Historic England's damp guidance, explained in practice
In short
On 13 July 2026, Historic England published "Assessing Damp in Historic Buildings: A Practical Guide to Investigation and Diagnosis" (product code HEAG311), a 92-page guide on assessing and monitoring moisture in traditional buildings. This page is our own practical breakdown of the thinking behind it — how to look at damp in a pre-1919 solid-wall building, why modern "quick fix" materials often make things worse, and how to assess before you treat — plus a free downloadable checklist. It is not Historic England's document; read the original via the link below.
Authoritative source
Assessing Damp in Historic Buildings (HEAG311) — Historic England, published 13 July 2026
Summarising Historic England's guidance, © Historic England — read the original document.
Damp in a Georgian terrace, a Victorian villa or a listed cottage rarely behaves like damp in a 1990s cavity-wall semi — and treating it the same way is one of the most common (and expensive) mistakes in older-property maintenance.
The breathability principle
Most buildings put up before around 1919 have solid masonry or stone walls with no cavity and no damp-proof course as we'd recognise one today. They were built with permeable materials — lime mortar, lime render, lime or earth plaster — designed to let moisture move through the fabric and evaporate from the surface, rather than to exclude it entirely. A useful working rule for these buildings is that moisture getting in only becomes a problem once it consistently outpaces the wall's ability to evaporate it out — not the moment any dampness is detected at all. Chasing bone-dry readings on a solid wall with sealants or impermeable coatings fights against how the building was designed to work.
Why modern "quick fixes" can make it worse
Cement-rich renders, gypsum plasters and plastic-based masonry paints are far less permeable than the traditional materials they often replace. Applied over a solid wall that still receives some moisture — as most do — they don't stop that moisture; they redirect it. It tends to find the nearest breathable route out, which is often further up the wall, into adjoining timber, or into a neighbouring, more permeable finish. The result can look like a new problem months or years later, in a different spot to where the render or plaster was applied, which is exactly the kind of misdiagnosis that wastes time and money that Historic England's guidance is aimed at preventing.
How a proper assessment works
A defensible diagnosis starts before anyone opens a wall. In line with the whole-building approach set out in the joint position statement Historic England published with RICS and the Property Care Association, a proper investigation typically covers:
1. Desk study first
Age and construction of the building, local ground geology and water table, any past extensions or alterations, and whether external ground levels have crept up over the years — a raised path, patio or flowerbed is one of the most common, and most fixable, causes of ground-related damp.
2. A visual survey, room by room and component by component
Roof coverings and rainwater goods, external masonry and render, ground level and air bricks, then internal plaster, salts and odours — recording what is actually observed rather than defaulting to a favourite diagnosis.
3. A staged response
Address the obvious, low-cost defects first — blocked gutters, raised ground levels, blocked vents, condensation-generating habits — then allow a period for monitoring and natural drying before considering anything more invasive.
What the instruments can — and can't — tell you
Historic England's new HEAG311 guidance devotes a substantial section to the accuracy and limitations of the tools commonly used to assess moisture — because the honest answer is that no single instrument gives a complete picture in solid masonry. A hand-held pin-type meter reads electrical conductivity, not moisture content directly; hygroscopic salts, embedded metalwork and foil-backed boards can all push readings up even where the masonry itself isn't unusually wet. Hygrometers (for air temperature and relative humidity) and thermal imaging are useful for spotting condensation patterns and cold bridges, while laboratory-based gravimetric or carbide testing of a small sample remains the most reliable way to confirm actual moisture content when precision genuinely matters. The point isn't to distrust every tool — it's to know what each one is actually measuring before you act on the number it gives you.
The three usual causes
Penetrating damp
Localised, and usually correlates with weather — a storm, wind-driven rain, or a specific roof or gutter defect. Look for a defect directly above or beside the damp patch before assuming anything about the wall as a whole.
True rising damp vs. hygroscopic salt contamination
Genuine capillary rising damp is real but less common than the number of "rising damp" quotes issued each year would suggest. As the SPAB explains, true capillary rise in a solid wall is generally confined to roughly the lowest 300–900mm above floor level and rarely reaches much further, even in unfavourable conditions. Salts left in plaster from an earlier, long-since-resolved problem — or from a wall that was once next to a stable, or had a chemical DPC installed decades ago — can mimic the same tide-mark pattern indefinitely, which is why salt testing (not just a meter reading) matters before specifying treatment.
Condensation
Often made worse, not better, by well-intentioned "draught-proofing" — sealing a chimney that used to ventilate a room, or fitting unventilated double glazing into an old sash box — which removes background airflow the building relied on. Look for mould at cold bridges rather than at floor level, and record temperature and humidity rather than guessing.
A conservative, staged approach to remediation
Once the cause is understood, the least invasive, most reversible fix that addresses it is usually the right starting point: clear and repair rainwater goods, lower external ground levels to at least around 150mm below the internal floor where practical, replace hard cement pointing with a compatible lime mix, and reinstate the background ventilation the building was designed around. Chemical damp-proof-course injection is often oversold for solid or rubble-filled walls, where the fluid cannot reliably spread through an uneven wall core — treat it as a last resort, not a first quote.
Free download: the on-site damp checklist
Our own plain-English checklist, built around the assessment framework above — print it, take it round the property, and use it to decide what needs a specialist before you spend money on a treatment.
Roof, gutters & downpipes
2 checks
External ground levels & paving
2 checks
Sub-floor & background ventilation
3 checks
External masonry & render
2 checks
Internal walls at low level
2 checks
Internal walls higher up & storm-related staining
2 checks
Kitchens, bathrooms & condensation
3 checks
Before instructing any remedial work
3 checks
No sign-up required. Generated on your device — nothing is uploaded.
Where dew point and standards-referenced reporting fit in
Distinguishing condensation from rising or penetrating damp is a data problem as much as a visual one. DampApp Pro's on-device psychrometric calculations turn a temperature and relative-humidity reading into dew point, vapour pressure and specific humidity (per BS 5250), so you can evidence a condensation diagnosis rather than assert it — and carry those figures straight into a standards-referenced PDF report. It doesn't replace the judgement a heritage-experienced surveyor brings to a solid-wall building, but it takes the guesswork out of the psychrometrics.
Frequently asked questions
What exactly did Historic England publish, and is "HEAG311" a real reference?
Yes — HEAG311 is genuine. It is Historic England's product code for "Assessing Damp in Historic Buildings: A Practical Guide to Investigation and Diagnosis", a 92-page guidance document published 13 July 2026. It focuses on the accuracy and limitations of the tools used to assess and monitor moisture, alongside practical advice on investigating and diagnosing damp in historic buildings. Read the original at historicengland.org.uk.
Is rising damp as common as older damp-proofing quotes suggest?
Genuine capillary rising damp is less common than it is often diagnosed. Conservation bodies including the SPAB note that true capillary rise in a solid wall is usually confined to roughly the lowest 300–900mm above floor level and rarely climbs much further, so tide-marks or plaster failure higher up a wall usually have a different cause — penetrating damp, condensation, or hygroscopic salts left behind by an earlier, since-resolved problem.
Why can modern repairs make damp in an old building worse?
Pre-1919 solid-wall buildings were generally built to manage moisture by absorption and evaporation through breathable materials (lime mortars, renders and plasters), not to exclude it entirely. Cement render, gypsum plaster and plastic-based coatings are far less permeable, so applied to old solid walls they can trap moisture in the fabric and push it toward the nearest breathable surface or timber in contact with the wall — often making the original symptom worse rather than curing it.
Does DampApp Pro follow Historic England's guidance?
DampApp Pro is not certified or endorsed by Historic England, the SPAB, RICS or the PCA. It is general-purpose damp and mould survey software: you can record traditional construction, breathable finishes and non-destructive observations in your own words, and its psychrometric calculations (dew point, vapour pressure and relative humidity per BS 5250) help you evidence a condensation diagnosis with data rather than opinion. The surveyor remains responsible for diagnosis and the final signed report.
Is the checklist below a substitute for a professional survey?
No. It is a free triage aid to help you look in the right places and ask the right questions before calling in help. For listed buildings, older solid-wall construction, or anything unclear after working through it, involve a heritage-experienced surveyor or conservation specialist rather than relying on the checklist alone.
Related reading
This page summarises, in our own words, the general approach behind Historic England's published guidance on damp in historic buildings, accessed and verified July 2026. It is not the guidance itself, is not endorsed by Historic England, RICS, the Property Care Association or the SPAB, and is not a substitute for a professional survey. Always read the current official guidance at historicengland.org.uk and the joint position statement at historicengland.org.uk before relying on any figure, reference number or recommendation quoted here.