Most defect lists online are either a spreadsheet of checklist ticks or a photo gallery with no explanation of what the photo shows. This guide is the version an inspector actually needs on site: forty defects, grouped by the trade responsible for fixing them, and for each one the same four things, what it looks like, what usually caused it, how seriously to treat it, and what to write down so the person reading the report can price it without a second visit.
Severity here uses four bands. Low is cosmetic. Medium affects function or will worsen if ignored. High is a safety, water or compliance problem. Critical means stop, isolate or do not occupy. Bands are a starting point; a low defect in a client's kitchen and a low defect in a plant room are not the same conversation.
How to use this guide
Walk the building by trade, not by room, when you are looking for defects; walk it by room when you are writing them up. The numbering below is the trade order most inspectors use, because it matches the order the work went in: structure first, envelope second, finishes last. If you are snagging a new home rather than inspecting a commercial build, items 1–6 will mostly be reading cracks, and the bulk of your list will come from sections three and four.
Every entry ends with a "record it" line. That is deliberate: a defect that is described well enough to be priced gets fixed, and a defect that is described as "crack in wall" gets argued about. If you want the wider structure of the document those lines go into, the defect report guide covers it, and the punch list template has the field list.
Structure and substructure
Few structural defects are visible at handover, and most cracks are not structural. The job in this section is to tell the two apart quickly and to know when to stop guessing and call an engineer.
1. Diagonal cracks above door and window openings Medium
What you see: A crack running at roughly 45° from the corner of an opening, usually in plaster or blockwork, often on both sides of the wall.
Likely cause: Drying shrinkage of blockwork or plaster in the first year is the common one, concentrated at openings because that is where the wall is weakest. Consistent widening, a crack wider than about 3 mm, or a matching crack outside points to movement instead.
Record it: Location, length, widest point measured with a gauge, and whether it is visible externally. If under 2 mm and static, it is a filling job after the first heating season; if wider or growing, it is monitoring and an engineer, not filler.
2. Stepped cracking in brickwork or blockwork High
What you see: A crack that follows the mortar joints in a staircase pattern, usually near a corner, under a window or above a lintel.
Likely cause: Differential settlement, subsidence, a failed lintel or thermal movement in a long unjointed wall. Stepped cracking is masonry moving as blocks, which is rarely just shrinkage.
Record it: Photograph the whole elevation for location, then the crack with a scale. Note whether the crack is wider at the top or bottom (it tells the engineer which way the wall is moving). Recommend a structural engineer's inspection before any repair; do not write "repoint".
3. Corroded exposed steel and spalling concrete High
What you see: Rust staining on concrete, then concrete breaking away to expose rusting reinforcement or a column base with flaking, laminated steel.
Likely cause: Insufficient concrete cover, chloride exposure, or steel left unprotected at a base or penetration. Rust expands, which is what pushes the concrete off.
Record it: Extent of the spall in millimetres, whether the exposed bar is pitted or just stained, and the element it is on. Cosmetic patching over corroding steel is the wrong fix; the line is to break out to sound concrete, treat the steel and reinstate cover.
4. Honeycombing and voids in concrete Medium
What you see: Patches of exposed coarse aggregate with no cement paste between the stones, usually at the base of a wall pour, around reinforcement congestion or at formwork joints.
Likely cause: Poor compaction, a mix that was too dry, or formwork that leaked grout. Shallow honeycombing is cosmetic; deep honeycombing around reinforcement removes the cover that protects it.
Record it: Location, approximate area, and whether reinforcement is visible in the void. Small and shallow: cut back and make good with a repair mortar. Reinforcement visible: engineer to assess before repair.
5. Cracks in ground-floor slabs and screeds Medium
What you see: A crack across a floor slab, often crossing a control joint rather than following it, sometimes with one side slightly higher than the other.
Likely cause: Shrinkage cracking where joints were too far apart or cut too late; a level difference across the crack means the sub-base has settled and it is no longer just shrinkage.
Record it: Width, length, and whether there is a step across the crack (run a straight edge). No step and under 1 mm: seal before the floor finish goes down. A step or a widening crack: monitor and investigate the sub-base.
6. Excessive floor deflection or bounce Medium
What you see: A timber floor that bounces underfoot, a visible dip between joists, or cracked ceiling plaster below a floor that is being walked on.
Likely cause: Undersized or over-spanned joists, joists notched or drilled too deeply for services, missing strutting, or a load the floor was not designed for.
Record it: Which room, where in the span, and what is above it. If services have been cut through joists, photograph the notch with a tape. Recommend an engineer's check on the joist sizes and any notching before the ceiling is closed up.
External envelope: roofs, walls, windows and doors
The envelope is where the expensive defects live, because every one of them is a water path. A slipped tile is a ten-minute fix in October and a rotten rafter in February. Weight this section accordingly.
7. Slipped, cracked or missing roof tiles High
What you see: A tile out of line with its course, a visible gap, a cracked tile, or mortar missing from a verge or ridge.
Likely cause: Tiles not nailed or clipped to the specification, wind uplift at verges and eaves, or simply damage during later trades' work on the roof.
Record it: Photograph from the ground with a long lens or a pole camera, identify the slope and approximate course, and state "re-fix and replace" rather than "check roof". Note any daylight visible from the loft.
8. Gutters holding water or discharging in the wrong place Medium
What you see: Standing water in a gutter after rain, a gutter overflowing at one point, or a downpipe that discharges onto a wall or a path instead of into a drain.
Likely cause: Wrong or no fall to the outlet, brackets too far apart so the gutter sags, or a downpipe that was never connected to the gully below.
Record it: Which elevation, which run, and where the water goes. Recommend re-setting the fall to the outlet and connecting the downpipe; if there is staining on the wall below, add a separate item for the damp check.
9. Damp staining above openings or at the base of walls High
What you see: A tide mark or dark patch on the inside of an external wall above a window or door, or along the bottom of a ground-floor wall.
Likely cause: A missing or badly formed cavity tray or stop end above the opening, missing weep holes, a bridged damp-proof course, or external ground built up above the DPC (see item 39).
Record it: Photograph inside and outside at the same point. Take a moisture reading if you carry a meter and record the number. The line is to open up and confirm the tray or DPC detail; not "redecorate".
10. Render cracking, hollow render and staining Medium
What you see: Hairline map cracking, a single crack from a corner, patches that sound hollow when tapped, or dark streaks below cills and copings.
Likely cause: Shrinkage of a strong render on a weak background, no movement joints, render carried down over the DPC, or missing drips on cills so water runs down the face.
Record it: Tap-test the area and mark the hollow extent. Distinguish shrinkage crazing (low) from a single opening crack (medium). Recommend cutting out hollow render and reinstating with a matching mix; fill and paint over hollow render is a fail.
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11. Efflorescence on new brickwork Low
What you see: A white powdery deposit on the face of new brick or block, usually in the first months, worst after wet weather.
Likely cause: Soluble salts in the bricks or mortar carried to the surface as the wall dries. Usually harmless and self-limiting; persistent efflorescence in one place suggests water is getting in and coming out there.
Record it: Note it, photograph it, and set expectations: it should be dry-brushed, never washed, and should stop within a year. If it recurs in one location only, raise a separate water ingress item.
12. Poor pointing and mortar joints Low
What you see: Joints of uneven width or depth, smeared mortar on the brick face, unfilled perpends, or a joint profile that differs between elevations.
Likely cause: Workmanship and weather: perpends left unfilled to save time, mortar smeared during cleaning, or joints struck at different times by different bricklayers.
Record it: Elevation, extent and the specific fault ("unfilled perpends, approx. 30 over the garage elevation"). Unfilled joints are a water and thermal issue and should be pointed up; cosmetic inconsistency is a conversation about what the specification says.
13. Damaged glazing and failed double-glazed units Medium
What you see: A cracked pane, scratches visible from a metre away in daylight, or misting between the panes of a sealed unit that does not clear.
Likely cause: Damage during following trades, glass scratched during cleaning with a blade, or a failed edge seal on the unit letting moist air in.
Record it: Identify the window by room and position, photograph the defect against a plain background, and use the industry viewing standard (scratches visible at 2 m in daylight count). Misting is a replacement unit, not a clean.
14. Doors and windows that bind, do not latch or have uneven gaps Medium
What you see: A door that catches on the frame or floor, a latch that needs the door lifted to close, gaps visibly wider at the top than the bottom, or an opening light that will not lock.
Likely cause: Frames fitted out of square or not packed, hinges not adjusted, the building drying and moving, or ironmongery fitted before the door was hung.
Record it: Which door, what it does, and what happens when it is closed normally. Adjust or re-hang, not "check door". For a fire door add the gap measurements: over 4 mm at the head or sides is a compliance item, not a snag.
Internal finishes: plaster, paint, tiles and joinery
This section produces the longest list and the smallest bills. The temptation is to treat it as noise. Resist it: finishing defects are what the client sees every day, and how they are written decides whether the decorator gets a clear list or a complaint.
15. Hollow, blown or uneven plaster Medium
What you see: Plaster that sounds hollow when tapped, a bulge, an area that has come away from the wall, or trowel marks and undulations visible in raking light.
Likely cause: Poor key to the background, plaster applied too thick or to a dusty surface, or the building drying faster than the plaster could cope with.
Record it: Tap the wall and mark the hollow extent with tape before photographing. The line is to hack off to a sound edge and re-plaster; skimming over hollow plaster fails within a year.
16. Visible board joints, popped fixings and cracked tape Low
What you see: A straight line or ridge where two plasterboards meet, a small circular bump or hole where a screw has pushed through, or a crack along a taped joint.
Likely cause: Joints not feathered, screws driven too deep or not deep enough, boards fixed to timber that then dried and shrank, or a ceiling that was loaded before the joints had set.
Record it: Room, wall or ceiling, and count. "Popped screws, ceiling, approx. 12" is a list the decorator can price. Recommend re-fix, fill and sand; if the whole ceiling has popped, the boards are not fixed to the joists and that is a different item.
17. Paint: misses, runs, poor coverage and flaking Low
What you see: Grinning (the previous colour showing through), runs and sags on doors, brush marks in gloss, missed areas behind radiators, or paint flaking off in sheets.
Likely cause: Too few coats, paint applied to a dusty or damp surface, no primer on bare plaster, or simply rushed work at the end of a programme.
Record it: Photograph in raking light from a window or torch so the defect shows. State the standard: finishes are viewed from 2 m in natural light, and if it is visible from there it is a defect. Flaking sheets mean a moisture or preparation problem and need the cause noted.
18. Tiles: lipping, cracked tiles and hollow tiles Medium
What you see: A tile edge standing proud of its neighbour so you can feel it with a fingernail, a cracked or chipped tile, or tiles that sound hollow when tapped.
Likely cause: Uneven background, adhesive spotted rather than solid-bedded, tiles walked on before the adhesive cured, or a crack in the substrate coming through.
Record it: Room, wall or floor, and count. Lipping over 1 mm on a floor is a trip and a cleaning problem. Hollow tiles fail later; recommend lifting and re-bedding rather than "monitor". For a single cracked floor tile, note whether the crack lines up with a substrate joint.
19. Grout: cracked, missing or inconsistent Low
What you see: A crack along the grout line at an internal corner or where a wall meets a bath, missing grout at the edge of a tiled area, or grout colour varying across a wall.
Likely cause: Rigid grout used at a junction that needs to move (internal corners and wall-to-tray junctions should be silicone), grout applied too thin, or mixed in batches that did not match.
Record it: Location and a count of the affected joints. Internal corners: rake out and replace with a matching sealant, not more grout. Elsewhere: rake out and re-grout. A hairline in a single joint is a snag; a corner that has cracked all round is a water path.
20. Sealant: missing, badly tooled or already mouldy Medium
What you see: No sealant where a worktop meets a wall, a bead that is lumpy or smeared, a gap behind a bath or shower tray, or black spots in sealant within weeks of handover.
Likely cause: Left off, applied to a wet or dusty surface, tooled with a finger and no release agent, or the wrong product (acrylic where sanitary silicone was needed).
Record it: Every junction that should be sealed and is not, by room. Missing sealant at a shower tray or bath is high, not low: it is the single most common cause of water damage to the room below. See item 25.
21. Skirtings, architraves and trim Low
What you see: Open mitres at corners, nail holes not filled, a gap between skirting and floor or wall, or a length of trim with a visible join in the middle of a wall.
Likely cause: Timber fitted before the building had dried, so it shrank; joinery cut short and packed; or walls out of plumb that the skirting could not follow.
Record it: Room and the specific fault. "Open mitre, hall, left of front door" is a five-minute fix. Gaps under skirting wide enough to see daylight through a suspended floor are a draught item too, so say so.
22. Flooring: gaps, lifting edges, squeaks and wrong falls Medium
What you see: Laminate or engineered boards with open joints or lifted ends, a floor that squeaks in one spot, vinyl with a bubble, or a wet-room floor that holds water away from the drain.
Likely cause: No expansion gap so the floor buckles, a subfloor that was not flat, moisture in a screed that was not tested before the floor went down, or a fall laid the wrong way.
Record it: Room, location within the room, and the measured defect ("joint open 2 mm, 1.2 m from window wall"). A squeak is usually a subfloor fixing. A wet-room fall away from the drain is a rebuild of the floor, however good the tiling looks.
23. Kitchen and bathroom units: alignment, damage and gaps Low
What you see: Doors and drawers with uneven gaps, a worktop with a chip or a swollen joint, a gap between the worktop upstand and the wall, or end panels with a visible cut edge.
Likely cause: Units fitted to walls that are out of plumb without being scribed, worktops cut on site without sealing the cut edge, or damage during later trades.
Record it: Unit by unit, with the fault. Swelling at a worktop joint is water getting into the chipboard core and will only get worse; it is a replacement, not a filler. Adjustment of doors and drawers is a single line for the whole kitchen.
Wet areas and plumbing
Water does not stay where the defect is. A failure in a first-floor bathroom is an item in the bathroom and an item in the ceiling below it, and it is usually the second one that the client finds first.
24. Shower tray and bath junctions that let water through High
What you see: A gap or a cracked sealant line where the tiling meets the tray or bath, a tray that flexes when stood on, or staining on the ceiling directly below the shower.
Likely cause: The tray was not bedded solid so it moves and breaks the seal, the tiling was sealed before the tray was loaded, or the upstand was never fitted.
Record it: Stand in the tray and watch the junction. Photograph the junction and the ceiling below. The line is to remove the sealant, confirm the tray is bedded, and re-seal with the tray loaded; if the ceiling is stained, add the ceiling as its own item.
25. Sealant failure and lack of fall in wet rooms High
What you see: Water pooling in a corner of a wet room after a shower, sealant peeling from a tiled floor-to-wall junction, or a damp smell in a room that looks dry.
Likely cause: A fall laid too shallow or towards the wrong corner, tanking omitted or not lapped into the drain, or the sealant asked to do the job the tanking should have done.
Record it: Run water and photograph where it goes. State the fall in the item ("pooling at the north-east corner; no fall to the drain"). This is a floor-up rebuild, and the report should say so plainly rather than recommend re-sealing.
26. Leaking joints, traps and valves High
What you see: A drip at a compression joint or trap, a damp patch under a basin, a stain in a cupboard below a sink, or water at the base of an external stop valve.
Likely cause: Joints not tightened after testing, a trap disturbed when the unit was fitted, a cross-threaded fitting, or a valve gland that was never nipped up.
Record it: Photograph the joint and anything the water has reached. Turn off the isolation valve if there is one and say so in the item. Recommend remaking the joint and checking the surrounding materials for damage; a plumber can price "remake trap connection, basin, WC2" without visiting.
27. Damaged, loose or incorrectly fitted sanitaryware Medium
What you see: A basin that moves when leant on, a WC pan that rocks, a chipped or crazed glaze, taps fitted hot-right, or a bath panel that does not sit flush.
Likely cause: Fixings omitted or fitted into plasterboard without a pattress, sanitaryware fitted before the wall was finished so the fixings had nothing to bite into, or damage in transit that nobody reported.
Record it: Item, room and the specific fault. A rocking pan will break its pan connector and leak; it is medium now and high in a month, so say that. Chips and crazing are a replacement under most specifications and the photograph is the evidence.
28. Water staining on ceilings and around windows High
What you see: A yellow-brown ring or patch on a ceiling, staining that follows a line (a pipe or a joist), blistered plaster below a window, or a stain that reappears after decoration.
Likely cause: Anything above it: a bath or shower junction, a pipe joint, a roof, a flashing, a window that is not sealed to its frame. The pattern narrows it down: a ring is a single point leak; a streak is a run.
Record it: Photograph the stain with something for scale and mark its edge with pencil and a date so growth can be seen on the re-inspection. Recommend tracing the source before any redecoration. Never write "stain block and repaint" on a stain with an unknown cause.
29. Mould growth in cold or unventilated spaces High
What you see: Black spotting on a ceiling corner, along a window reveal, behind furniture on an external wall, or spreading across a basement or utility wall.
Likely cause: Condensation on cold surfaces where ventilation is inadequate (see items 35 and 36), a cold bridge in the construction, or a water ingress that has not been found.
Record it: Extent in square metres, the surface it is on, and a moisture reading if possible. If it is in a habitable room, say that occupation should wait until the cause is fixed. The recommendation is cause first, remediation second, redecoration last.
30. Heating: radiators not level, valves missing, no isolation Low
What you see: A radiator visibly out of level, a lockshield valve without its cap, a radiator with no thermostatic valve where the specification called for one, or an appliance with no isolation valve within reach.
Likely cause: Rushed second fix, valves swapped between rooms, or a specification that was not read.
Record it: Room and fault, one line per radiator. Missing isolation valves on appliances are a compliance item in most jurisdictions and should be flagged as such. A radiator that is cold at the top is bleeding, not a defect, unless it recurs.
Electrical
You are not testing the installation; the electrician's certificate does that. You are recording what is visible, and anything visible that is live and accessible is critical regardless of how the rest of the building looks.
31. Exposed wiring and missing enclosures Critical
What you see: Cable cores visible, a junction box with no lid, cables running unsupported across a ceiling void that is about to be closed, or a cable clipped across a hot pipe.
Likely cause: Second fix not finished, an unfinished alteration, or accessories removed by a following trade and not replaced.
Record it: Photograph from a safe distance, showing the location. Do not touch it. The item should say "isolate the circuit at the consumer unit" and name the electrician's action; it should also say that no other work should continue in that area until it is made safe.
32. Damaged, loose or unfinished sockets and switches High
What you see: An accessory that is cracked, one that moves in the wall, a back box with no faceplate, or a socket fitted upside down or at the wrong height.
Likely cause: Back boxes not fixed, accessories fitted to a wall that was later plastered around them, damage from decorating, or an accessory omitted from the second fix.
Record it: Room, position and the fault. A loose accessory can pull its conductors; treat it as high, not cosmetic. Heights and positions are a compliance question in most codes, so cite the requirement if you know it and let the electrician confirm.
33. Missing earth bonding and unlabelled consumer units High
What you see: No visible bonding conductor to incoming water and gas pipes, a consumer unit with blank circuit labels, or a residual current device with no test record.
Likely cause: Bonding forgotten or removed when the pipework was altered; labels never filled in; the installation certificate not yet issued.
Record it: Photograph the incoming services and the consumer unit with the door open. The item is a request for the electrical installation certificate and for the bonding to be confirmed and labelled; you are not certifying it, you are recording that it has not been.
34. Light fittings, extractor fans and smoke alarms not working Medium
What you see: A fitting that does not switch on, a fan that does not run when the light is on, a smoke or heat alarm with no power indicator or one that does not respond to its test button.
Likely cause: Not connected, connected to the wrong circuit, a fan wired without the permanent live it needs, or alarms fitted without their batteries.
Record it: Test every switch and every alarm test button and list what does not respond. A smoke alarm that does not test is a do-not-occupy item in a dwelling; say so. Everything else is second-fix completion.
Heating and ventilation
Ventilation defects are invisible on the day and expensive in the first winter, because condensation and mould are what an unventilated building produces. The inspection has to look for them deliberately.
35. Extract fans that do not extract Medium
What you see: A fan that runs but moves no air at the grille, a duct that terminates in the loft or ceiling void instead of outside, or an external grille with its flap sealed shut by paint.
Likely cause: Duct never connected, duct crushed, an external terminal never fitted, or a fan sized for a duct run half the length of the one installed.
Record it: Hold a tissue to the grille with the fan running and photograph the result. Check the loft for a duct that ends in mid-air. The item is to connect and terminate the duct externally and confirm the extract rate; "fan noisy" is a different, lower item.
36. Trickle vents missing, blocked or painted shut Low
What you see: No trickle vent in a window where the ventilation strategy relies on one, a vent with its slider sealed by paint, or a vent installed with no slot cut through the frame behind it.
Likely cause: Windows ordered without vents, decorated with the vents closed, or vents fitted for appearance without the frame being routed.
Record it: Window by window. Confirm the vent opens and that air moves through it. If the whole house has no background ventilation and no mechanical system, that is one high item about the ventilation strategy, not twelve low items about vents.
37. Boilers and heat pumps not commissioned or badly installed High
What you see: No commissioning certificate or benchmark record, a condensate pipe discharging outside without insulation or into nothing, a flue terminal too close to an opening, or a pressure gauge sitting at zero.
Likely cause: The installer left before commissioning, the certificate was not handed over, or the flue and condensate routes were changed on site without being checked.
Record it: Photograph the appliance data plate, the flue terminal from outside, and the condensate discharge. Request the commissioning documents in the item. Flue clearance is a manufacturer's figure and a regulation; quote the distance you measured and let the installer respond.
External works and drainage
External works go in last, get inspected least, and are where the defects that affect the building itself hide: ground levels, falls and drains. Ten minutes outside with a level is the best-spent ten minutes of the visit.
38. Paving that falls towards the building or lips at joints Medium
What you see: A puddle against the wall after rain, a path that visibly slopes back to the house, or a slab standing proud of the next one by more than a few millimetres.
Likely cause: Paving laid to the wrong fall, a sub-base that has settled, or slabs bedded on spots rather than a full bed.
Record it: Photograph after rain if you can, or pour a bottle of water and photograph where it goes. Measure the lip with a rule. Falls should be away from the building; lipping over 5 mm on a walked route is a trip hazard and should be written as one.
39. Ground levels bridging the damp-proof course High
What you see: Soil, gravel, paving or a raised bed sitting at or above the line of the damp-proof course, usually visible as the horizontal joint about 150 mm above finished ground level.
Likely cause: Landscaping done after the walls without reference to the DPC, or paving levels set from a threshold rather than from the DPC.
Record it: Photograph the wall base with a tape from the DPC to the ground. The item is to lower the external level to at least 150 mm below the DPC or to install a proper channel detail; it is also a note to check inside for damp at the same point.
40. Blocked gullies, uncovered chambers and debris in drains High
What you see: A gully full of mortar and site debris, an inspection chamber with no cover or a cover that rocks, a downpipe discharging next to a gully rather than into it, or water standing in a chamber that should be dry.
Likely cause: Site debris washed in during construction, covers never fitted or damaged by plant, and drainage runs that were not jetted and tested before handover.
Record it: Lift every accessible cover and photograph what is inside. Missing or loose chamber covers are a fall hazard and go in as high. Recommend a CCTV survey and jetting if any chamber shows debris or standing water, and ask for the drainage test certificate in the same item.
How to write these up so they get fixed
Forty defects on a walk is a normal afternoon. What separates a report that clears in two weeks from one that generates two months of email is not the finding; it is the line. Every item above ends with the same shape, and it is worth being explicit about the pattern:
- Where, precisely enough that someone who has never been on site can walk to it: room, wall or element, position on it.
- What, in terms that can be priced: the defect, its extent with a number, and one photograph that locates it plus one that shows it.
- How serious, in a band the contractor understands and the client can prioritise by.
- What to do, as an action, not an observation. "Re-bed and re-seal the tray" is an instruction; "shower leaks" is a complaint.
The defect report guide covers the document those lines go into and the wording that avoids disputes; the pre-handover snag list is the short version of this guide for new homes. If you are doing this for a living and the write-up is where your evenings go, the app this site belongs to was built for exactly that step: photograph the defect, get a draft description, severity and recommendation to edit, and export the report, the free tier covers a full small inspection, and the snagging inspector page shows the workflow end to end.
A note on judgement. Nothing in this guide replaces looking properly. The severity bands are a starting point, the causes are the common ones and not the only ones, and every "recommend an engineer" line means exactly that. The value of an inspector is knowing which of the forty is the one that matters today.
Questions people ask
What is the most common construction defect?
On new housing, finishing defects outnumber everything else: paint, plaster, sealant, grout, doors that bind. They are cheap individually and expensive as a list, because there are so many of them. Water-related defects are fewer but far more costly, which is why an inspection weights them differently. The 14 snags found on almost every handover covers the frequency question in more detail.
What is the difference between a defect and a snag?
In practice, none. A snag is a defect small enough to list and fix without a redesign; in UK usage the words are interchangeable and on the report they should be. Latent defects are the ones that cannot be seen at handover and appear later, which is what the defects period exists for.
How do you classify the severity of a construction defect?
By consequence, not by size. Anything that is a safety hazard or an active water path is high or critical however small it looks; anything cosmetic is low however large the area. A workable four-band scale is low (cosmetic), medium (functional or will worsen), high (safety, water, or non-compliance) and critical (stop, isolate, or do not occupy).
Do I need a photograph for every defect?
Yes, if it is going on a report, and two are better: one wide enough to locate it, one close enough to see it. A written description alone is disputed; a photograph with a location and a date is not. How to structure the report covers what goes around the photograph.
Can an app identify construction defects from a photo?
Visible ones, reasonably well: cracking, staining, failed finishes, exposed services, missing components. It cannot judge cause, hidden work or code compliance, and it should not set the severity unsupervised. Treat the output as a draft of the description; the judgement on the report is the inspector's.