Performance · North London
Insulation & Retrofit in North London
Targeted, measured retrofit and insulation upgrades — designed using Passive House principles and verified with testing where required. Specialist building-performance diagnostics across North London — N1-N22 · NW (NW1, NW3, NW5, NW11) · EN (Enfield).
Insulation & Retrofit in North London
What we typically diagnose across North London.
North London's heavyweight Victorian and Edwardian housing stock — from the bay-windowed terraces of Holloway and Finsbury Park through the substantial detached homes of Highgate and Hampstead Garden Suburb to the inter-war semis of Finchley and Barnet — is well-known for cold floors, single-skin extensions and condensation in north-facing rooms. We use FLIR thermal imaging, blower door testing and moisture diagnostics to identify the actual problem before any insulation or remedial work is specified.
- Victorian solid-wall terraces in Islington, Holloway, Archway and Finsbury Park with high heat loss through original brickwork
- Single-storey rear-extension flat roofs in 1930s semis (Finchley, Barnet) with compressed or absent insulation
- North-facing bedrooms and bathrooms in N1, N5, N7 Victorian terraces with chronic winter mould
- Camden conversion flats with inadequate kitchen extract and bathroom ventilation
- Suspended floor perimeters in Holloway, Finsbury Park and Wood Green Victorian terraces
What this service is
Insulation & Retrofit — in plain English.
Internal Wall Insulation (IWI) bonds a high-performance insulation layer to the inside of an existing solid wall, dramatically improving its U-value while keeping the external appearance untouched. Specified incorrectly, IWI causes interstitial condensation and hidden mould. Specified properly — with measured data — it transforms comfort and energy use.
Common problems we solve
The symptoms that bring people to this service.
- 01Cold, solid-wall Victorian and Edwardian homes losing heat through every external wall
- 02Condensation forming on internal wall surfaces in winter
- 03Conservation areas where External Wall Insulation isn't permitted
- 04Cold reveals and lintels driving mould around windows
- 05Homes where existing IWI has failed (peeling paint, hidden damp, black mould)
- 06Solid-wall flats where only the occupied unit is being upgraded
How we investigate
Our diagnostic approach
- 01Full thermal-imaging survey to baseline wall surface temperatures
- 02Moisture-meter readings on walls, skirting, plaster and floor junctions
- 03Surface humidity + dewpoint logging in the affected rooms
- 04Construction build-up confirmed by borescope or test opening
- 05Condensation-risk modelling (WUFI / Glaser) on the proposed IWI build-up before any work
Diagnostic equipment used
What we bring on site
- FLIR thermal camera — to map cold surfaces and reveal cold bridges
- Pin-type and pinless moisture meter (multiple substrates)
- Surface temperature probe + RH/dewpoint logger
- Borescope camera for non-invasive build-up confirmation
- Hygrothermal modelling software for vapour-flow simulation
Building physics — why this works
The science behind the diagnosis.
Insulating the inside of a wall makes the original masonry colder. Warm, moist internal air must NOT reach that cold masonry — otherwise vapour condenses inside the build-up. That's why a properly designed IWI system uses a vapour control layer, airtight detailing at every junction, and a hygric-safe insulation (wood fibre / PIR with VCL / aerogel) appropriate to the wall. Get the physics wrong and you build a hidden mould factory.
What you get
Measured benefits — not vague promises.
- U-values typically improving from 2.0–2.2 W/m²K → 0.30–0.40 W/m²K
- Internal wall surface temperatures lifted by 4–8 °C in winter
- Condensation and mould risk on internal surfaces eliminated
- Heating energy use on the upgraded walls reduced by ~60–80%
- Compatible with conservation areas, listed buildings and flat-only retrofits
Scope of works
Scope of works
- Internal Wall Insulation (IWI) with hygrothermal-aware build-ups
- Loft, roof and ceiling insulation upgrades
- Suspended timber and solid floor insulation
- Thermal bridge mitigation at junctions and reveals
- Whole-house airtightness improvements
Why our approach is different
Why our approach is different
- Diagnosis-led — we measure before recommending
- Hygrothermally safe build-ups, not 'one size fits all'
- Detailing focused on junctions, the real source of failure
- Optional post-works verification through testing
Typical findings
What we commonly discover during insulation & retrofit investigations
- 01Cold internal walls and external-wall corners sitting below dewpoint
- 02Cold floors caused by uninsulated suspended-timber voids
- 03Loft insulation compressed below 100 mm, displaced around eaves
- 04Thermal bridges left untreated at wall/floor and wall/ceiling junctions
- 05Existing retrofit with workmanship gaps, no airtightness layer continuity
Findings reflect patterns observed across completed RetrofitIQ projects — every survey is interpreted in the building’s specific context.
Real project examples
See this service applied on real, completed projects
FAQs
Insulation & Retrofit — common questions
What is a retrofit assessment?+
A retrofit assessment is the diagnostic stage of a deep building-performance upgrade. We measure the existing performance of the building (thermal imaging, blower door, moisture, humidity, ventilation), identify the highest-impact improvements (fabric, airtightness, ventilation), model the proposed measures (U-value, condensation risk, ventilation balance), and produce a written specification and costed plan. The retrofit assessment is the difference between a measured, low-risk upgrade and a guess that may make things worse.Should I insulate internally or externally?+
It depends on the property, the planning constraints and the building physics. External Wall Insulation (EWI) keeps the masonry warm and is the safest option from a moisture-risk perspective, but is not always permitted (conservation areas, listed buildings, terrace-front elevations). Internal Wall Insulation (IWI) preserves the external appearance but is much higher-risk and requires careful vapour control, airtight detailing and condensation modelling. Every case is decided on measured data and PHI-level analysis — not on assumption.What are the risks of Internal Wall Insulation?+
Three main risks: (1) interstitial condensation — warm moist room air reaching the now-cold masonry behind the IWI and condensing there; (2) cold-bridging at intermediate floor zones, party walls and reveals where the insulation cannot continue; (3) trapped joist-ends rotting because they are now embedded in the cold masonry. Done correctly with a continuous vapour control layer, condensation-modelled materials and detailed junctions, IWI is safe and transformative. Done incorrectly, it builds a hidden mould factory.Can insulation cause condensation if installed incorrectly?+
Yes — and this is one of the most frequent and most expensive retrofit failures. Adding insulation makes the original masonry colder than before. If the airtightness barrier and the vapour control layer are imperfect, warm moist room air reaches the cold side of the build-up and condenses interstitially. The new lining looks fine; the rot, mould and damage develop slowly inside the wall. WUFI / Glaser condensation modelling and proper sequencing of the airtight and vapour layers prevent this.What is a thermal bridge?+
A thermal bridge is a localised path of high heat loss through the building envelope — a concrete lintel, a steel beam, an uninsulated reveal, a slab edge, an intermediate floor zone. It conducts heat far more efficiently than the surrounding insulated fabric. Two consequences: (1) measurable additional heat loss (Ψ-value, typically 0.05-0.30 W/m·K per linear metre); (2) localised cold internal surface temperature, often below dewpoint, driving condensation and mould.How do you assess heat loss before insulation works?+
Our protocol: FLIR thermal imaging of every external wall, ceiling and floor; blower door testing to quantify air leakage; moisture meter and dewpoint readings; construction inspection (often with borescope) to confirm the existing build-up; and U-value modelling of the existing and proposed assemblies. The output is a quantified baseline — actual measured performance — against which the proposed retrofit can be planned and afterwards verified.Can thermal imaging help plan insulation upgrades?+
Yes — it is the single most useful planning tool. Thermal imaging tells us *where* the insulation is missing, *where* the thermal bridges are, *where* the air leakage occurs, and *where* the surface temperatures fall below dewpoint. Without that data, an insulation upgrade is guesswork. We always insist on a thermal-imaging baseline before specifying retrofit insulation.What is the role of airtightness in insulation performance?+
Critical. Insulation only performs when air does not bypass it. Cold outside air leaking through gaps and penetrations short-circuits the insulation completely; warm moist indoor air leaking outwards condenses inside the build-up and degrades it from inside. Airtightness is therefore not optional alongside insulation — it is essential. Passive House standard requires 0.6 ACH50 because at that level the insulation actually does what its U-value claims.Can insulation reduce energy bills?+
Yes — substantially, when designed correctly. A typical solid-wall Victorian terrace heated to 20 °C costs around £2,200-£3,000/year in gas at current prices. A properly-specified retrofit (EWI or IWI + airtightness + MVHR) can drop that to £700-£1,100/year — a 65-70% reduction. The payback is measured in years, not decades, but only when the work is done to building-physics standards.Can loft insulation create ventilation problems?+
Yes — and this is a routinely overlooked retrofit failure. Stuffing the eaves with insulation can block the cross-ventilation path that keeps the loft cold and dry; the consequence is condensation on the rafters, mould on the underside of the boarding, and slow rot. Every loft insulation upgrade we specify includes continuous eaves ventilation (or a vapour-controlled airtight ceiling line) — never just 'more wool'.Do you check moisture risk before specifying insulation?+
Yes — every project. We measure indoor humidity, surface temperatures and the existing dewpoint margin; we inspect the external envelope for water-entry paths; and we model the proposed build-up in WUFI / Glaser condensation-risk software before specifying any materials. The output is a documented assessment that the build-up will dry safely under expected internal and external conditions.Do you provide remedial recommendations as well as the assessment?+
Yes — every retrofit assessment is delivered with a written specification of the recommended works (insulation type, thickness, vapour control, airtightness detailing, ventilation strategy), a prioritised costing, and a sequencing plan so the works can be staged over time if the full budget is not available immediately.Can you verify the retrofit performance after works are complete?+
Yes — this is the 'Verify' stage of our Investigate → Diagnose → Design → Remediate → Verify process. A post-works blower door re-test, a thermal-imaging comparison, and (where instrumented) before/after temperature and humidity logging produce documented evidence of the improvement. The output is a verified retrofit — not an assumed one.What is the difference between design, installation and verification?+
Design = the building-physics-led specification of what to do and why (insulation, airtightness, ventilation, materials, detailing). Installation = the works on site, with airtightness, vapour control and detailing executed correctly. Verification = measured proof afterwards. Most retrofit failures occur because design, installation and verification are split across three different contractors with no single accountable party. Our 'one company, one process' model fixes this by carrying all three under one Certified Passive House Designer.Why is a Passive House approach useful in retrofit?+
Passive House (and its retrofit equivalent EnerPHit) is the most rigorous, building-physics-led approach to fabric performance, airtightness, thermal-bridge correction and ventilation in the world. Even where full PH certification is not the goal, applying PH principles (continuous insulation, ≤0.6 ACH50 airtightness target, MVHR with heat recovery, thermal-bridge-free detailing) produces dramatically better-performing buildings than standard UK retrofit practice. Our work is grounded in these principles whether or not the project is being certified.Do you work on Listed buildings and conservation-area properties?+
Yes — we work regularly on Listed and conservation properties across London. The constraint is that External Wall Insulation usually is not permitted, so the retrofit strategy is internal insulation + airtightness + ventilation, designed with extra care for moisture risk. We are also experienced at obtaining and presenting the building-physics evidence needed for Listed Building Consent applications.
Next step
One company. One process. One point of responsibility.
We don’t simply identify problems. We investigate, diagnose, design solutions, carry out the work and verify the results. Book a Home Health Diagnostic Survey and we’ll tell you exactly which remedial works (if any) are actually needed.