Description
Where does a window sill go when EWI insulation reaches 150–170 mm? The Over Sill Anthracite 2.5 m × 220 mm is the deepest projection in the anthracite family, carrying the original sill outward over the deepest current UK build-ups — typically PAS 2035 deep-retrofit and EnerPHit refurbishment — where a standard 170 mm profile runs short of the finished render face. Powder-coated aluminium in RAL 7016, film-protected, stocked for trade self-collection from Southampton.
What the 220 mm Anthracite Oversill Does in a UK Render or EWI System
Can a standard oversill reach past a deep insulation build? At 150–170 mm of insulation it usually cannot, and the 220 mm Anthracite Oversill exists to carry the original window sill outward over exactly that band, providing the drip overhang that protects the rendered reveal below from rainwater tracking back against the substrate. At 2.5 m length and 220 mm projection in RAL 7016 anthracite powder coat, the profile addresses the deepest end of current UK EWI specification, and it sits within the wider window sill extensions and oversills range for coordinated deep-build detailing.
An oversill at this projection is the transition between the masonry sill that remains in place and the finished render face that now sits 170–190 mm proud of the original wall plane. The visible architectural mass is meaningful at this depth: a 220 mm trim becomes part of the facade composition rather than an unobtrusive detail, which is why anthracite is the dominant colour choice, since the dark trim reads more sympathetically than white against the visual weight of a deep window reveal.
Why Specifiers Choose the 220 mm Anthracite Oversill for Deep Builds
- Sized for 150–170 mm insulation builds: the projection delivers the 30–40 mm drip overhang past finished render needed on deep-retrofit specifications, where shallower oversills would sit flush with or behind the render face.
- RAL 7016 industrial powder coat: the factory-applied coating gives consistent colour density, holding the contemporary aesthetic that aligns with the deep-retrofit project character on which this depth is most often specified.
- PVC protective film through extended programmes: deep-retrofit work brings multiple trades through the window detail across weeks, and the factory film keeps the dark powder coat clear of render splatter and tooling marks until taping-clean handover.
- Single 2.5 m profile per opening: covers domestic window widths in one length, avoiding the intermediate joint that would read as a visible architectural line at 220 mm depth.
- Matched anthracite end caps available: the anthracite end-cap pair closes both ends of the run in the same RAL 7016 finish, ordered alongside for a coordinated install.
Technical Specifications — 220 mm Anthracite Oversill Data Sheet
| Property | Value |
|---|---|
| Profile type | Window oversill extension — deep projection |
| Material | Powder-coated aluminium extrusion, exterior grade |
| Colour | Anthracite, RAL 7016 family |
| Length | 2.5 m (single unit) |
| Projection (depth) | 220 mm |
| Insulation build accommodated | 150–170 mm typical |
| Finish | Industrial-grade powder coating, both faces |
| Surface protection | Factory-applied PVC film, removed post-install |
| Recommended outward fall | 5–10° for rainwater shedding |
| Compatible end caps | Anthracite end-cap pair (sold separately) |
| Delivery route | Self-collection only — Southampton counter |
| Storage | Flat, dry, protective film retained until install |
How the 220 mm Anthracite Oversill Installs Over Deep EWI
Fit the oversill after the basecoat and reinforcing mesh have cured but before the decorative finish coat, so the trim beds into a stable substrate while the render face can be worked tight against the profile edge afterwards. Set the trim with a 5–10 degree outward fall so rainwater drains clear of the wall rather than tracking back behind the upstand toward the substrate. Bed the back upstand into a continuous neutral-cure silicone seal against the original masonry sill, then fix mechanically at recommended centres along the upstand, pairing with the matching anthracite end-cap pair at each reveal to close the termination.
At 220 mm projection the trim works structurally harder than shallower profiles, so verify wind-uplift fixing capacity against the project's exposure category, particularly on south-westerly elevations facing prevailing UK weather. Retain the PVC film until all surrounding render and finishing work has cured to taping-clean, peeling it only at handover. For the full installation sequence covering oversills, verge trims and end caps as a system, the window sill extensions installation guide walks through the order of work and detailing logic across the whole trim family.
Installation Notes — Wind Uplift, Sequencing, Film Removal
For the best result, plan the oversill fit between basecoat cure and decorative finish so the render face can be worked cleanly against the trim edge. Confirm the back upstand sits flush against the original masonry sill before sealing, since gaps behind the upstand are difficult to remediate once the silicone bead cures and the surrounding render is applied. This depth is most often specified on PAS 2035 Whole-House and EnerPHit refurbishment, where fabric calculations typically drive insulation into the upper depth band, subject to project-specific building physics assessment.
The 220 mm projection means the visible face sits substantially proud of the wall plane, so on high-exposure facades supplementary mechanical fixings along the upstand may be advisable beyond standard centres, confirmed against the EWI system-supplier guidance in use. Keep the protective film intact through every adjacent trade interface, since window installers, EWI applicators and finishing teams all pass over the trim across the programme, and the powder coat is most reliably protected by leaving the film in place until the end of the build sequence.
How the 220 mm Depth Compares to Shallower Anthracite Oversills
The anthracite oversill family runs across four projections, each matched to a different EWI insulation band. Choosing the right depth is a measurement decision: total finished build from the original masonry face outward should sit 30–40 mm short of the oversill projection to deliver proper drip clearance past the render face.
| Variant | Key Spec | When to Choose |
|---|---|---|
| 140 mm anthracite oversill | 140 mm projection | Shallow refurbishment EWI, 70–90 mm |
| 170 mm anthracite oversill | 170 mm projection | Standard workhorse EWI, 90–120 mm |
| 220 mm anthracite oversill | 220 mm projection | Deep-retrofit, EnerPHit, 150–170 mm |
If the insulation build falls outside the 150–170 mm band, the 170 mm or 140 mm anthracite oversill is the correct route, since over-specification at 220 mm creates a visible architectural step at the window detail that is rarely intentional. Where the project specifies white trim, the matched 220 mm white oversill covers the same insulation band in a white powder coat.
Pro Tips From UK Installers Fitting Deep-Projection Oversills
Deep-projection oversills reward a different discipline to shallow trims, since at 220 mm every small variation reads on the facade; the habits below are what experienced UK installers consistently get right on deep-retrofit work.
- Order the end caps with the oversill, not after: the matched anthracite pair carries its own lead time, and arriving without caps leaves a deep trim run looking unfinished through inspection visits.
- Mark the fall before bedding: a pencil line on the masonry sill showing the 5–10 degree outward angle keeps the trim consistent across openings, since small variations that vanish at 110 mm are visible at 220 mm projection.
- Validate the projection on elevational drawings first: 220 mm is a facade element, not a trim, so the architectural impact is worth reviewing before the depth is committed, particularly on heritage-adjacent or sensitively-sited buildings.
- Leave the PVC film on until handover: deep-retrofit programmes routinely run multiple weeks of post-render trade work around the window, and the powder coat survives those weeks reliably only with the factory film intact.
- Check wind-uplift on exposed elevations: on south-westerly and coastal sites the deeper projection benefits from supplementary mechanical fixings along the upstand beyond the standard centres specified for shallower trims.
Is the 220 mm Anthracite Oversill Right for Your Project?
- Deep-retrofit and PAS 2035 Whole-House work: the correct projection where fabric specifications drive insulation depth into the 150–170 mm range, subject to project-specific U-value calculation.
- EnerPHit certified refurbishment: sized for the insulation depths typical of Passivhaus-standard refurbishment, subject to project building physics assessment.
- Forward-specified new-build EWI: a sound choice where the project anticipates tightening fabric requirements over its programme and the team wants to lock the trim depth on a future-proofed basis.
- Standard EWI at 90–120 mm insulation: the 170 mm anthracite oversill is the workhorse depth, since the 220 mm projection would sit proud of the render face and create a visible architectural step.
- Mid-range builds at 70–90 mm insulation: the shallower 140 mm anthracite oversill matches the build depth without over-specification.
FAQ — 220 mm Anthracite Oversill Specification, Ordering, Fitting
How many oversills do I need for a typical window opening?
One 2.5 m oversill covers most domestic window widths in a single length, which matters at 220 mm projection because any intermediate joint becomes architecturally visible on a deep trim. Measure the opening width and add 30–50 mm overhang each side past the reveal. For openings exceeding 2.5 m clear, two profiles join with a manufacturer-approved jointing strip, so plan the joint position to fall away from the visual centre of the opening.
How do I confirm 220 mm is the right depth for my project?
Measure the total finished build from the original masonry face outward — insulation thickness plus adhesive layer plus basecoat plus decorative finish — and compare against the projection. The oversill should exceed total build thickness by 30–40 mm for proper drip clearance past the render face. Total builds in the 170–190 mm range are the right match for 220 mm depth; builds shallower than around 160 mm should typically run on the 170 mm oversill instead.
Are end caps included with the oversill?
End caps are sold separately as a matched pair. Order the anthracite end-cap pair alongside the oversill so both arrive together — one pair closes both ends of a single oversill run, and a coordinated delivery keeps the install sequence on programme.
Are there fixing implications at this projection depth?
At 220 mm projection the trim works structurally harder than shallower alternatives, and wind-uplift loading on south-westerly elevations facing prevailing UK weather should be verified against the project's exposure category. Supplementary mechanical fixings along the upstand may be advisable on high-exposure facades — confirm against the project specification and the EWI system-supplier guidance covering the build-up in use.
How is the powder-coated finish maintained over the building's life?
The RAL 7016 powder coat is built for long-term exterior durability and typically needs only periodic rinsing with clean water to remove airborne deposits. Avoid solvent cleaners and abrasive pads, which can dull the coating sheen over time. Localised impact damage during the building's life can be touched in with a matched RAL 7016 exterior-grade paint.
Will the deep projection affect heritage or conservation planning consent?
On listed buildings or properties in conservation areas, a 220 mm projection is often a planning consideration regardless of trim colour, because the visible architectural mass changes the window detail proportion. It is worth validating the projection through elevational drawings at the planning application stage and consulting the local planning authority where heritage sensitivity applies, rather than committing to the depth in advance.