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🏗️ Purpose-Built for ICF Construction

Window Sills for ICF Builds Measured Per Opening. Made to Fit.

ICF walls are 300-400mm thick. Standard sills don't fit. Every aluminium window sill from Cills.ie is manufactured to the exact depth and projection of your ICF reveal, powder coated in your chosen RAL colour, and delivered ready to install with no rework.

80-120mm projection depths Per-opening measurement 3D preview before manufacture Zero reorder rate
Order ICF Sills Now See Full Specs on Cills.ie
CILLS app showing guided digital measurement interface for ordering aluminium window sills for ICF builds in Ireland
⚠️ The Problem

The Window Sill Is Where ICF Houses Leak, Grow Mould, and Fail

The junction between the window frame, EWI render, and window sill is the number one source of water ingress on ICF houses in Ireland. In nearly every case, it is entirely preventable.

Ask any experienced ICF contractor in Ireland where the most common moisture problems occur on a finished build and the answer is almost always the same: the window reveals. ICF walls perform exceptionally well as a thermal and structural system, but they create a reveal geometry that standard finishing products are not designed for.

When a contractor fits a sill that is too narrow, too shallow, or the wrong profile for the wall buildup, they create a moisture trap at the base of the window frame. Water doesn't shed clear. It sits, it tracks, and it gets in.

Water Ingress at Reveals

The sill doesn't project far enough beyond the render face. Rainwater runs back along the underside and into the reveal junction, saturating the EWI system within months.

Internal Mould Growth

Persistent moisture at the outer reveal migrates inward through the wall buildup. Condensation and mould appear on internal plaster around the window, often misdiagnosed as a ventilation problem.

Render Delamination

Water trapped at the base of the EWI system saturates the insulation board and breaks adhesion between insulation and render coat. Cracking and bubbling typically appear within 2-4 years.

Window Frame Degradation

Standing water at an incorrectly detailed sill-to-frame junction degrades sealants, causes frame discolouration, and eventually compromises the weatherseal entirely.

Structural Damp in ICF Block

In severe cases, moisture works into the EPS formwork of the ICF block itself, reducing insulation value and creating a persistent cold bridge at the reveal.

Failed Airtightness Tests

ICF builds target Passive or near-Passive airtightness. A poorly detailed sill junction is a direct air leakage path that undermines whole-house performance and shows up on blower door tests.

None of these failures are dramatic on day one. A slightly short sill looks fine when it's fitted. The problems show up six months later, after the first winter of rain. By that point the render is on, the windows are fitted, and rectification means cutting out render, removing the sill, remeasuring, reordering, refitting, and rerendering. The cost is multiples of what the correct sill would have cost in the first place.

Why Standard Window Sills Don't Work on ICF Builds

ICF walls are typically 300-400mm thick once the insulation formwork, EWI system, and render coat are applied. A standard window sill sold in a builders' provider is designed for a cavity wall with a 100-150mm reveal. It has the wrong projection, the wrong profile, and the wrong fixing detail for an ICF opening.

When you fit an undersized sill to an ICF reveal, the sill cover doesn't extend far enough beyond the face of the render. Rainwater runs back towards the wall rather than shedding clear. Over time this saturates the base of the EWI system, causes render delamination, and creates persistent damp at the reveal.

300-400mm
Typical ICF wall thickness
€400+
Cost of a single reorder
~0
Reorder rate with per-opening measurement
Aluminium window sill measurement for ICF build showing deep reveal and correct projection depth
⚠️ Important Warning

Passive Cills Are Not the Answer And Not NSAI Approved

Prefabricated passive cills are marketed for high-performance builds, but they create serious problems on ICF projects.

Not NSAI Approved

Passive cills have not been assessed or approved by the National Standards Authority of Ireland. Using them on a compliant build is an unverified product decision at a critical weatherproofing junction. This flags during Stage 4 inspections and BER assessments.

Fixed Sizes Only

Passive cills come in standard dimensions. They cannot be manufactured to the exact projection and width required by each individual ICF reveal. The 80-120mm projection depths typical of ICF/EWI buildups are not available in passive cill ranges.

  • No per-opening measurement verification process
  • No 3D preview or confirmation before manufacture
  • Thermal performance claims unverified without NSAI certification
  • Wrong for deep reveals and full ICF/EWI wall buildups
✅ The Right Detail

What a Correct ICF Aluminium Sill Detail Looks Like

The correct aluminium sill specification for an ICF build includes five critical elements that standard products don't provide.

Full-Width Coverage

The sill spans the complete reveal width including any EWI upstand at the jambs. No gaps, no exposed edges.

Correct Projection

Calculated from the face of finished render. Typically 80-120mm on a full ICF/EWI buildup to throw water clear of the insulation layer.

Drip Edge

An extruded groove on the underside of the leading edge, approximately 10-15mm back, that breaks surface tension and prevents water runback.

Welded End Caps

Factory-welded sealed end returns that prevent water tracking into the reveal at the jamb junction, the most vulnerable point on the detail.

Rear Upstand

A raised lip that beds into the frame rebate and creates a weathertight junction at the back of the sill, sealed with low-modulus silicone.

Any RAL Colour

Powder coated in a controlled factory environment to match window frames, render system, or any RAL Classic colour specification.

Why Aluminium Is the Right Material for ICF Window Sills

Once you accept that a standard product won't do the job, the material question becomes straightforward. Timber rots at the exposed leading edge of a deep reveal. uPVC warps in direct sunlight and can't be colour-matched to system renders. Stone and concrete are heavy, expensive to cut to non-standard projections, and carry thermal bridging risk.

An aluminium window sill, specifically a powder-coated extruded aluminium profile, solves all of these problems. It can be manufactured to any width and projection, is dimensionally stable across Irish temperature ranges, takes any RAL colour, and is light enough to handle on-site without additional support.

  • 2mm marine-grade aluminium
  • Dimensionally stable in all weather
  • Full RAL Classic colour range
  • 30+ year maintenance-free lifespan
  • No cracking, warping, or staining
  • Lightweight for easy on-site handling
Powder coated aluminium window sill for ICF construction showing deep projection and drip edge detail
30+
Years maintenance-free
📐 Critical Step

Measurement Is Where ICF Sill Projects Go Wrong

The most expensive mistake on any ICF sill order isn't the wrong product. It's the wrong measurement.

ICF reveals are formed in the block during construction and are subject to small but meaningful variation across a building. The reveal depth at window one may differ from window twelve by 8-15mm, particularly on larger projects where EWI is applied in sections by different operatives.

If you order window sills from a drawing rather than from site measurements, you will get some wrong. A single reorder on a made-to-measure aluminium product, once you factor in lead time, site delay, removal, and reinstallation, typically costs three to four times the original product cost.

On a 25-opening ICF project with even a 10% error rate, that's two or three reorders and €500-€800 in avoidable cost before you count the programme delay.

Do not batch openings by assumed similarity

On ICF builds, the assumption that all reveals are the same size is almost always wrong on at least one opening. Measure every opening individually on site. That's how you eliminate reorders.

🏭 The Cills.ie Process

The Only Way to Measure Precisely for an ICF Aluminium Sill

Every other route to sourcing aluminium window sills operates on fixed sizes, catalogue dimensions, or bulk orders measured from drawings. None of them measure per opening. None of them generate a 3D preview for confirmation before manufacture.

01

Measure Per Opening

Take individual measurements on site for every window. Width, projection, depth. No batching by assumed size.

02

3D Preview

A 3D shape preview is generated so you can confirm the profile and projection before anything is manufactured.

03

Choose RAL Colour

Select any RAL Classic colour to match your window frames or render system. Powder coated in a controlled environment.

04

Made in Dublin

Each sill is manufactured to the exact dimension of the reveal it's going into. 3-5 day turnaround with nationwide delivery.

Start Your ICF Sill Order

Door Thresholds on ICF The Same Problem at Ground Level

The window sill problem has a direct equivalent at floor level. The door threshold on an ICF build faces the same challenge: a thick wall, a deep reveal, and a transition between interior floor level and external ground that has to manage water, thermal performance, and accessibility simultaneously.

A standard door threshold is designed for a 100mm cavity wall leaf. On an ICF build where the structural wall alone is 150-200mm before insulation, a standard threshold leaves an exposed gap at the base of the reveal that no amount of sealant fixes permanently.

The correct solution is a purpose-made aluminium threshold profile manufactured to the actual reveal depth. If you're specifying aluminium window sills for an ICF project, the door threshold should be part of the same conversation with the same supplier. Consistent material, consistent colour, consistent detail.

  • Same material and RAL colour as window sills
  • Made to actual reveal depth
  • Manages water, thermal performance, and accessibility
Purpose-made aluminium door threshold for ICF build with deep reveal

What the Installed Detail Actually Looks Like

Understanding the installed configuration is essential for getting the specification right.

The sill sits in the rebate at the base of the window frame, with a rear upstand tucked under the frame and sealed with low-modulus silicone. The body of the sill runs across the full width of the opening. The leading edge, the visible window ledge, projects beyond the render face by the specified distance, with the drip groove on its underside approximately 10-15mm back from the leading edge.

At the jambs, end caps are factory-welded as part of the manufacture. A properly formed end cap turns water away from the EWI upstand at the reveal edge and prevents tracking back into the wall at the most vulnerable point, the junction between the sill and the render system.

The window sill in this configuration is not a finishing product. It's a critical weatherproofing element. Treating it as an afterthought, ordering off the shelf, measuring from drawings, fitting what arrives without checking the projection, is how expensive defects get built into otherwise high-quality ICF projects.

Who Orders ICF Window Sills from Cills.ie

ICF Contractors

Specialist ICF builders who need precision sills for thick wall buildups. Per-opening measurement eliminates the reorder problem that costs time and money on every project.

EWI Installers

External wall insulation contractors fitting deep projection sills as part of SEAI-funded energy upgrade projects. Compatible with EPS, mineral wool, and phenolic insulation systems.

Passive House Builders

Contractors building to Passive House and NZEB standards who need precision sills for thermal envelope continuity at window junctions without compromising airtightness targets.

Architects and Specifiers

Design professionals specifying made-to-measure aluminium sills with exact RAL colour matching and welded end cap detailing for high-performance residential and commercial projects.

Self-Build Homeowners

Homeowners building ICF homes who want the right sill detail from the start, not a rework after the first winter. The 3D preview process makes it straightforward even on a first project.

Multi-Unit Developers

Volume supply with batch consistency for ICF apartment schemes and housing developments. Every sill manufactured to the exact dimension of its specific opening.

Frequently Asked Questions ICF Window Sills

ICF walls are typically 300-400mm thick after the insulation formwork, EWI system, and render coat are applied. Standard sills are designed for cavity walls with 100-150mm reveals. They have the wrong projection, wrong profile, and wrong fixing detail for ICF openings. An undersized sill allows rainwater to run back towards the wall, saturating the EWI system and causing render delamination and persistent damp.
ICF window sills typically require 80-120mm projection beyond the render face, depending on the total wall buildup. This is significantly more than the 30-50mm projection on standard cavity wall sills. The exact projection must be calculated from the face of the finished render to ensure water sheds clear of the insulation layer below.
Always measure on site, per opening. ICF reveals are formed in the block during construction and are subject to 8-15mm variation across a building. Measuring from drawings leads to reorders. A single reorder typically costs 3-4 times the original product cost when you factor in lead time, removal, and reinstallation.
Passive cills are not recommended for ICF builds. They come in fixed sizes and cannot be manufactured to the exact projection and width required by each individual ICF reveal. They are also not approved by the NSAI (National Standards Authority of Ireland), which creates compliance risk on any project requiring BER certification, airtightness testing, or planning compliance sign-off.
The correct ICF aluminium sill detail includes full-width coverage spanning the complete reveal width, correct projection calculated from the render face (typically 80-120mm), a drip edge groove on the underside to prevent water runback, sealed end caps to prevent water tracking at jamb junctions, and a rear upstand that beds into the frame rebate for a weathertight junction.
ICF aluminium window sills from Cills.ie start from approximately €45 for smaller openings and can reach €300 for large bay windows with deep projections. Pricing depends on width, projection depth, RAL colour, and whether welded end caps or upstands are specified. You can get an instant price online through the Cills.ie platform.
Yes. Cills.ie manufactures purpose-made aluminium door threshold profiles for ICF reveals at ground level, using the same per-opening measurement process. Door thresholds are supplied in the same RAL colour as the window sills for a consistent finish across the project.

Related Products

Window Sills

All aluminium window sill types

Welded End Caps

Factory-sealed sill ends

Welded Upstands

Raised lip for frame junction seal

Parapet Capping

Made-to-measure aluminium capping

Order ICF Window Sills

Enter your per-opening measurements, choose your RAL colour, and get an instant price. Manufactured in Dublin with 3-5 day turnaround and nationwide delivery.

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Per-opening measurement 3D preview before manufacture SEAI grant compatible

Aluminium Window Sills Across Ireland

Manufactured in Dublin. Delivered nationwide. Explore county-specific guides for installation, EWI retrofits, and SEAI grant projects.

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