Lofts and cellars are where you actually see the wiring on an EICR, and they are where most of the arguments about codes start. The rule from Electrical Safety First's Best Practice Guide 4 (Issue 7.4, August 2026) is simple: code the danger, not the location. A 2.5 mm² twin and earth totally surrounded by loft insulation for half a metre or more is rated at half its clipped-direct figure under Regulation 523.9, so 13.5 A instead of 27 A. That is a design shortfall and usually C3. The same cable chewed by rats down to bare copper is C2 or C1, however rarely anybody goes up the ladder.
- Code loft and cellar defects on the risk they present today, not on how often the space is used (BS 7671 Chapter 65, ESF Best Practice Guide 4 Issue 7.4).
- Cables in thermal insulation are a current-carrying capacity question: Regulation 523.9, Table 52.2 and installation methods 100 to 103 in Table 4D5. Work out the derated figure before you code.
- Junction boxes must be accessible unless they are one of the exceptions in Regulation 526.3. Inaccessible but sound is normally C3; lid off or heat-marked is C2.
- Cellars bring damp, corrosion and extraneous-conductive-parts. Missing main bonding is the classic C2, and the clamp should be within 600 mm of the meter or point of entry (Regulation 544.1.2).
- If you could not get in, or could only see two metres from the hatch, say so as a limitation. "No defects" over a space you did not inspect is indefensible.
- Sources used: BS 7671:2018+A4:2026, IET Guidance Note 3, ESF Best Practice Guide 4, NICEIC/Voltimum technical articles and the IET EngX forum.
Why do lofts and cellars need their own routine on an EICR?
Because most of an EICR is done from accessories and the board, and you are inferring what the cables are doing behind the plaster. The loft and cellar are the two places where you can see the cable route, the fixings, the joints and every alteration since the house was built: the original lighting, the 1990s shower feed, a newer extractor, the PV DC cables and the smart-doorbell transformer someone screwed to a rafter.
IET Guidance Note 3 expects the inspection to include, where accessible, wiring systems in roof spaces and under floors, and it expects any part you could not inspect to be agreed and recorded as a limitation. So plan for both spaces before you start testing. Take a decent torch, a camera, a crawl board and a dust mask (loft insulation is not kind to lungs), and allow a realistic slot for each space rather than a glance at the end of the day.
If the hatch is painted shut, the loft is boarded wall to wall with stored boxes, or the cellar is locked, record it. EICR sampling and limitations explained covers how to word the extent and limitations section so the report stays honest and usable.
How do you code cables buried in loft insulation?
Start with the numbers, because the code follows from them. Table 4D5 in Appendix 4 of BS 7671 gives flat twin and earth ratings for installation methods 100 to 103, which exist precisely for cables in insulated ceilings and stud walls:
| Method | Installation | Notes |
|---|---|---|
| 100 | Above a plasterboard ceiling, covered by insulation not exceeding 100 mm | Typical older loft with a thin quilt |
| 101 | Above a plasterboard ceiling, covered by insulation exceeding 100 mm | Typical modern loft, 270 mm or more of mineral wool |
| 102 | In a stud wall with thermal insulation, cable touching the inner wall surface | Loft conversions, dormer walls |
| 103 | In a stud wall with thermal insulation, cable not touching the inner wall surface | Lowest rating of the four |
| 523.9 rule | Totally surrounded by insulation for 0.5 m or more | 0.5 × the Method C (clipped direct) rating |
Two worked figures you can use on site. A 2.5 mm² twin and earth clipped direct (Method C) is rated at 27 A; totally surrounded for 0.5 m or more, Regulation 523.9 gives 0.5 × 27 = 13.5 A. A 10 mm² cable under deep loft insulation on Method 101 is rated at 36 A, and a 6 mm² on Method 101 at 27 A, falling to 23.5 A on Method 103. Remember the cable takes the lowest-rated method anywhere along its route, and that the method number goes in the reference method column on the schedule.
Now apply it. A 32 A ring final to the bedrooms with a few metres buried in insulation carries a light, diverse load and the two legs share it. It is outside its design assumptions, but nothing is cooking, and C3 with the length and location recorded is the usual call. Compare a 9.5 kW shower (rated at 240 V, so roughly 38 A at 230 V) fed in 10 mm² that someone has buried under 300 mm of insulation on the way to the bathroom, protected by a 40 A device. The device rating exceeds the 36 A Method 101 capacity, so Regulation 433.1.1 is not met on a long continuous load. Look closely at that cable. If the sheath is discoloured, soft or stuck to the joist, it is C2. If it is clean, many inspectors still give C2 because the protective device is not protecting the cable; at the very least it is C3 with a clear explanation. The electric shower installation guide and cable sizing and volt drop basics have the full derivation.
One related loft finding: PVC-sheathed cable lying on expanded polystyrene. Plasticiser migrates out of the PVC into the polystyrene and the sheath goes brittle. Cable manufacturers advise keeping PVC products out of contact with polystyrene (Doncaster Cables' advice is quoted in IET EngX thread 28216). Where you find it with the sheath still flexible, recommend separation as C3; where the sheath is cracking or sticky, it is C2.
What are the most common loft observations and their codes?
The table gives the normal starting code under BPG4-style reasoning. The condition on the day can always move a code up.
| Loft finding | Regulation | Usual code | Moves up when |
|---|---|---|---|
| Cable in insulation, sound, derated rating below device | 523.9, 433.1.1 | C3 | Sheath discoloured, softened or heat-damaged: C2 |
| Cables unclipped across joists in an unboarded loft | 522.8 | Usually no code or C3 | Under boards that are walked on, or crushed: C2 |
| Cables through joists less than 50 mm from top or bottom under boarding | 522.6 | C3 | Damage visible from a fixing: C2 |
| Screw-terminal junction box, lid on, buried under insulation | 526.3 | C3 | Loose, heat-marked or terminals visible: C2 |
| Junction box lid missing, live terminals exposed | 416.2, 526.5 | C2 | Within reach from the hatch or boards: C1 |
| Choc-block joints taped and loose in the loft | 526.1, 526.5 | C2 | Exposed live conductor: C1 |
| Rodent damage, sheath gone, insulation intact | 522.10 | C2 | Bare copper visible: C1 |
| Rubber (VIR) cable, insulation brittle at terminations | 621.2 condition | C2 | Insulation crumbling with conductor exposed: C1 |
| Class I metal fitting with no cpc | 411.3.1.1 | C2 | Fitting live on test: C1 |
| Old lighting circuit with no cpc, all fittings Class II, plastic switches | 411.3.1.1 | C3 | Any Class I fitting or metal switch on it: C2 |
| Downlight smothered in insulation, not rated for contact | 421.1, 422.3 | C3 | Scorching on the fitting or timber: C2 |
| PVC cable in contact with polystyrene | Manufacturer guidance | C3 | Sheath cracked or sticky: C2 |
| Tank overflow or roof leak dripping onto a joint or fitting | 522.3 | C2 | Water inside a live enclosure: C1 |
The trap in lofts is over-coding things for being old. Age alone is not a code in BPG4. Rubber cable that is still flexible, tested at a decent insulation resistance and is not being disturbed can be noted with a recommendation to plan replacement; once the insulation flakes when you flex it at a terminal, it is C2. The insulation resistance testing guide covers the readings that back that judgement up.
Downlights deserve a separate look. Pull back the insulation around a few: halogen and some older LED fittings need clearance, and charred joist timber or a melted cover tells you the answer. If the ceiling below is fire-separating (a flat or an integral garage), note whether fire-rated fittings have been used, because a hole full of non-rated downlight changes the ceiling's performance.
What should you check in a cellar?
Cellars in UK housing are usually damp, sometimes flood, and often house the meter, the tails and the board. Classify the environment before you code anything. Appendix 5 of BS 7671 gives water codes: AD2 for dripping (equipment needs at least IPX1), AD3 for spray (IPX3) and AD4 for splashing (IPX4). A dry, sound cellar needs nothing special; one with condensation running down the walls and a standing tide mark does.
Work from the wall inwards:
- Enclosures. Metal boxes rust from the bottom up, so open them and look at the terminals. Corroded terminals in a live accessory are C2.
- Cables. Twin and earth clipped to a wet brick wall corrodes from the inside: the cpc is often the first casualty, and you find it as a high R1+R2. Test from the far end of each circuit, not just the first point. Continuity testing: R1+R2 method explains why.
- Fixings and route. Cables run below the old flood line, or lying on the floor, get a C2 where they are wet or damaged.
- Supply equipment. A corroded cut-out or meter is the network operator's, not yours to fix, but record it and tell the client to contact them. The smart meter, isolator and tails guide covers what you can and cannot touch.
| Cellar finding | Usual code | Notes |
|---|---|---|
| Standard socket, dry cellar, sound, no RCD | C3 | 411.3.3 is not retrospective |
| Socket in a damp cellar, no RCD, used for portable or outdoor equipment | C2 | Explain the reasoning in the observation |
| Corroded terminals inside a socket, switch or isolator | C2 | Photograph with the cover off |
| Main bonding missing to water, gas or oil | C2 | Prove the pipe is extraneous first |
| Main bonding present but undersized for the supply | C2 or C3 | Depends on size and system; see the bonding guide |
| Cables clipped to a wet wall, sheath cracked | C2 | Check R1+R2 on that circuit |
| Lamp holder or batten with no cover, below head height | C2 | C1 if live parts can be touched |
| Cables or accessories submerged or in standing water | C1 or C2 | Make safe before leaving if live and wet |
How should you deal with bonding in the cellar?
The cellar is usually where the water main, the gas service and sometimes an oil line come in, so it is where you confirm main protective bonding rather than assume it. Regulation 411.3.1.2 requires each extraneous-conductive-part to be connected to the main earthing terminal. Before you code a missing bond, prove the pipe is extraneous: an insulation resistance test from the pipe to the MET giving a high reading (GN8 uses roughly 22 kΩ as the threshold for domestic premises) suggests it may not be.
Then check the connection itself. Regulation 544.1.2 asks for the bonding connection to be as near as practicable to the point of entry, and where there is a meter, within 600 mm of the meter outlet union on the consumer's side and before any branch. Size it against Table 54.8 on PME: with a PEN conductor up to 35 mm² copper, that is 10 mm² copper main bonding. Look at the clamp too: a BS 951 clamp with its "Safety electrical connection – do not remove" label, on clean pipe, not on painted copper or a plastic section. The main protective bonding guide has the size bands and the coding table for 6 mm² on PME.
How do you separate C3 from C2 and FI in these spaces?
Ask two questions. Is there a real risk of shock or fire today? Does the defect take away or weaken a protective measure? Two "no" answers make it C3 or a note. One "yes" makes it C2. If a live part can be touched without a tool, it is C1 and you make it safe before you leave site, with the client's agreement recorded.
The cellar trap is under-coding because "it has always been like that". Damp and corrosion only get worse, and a rusting isolator coded C3 reads badly in a fire investigation two winters later.
Use FI only where you genuinely cannot see enough to decide and further work could reveal danger, and say exactly what needs investigating: "Junction box under loft boards above bedroom 2, not accessible without lifting flooring; circuit 3 R1+R2 higher than expected for its length, FI." On the A4 model forms FI is advisory and only C1 or C2 make the overall assessment unsatisfactory, but in England a landlord who receives a report requiring further investigation still has to arrange that work within 28 days, or sooner if the report says so. Unsatisfactory EICR: what happens next covers the follow-up.
How should loft and cellar observations be worded?
Every observation needs three things: where it is, what it is and why it matters. "Loft, above bedroom 2: approx. 4 m of 2.5 mm² T&E (circuit 4, upstairs sockets) totally surrounded by 270 mm mineral wool insulation; current-carrying capacity reduced under Regulation 523.9; no heat damage seen. C3." That tells the next electrician exactly where to go and what to do. "Cables in insulation C3" does not.
Photographs matter more here than anywhere else because the client will never go up and look. Take one wide shot showing where the defect is relative to the hatch or the stairs and one close-up, and number them to match the observation. How to write EICR observations has wording templates, and EICR codes C1, C2, C3 and FI has the definitions.
Be honest about the extent. "Loft inspected from the hatch only; cables beyond approx. 2 m not visible" is defensible. Silence is not.
How Certio helps
Certio produces the EICR, EIC, Minor Works certificate and PAT records on the BS 7671 model forms and turns them into branded PDFs. Photograph the consumer unit and the circuit schedule drafts itself; point the phone camera at a Megger MFT-X1 and the reading goes straight into the schedule of test results, or dictate it while your hands stay on the probes. Suggested observation wording with the regulation reference is there for you to check and confirm. The judgement stays yours; the typing goes. Starter is £4.99 a month, charged when you sign up.