Condensation and U-value analysis

Condensation & U-value analysis estimates a wall, roof or floor construction’s U-value and its risk of interstitial (within-the-structure) condensation over a full year — a genuine engineering screening tool, with clearly stated limits.

What it is

You describe a construction as a set of layers (material, thickness) from a built-in library of standard materials with published thermal and vapour-resistance properties. From that build-up the app calculates a U-value (W/m²K) using BS EN ISO 6946, and runs a full twelve-month interstitial condensation simulation using the BS EN ISO 13788 (Glaser) method against monthly climate data for the property’s location — either from a built-in table of UK locations or, where a connection allows it, live-resolved and then saved so the same assessment works offline afterwards. The result is a verdict of no risk, condensation that fully dries out within the year, or condensation that accumulates and fails the annual moisture balance, alongside a temperature-factor check against the UK’s surface-condensation/mould-risk criterion.

This is a steady-state screening method, not a full hygrothermal simulation. It models vapour diffusion only — not liquid or capillary moisture movement, air leakage, convection, hygroscopic buffering, driving rain or solar gain — and the app states this explicitly alongside the result. For a marginal or complex construction, a transient hygrothermal simulation (BS EN 15026 / WUFI) is the more rigorous next step, not something this tool replaces.

How to do it

1. Open Condensation & U-value for the room or element you’re assessing.
2. Build the construction layer by layer, picking materials and thicknesses from the library.
3. Review the calculated U-value and the twelve-month condensation verdict.
4. Read the Method & limitations note before treating the result as more than a screening indication — it names exactly what the calculation does and doesn’t account for.

How it integrates

This analysis sits alongside room-level psychrometric readings as part of the same damp & mould evidence set — see Rooms, readings and psychrometrics. A saved climate snapshot means an assessment built with a live connection still works, unchanged, if you revisit it offline later. The verdict and U-value feed into the report’s condensation-analysis section.

Common problems

• The verdict seems more severe than what I’m actually seeing on site. The Glaser method is a screening tool based on standard climate and material data — treat a “fail” verdict as a prompt to look more closely, not as a diagnosis on its own; your own on-site observation always takes precedence in the report.
• I can’t find the exact material I used. Pick the closest standard equivalent from the library — this is a modelled screening assessment, not a bespoke lab test.
• The result looks the same as last time even though I’m offline. That’s expected if a climate snapshot was already saved for this location on an earlier visit.