The Transom Set — revisions and re-issued tests https://transom.top/ Dated assembly measurements, method comparisons and disagreements. Assemblies are not syndicated: they carry a revision letter and an issue instead. en 2026-09-16 09:00:00 +0000 How a U-value is measured, calculated, or modelled https://transom.top/jobs/measure-a-u-value/ https://transom.top/jobs/measure-a-u-value/ 2026-09-16 09:00:00 +0000 Four routes give a U-value for the same window: hot-box test, calculation, component modelling and a manufacturer's tool. They are not interchangeable. How a water penetration test is run and when it voids https://transom.top/jobs/run-a-water-penetration-test/ https://transom.top/jobs/run-a-water-penetration-test/ 2026-09-16 09:00:00 +0000 A water penetration test applies a pressure and a spray rate for a fixed time. The pressure level, the nozzle and the duration are all in the method. How to tell whether a window will condense inside https://transom.top/jobs/take-a-dew-point-reading/ https://transom.top/jobs/take-a-dew-point-reading/ 2026-09-16 09:00:00 +0000 Condensation happens when a surface is colder than the air's dew point. Two readings decide it, and one of them is not taken on the glass at all. How air leakage through a window is measured and reported https://transom.top/jobs/measure-air-leakage/ https://transom.top/jobs/measure-air-leakage/ 2026-09-16 09:00:00 +0000 Air leakage is measured at a stated reference pressure, on a stated specimen. Change either one and the number changes, which is why certificates quote both. How to model or check a thermal break in a frame https://transom.top/jobs/check-a-thermal-break/ https://transom.top/jobs/check-a-thermal-break/ 2026-09-16 09:00:00 +0000 A thermal break is checked by simulating the frame section, not by reading a data sheet. The boundary conditions and the cut line decide the answer. Argon loss over time: what the measurements show https://transom.top/notes/2026-09-05-argon-loss-over-time/ https://transom.top/notes/2026-09-05-argon-loss-over-time/ 2026-09-05 09:00:00 +0000 Argon is filled into an insulating glass unit to cut conduction across the cavity. Measured retention after ten years differs from the fill figure on the order. One unit, two edges: warm edge against aluminium https://transom.top/notes/2026-08-27-warm-edge-vs-aluminum-spacer/ https://transom.top/notes/2026-08-27-warm-edge-vs-aluminum-spacer/ 2026-08-27 09:00:00 +0000 The same insulating glass unit was scored with an aluminium spacer and a warm-edge spacer. The centre-of-glass number did not move. The edge did. Condensation on the frame rather than on the glass https://transom.top/notes/2026-08-18-condensation-on-the-frame-not-the-glass/ https://transom.top/notes/2026-08-18-condensation-on-the-frame-not-the-glass/ 2026-08-18 09:00:00 +0000 A better spacer moves the coldest surface from the edge of the glass to the frame. The occupant still sees condensation, in a place they did not expect. Water penetration test pressure ratings, decoded https://transom.top/notes/2026-08-06-water-penetration-pressure-ratings/ https://transom.top/notes/2026-08-06-water-penetration-pressure-ratings/ 2026-08-06 09:00:00 +0000 A water penetration rating is a pressure, a duration and a spray condition. It is not a wind speed and it does not scale to one by a simple factor. Two U-values for the same window, and both are correct https://transom.top/notes/2026-07-24-two-u-values-one-window/ https://transom.top/notes/2026-07-24-two-u-values-one-window/ 2026-07-24 09:00:00 +0000 The same window can carry two published U-values, because the two routes use different edge treatment and different frame areas. Neither is wrong. Thermal break debond: the section that came apart https://transom.top/notes/2026-07-10-thermal-break-debond/ https://transom.top/notes/2026-07-10-thermal-break-debond/ 2026-07-10 09:00:00 +0000 A cast thermal break separated from its aluminium at a corner, twelve years after installation. The inspection found the failure at the cut end of the section.