Damp and Mould: Root-Cause Diagnostics vs Cosmetic Fixes

Peeling paint, black spots on corners, a musty smell. It is tempting to wipe, repaint and move on. But cosmetic fixes do little if the causes remain. Effective remediation starts with diagnosis, then a whole house plan that tackles moisture sources, ventilation, insulation and airtightness together.

Below, we outline a simple route to getting it right, with examples drawn from recent Target Green projects.

The four main causes (often overlapping)

1. Bulk water ingress: Leaks from roofs, gutters, flashings, cracked render, failed sealants, defective DPCs, bridging at thresholds.

2. Interstitial or surface condensation: Warm moist air meeting cold surfaces or cold layers within the construction, for example behind insulation where detailing is poor.

3. Rising damp (true, but uncommon): Moisture wicking up where DPCs are missing, bridged or saturated. Often misdiagnosed.

4. Occupancy and ventilation mismatch: Moisture generation from cooking, drying clothes and showers without adequate extract or background air supply.

Why wipes and paint do not work

• Anti mould paints can buy time, but if the wall is still cold or damp, mould returns.

• Dehumidifiers can help short term, but they do not fix leaks or cold bridges.

• Ad hoc vents may relieve symptoms while creating new cold spots if not designed as part of a balanced system.

The cure is almost always a combined approach: fix water, manage vapour, warm up surfaces, and balance the air.

A practical diagnostic sequence

1. Triage and evidenceLog Day 0, photograph affected areas, note smells, seasons and room use. Record humidity and temperature if possible.

2. Check for water ingressInspect roofs, gutters, downpipes, penetrations, ground levels, sills and flashings. Look for staining, salts and soft plaster.

3. Measure and mapUse moisture meters and, where useful, thermal images to spot cold bridges and hidden damp. Note ventilation provision and flow rates.

4. Review constructionSolid wall vs cavity, system build or no fines. Previous insulation, risk of trapped moisture, junction details at canopies and eaves.

5. Match ventilation to useAssess extract in kitchens and bathrooms, background air supply, and whether existing systems actually move air.

6. Plan a sequenced fixAddress leaks first, then ventilation, then fabric measures such as insulation and airtightness with careful junction detailing.

What good looks like from our projects

1) Cavity remediation and EWI done properly

The Retreat, Monmouth five 1970s bungalows

Failed cavity insulation and wall tie defects were allowing moisture pathways. We extracted the failed fill, repaired ties where required, then installed mineral based EWI with extended eaves and integrated detailing around rainwater and soil stacks. Ventilation was upgraded with dMEV and PIV and door undercuts introduced to balance air paths. Result: warmer internal surfaces, controlled moisture, and no reliance on paint and hope.

2) Designing out cold bridges at junctions

NCH, Newport 52 homes

A very severe wind driven rain zone demanded robust EWI and enhanced junction detailing at canopies and rooflines. We extended overhangs and coordinated fixtures through the insulation layer to avoid cold bridges that can drive surface mould. Background and extract ventilation were upgraded in line with Part F to keep moisture moving.

3) Choosing systems to suit the fabric

St Mary’s Place, Portskewett 33 homes, mixed archetypes

Different wall types needed different insulation systems. Rockwool for flats for fire performance, PIR for bungalows due to clearance and exposure constraints, EPS where appropriate for exposure and rain shed. One size never fits all. The right system and the right details prevent interstitial condensation later.

4) Phased measures still need rigour

Port Talbot 58 PV only homes

Even when the measure is generation rather than fabric, we followed PAS 2035 coordination principles: evidence, sequencing and resident engagement. In a future phase, fabric and ventilation upgrades can be layered on without undoing previous work. This is how you avoid piecemeal fixes and performance gaps.

Common mistakes that keep problems coming back

• Insulating without ventilation upgrades. Warmer, tighter homes need designed extract and background air.

• Blocking or removing vent paths in the loft. Insulation top ups must retain eaves ventilation.

• Bridged cavities and ground levels too high. EWI and landscaping need considered drip and DPC details.

• Ad hoc fans with no commissioning. If it does not pull the litres per second on the grille, it will not do the job.

• Painting over hygroscopic salts. Treat the cause first or stains reappear.

A simple, whole house fix plan

1. Eliminate water ingress: Roofs, gutters, overflows, ground levels, cracked masonry, failed sealants.

2. Right size and commission ventilation: dMEV in wet rooms with verified flow rates. Make up air via background vents or designed supply. Consider PIV where appropriate.

3. Warm the surfaces: Target cold spots with fabric first measures. EWI or internal insulation with moisture safe build ups, loft top ups with vent paths maintained, high performance windows and doors with competent installation.

4. Close the gaps intentionally: Airtightness at junctions, service penetrations and canopies, paired with the ventilation strategy.

5. Verify and hand over: Basic post works checks. Moisture readings, thermal scans where useful, fan flow tests, simple user guidance for residents.

How Target Green can help

• Root cause diagnostics using site surveys, moisture mapping and thermal imaging.

• Retrofit design that integrates ventilation, insulation and airtightness, with junction details that prevent cold bridges.

• Coordination to PAS 2035 so works are sequenced, evidenced and compliant.

• Resident friendly handover so the home is easy to live in and stays dry.

If you are facing repeat damp and mould issues, we will help you stop treating symptoms and start solving causes.