Description
For first-time EWI applications on traditional UK housing stock — pre-1970s solid-wall homes adding their initial 40–60 mm of external insulation under budget-driven or planning-constrained refurbishment scopes — the White Oversill 2.5 m × 110 mm is the shallowest projection in the white oversill family and the most-specified depth across light-touch retrofit work. Sized to accommodate insulation up to 60 mm, the profile pairs with the white fascia, rainwater goods, and trim systems that define traditional UK residential character. Sold here through our window sill extensions and oversills collection, finished with industrial-grade powder coating and arriving wrapped in factory-applied PVC protective film. Trade self-collection from our Southampton counter.
Product Overview
An oversill carries the original window sill outward over the new insulation depth, restoring rainwater shedding and visual proportion to a window detail that the EWI layer has fundamentally changed. The 110 mm projection sits at the shallowest end of the oversill range, sized for insulation builds up to 60 mm — covering the budget-constrained refurbishment work that represents the largest share of UK domestic EWI installations on traditional housing stock.
The white finish remains the default specification across this market segment. Pre-1970s terraces, semi-detached and detached homes with white-painted timber fascia, white uPVC rainwater goods, or white-painted cast iron downpipes pair visually with white oversill trim — anthracite alternatives would clash with the established trim colour scheme. At 2.5 metres per unit, a single profile typically serves windows up to 2.0 m wide once end-cap allowances are deducted.
Key Benefits
- Sized for first-time EWI builds: the 110 mm depth accommodates insulation up to 60 mm — the depth band typical of light-touch refurbishment work and budget-constrained EWI on traditional UK housing.
- Industrial powder-coat white finish: the factory-applied coating delivers consistent colour density across the trim — outperforming painted alternatives that show edge wear and colour drift over service life.
- PVC protective film during install: the factory-applied film safeguards the visible face through transport and on-site handling, peeling away cleanly after surrounding render work has cured.
- 2.5 m unit length: a single profile covers most domestic window widths without an intermediate joint, delivering the unbroken trim line that residential refurbishment work depends on.
- Coordinated with traditional trim systems: aligns visually with white fascia, white uPVC rainwater goods, and white-painted timber detailing typical of UK pre-1970s housing.
Technical Specifications
| Property | Value |
|---|---|
| Profile type | Window oversill extension |
| Material | Powder-coated metal extrusion, exterior grade |
| Colour | White |
| Length | 2.5 m |
| Projection (depth) | 110 mm |
| Insulation depth accommodated | Up to 60 mm |
| Finish | Industrial-grade powder coating |
| Surface protection | Factory-applied PVC film, removed post-install |
| Compatible end caps | White end-cap pair (sold separately) |
| Delivery | Self-collection from Southampton — courier transit excluded |
| Storage | Flat, dry, protective film retained until install |
Application & Compatibility
The 110 mm white oversill is the correct projection for light-touch EWI refurbishment work where the external insulation layer adds 40–60 mm to the existing wall — the typical scope on budget-driven retrofits, ECO-funded shallow EWI installations, and Article 4 conservation areas where insulation depth is constrained to preserve sightlines. Pair the profile with the matching white end-cap pair to close both ends of the run — caps are sold separately and must be ordered alongside for the install to proceed in one coordinated sequence.
For installation principles across the trim system — including the order of work between oversill, end caps, surrounding render termination, and coordinated trim detailing — our window sill extensions installation guide walks through the typical sequence and detailing logic.
Installation Notes
For the cleanest result, fit the oversill after the basecoat and reinforcing mesh have cured but before the decorative finish coat goes on. The profile must be set with a slight outward fall — typically 5–10 degrees — so rainwater drains away from the wall rather than tracking back behind the oversill toward the substrate. Bed the back upstand into a continuous neutral-cure white silicone seal against the original masonry sill, and fix mechanically at recommended centres along the back upstand.
Retain the protective PVC film through render application and surrounding finishing work. White surfaces show cementitious render runoff and basecoat residue more visibly than darker trim, and once cement starts to set on PVC or powder coating the residue can leave a permanent shadow on the white face. The film prevents this contact during the install sequence — peel it only after all render work has cured to taping-clean and any surface cleaning around the window has been completed.
Trade Insight: The Most Common Shallow-Build Scenario in UK EWI
Across the four white oversill depths, the 110 mm projection is the workhorse of light-touch refurbishment work — a different category from the deeper "workhorse" 170 mm depth that dominates standard EWI specifications. The 110 mm white earns its specification on a genuinely common scenario: pre-1970s solid-wall housing receiving its first EWI layer under ECO-funded or budget-driven scopes, where the insulation strategy maxes out at 40–60 mm to balance cost, planning constraints, and disruption against achievable U-value improvement. Step up to the 140 mm white oversill when insulation depth pushes into the 70–90 mm band — typical of conservation-permitted upgrades or moderate-spec refurbishments. The 170 mm white oversill becomes correct once the build reaches 90–120 mm, the standard depth for graphite EPS at 90 mm and standard EPS at 100 mm. Selecting the depth that matches the actual build avoids the visible step that overspecified profiles create at the window detail. Self-collection from our Southampton counter is the standard delivery route — courier transit damages the powder-coat edge too frequently to remain economic on visible trim work.
Is This Product Right for Your Project?
- Light-touch first-time EWI (up to 60 mm insulation): the most-specified projection for traditional UK housing stock receiving its initial external insulation layer under budget-driven or planning-constrained refurbishment.
- Light-to-medium retrofit (60–90 mm insulation): step up to the 140 mm white oversill — the 110 mm projection would underdeliver on overhang past the finished render face.
- Standard EWI (90 mm and above): use the workhorse 170 mm white oversill for graphite EPS at 90 mm or standard EPS at 100 mm.
- Traditional and heritage facades: the white finish coordinates with white fascia, rainwater goods, and trim systems typical of UK pre-1970s residential housing where dark-trim alternatives would clash.
FAQ
Is 60 mm of insulation enough for meaningful U-value improvement?
For a solid uninsulated wall the U-value reduction from 60 mm of EPS or mineral wool is substantial — typically taking the wall from around 1.7 W/m²K down toward 0.4–0.5 W/m²K depending on the existing wall construction and the insulation lambda. For Part L compliance on extensions or major refurbishments deeper builds may be required; for general thermal upgrade work on existing housing, 60 mm delivers genuine performance gains while keeping the project scope manageable. Final U-value calculation is project-specific and subject to the relevant standard.
How do I confirm the 110 mm depth is right for my project?
Measure the total finished build from the original masonry face outward — insulation thickness plus adhesive layer plus basecoat plus decorative finish. The oversill projection should exceed this measurement by 30–40 mm to deliver proper drip clearance past the finished render face. For builds totalling around 60–70 mm, the 110 mm depth gives the right overhang.
Are end caps included with the oversill?
No — end caps are sold separately as a matched pair. Order the white end-cap pair alongside the oversill so both arrive ready for the install sequence. One pair closes both ends of one oversill run.
Why is delivery limited to self-collection?
Powder-coated extrusions of this length sustain corner damage during courier transit at a rate that makes shipping uneconomic for visible facade trim. Self-collection from our Southampton counter ensures the profile arrives with the powder-coat edge intact, ready for install. Trade buyers regularly collecting larger orders can arrange scheduled pickup in advance.
Will the white finish stain from cementitious render runoff?
White trim shows render runoff and efflorescence-style staining more visibly than darker alternatives. The PVC protective film prevents direct contact during the install — keep the film in place until all render work has cured, and any post-install runoff can be cleaned with mild detergent before it sets. Proper bedding and drainage detailing during install minimises the risk that runoff reaches the trim face during service.
PLEASE NOTE!
Due to frequent damage during courier transport, the product is for self-collection only.