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Reviewed: 22 September 2026Insulation and external wall insulation
Why substrate, moisture, junctions, fire, fixings and finish must be assessed as a compatible system.
Practical Points
- 1.
Survey wall construction, exposure, damp, openings, eaves, plinths and services.
- 2.
Use one system's current details for fixings, reinforcement, reveals and render.
- 3.
Sequence water repairs and rainwater goods before closing the envelope.
Considerations & Trade-offs
EWI changes reveals, boundaries, eaves and external appearance.
Scaffolding, detailing and moving services add disruption and cost.
Concept Scenarios
CONCEPT CASE STUDY — NOT A D-CORE PROJECT
External wall insulation upgrade concept
A concept for improving an external envelope while testing moisture, junctions, rainwater goods, openings and finish compatibility.
Options Included:
- System EWI with revised reveals and sills
- Targeted insulation at constrained elevations
- Whole-envelope sequence with roof and services
Related Internal Resources
Official Guidance & Technical Sources
Content angles / Explore further
- • Pinterest: compare reveal, sill, eaves and rainwater details around an EWI build-up.
- • Nextdoor: share the moisture and substrate questions to ask before external insulation.
- • YouTube: show why a render finish is not, by itself, an EWI system.