1. Source priority order
Every claim on this site has exactly one primary source. When two sources disagree, we use this fixed PSDS-specific order and record the loser as a footnote, not a citation:
- Salix Finance portal - the scheme administrator. The PSDS application portal, grant conditions, and funded-project schedule are the canonical record for any live-bid mechanic, scheme reference, or award figure [Salix].
- DESNZ (Department for Energy Security and Net Zero) - the policy owner. Used for Phase scope, the £325/tCO2e ceiling, GCC formula, and the Warm Homes Plan envelope [DESNZ].
- DfE - used only for school-estate funding alternatives (CIF, R&R, School Rebuilding Programme) and where DESNZ defers to DfE on academy eligibility.
- LGA / Local Net Zero Hubs / CCS - used for delivery frameworks (Re:Fit, RM6238) and regional advisory routes, never for scheme rules.
- HMT - used only for the Spending Review envelope context, never for PSDS scheme mechanics.
Trade press (CIBSE Journal, edie, Net Zero Buildings), consultancy reports (Arup, Mott MacDonald) and aggregator sites are never used as a primary source for a numeric claim. They may appear in editorial commentary clearly marked as such.
2. Refresh trigger and cadence
The site is on a two-track refresh schedule, both PSDS-specific:
- Event-driven (Phase 5 watch) - any DESNZ or Salix announcement touching Phase 5 scope, opening window, ceiling, or eligible-body list triggers a full re-verification within 48 hours. The Phase 5 watch banner at the top of every page reflects this state.
- Calendar (quarterly) - in the absence of an announcement, every primary source on /sources is re-fetched at the start of each quarter (1 January, 1 April, 1 July, 1 October). The last-verified stamp on the footer and the /sources page reflects the most recent of these two paths.
Phase-window changes, ceiling changes, and eligible-body changes are mirrored to the countdown strip and the eligibility wizard within the same 48-hour window. Award case figures on /case-awards are not on the quarterly cadence; they are refreshed only when DESNZ publishes a new funded-projects schedule.
3. Verification cadence
Each primary URL on /sources carries a verified date in ISO short form (e.g. “22 Jun 2026”). Verification means: the URL returned a 200, the page title still matches the cited document, and the specific clause or figure cited is still present and unchanged. A URL that 404s, redirects to a generic landing page, or has had the cited figure withdrawn is removed from /sources and any page citing it is re-sourced or flagged within the same 48-hour window.
The verification log is the git history of this repository. Every “verified” date corresponds to a commit that touched the cited file.
4. Correction window
Any reader-reported error or omission is acknowledged within one working day and corrected within five UK working days of report. Corrections are made in-place on the affected page, with a one-line dated correction note in the page footer of any page that previously carried the wrong figure. Reports go to the author address on /about/author. Trivial typographical fixes do not carry a correction note; numeric, eligibility or scheme-rule corrections always do.
5. The £325 / tCO2e ceiling test
The Value-for-Money (VfM) calculations on the homepage, /vfm-ceiling and the grant-size estimator follow a fixed three-step test:
- Lifetime kgCO2e is computed using the lifetime years published in the DESNZ PSDS guidance for that measure type (typically 20 years for fabric and heat-pump measures, 15 years for LED). We use the guidance figure, not the manufacturer claim.
- Capital £ is the grant-eligible capital cost as defined by the PSDS grant conditions, excluding any contractor margin or VAT-recoverable element a school cannot reclaim.
- £ / tCO2e is capital £ divided by lifetime tonnes (kgCO2e ÷ 1000). A measure PASSES the ceiling test if and only if this ratio is at or below £325. A measure failing the ceiling does not necessarily fail PSDS - it is one of several gates - but it is the gate most often missed at portal-submission stage.
6. Eligibility-wizard logic
The three-question wizard at /eligibility-checker is a pure decision tree. It returns ELIGIBLE / CONDITIONAL / OUT-OF-SCOPE based only on (a) body type per the PSDS grant conditions eligible-body list, (b) whether the site is a UK public-sector building in scope of the heat-and-buildings remit, and (c) whether the bid pre-meets the £325 ceiling on its strongest measure. The wizard never asks for personal data, never logs an answer, and is fully client-side. CONDITIONAL is returned where DESNZ guidance is unsettled (e.g. mixed-use academy estates with non-school floor area >30%).
7. Author and editorial independence
Authored by Oliver Wakefield-Smith, Founder of Digital Signet. This site is independent. It is not commissioned, sponsored or reviewed by Salix Finance, DESNZ, DfE, HMT, LGA, CCS or any framework provider. No affiliate links appear on PSDS pages; any links to consultancy or delivery partners are listed without commercial relationship. Crown copyright extracts are used under the Open Government Licence v3.0.
8. What we do not do
- We do not solicit or accept Phase 5 bid drafts for review.
- We do not estimate award probability for a named site.
- We do not republish award figures before DESNZ publishes the funded-projects schedule.
- We do not use AI-generated figures; every numeric claim has a primary URL.