How to Upgrade my G rated house (you need open heart surgery)

If you live in an older Irish home—let’s say, anything built before the Celtic Tiger started purring in the mid-90s—you might be familiar with a specific sensation. It’s a feeling that settles in around late October and doesn’t leave until April.

It’s the sensation that your house is not actually a shelter, but rather a very expensive, structurally elaborate wind tunnel designed to transfer money from your bank account to your utility provider.

You might have a Building Energy Rating (BER) certificate that confirms this suspicion with a big, angry letter: G.

A G-rating is the bottom of the barrel. It’s the academic equivalent of failing the exam because you ate the paper. But here is the thing: most people misunderstand why their house is a G. They think it’s because the windows are a bit draughty or the boiler is old.

They are wrong.

Your house is a G because of Physics. Specifically, it is suffering from a series of catastrophic thermal failures that are baked into the very materials it is made of. The stone, the concrete, the copper pipes—they are all conspiring against you.

And because the problem is physics, the solution cannot be “a bit of work here and there.” You cannot fight thermodynamics with a tube of caulk and a prayer. You need a “Total Reset.” You need to fundamentally change the biology of the building.

This post is a deep dive into the specific, heavy-duty upgrades required to turn a G-rated energy sieve into a high-performance machine. We are going to ignore the logistics of who does the work and focus entirely on what needs to be done, and more importantly, why.

Part 1: The Data Profile of Doom

Before we pick up a sledgehammer, we need to look at the invisible enemy: The Data.

When a BER assessor evaluates a pre-1920s or derelict property, they usually find zero documentation. They don’t know what insulation is in the floor (spoiler: none) or the density of the blockwork. In the absence of proof, the software used to calculate energy ratings (DEAP) is programmed to assume the worst-case scenario.

These are called Default Values.

If you don’t have a certificate proving your wall has insulation, the system assigns a “U-value” (heat loss rate) that effectively assumes your walls are made of frozen butter. The same goes for the roof and the floor. This “Data Profile” creates a mathematical ceiling for your home’s performance. You could install a nuclear reactor in the basement to heat the place, but if the Data Profile says your walls are leaking heat faster than you can generate it, you will still be cold, poor, and G-rated.

The “Total Reset” is about physically ripping out the materials that cause these defaults and replacing them with certified, high-performance systems. It is about erasing the question marks and replacing them with hard numbers.

Part 2: The Walls (The Stone Sponge)

Let’s start with the biggest surface area: the walls.

If your house is a classic G-rated candidate, you likely have solid masonry walls. Maybe it’s rubble stone, maybe it’s solid brick. It looks sturdy. It looks like it could survive a siege. And sure, it stops cannonballs fine. But it does not stop heat.

The Physics of Stone

Stone is dense. In physics terms, it has high “thermal mass” but terrible “thermal resistance.” It absorbs heat from your radiator, conducts it through the solid mass, and dumps it outside. It acts as a bridge, carrying your expensive warmth from the inside to the outside world.

The default U-value for a 500mm stone wall is roughly 2.10 W/m²K. To put that in perspective, current building regulations demand a U-value of 0.18 W/m²K. Your sturdy stone wall is over ten times less efficient than it needs to be. It’s not a barrier; it’s a heat pump working in reverse.

The Upgrade: External Wall Insulation (The Tea Cosy)

There are two ways to insulate a wall: from the inside (Internal Dry Lining) or the outside (External Wall Insulation).

For a G-rated “Total Reset,” External Wall Insulation (EWI) is almost always the superior technical solution. Why?

Imagine you are cold. You could: A) Swallow a hot coal (Internal heating). B) Put on a thick coat (External insulation).

Putting the insulation on the outside does something magical to the physics of the wall. It brings the masonry “inside” the thermal envelope. The stone wall warms up to the room temperature and stays warm. It becomes a heat battery (thermal store), radiating warmth back into the room when the heating turns off.

More importantly, EWI eliminates “Thermal Bridging.” If you insulate internally, every time the wall meets a floor or an internal partition, there is a gap in the insulation where heat leaks out (a bridge). With EWI, you wrap the entire building in a continuous sheet of rigid foam (usually Expanded Polystyrene or Mineral Wool), cutting off all escape routes. It is a big job—it changes the look of the house and requires extending eaves—but for solving the G-rated wall problem, specifically regarding external wall insulation Dublin homeowners often find it is the only way to achieve true comfort.

Part 3: The Roof (The Hat Problem)

Heat rises. We all know this. If your roof is a sieve, your boiler is essentially working to heat the clouds.

In many older homes, the attic insulation is a sad, thin layer of fiberglass that was rolled out sometime in 1982 and has since been compressed to the thickness of a crepe by years of Christmas decorations stored on top of it. Compressed insulation is useless because insulation works by trapping air. No trapped air, no insulation.

The Physics of the “Cold Roof” vs. “Warm Roof”

The standard upgrade is to just roll out more mineral wool on the attic floor. This creates a “Cold Roof”—the attic space is freezing, but the rooms below are warm. This works fine for simple houses.

However, for a Total Reset—especially in homes with dormer windows or converted attics—you often need a “Warm Roof” upgrade. This involves placing rigid insulation boards over or between the rafters, directly under the tiles/slates.

Why go to this trouble? Because of the Dew Point.

In a G-rated house, water vapour from your shower and kettle rises into the attic. If the roof timbers are freezing cold (because of the insulation on the floor), that vapour condenses on the wood. Over time, this rots the structure. By moving the insulation to the rafter line (a Warm Roof), you keep the timbers warm and dry. This is a critical structural upgrade, not just a thermal one. It’s why proper attic insulation is often the first line of defence in any retrofit strategy.

Part 4: The Floors (The Cold Feet Paradox)

Here is a depressing fact: The ground temperature under your house is usually about 10-12°C. If you want your living room to be 21°C, and there is just a slab of concrete between you and the mud, the ground is constantly sucking heat out of your feet.

In DEAP, an uninsulated floor gets a punitive default U-value. But worse than the maths is the Radiant Cool effect. Humans perceive comfort based on the average temperature of the surfaces around them. If the floor is 12°C, the air can be 24°C and you will still feel cold.

The Upgrade: The Big Dig

To fix this in a Total Reset, you often have to do the unthinkable: get a jackhammer and destroy your ground floor.

You dig out the old concrete and soil to a depth of about 400mm. Then you rebuild the sandwich:

Hardcore (stone base).

Radon barrier (to stop radioactive gas, which is nice).

150mm of Rigid Insulation (The magic layer).

New Concrete Slab.

This drops the U-value from roughly 1.20 to 0.12. It disconnects your house from the cold earth. It is messy, expensive, and disruptive. But it is the only way to stop the floor from being a heat vampire.

Part 5: The Windows (The Eyes of the House)

Replacing windows seems easy. Pop the old one out, pop the new one in. Simple.

Except, in a G-rated retrofit, “simple” usually means “mould.”

The Isotherm Problem

If you take a high-performance triple-glazed window and install it in the same position as the old single-glazed one—right in the middle of the cold stone wall—you create a problem. The glass is warm, but the stone “reveal” (the side bit of the wall next to the window) is still freezing.

This creates a sharp temperature drop over a few centimetres. Moist air hits this cold strip and condenses. Black mould forms exactly where you spent thousands on new windows.

The Upgrade requires moving the window. In a Total Reset involving External Wall Insulation, the new windows are often moved outwards to sit flush with the original masonry, or even hang slightly outside it, so they are enveloped by the external insulation layer. This aligns the thermal barriers, keeping the internal reveal warm and mould-free. It’s a game of millimetres, and getting it wrong is a biological hazard.

Part 6: The Heating System (The Heart Transplant)

Now that we have fixed the shell (Fabric First), we can look at the engine.

Your G-rated house likely has a gas or oil boiler. It also probably has a copper cylinder in the hot press. In the data world, there is a specific field in the assessment software called “Column CD” which asks if this cylinder has a thermostat. In old houses, the answer is “No.”

This means your boiler heats water until it boils or until you turn it off. It is uncontrolled chaos. The copper cylinder, usually covered in a thin, sad jacket, bleeds that heat into the cupboard. It is wildly inefficient.

The Upgrade: The Heat Pump & The Unvented Cylinder

The “Total Reset” involves removing the fossil fuel boiler entirely and installing an Air-to-Water Heat Pump. But a heat pump is not a direct swap.

A boiler burns fire to make water hot (70°C). A heat pump squeezes heat from the outside air to make water warm (35-45°C). Because the water is cooler, you need more surface area to heat the room. This is why you often need to replace standard radiators with larger aluminium ones or install underfloor heating.

Crucially, the copper cylinder must go. It is replaced by a stainless steel Unvented Cylinder. These are factory-insulated with thick foam (losing almost no heat) and have huge internal coils designed specifically for the lower temperatures of a heat pump. They are also pressurized, meaning you can finally get rid of that grim cold water tank in the attic (and the risk of dead pigeons in your water supply).

This switch solves the “Column CD” problem instantly. You move from an uncontrolled, high-temperature system to a precision-controlled, low-temperature system. For a deeper technical dive into how heat pumps work, the Heat Pump Association offers excellent resources.

Part 7: Ventilation (The Lungs)

Here is the paradox of retrofitting: You spend a fortune trying to seal up your house to keep heat in (Airtightness). But if you succeed, you kill the occupants.

Old G-rated houses are “breathable.” That is a nice way of saying they are draughty. The wind blows through the cracks, bringing fresh air and taking away moisture. When you seal the floors, walls, and roof, and install airtight windows, you stop this natural ventilation.

If you don’t replace it with something intentional, CO2 levels rise, humidity spikes, and the air becomes stale and toxic.

The Upgrade: Mechanical Ventilation

A Total Reset mandates a mechanical lung for the house. There are two main types:

1. Demand Control Ventilation (DCV): Fans in the wet rooms (kitchen, bathroom) constantly sniff the air. If they detect humidity, they ramp up to suck the moist air out. Fresh air is pulled in through clever little vents in the living room walls.

2. Mechanical Ventilation with Heat Recovery (MVHR): This is the gold standard. A central unit sucks stale air out of wet rooms and pushes fresh air into living rooms. But—and this is the magic part—it passes both air streams through a heat exchanger. The warm stale air heats up the cold fresh air without mixing with it. You get fresh air at room temperature. You keep the heat but lose the stuffiness.

According to Part F of the Building Regulations, adequate ventilation is a legal requirement, but in a retrofit, it is a survival requirement.

Part 8: The Conclusion

The transition from a G-rating to an A-rating is not about aesthetics. It is not about new kitchens or fancy tiles. It is about correcting a fundamental misalignment between the physics of your house and the requirements of modern comfort.

It requires a “Fabric First” approach:

Wrap the walls (EWI).

Cap the roof (Warm Roof).

Seal the floor.

Replace the lungs (Ventilation).

Only then, upgrade the heart (Heat Pump).

It is violent work. It involves skips, dust, and noise. But the result is a home that defies the old logic of Irish housing. It is a home where the temperature stays constant, where the air is fresh, and where the energy bills are boringly low.

So, if you are shivering in your G-rated castle, stop buying throw blankets. Look at the walls. Look at the floor. The problem is physics. The solution is construction. And while it might seem daunting, understanding the sheer scale of the upgrades needed is the first step toward fixing it.

To really round off a whole-home energy strategy, once you’ve fixed the leaks, you might want to consider generating your own power—check out how Solar Panels Dublin can turn your roof into a power station.

If you are ready to stop fighting physics and start fixing it, the journey begins with a plan. Would you like me to analyze your current BER report to identify your home’s biggest “Data Culprits”?