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.
Four tools, and they chain: work out the wall, check it does not get wet inside, price the junctions, then add the lot up into a heat load in kilowatts. Same rules as everywhere: the formula and the standard on the page, no sign-up, nothing uploaded, all of it computed in your browser.
How they fit together
The wall passes. The house still needs 3 kW.
A wall at 0.274 looks like a job well done, and it is — but it is only 74 of the 133 watts per kelvin that size the heat pump. The rest is ventilation and the junctions nobody drew, and one of those junctions is sitting at 82 % humidity. Three calculations usually done by three people who never compare notes.
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 0.274 Moisture · liveInterstitial condensation
The Glaser method to EN ISO 13788: temperature and vapour pressure through every layer, and exactly where the wall gets wet. Then it tells you the vapour control layer that would fix it — and which side it goes on.
the default wall condenses behind the insulation by 416 Pa Thermal · liveWhole-house heat loss
The design heat load in kilowatts — the number a heat pump is actually sized on. Fabric, junctions and ventilation added up, with a breakdown that shows which one is really costing you and what the single best fix is worth.
the default house: 3.07 kW, and the biggest line is the air Thermal · liveThermal bridges
What the lintels, corners and floor junctions give back of the insulation you paid for. Turns ψ values and lengths into a y-value, compares it with the penalty default — and checks whether the junction will go mouldy, which happens long before it gets wet.
a junction at the legal minimum still hits 82 % surface RHWhy 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.
And because the same three questions keep coming back in a different order. A wall that passes on U-value can still get wet inside. A house full of good U-values can still lose a third of its heat through junctions and open windows. Only when all of it is added up does a number in kilowatts come out — and that number, not the floor area, is what the heating should have been sized on.