Surveys & Diagnostics
Before paying for a fix — or a home — it pays to measure what is actually happening. These guides explain the surveys and diagnostics that find the real cause, independently.
Do I need a thermal imaging survey?
A thermal imaging survey is worth it when you need to see what is happening inside your walls, roof and floors without opening them up — missing or slipped insulation, thermal bridges, air leakage paths and sometimes damp. It turns invisible performance problems into a clear, located picture, which is exactly what you need before insulating, after a retrofit, when snagging a new build, or when diagnosing cold spots, draughts and damp. It is a diagnostic tool, not a fix, and its value is in directing the right action.
Read the guideWhat is a blower door test and do I need one?
A blower door test measures how airtight your home is — how much air leaks in and out through gaps in the building — and, with smoke or thermal imaging, reveals exactly where. Since air leakage is often a leading cause of heat loss, cold draughts and high bills, the test turns an invisible, distributed problem into a measured figure and a map of leaks. You need one when you want to quantify and locate air leakage: before sealing, after a retrofit, when snagging a new build, or to diagnose a persistently draughty home.
Read the guideWhat is a building performance survey, and do I need one?
A building performance survey looks at how your home actually behaves as a system — heat loss, air leakage, moisture and ventilation together — rather than at any single symptom. It combines measurement (thermal imaging, a blower door test, moisture and humidity monitoring) with building-physics interpretation to find the root cause of cold, damp, mould, draughts or high bills, and to plan work in the right order. You need one when a problem keeps recurring, when several issues coincide, or before committing to a retrofit.
Read the guideDo I need a retrofit survey before I start?
A retrofit survey measures how your home performs and plans the measures in the right, moisture-safe order before any work begins — and it is one of the best investments you can make, because the most expensive retrofit mistakes come from acting without one. Insulating, sealing or replacing windows out of sequence or without regard to moisture can leave a home damper, no warmer, or with new mould. A survey turns retrofit into an evidence-based, sequenced plan rather than a series of hopeful, disconnected measures.
Read the guideHow much does a thermal imaging survey cost, and is it worth it?
The cost of a thermal imaging survey varies with the size and complexity of the property, what you need it to answer, and — most importantly — whether it is carried out properly under the right conditions and interpreted by someone who understands building physics. A cheap survey done in the wrong weather, with no temperature difference across the walls and no analysis, can be worthless; a well-conducted, properly interpreted survey can save many times its cost by directing money to the defects that actually matter and away from work that would not have helped. Rather than asking only what it costs, the better question is what makes a thermal survey worth commissioning, and when it pays for itself.
Read the guideDo I need a building survey before buying an older house?
Before buying an older house, a survey is almost always worthwhile — but it matters which survey you commission. A standard homebuyer report or mortgage valuation tells you about visible condition and broad value; it rarely tells you how the building actually performs — how much heat it loses, how airtight and well-ventilated it is, where it is at risk of condensation and damp, and what it will realistically cost to make warm, healthy and efficient. For a period or solid-wall property, those performance questions are exactly the ones that determine your running costs and the size of any retrofit bill. A building performance survey answers them with measurement, so you buy with your eyes open and can negotiate or budget accordingly.
Read the guideWhat does a damp and mould survey involve?
A damp and mould survey should do one thing above all: establish why the home is damp, so the right treatment follows. Done well, that means more than running a damp meter over a wall and naming a problem — it involves measuring the moisture, temperature and ventilation, distinguishing condensation from penetrating and rising damp, and identifying the cold surfaces and moisture sources that actually drive the mould. A survey that skips this diagnosis and recommends a single proprietary treatment can lead to money spent on the wrong fix. Knowing what a thorough survey involves helps you commission one that finds the cause rather than just confirming there is damp.
Read the guideHow do I evidence damp and mould for a housing disrepair claim?
If you are pursuing a housing disrepair claim over damp and mould, photographs of the mould are rarely enough on their own. A claim is strengthened by independent, measured evidence that establishes the cause of the damp, links it to a disrepair the landlord is responsible for, and distinguishes it from anything that could be blamed on how the home is used. That is a building-physics question — whether the damp is condensation driven by a building defect or inadequate ventilation, penetrating damp from a fabric failure, or rising damp — answered with monitoring, thermal imaging and inspection, and set out in an expert report. Understanding what such evidence involves helps you commission a report that actually supports the claim.
Read the guideDo I need an airtightness test for my extension?
A new extension may well need an airtightness test to satisfy Building Regulations, and even where it is not strictly required it is worth carrying out, because airtightness is one of the biggest factors in whether the new room is warm and comfortable or cold and draughty. Building Control increasingly expects new work to demonstrate its airtightness, and the energy calculations that justify the design often assume a level of airtightness that has to be proven on site. Beyond compliance, a test carried out as the extension is built locates leakage while it can still be sealed cheaply — turning an air test from a box-ticking exercise into the thing that ensures the extension actually performs.
Read the guideDo I need a survey before buying a leasehold flat?
Before buying a leasehold flat, a survey is worth considering — but the questions that most affect your daily comfort and running costs are ones a standard valuation or homebuyer survey rarely answers. A flat's warmth, damp risk, ventilation and, crucially, how much noise you will hear from neighbours are determined by its construction and its position in the building, and these performance issues are common in flats yet largely invisible to a visual inspection. A building performance survey measures how the flat actually behaves — heat loss, airtightness, condensation risk and acoustic transmission — so you know what living there will really be like, and can negotiate or budget, before you commit to a lease you cannot easily change.
Read the guideHow do I choose an independent surveyor?
Choosing a surveyor matters because not every 'survey' is impartial. A great deal of damp, condensation and insulation advice in the UK comes from firms that also sell the treatment — a 'free survey' that ends in a quote for chemical injection, render or coatings. That is a sales inspection, not an independent diagnosis, and it has a built-in incentive to find the problem the firm happens to treat. A genuinely independent surveyor earns their fee from the diagnosis alone, has no product to sell and no stake in the remedy, and is therefore free to tell you the cheapest correct answer — including that you need no treatment at all. Knowing how to spot the difference is what protects you from spending thousands on the wrong fix.
Read the guideWhat is the difference between a HomeBuyers Report and a building survey?
When you buy a home you will be offered different 'levels' of survey, and the names cause real confusion. A HomeBuyers Report (often called a Level 2 survey) is a moderate, mostly visual overview that flags obvious defects and gives a condition rating; a building survey (Level 3, sometimes called a full structural survey) is a deeper, more detailed inspection suited to older, larger, altered or unusual properties. Choosing between them depends on the age, type and condition of the house and how much risk you are willing to carry. But there is a third issue both share: a standard survey is about defects and condition, not how the building actually performs — so neither tells you whether the home will be cold, draughty, damp or expensive to run.
Read the guideDo I need a survey before buying a period home?
A period home almost always warrants a deeper survey than a modern one, and ideally a performance-aware one too, because old houses are built and behave differently. Solid walls with no cavity, lime-based breathable construction, suspended timber floors, original windows and decades of alterations all create risks — and opportunities to misdiagnose — that a light, modern-house survey will skim over. The two big questions a period-home buyer needs answered are whether the structure and fabric are sound, and how the house will perform: whether it will be cold, draughty and damp-prone, and what it would cost to make comfortable. A standard HomeBuyers Report rarely answers either properly for a period property.
Read the guideHow much does a blower door test cost, and is it worth it?
A blower door test — also called an airtightness or air-pressure test — measures how much uncontrolled air leaks into and out of your home, and locates where. The cost depends on the size and complexity of the property, whether it is a simple compliance test or a full diagnostic with smoke and thermal imaging to find every leak, and where you are in the country. For most homeowners the question behind the price is whether it is worth it, and the answer turns on what the leakage is costing you: in a draughty home, air leakage can be one of the largest heat losses, so a test that finds and prioritises the leaks usually pays for itself many times over in targeted, effective sealing.
Read the guideDo I need a survey if my house is cold and damp?
If your home is both cold and damp, a survey is usually worth it — because the two problems almost always share a cause, and guessing at fixes is the expensive way to solve it. Cold surfaces, heat loss, air leakage and poor moisture control tend to feed each other: cold walls and windows lose heat and also drop below the dew point so moisture condenses on them, and a home that is hard to heat is also one where surfaces stay cold enough to grow mould. A survey that measures where the heat goes and how moisture behaves identifies the real cause, so a single coordinated fix addresses both — rather than spending separately, and often wrongly, on heating, damp treatment and mould paint.
Read the guide