External Wall Insulation & Aluminium Window Cills in Ireland
A Complete Guide for Retrofit, New Build and Modern Construction
External wall insulation (EWI) has become one of the most important upgrades in Irish construction. From deep retrofit projects to new builds and passive homes, insulation performance and proper detailing now play a critical role in energy efficiency, durability and long-term building performance.
One of the most overlooked — yet most critical — components of any external wall insulation system is the window cill. Poor detailing around window openings is one of the most common causes of:
Water ingress
Thermal bridging
Render cracking
Premature failure of insulation systems
This guide explains how aluminium window cills support modern external wall insulation systems and why contractors, architects and homeowners across Ireland are increasingly choosing made-to-measure aluminium solutions.
What Is External Wall Insulation (EWI)?
External wall insulation (EWI) is a system where insulation boards are fixed to the outside of a building and finished with reinforced render or cladding.
It is commonly used in:
Home retrofit projects
SEAI-funded energy upgrades
New build homes
Passive house construction
ICF (Insulated Concrete Formwork) buildings
A complete EWI system typically includes:
Insulation boards (EPS, graphite EPS, mineral wool)
Mechanical fixings and adhesive
Reinforcement mesh and base coat
Render finish
External insulation window detailing and window cills
Without proper detailing around windows, even the highest quality insulation system can underperform or fail prematurely.
Why Aluminium Window Cills Matter in EWI Systems
Window cills play a critical role in managing water, protecting insulation and maintaining airtightness around window openings.
Poorly designed or incorrectly installed cills commonly lead to:
Water ingress beneath windows
Thermal bridging around window reveals
Cracking or staining of external render
Long-term moisture damage within the wall system
This is why aluminium window cills for external wall insulation are now considered best practice on many modern projects.
When correctly specified and installed, aluminium cills help:
Direct water away from the façade
Protect insulation edges
Support clean detailing around openings
Improve long-term durability of EWI systems
Benefits of Aluminium Window Cills
Aluminium outperforms traditional concrete or stone cills in almost every modern build scenario.
Key benefits:
Resistant to moisture and weathering
Lightweight yet structurally strong
Clean, modern appearance
Precise manufacturing tolerances
Compatible with all EWI systems
Long lifespan with minimal maintenance
Powder-coated aluminium cills can be finished in any RAL colour, including popular options such as RAL 7016 anthracite grey.
Aluminium Window Cills for EWI, Retrofit and Energy Upgrades in Irish Homes
Learn how aluminium window cills support external wall insulation systems, improve detailing around openings and provide durable, low-maintenance finishes for retrofit projects in Ireland.
Daniel Ganea
EWI & Retrofit Guide
Trusted & Used By Professionals From
Order Your First Custom Aluminium Product
Cills.ie makes it easy to measure, customise, and order aluminium cills, flashings, trims, and cappings & more. All online, with engineer support included.
