Stack the build-up
Pick materials from the library and stack them cold side to warm side. The U-value updates with every layer.
Insulation & retrofit toolkit for iPhone
Keep the heat on the warm side.
Stack layers cold side to warm side and read the U-value, check condensation at every boundary, size the insulation and take it all to site. Twelve calculators, 35 lessons and an assistant that knows your build-up — in one pocket toolkit.
● Free on iPhoneMetric · Works offline · Data stays on device
U-Value Builder
External wall · cavity + IWI
❄ coldwarm 🔥
Brick
Cavity
Mineral wool
VCL
Board
U-value
1.60W/m²K
Show Working
U = 1 / ΣR
ΣR = 0.13 + R₁ + … + 0.04
U = 1 / ΣR
ΣR = 0.13 + R₁ + … + 0.04
Condensation
Pass
Thickness
100 mm
How it works
From first layer to site diary
Every result recalculates as you type — and Show Working prints the formula with your numbers in it.
Check the physics
Run a Glaser condensation check at every boundary, find the dew point and the 80 % mould threshold.
Size & price it
Get the millimetres needed to hit a target U, then slabs, rolls, tapes and a cost by category.
Take it to site
Start a project from a template, close tasks, log moisture readings as timbers dry and read it back as report cards.
Features
Everything for the thermal envelope
Walls, roofs, floors and rooms — calculated, explained and organised.
Twelve metric calculators
From U-values to fan verdicts — each one shows its working, so you can check the maths, not just trust it.
U-Value BuilderInsulation ThicknessCondensation RiskRoom Heat LossThermal BridgingInsulation QuantityMembranes & TapesRoof VentilationRoom VentilationHeating DemandDew Point & Mould RiskMaterial Cost
35 lessons, drawn in section
Short lessons with a cross-section for each one — where the vapour control goes, where the air moves, where the bridges hide. Then test yourself in six quiz formats.
Building PhysicsWallsRoofs & LoftsFloors, Windows & DoorsAir, Moisture & Safety
Projects & take-off
Templates, stages, hours, take-off and budget together — plus a site diary with moisture readings.
Material & tool library
20 insulants with real conductivities — from PIR and wood fibre to blown cellulose — 12 typical build-ups and 18 site tools.
Private & offline
Calculations, projects and notes live only on your phone, and everything works without signal.
Meet Thermist
An assistant that knows your build-up
Plan a fabric-first retrofit, diagnose damp from symptoms, review a build-up layer by layer, or ask a plain question. Sessions are saved so you can come back.
Retrofit PlannerA fabric-first order of measures
Damp DetectiveSymptoms in, ranked causes out
Build-up ReviewLayer order, VCL, junctions
AskHeat, moisture and air
Thermist
Why is there mould after insulating the loft?
The cold strip at the eaves, most likely — the insulation stops short of the wall plate. Check the edge and the extract fan.
Which layer moves?
Not the insulation — the vapour control. Keep it on the warm side, tape the laps, and keep the eaves vent path clear. Want me to run Roof Ventilation for your pitch and span?
Achievements
Earn your badges
Sixteen milestones for study streaks, tidy take-offs and passive-level build-ups.
Privacy
It stays on this phone
Everything works offline. The one exception is Thermist: only the text you choose to send goes out, and you read a notice before the first request.
Projects & notes stay on device
Works fully offline
No account, no sign-up
Contact
Questions, ideas, a calculator you're missing?
We read every message. Write below or email us directly at inbox@divlandia.site.
Build it warm. Build it dry.
Free on the App Store. Twelve calculators, 35 lessons and your projects — in your pocket, on site, offline.