Making the Right Choice: A Decision That Affects Your Home for 30+ Years

If you're reading this, you're probably staring at heating bills that have doubled in the past few years, or you're tired of rooms that never quite feel warm no matter how high you crank the thermostat. You're not alone – over 500,000 Irish homes still have uninsulated solid walls, and many homeowners are now facing this exact decision.

Here's the thing: choosing between external and internal wall insulation isn't just a technical decision. It's about your family's comfort, your home's value, and how you'll live in your space for the next three decades. Let's break this down properly.

The Real Numbers: What Heat Loss Actually Looks Like

Before we compare methods, let's understand what we're dealing with. According to the SEAI, uninsulated solid walls lose heat at a rate of approximately 2.1 W/m²K. For a typical 3-bed semi-detached house, that translates to:

• €800-€1,200 per year in preventable heat loss
• Roughly 35% of your total heating bill going straight through the walls
• An estimated 2.5 tonnes of CO₂ emissions annually that could be eliminated

Now, both EWI and internal insulation can dramatically reduce this. But they do it very differently, and that difference matters more than most contractors will tell you.

External Wall Insulation: The Full Picture

How It Actually Works

External wall insulation creates a continuous thermal envelope around your entire home. We fix high-density insulation boards (typically 100-150mm of graphite-enhanced EPS or mineral wool) directly to your external walls, then apply a reinforced base coat with fibreglass mesh, followed by your chosen decorative render finish.

The key word here is continuous. Unlike internal insulation, EWI wraps around corners, covers wall junctions, and eliminates the weak points where heat loves to escape.

Real Benefits You'll Actually Notice

1. Your Walls Become Warm

This sounds obvious, but it's transformative. With EWI, your masonry walls stay at room temperature. They become part of your home's heating system – absorbing heat during the day and releasing it slowly at night. This thermal mass effect means more stable temperatures and less reliance on your boiler.

2. Condensation Problems Disappear

Cold walls attract moisture. That's why uninsulated homes get damp patches and mould, especially in bedrooms and bathrooms. With EWI, wall surfaces stay above the dew point, so condensation simply doesn't form. We've transformed homes that had black mould for years into dry, healthy spaces.

3. You Can Live Normally During Installation

All the work happens outside. You don't need to move furniture, empty wardrobes, or relocate for weeks. The scaffolding goes up, we do our work, and you carry on with your life. For families with kids or anyone working from home, this is massive.

4. Your Home Gets a Facelift

Let's be honest – many Irish homes from the 1950s-1970s are looking tired. EWI gives you a fresh, modern exterior in any colour you choose. We've seen homes increase in kerb appeal dramatically, which matters when you eventually sell.

The Downsides (Let's Be Honest)

• Planning Permission: If your home is in a conservation area or has protected status, you may face restrictions. Always check with your local authority first.
• Neighbour Considerations: EWI adds 100-150mm to your walls. If your home is terraced or close to boundaries, this needs careful planning.
• Upfront Cost: EWI typically costs more than internal insulation before grants are applied.

Internal Wall Insulation: When It Makes Sense

How It Works

Internal insulation (often called dry lining) involves fixing insulation boards to the inside face of your external walls, then covering with plasterboard. The total thickness is usually 50-100mm, which eats into your room space.

Where Internal Insulation Is Genuinely Better

• Protected Structures: If you live in a Georgian townhouse or any building with architectural significance, external changes are usually prohibited. Internal insulation is your only option.
• Apartment Blocks: When you can't alter the external facade, internal insulation lets you improve your individual unit without needing agreement from other owners.
• Partial Improvements: If you only want to insulate one or two particularly cold rooms, internal insulation can be done surgically without affecting the rest of the house.

The Problems Most Contractors Won't Mention

1. Thermal Bridging Creates Cold Spots

This is the big one. Internal insulation stops at internal walls and floors. These uninsulated junctions become "thermal bridges" – cold spots where moisture condenses. We've seen internal insulation jobs cause MORE damp problems than they solved because this wasn't addressed properly.

2. You Lose Significant Floor Space

In a typical 3-bed semi, internal insulation on all external walls removes approximately 3-4 square metres of floor area. That's not nothing – it's the equivalent of a small bathroom. Rooms feel noticeably smaller.

3. Total Disruption

Every room needs to be completely emptied. Radiators come off the wall. Electrical sockets and light switches need relocating. Then you need full redecoration afterwards. For a whole house, expect 6-8 weeks of chaos.

4. Window Reveals Get Awkward

After internal insulation, your windows are now set deep into the wall. This creates dark reveals, awkward curtain hanging, and a "tunnel" effect that many homeowners find ugly.

The Real Cost Comparison (2026 Figures)

Project	Total Cost	SEAI Grant	Your Cost	Annual Savings
EWI (Semi-D)	€12,000-€18,000	€4,500	€7,500-€13,500	€600-€900/yr
Internal (Semi-D)	€8,000-€14,000	€2,000-€3,000	€5,000-€11,000	€400-€650/yr

But here's what the table doesn't show: Internal insulation costs don't include redecoration (add €3,000-€6,000), or the potential costs of fixing moisture problems if thermal bridging isn't managed properly. When you factor these in, the cost gap narrows considerably.

What We Actually Recommend

After completing over 200 insulation projects across Ireland, here's our honest take:

Choose External Wall Insulation if:

• You want the best thermal performance and long-term value
• You're planning to stay in your home for 10+ years
• You want to avoid months of disruption
• Your home's exterior could use a refresh anyway
• You're concerned about damp or mould issues

Choose Internal Insulation if:

• Your home is in a conservation area with planning restrictions
• You're in an apartment where external changes aren't possible
• Budget is severely constrained and you understand the trade-offs
• You only need to insulate one or two specific rooms

The Finishing Details That Make or Break Any Job

Regardless of which method you choose, the quality of finishing details determines whether your insulation performs properly for decades or causes problems within years.

Window cills are particularly critical. With EWI, your original cills are now set back from the new wall face. They need replacing with properly sized, properly draining aluminium cills that prevent water ingress. This is why we work exclusively with CILLS.ie for custom-manufactured aluminium components – their digital measuring system eliminates the fitting errors that plague traditional approaches.

Your Next Step

The best insulation is the one that's installed correctly and suits your specific situation. Before making any decision, get a proper survey from an SEAI-registered contractor who can assess your walls, check for existing moisture issues, and give you honest advice about what will work for your home.

→ Book a Free Survey with Casa Verde – we'll give you a straight answer about what your home needs, even if that means recommending a different approach than EWI.