How do I tell if my house has bridging problems?

Visual signs: black mould at corners of external walls, dampness near window reveals, condensation on windows in winter, cold areas of wall to the touch when central heating is on. Thermal imaging survey (£350–£950) confirms — shows cold pathways through fabric. EPC report mentions Y-value; default 0.08 unless improved.

Does external wall insulation eliminate bridging?

Largely yes — EWI wraps the external envelope continuously, bypassing internal junctions. Remaining bridges: window/door openings (where EWI thickness wraps reveals — 25–40mm PIR in reveal), party walls (heat lost into neighbouring loft/basement — can't be EWI'd from your side), balcony cantilevers (concrete through-wall — requires Schöck thermal break or insulated balcony retrofit).

Can I retrofit thermal break details to an existing house?

Partially. Balcony Schöck retrofit £4,800–£18,500 per balcony — major intervention. Window thermal break: only via replacement (thermal-break frames). Lintels and cills: replacement only at major refurb. Most cost-effective intervention: EWI to walls + IWI to party wall faces + continuous insulation at roof and floor — reduces total bridging significantly without addressing every individual bridge.

Thermal Bridging London Renovation 2026 | Builderr

What Is Thermal Bridging in a London Renovation and How Is It Managed?

Thermal bridging is heat-loss through fabric junctions where insulation continuity breaks — window reveals, balconies, wall-roof, wall-floor, party walls. Quantified as Y-value (W/m²K of total dwelling envelope). Standard Y-value 0.08; Passivhaus <0.04. Bridges cause cold spots inside (condensation + mould risk) and significantly reduce calculated heat-loss benefit of bulk insulation. Managed through detail design at RIBA Stage 4 and skilled installation.

Where bridges occur

Common bridge locations in London renovations: (1) Window and door reveals — insulation thinner here than wall bulk; reveal cold internally. (2) Wall-roof junction — eaves detail where wall meets roof; insulation discontinuity through joist or rafter. (3) Wall-floor junction — slab-on-ground meets wall; insulation under slab must overlap wall insulation. (4) Balconies and cantilevers — concrete projects through insulated wall; massive bridge. (5) Steel beams in extensions — uninsulated steel bridges wall + floor. (6) Party walls — heat lost into neighbouring (unheated) loft or basement spaces. (7) Lintels and cills — uninsulated structural members above/below openings. (8) Penetrations — soil stacks, vents, services bridge insulation locally.

Consequences

Increased heat loss: bridges reduce effective U-value of whole element by 5–25%. A wall calculated as 0.18 U-value might perform at 0.22 due to bridges. EPC calculation includes Y-value (default 0.08 if not designed; lower if Accredited Construction Detail used; site-measured for Passivhaus). Internal cold spots: temperature drops 4–8°C below room ambient at bridge surfaces. Condensation when warm humid air meets cold surface — mould growth in window reveals, behind cabinets, at floor-wall junctions. Comfort impact: cold radiation off cold internal surfaces — feels colder than ambient even with same heating. Particular London problem: 1900s solid-wall houses with internal wall insulation create new bridges at every joist/floor junction.

Management

Design: Accredited Construction Details (ACDs) at RIBA Stage 4 — pre-tested junction details with verified low Y-value (<0.04). For Passivhaus/EnerPHit: ThermalBridgeBoard (Schöck Isokorb for cantilevers), Compacfoam at lintels and door thresholds, continuous external insulation wrapping all junctions. Install: insulation must be continuous across junction — common failure is leaving 50mm gap at wall-roof or wall-floor where insulation easier to install separately. Window reveals: insulate reveals with 25–40mm PIR (slimmer wall insulation continues into reveal); thermal break frames for windows (timber, alu with thermal break, uPVC). External wall insulation (EWI) — most effective bridge management because insulation wraps the entire envelope without internal interruption. Internal wall insulation (IWI) — creates bridges at every internal partition and floor junction; thermal model required to verify acceptable performance.