagery, then adjusted with actual site data before final submission.
Which input wins when satellite imagery and site measurements disagree?
Measured site data. Imagery lets the design move fast early; once real dimensions arrive they overwrite it, and any remaining assumptions stay flagged on the sheet.
Will the drawings be reworked after a site visit?
Yes. Microdras supports revision and markup across stages and makes quick design modifications at any stage, so a corrected roof dimension flows through layout, stringing, BOM, and SLD.
What do you need from us to start a layout?
Roof dimensions, tilt angle, shading information (if any), preferred inverter make, and local code or utility requirements. Photos, sketches, and Google Maps imagery help.
What does residential solar PV drafting cost?
Pricing starts at USD 35 per set, with hourly, per-sheet, or full-project models. Final pricing depends on scope, standards, and documentation requirements, and is quoted upfront with no hidden charges.
Send us the roof you actually measured.
Drop in the roof dimensions, photos, or just a Google Maps pin. Microdras drafts the PV layout, string map, SLD, and permit set — then reworks it when the site disagrees.
Starting from$35per set
- Hourly, per-sheet, or full-project pricing
- Upfront quote, no hidden charges
- Revisions supported at every stage
