Plain-English building science — for homeowners, landlords and architects.
Every article is written by a Certified Passive House Designer. We unpack the building-physics behind damp, condensation, air leakage, thermal performance, ventilation and acoustics — so you can make informed decisions about your home.
Got a specific problem? Start with the symptom.
Cold rooms, condensation, mould, damp, draughts and noise all have measurable causes. Our symptom-first knowledge base explains what is really happening in your home — and how we diagnose it before a penny is spent on fixes.
Comprehensive pillar guides
Each guide is a structured, technically rigorous deep-dive into one area of building performance — with a cluster of supporting articles.
Home Problems Knowledge Base
Symptom-first guides to cold homes, condensation, mould, damp, draughts and noise — and how we diagnose the real cause.
Passive House
The international fabric-first standard for ultra-low-energy buildings — the five principles, certification, PHPP and the EnerPHit retrofit pathway, explained by a Certified Passive House Designer.
Airtightness & Blower Door Testing
What airtightness really means, how the blower door test works, how to read ACH₅₀ and m³/h·m², and why air leakage drives heat loss, condensation and poor air quality.
Building Physics & Moisture
Dew point, relative humidity, vapour diffusion, surface temperature, interstitial condensation and thermal bridging — the moisture physics behind damp, mould and failed retrofits.
Thermal Imaging
How infrared thermography works, the temperature differential it needs, and how it reveals heat loss, missing insulation, thermal bridges, air leakage and condensation risk.
Ventilation & Indoor Air Quality
MVHR, PIV, extract and trickle ventilation, and the four IAQ numbers that matter — CO₂, relative humidity, PM2.5 and VOCs — plus ventilation strategy for retrofit.
Retrofit & Insulation
Internal and external wall insulation, floor, loft and roof insulation, retrofit sequencing, thermal-bridge reduction and moisture-safe, whole-house retrofit design.
Soundproofing & Acoustics
Airborne vs impact noise, flanking transmission, and the mass–decoupling–absorption principles behind floor, wall and ceiling soundproofing systems that actually work.
Cold, Damp & Mould — Home Problem Guides
Plain-English answers to the real problems homeowners search for — cold rooms, cold walls, draughts, condensation, recurring mould and damp smells — with the building physics and the measured way to fix each one.
Heat Pump Readiness
Is your home ready for a heat pump? Fabric-first guides to heat loss, insulation, airtightness, ventilation and emitters — so a low-temperature heat pump runs efficiently instead of hot and expensive.
Every Retrofit IQ Academy article
What is Passive House? The complete UK guide.
Not a brand or a product — a set of physics-based, measured performance targets. The standard, the building science and why it underpins every retrofit we design.
The five Passive House principles, explained.
Continuous insulation, thermal-bridge-free detailing, airtightness, high-performance glazing and MVHR — one interdependent system, not a shopping list.
Thermal-bridge-free design — the physics of cold spots.
Why insulation must be continuous, how ψ-values quantify thermal bridges, and how cold junctions cause the condensation and mould that recur in the same corners.
High-performance windows — U-values, glazing and comfort.
Ug vs Uf vs Uw, triple glazing, warm-edge spacers, g-value and solar gain, installation in the insulation plane — and the comfort criterion behind the numbers.
MVHR explained — mechanical ventilation with heat recovery.
How the heat exchanger recovers 75–95% of ventilation heat, why airtightness is its prerequisite, and what separates a silent, healthy system from a noisy, ineffective one.
PHPP explained — how Passive House energy is calculated.
The energy-balance model that predicts heating demand, comfort and overheating before a brick is laid — and why it closes the performance gap that SAP leaves open.
Passive House vs Building Regulations — the performance gap.
Why a Part L-compliant home is not the same as a low-energy one: airtightness limits, SAP vs PHPP, and the documented gap between predicted and actual energy use.
EnerPHit — Passive House principles applied to retrofit.
The retrofit standard: two certification routes, moisture-safe sequencing, party-wall and embedded-joist challenges, and why 'fabric first, plant last' saves money.
How sound travels in buildings — and the four principles of soundproofing.
How sound moves — airborne, impact and flanking — and the four principles that control it: mass, decoupling (isolation), absorption and damping.
Airborne vs impact sound — the two problems, and how they're rated.
The difference between airborne and impact sound, why they need different treatments, how they're measured (DnT,w + Ctr and L'nT,w), and what Part E requires.
Flanking sound explained — why soundproofing so often fails.
What flanking transmission is, why it's the commonest reason soundproofing underperforms, the typical flanking paths, and how a whole-system approach addresses it.
Soundproofing walls — independent linings, resilient bars and mass.
The independent (isolated) wall vs resilient-bar systems, adding mass and damping, cavity absorption, sealing, and why flanking and space trade-offs matter.
Soundproofing floors and ceilings — impact, footsteps and headroom.
Floating floors and resilient layers at source, isolated ceiling systems, the headroom trade-off, why treating the floor above beats the ceiling below, and the flanking factor.
Soundproofing myths and mistakes — what doesn't work, and why.
Egg boxes and foam, 'acoustic' paint, confusing absorption with insulation, ignoring flanking and gaps, partial treatment — debunked, with what actually works.
Whole-house retrofit and PAS 2035 — why a plan beats piecemeal measures.
Why retrofit should be planned whole-house, what PAS 2035 requires, the role of the assessment, coordinator and risk pathways, and how a Medium-Term Improvement Plan avoids costly lock-in.
Fabric first and retrofit sequencing — the right order of works.
Why 'fabric first, plant last' saves money, the correct sequence of works, how to phase a retrofit without lock-in, and why sizing the heat source before reducing demand is the costly mistake.
Internal vs external wall insulation — choosing safely.
A clear comparison of IWI and EWI: performance, moisture risk, thermal bridging, cost, disruption, space and planning — and how to choose the right one for your solid-wall home.
External wall insulation (EWI) — how it works and when to use it.
How EWI wraps the structure in a continuous warm blanket to control thermal bridging and moisture, the build-up and finishes, the detailing that makes or breaks it, and when it's the right choice.
Insulating solid walls safely — moisture, breathability and risk.
Why solid-wall insulation carries moisture risk, how traditional walls manage water, the role of vapour-open build-ups, wind-driven rain, and why hygrothermal assessment is essential.
Loft and roof insulation — cold roofs, warm roofs and condensation risk.
Cold-roof vs warm-roof strategies, why ventilation and air-tightness matter, the condensation risk of insulating at ceiling vs rafter level, room-in-roof detailing, and recommended depths.
Floor insulation in retrofit — suspended timber and solid floors.
How to insulate ground floors: suspended timber floors and their air-leakage role, solid floor insulation, maintaining underfloor ventilation, air-tightness and the moisture considerations.
Avoiding unintended consequences in retrofit — the risks, and how to design them out.
Condensation, mould, moved dew points, new thermal bridges, trapped moisture and overheating — the unintended consequences of poor retrofit, and the diagnose-model-design-verify approach that prevents them.
PIV explained — positive input ventilation, and where it fits.
How PIV works, what it's good at (and not), how it compares to MVHR and extract, its lack of heat recovery, and when it's the right ventilation strategy.
Extract ventilation explained — intermittent, dMEV and MEV.
Intermittent extractor fans, continuous decentralised extract (dMEV), centralised MEV, humidity-sensing controls, Part F, and where each fits in a moisture-control strategy.
Trickle vents and background ventilation — what they do, and don't.
What background ventilators are for, how they fit Part F, why people block them and shouldn't, and how background ventilation interacts with airtightness and mechanical systems.
CO₂ monitoring — the simplest measure of whether you're ventilating enough.
Why indoor CO₂ is the best single proxy for ventilation adequacy, what the ppm thresholds mean, the effect on sleep and cognition, and how to use a CO₂ monitor.
PM2.5 and particulates indoors — sources, health and filtration.
What PM2.5 and PM10 are, where indoor particulates come from (cooking, wood burning, candles, outdoor air), their health effects, WHO guideline levels, and how MVHR filtration and source control reduce them.
VOCs and indoor pollutants — formaldehyde, off-gassing and source control.
What VOCs are, common indoor sources (paints, furnishings, MDF/formaldehyde), how they affect health, what TVOC readings mean, and why source control plus ventilation is the answer.
Ventilation and mould prevention — the humidity connection.
How ventilation controls indoor humidity, the moisture households generate, the link between ventilation rate and surface RH, and why ventilation plus warm surfaces is the durable mould fix.
Ventilation strategy for retrofit — matching ventilation to airtightness.
How to choose the right ventilation as airtightness improves: when extract, PIV or MVHR is appropriate, 'build tight ventilate right', commissioning, Part F, and avoiding the post-retrofit mould trap.
How thermal imaging works — emissivity, reflected temperature and resolution.
How a thermal camera measures surface temperature, the role of emissivity and reflected apparent temperature, thermal vs spatial resolution, and the difference between a qualitative and a quantitative survey.
The temperature differential — why a valid thermal survey needs a cold day.
Why thermography needs a sufficient inside-to-outside ΔT, how much is enough, the role of conditioning, weather, solar loading and timing, and the standards behind a valid survey.
Thermal imaging for insulation defects — missing, slumped and bridged.
How thermal imaging reveals missing, slumped and gapped insulation, cavity-fill defects and cold bridging — reading the signatures, and why internal and external surveys complement each other.
Thermal imaging for air leakage — finding draughts under depressurisation.
How thermal imaging detects air leakage when combined with a blower door: the cold 'fingers' of incoming air, how they differ from insulation defects, and why the two techniques belong together.
Thermal imaging for condensation and damp — cold surfaces and dew point.
How thermography locates surfaces below the dew point, the evaporative-cooling signature of damp, distinguishing it from missing insulation, and why it's combined with humidity logging and moisture meters.
Thermal imaging for retrofit verification — proving the work was done right.
Before-and-after surveys, checking insulation continuity and install quality, confirming thermal bridges are designed out, and providing the as-built evidence that closes the performance gap.
Common thermal imaging mistakes — and how to spot a bad survey.
Solar loading, insufficient ΔT, wrong emissivity, reflective surfaces, auto-scaled palettes, thermal-mass lag and over-claiming — plus how to tell a credible thermal survey from a worthless one.
Dew point explained — the temperature where condensation begins.
The single most useful number in moisture diagnostics: what dew point is, the psychrometrics behind it, and how comparing it against surface temperature decides whether a surface stays dry or grows mould.
Relative humidity explained — and why 80% at a surface means mould.
What RH actually measures, how it differs from absolute humidity and vapour pressure, why it changes with temperature alone, and the 80% surface-RH threshold that governs mould.
Vapour diffusion and permeability — μ-values, sd-values and 'breathability'.
How vapour diffuses through materials: vapour pressure, the μ resistance factor, the sd-value (equivalent air layer), vapour control layers, and what 'breathable' really means.
Moisture transport mechanisms — the five ways water moves through buildings.
Vapour diffusion, air convection, capillary transport, gravity/bulk water and built-in moisture — five mechanisms, each with a different driver and a different fix, plus hygroscopic sorption.
Surface condensation and mould — the mechanism, and the real fix.
How surface condensation and mould form: the 80% surface-RH germination threshold, growth isopleths, the fRsi temperature factor, common species and health effects, and why warming surfaces beats bleach.
Interstitial condensation explained — the damp you can't see.
How warm moist air and vapour reach the dew point inside a wall or roof, where the condensation plane forms, why it rots timber and insulation unseen, and how it's designed out.
Condensation risk analysis — Glaser vs WUFI hygrothermal modelling.
How interstitial condensation risk is predicted before building: the steady-state Glaser method (BS EN ISO 13788), its limitations, and transient WUFI simulation — and when each is needed for moisture-safe retrofit.
Moisture measurement methods — meters, loggers and their limitations.
What resistance and capacitance meters really measure, the false readings from hygroscopic salts, the carbide and gravimetric reference tests, RH data loggers, interstitial probes and thermal imaging.
What is airtightness? ACH₅₀, air permeability and 50 Pa explained.
What airtightness really means, the difference between ACH₅₀ and air permeability, what 50 pascals represents, and why air leakage drives heat loss, condensation and poor air quality.
How a blower door test works — methodology, equipment and standards.
The fan and door panel, the manometer, pressurisation vs depressurisation, single-point vs multi-point (regression) tests, BS EN ISO 9972 and ATTMA, preparation and sources of error.
Interpreting blower door results — ACH₅₀, q50 and what 'good' looks like.
How to read an airtightness result: ACH₅₀ vs air permeability, UK benchmarks, Passive House and EnerPHit targets, the flow exponent, equivalent leakage area, and pass vs genuinely good.
UK airtightness standards and regulations — Part L, ATTMA and Passive House.
Approved Document L air-permeability limits, mandatory testing and ATTMA registration, the Part F ventilation link, and how Building Regs compare to Passive House (0.6 ACH₅₀) and EnerPHit.
Common air-leakage pathways in UK homes — where buildings actually leak.
Service penetrations, loft hatches, floor-to-wall junctions, suspended timber floors, skirtings, sockets, chimneys, intermediate floor voids and party-wall bypass — mapped element by element.
Smoke tracing and leak detection — finding exactly where a building leaks.
Smoke pencils, puffers and foggers under depressurisation, anemometer airflow measurement, thermal imaging of incoming cold air, and how leaks are documented into an actionable sealing plan.
Airtightness strategy and detailing — the continuous air barrier.
The continuous air barrier and the 'red pen' rule, choosing the airtight layer, detailing junctions and penetrations, the service void, sequencing and the airtightness champion.
Airtightness and condensation risk — why leaky buildings rot from the inside.
Air-transported moisture vs vapour diffusion, exfiltration condensation, and why an airtight, well-ventilated envelope is the moisture-safe one — plus the dangerous mistake of sealing without ventilating.
Why most damp treatments fail — and what actually works.
Injected damp-proof courses, chemical creams and waterproof renders rarely solve the problem because they treat the symptom, not the cause.
Condensation vs damp — how to tell the difference (with measured data).
The single most misdiagnosed problem in UK homes. Here's how building physics — not guesswork — tells the two apart.
What a blower door test actually tells you about your house.
ACH₅₀, m³/h, smoke trails and thermal-under-depressurisation — the four outputs of a proper test and what each one means for your retrofit.
Thermal imaging — what it can (and can't) see.
Used properly, a FLIR survey is the single highest-value diagnostic tool we own. Used badly, it produces beautiful images that mean nothing.
Internal Wall Insulation — how to upgrade a solid wall without causing hidden mould.
IWI is the single highest-risk retrofit measure. Done badly, it creates interstitial condensation behind the new lining. Done properly, it transforms comfort.
Soundproofing a flat without losing headroom (or your sanity).
Mass, decoupling, absorption — the three things every effective soundproofing build-up needs, and the flanking paths that quietly ruin the result.
MVHR vs PIV — which ventilation strategy is right for your home?
MVHR, PIV, dMEV and intermittent extract — four ventilation strategies with very different running costs, performance and suitability.
Indoor air quality — the four numbers that actually matter.
CO₂, humidity, PM2.5 and VOCs. Get these four right and almost every other 'air-quality' worry resolves itself.
Why is my house cold? The real reasons — and how to find them.
Heat is escaping faster than you can replace it. Here is how to measure where it's going.
Why are my walls cold to the touch?
Cold walls lose heat and risk condensation — both measurable, both fixable.
Why is one room colder than the rest of the house?
One persistently cold room almost always has a specific, fixable cause.
Cold floors in winter — why they happen and how to fix them.
Usually an uninsulated suspended floor over a cold, draughty void — and very fixable.
Why is my house so hard to heat?
Slow to warm and quick to cool means high heat loss — reduce it before upgrading heating.
High energy bills but the house is still cold — what's going on?
You're paying to heat the outside. Here's how to find and stop the loss.
Why does my home feel draughty?
Draughts are uncontrolled air leakage — invisible, but entirely measurable.
Air leakage around windows and doors — the hidden draught.
Even new windows leak around the frame perimeter. Here's how we find and seal it.
Condensation on windows — what it means and how to stop it.
Streaming windows are high indoor humidity meeting cold glass — a warning, not just a nuisance.
Damp around window frames — condensation, leak or cold reveal?
Telling condensation on a cold reveal from water ingress is the difference between the right fix and a wasted one.
Mould in the corners of rooms — why it always starts there.
Corners are the coldest spot in the room — a geometric thermal bridge that condenses and grows mould.
Mould behind wardrobes and furniture — the cold-wall trap.
Furniture against a cold external wall creates a cold, still, humid micro-climate — perfect for mould.
Black mould in bedrooms — why bedrooms are the worst affected.
Occupants, cool nights, cold walls and closed doors make bedrooms the prime spot for condensation and mould.
Why does the damp or mould keep coming back?
Recurring damp means the cause was never diagnosed — only the symptom was treated.
Why does my house smell damp or musty?
A musty smell is your nose detecting hidden moisture and microbial growth. Find the source, lose the smell.
Loft insulation problems — why a 'fully insulated' loft still loses heat.
Gaps, compression, eaves shortfalls and a leaky hatch undo much of the benefit — invisibly.
Condensation in loft spaces — wet timbers, mould and dripping felt.
Warm moist air leaking up meets a cold roof and condenses. Seal the air, keep the loft ventilated.
Mould after new windows — why upgrading glazing can backfire.
Tighter windows removed the old accidental ventilation; the trapped moisture had to go somewhere.
Is my home ready for a heat pump?
Readiness means low heat loss and emitters that can deliver heat gently — not just the heat pump itself.
Why you need a heat loss survey before a heat pump.
A measured heat loss survey sizes the system correctly and prevents an oversized, inefficient heat pump.
What insulation levels do you need before a heat pump?
There's no single number — what matters is whole-house heat loss low enough for low-temperature operation.
Airtightness and heat pumps — the overlooked half of readiness.
Air leakage adds directly to heat demand — a blower door test is central to readiness.
Ventilation requirements when you fit a heat pump.
Tightening the home for efficiency makes controlled ventilation essential — build tight, ventilate right.
Underfloor heating and heat pumps — and what to do with radiators.
Heat pumps love large, low-temperature emitters — but correctly sized radiators can work too.
Why some heat pumps perform poorly (and how to avoid it).
Almost always the building wasn't ready, the unit was oversized, or it was run hot like a boiler.
Common heat pump retrofit mistakes — and how to avoid them.
Oversizing, skipping the fabric, ignoring airtightness and running too hot — nearly all avoidable before install.
Building regulations and heat pumps — what you need to know.
How the rules on heating, ventilation and fabric relate to readiness — and where minimum compliance ends.
Fabric first, before heat pumps — the principle that makes them work.
Reduce heat loss before sizing the heating and the heat pump runs small, efficient and cheap.
Reading is useful. Measured data is conclusive.
We carry out diagnostic surveys across London, Greater London, East London, Essex, Kent, Surrey, Hertfordshire. A two-hour Home Health Diagnostic Survey gives you measured answers — not generic advice.