Collection 03
Building envelope
A building loses heat through whichever part you thought about least. The glass, the frame and the wall are three calculations that people do in three different places with three different assumptions, and the answer that matters is the one that puts them side by side. These tools finish the set: the glass and the window are already here, and this is the wall they sit in.
Same rules as everywhere: the formula and the standard on the page, no sign-up, nothing uploaded, all of it computed in your browser.
Wall and roof U-value
Build the construction layer by layer to EN ISO 6946 and see which one is actually doing the work — it is almost never the one that costs the most. Also tells you the insulation thickness you need to hit a target U.
render + brick + 100 wool + block + board → U 0.274Condensation risk inside the wall
Where the dew point falls through the build-up, and whether the construction will dry out again. This is the calculation that decides whether a wall rots, and almost nobody does it.
Whole-house heat loss
Add up the walls, the roof, the floor and the windows you have already worked out, plus ventilation, and get the heat loss the boiler or heat pump actually has to cover.
Thermal bridges
What the studs, the ties and the junctions give back of the insulation you paid for — the correction that turns a good U-value on paper into a worse one on site.
Why this collection exists
Because the three parts of an envelope are usually calculated by three different people who never compare notes. A wall at 0.25 W/(m²·K) sounds excellent until you notice the window beside it is at 1.30 and covers a quarter of the facade — at which point the window is losing more heat than the entire wall around it. Having the glass, the window and the wall in the same place, with the same rules and the same honesty about what they leave out, is the point.