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Supplied floors and rafts
Some floors do not have a layer stack you can build from products. A proprietary insulated raft (an engineered pod-and-rib slab system) has an R-value that depends on the specific geometry of the job, and the manufacturer determines it. Thermly has a dedicated path for these: you enter the supplied R-value and record where it came from.
Why a raft's R-value is per-project
A raft slab's thermal resistance depends on its area-to-perimeter ratio and its rib and pod geometry, both specific to your building. There is no single catalogue R-value that is correct for every job. Manufacturers publish a calculator (or an H1/VM1 determination) that produces the R-value for your particular floor's dimensions and configuration.
So Thermly does not store a raft R as a catalogue constant. Instead you run the manufacturer's calculator for your floor, then enter the result with its source. This keeps the number honest and traceable to the determination it came from.
Your floor geometry, before you leave for the calculator
The panel opens with a read-only Your floor geometry block: this floor's area, its perimeter, and the area-to-perimeter (A/P) ratio they give. Those are exactly the numbers the manufacturer's calculator asks for, so you no longer have to guess them or re-measure off the plan. A Copy button puts all three on the clipboard, since you are about to retype them into someone else's web form.
The basis is stated under the figures: internal dimensions (H1/AS1 Equation E.1) - walls are traced on the inside face, so a floor traced on the plan, or derived from your traced walls, is already measured the way H1 wants. Thermly computes the ratio itself; it is the same calculation the slab table lookup uses.
Two things to check against your own drawing:
- A party wall is not part of the perimeter. A wall shared with another conditioned dwelling - a duplex or terrace unit - is not thermal envelope (H1/AS1 §2.1.2.4), so it must come out of the perimeter. A wall between the house and an unconditioned space such as a garage stays in (E.1.2.2 says so explicitly).
- No traced outline, no perimeter. If the row has no floor polygon on the plan, Thermly shows the area alone and says so. It never invents a perimeter. Trace the floor - or derive it from your walls - and the perimeter and ratio appear.
Entering a supplied floor
For a proprietary raft, open the supplied-floor path ("Proprietary insulated raft - supplied R-value") and complete:
| Field | What to enter |
|---|---|
| Raft system | Pick the manufacturer system from the list (or "Other / not listed"). |
| Manufacturer / system | The system name, for example "MAXRaft". |
| Construction R-value (m²·K/W) | The R-value from the manufacturer's determination for this floor. |
| Determined at A/P ratio | The ratio the calculator was actually run at. Pre-filled with this floor's own A/P; correct it if the determination was made for different dimensions. |
| Source document / determination reference | Where it came from, for example "[manufacturer] R-value calculator output (job 12345), 2026-06-22". |
| How was it determined? | Manufacturer R-value determination, H1/VM1 Appendix E calculation, ISO 13370, or another basis. |
If the selected system publishes a calculator, Thermly shows a "[system] calculator →" link that opens it in a new tab. Run it for your floor's area-to-perimeter and configuration, then enter the result - it is valid only for the geometry you computed. Where the system's own catalogue record says its calculator needs the A/P ratio, Thermly points you back up at the geometry block.
Why the ratio is recorded. A raft's R-value is not a property of the system - it is a property of the system on this floor. Appendix E's own tables run from R0.8 at an A/P of 0.6 to R4.3 at 10.0, so the geometry is the dominant driver. Recording what the determination was run at is what lets a processing officer tell a figure computed for this building from one carried over from another job. If it differs from this floor's own A/P by more than 5%, Thermly raises a caution - it does not change the R-value or stop you, it asks you to confirm the figure describes this floor.
Which systems are offered
The Raft system list holds systems that determine a whole-floor R-value: raft and waffle foundations, insulated slab-on-ground systems, insulated foundation systems.
Slab-edge and under-slab insulation products appear in the list greyed out, with a note pointing to the slab table lookup. That is not an omission. Those products are inputs to the Appendix E performance tables - the tables already cover vertical edge R1.0 and under-slab R1.2/R2.4 as insulation configurations you select (E.1.1.1(a)) - so entering their calculator output as a supplied whole-floor R would take the wrong clause route and skip the A/P ratio altogether. Use the slab wizard and pick the matching insulation configuration.
Whole-floor systems whose published R-value does not state a basis E.1.1.1 admits (E.1.1.1 allows only the Appendix E performance tables or a calculation to H1/VM1 Appendix E) are also listed greyed out, each with its reason: "published R-value states a basis H1/AS1 E.1.1.1 does not admit" where the manufacturer's table names another method, or "no manufacturer whole-floor determination is published" for a plain pod raft or a system with no published R at all - both point you at the slab table lookup. When you pick a system, an expandable "What the catalogue records about this system and its stated basis" note shows the catalogue's own account of the system and the basis its manufacturer states, with the document it came from - read it before you confirm the method.
If a manufacturer genuinely did determine a whole-floor construction R for your specific floor, you can still record it: choose "Other / not listed" and name the determination as your source. If you have a saved project where an insulation product was entered as a supplied whole-floor R, Thermly clears that R on load and flags the row, so you re-enter it by the right route rather than carrying an unverifiable figure onto a consent document.
Thermly requires both the manufacturer and the source document: "A supplied floor R-value must record its manufacturer and source document (E.1.1.1(b))." That is what makes the value defensible on the consent record.
You also confirm the method. E.1.1.1(b) is not permission to copy a published figure - it is "calculation in accordance with H1/VM1 Appendix E", a method - and whether a manufacturer's calculator really implements it is a fact about someone else's software that Thermly cannot check. So entering a manufacturer-calculator R requires ticking "Confirm the manufacturer's calculator determines the construction R-value in accordance with H1/VM1 Appendix E." Your account and the date are recorded against the value, and the report states that the method basis was confirmed by the preparer - never a confirmation nobody gave. (Routes that name their own method, such as an H1/VM1 or ISO 13370 determination, need no such confirmation.) Reopening the panel later starts from the stored values, so fixing a typo does not mean retyping everything - only the confirmation checkbox is never pre-ticked, because applying records a fresh confirmation.
How it appears on the report
A supplied floor is not recomputed - Thermly uses the figure you entered - and its basis is stated as labelled facts, never a sentence your text can reshape:
- "Basis: H1/AS1 Appendix E E.1.1.1(b) - supplied whole-floor construction R, not the E.1.2.1 performance tables"
- Determined by, Method, the preparer's method confirmation with its date, the whole-floor R, the A/P ratio it was determined at, the Source and the date it was retrieved.
The determination ratio also prints in the element schedule's construction details, next to the R-value. The schedule's Insulation / system cell carries the row's own description if you gave it one, otherwise the catalogue name of the system you picked (for example "EXPOL Tuff Pod raft slab + SLABX200 under-slab insulation"), resolved from the catalogue each time the report is generated - so a reviewer can see which configuration the figure belongs to without you retyping it. The schedule carries each element's area but not its perimeter, so without it a reviewer could not reconstruct what geometry the supplied figure describes - the same fact the table route has always printed as "A/P ratio: … (computed …)".
The same record appears three ways: on the floor row's Provenance expander (with a "Supplied R" badge), in the schedule's construction details, and as a full entry under References & sources → Product datasheets - with the manufacturer's calculator page as a live link and its full URL printed, since the report is read on paper and in council record systems where a link target is invisible. The provenance is rebuilt from the stored record each time a report is generated, so a wording correction reaches previously saved projects too.
A sense-check, not a cap
Thermly does not alter a supplied R-value, but it will flag one that looks physically implausible. A value above R6.5 - a deliberately generous ceiling, set just above the Appendix E tables' maximum - raises a caution on both the calculator and the report (it catches a decimal slip, for example R28.7 typed for R2.87). The value is used as entered; the caution simply asks you to confirm it.
Standard slabs and generic rafts
A plain slab-on-ground, or a generic system used generically (standard RibRaft, uninsulated EXPOL Tuff Pods, a plain waffle pod), is not a supplied-R case. (An EXPOL Tuff Pod raft with SLABX200 under-slab and/or ThermaSlab Edge / MAXEdge edge insulation is different: EXPOL publishes an H1/VM2 Appendix F table for those configurations, so they are offered on the supplied-R path above and you read the R for your cladding and ratio from EXPOL's table.) Those use Thermly's slab wizard, which looks the R-value up from the floor's area-to-perimeter ratio, edge insulation and cladding per H1/AS1 Appendix E (Paragraph E.1.1.1(a) and the performance tables). The wizard pre-fills the area and perimeter from the row's plan take-off - including the perimeter of a floor polygon derived from your traced walls - and falls back to the figures your last lookup used, so reopening it to fix a typo never starts from an empty field. Each field says where its number came from, and the report records whether the geometry was measured off the plan or typed in. See How Thermly calculates compliance.
A slab is never a layer stack: the calculator deliberately declines to total one from layers (the surface films and layer arithmetic that are right for a wall double-count what the Appendix E tables already include), so the slab entries in the build-up picker are signposts that route you to the wizard or to this supplied-R path.