The Wrap That Quit at the Sill

The wall is cream. The WhatsApp photograph is eaves to damp-proof course, and someone in the group chat has written “wrap done”. Under every window there is a thin grey ledge — the original concrete sill — still sitting there like a shelf the coat refused to wear. Rain is on it. The new thickness and the old ledge do not agree. That ledge is where the coat quit.

A winter coat that ends at the belt is not a coat. Heat does not applaud the cream. Heat leaves along the shelf.

The ledge is not a reveal

Let us invent a person. We will call her Róisín. 1976 semi, Drumcondra. Yellow brick, a cavity filled whenever that was, later a cream wrap on the front and the side. The kitchen is “grand now” except for a cold stripe of plaster under the window, the width of a ruler. She puts a row of spice jars in front of it. The jars are not insulation.

That stripe is the inside of a shelf. The outside is the original thin sill — concrete, sometimes timber, the trade still says cill — poured or nailed when the wall was 1976 thick. The wrap is a new thickness. The sill is the old thickness. They disagree, and rain sits on that step because the old ledge no longer sticks out past the coat.

This is not a reveal. A reveal is the vertical side of the opening: the jamb, the picture-frame return. The live piece on the window reveal that is a radiator is about the sides. You can return boards into every jamb and still own a horizontal shelf that dumps heat and holds a puddle. Look at the ledge.

This is also not a boiler flue, a meter cabinet, a satellite dish, or a lintel. Those are other Saturdays. The sill is the shelf under the glass, the one you put a plant pot on and then forgot was part of the wall.

The coat that ends at the belt

Insulation only works if it is continuous. A wall is a fence. A window is a gate. The sill is the step: a thin, dense slab that sheds like a tray if you give it an overhang, or sits like a birdbath if you do not.

U-value is the score for the field: how easily heat walks through a square metre of wall. Psi-value is the score for the line. The sill line is a line. A beautiful U-value with a rude sill is a winter coat that ends at the belt. You will still be cold at the waist.

Building Science’s digest on thermal control is not a Dublin sales brochure. It is the boring rule that heat walks the path you left open. Leave a thin concrete shelf through a cream coat and the path is the shelf. GreenSpec’s page on thermal bridges then names the junction: the place two fabrics meet and one of them is still 1976. A wrap that stops at the old sill is a meeting you paid to look finished.

Three jobs the old sill still does

The original ledge still does three jobs. After a wrap that quits, it does them badly.

Job one: it is a cold bridge. Concrete and old timber are a ruler of dense stuff from the weather, under the frame, into the plaster. The kitchen stripe is the inside of that ruler. The field can be dark on a camera and the sill line still glows.

Job two: it is a tray. Rain used to hit a sill that stuck out past the brick and left. The wrap added a thickness. The old sill did not grow. Water sits. Building Science’s moisture digest is blunt about openings: if you do not throw the rain past the coat, the coat drinks. A puddle on the original concrete is a wet edge against the boards.

Job three: it is a thickness argument. The wrap is fifty to a hundred millimetres of board, mesh, and render. The old sill is a thin slab sized for a thin wall. They make a step, not a coat: a belt of original wall under every pane.

Carry the coat to the frame

There are two costumes in Dublin, and they fail the same exam at the glass.

Costume one: cavity fill. Two leaves, a gap, a hopper, a weather of beads. The gap is the job. The sill is not the gap. The sill is a slab sitting across both leaves, sometimes with a damp-proof tray, sometimes with a prayer. Fill the field and the camera looks dark. Under the window it looks like a ruler. “Do not fill the window” is not a licence to leave a shelf of original cold.

Costume two: the wrap. Boards, mesh, render. A cream house. External wall insulation Dublin as a weather coat, not a paint job. The coat is correct for the field. The coat is a lie at the ledge if the boards stop on the old thin sill. The fix is a new extended sill — a proper overhang, a drip, the coat carried to the frame. Left: the wrap quits and rain sits. Right: the wrap meets the window.

The second-wall ticket in 2026 is how a 2014 hopper and a 2026 wrap end up on the same house. If you already used the cavity grant, you can still talk about a wrap. Close the sill or you own two certificates and the same cold stripe under the spice jars.

The cold stripe under the window is physics

Mould is not a lifestyle. Mould is a surface that got cold enough, long enough, in a room that makes water the way kitchens and bedrooms make water: the kettle, the washing, people asleep. The field of an insulated wall stays above the trouble. A naked sill line drops. Indoor air hits the plaster under the glass, drops its drink, and the ruler starts a hobby.

Róisín wipes. She blames the window. She buys a thicker curtain. The curtain is not insulation. The bedroom upstairs has the same stripe, paler.

You can feel it without a camera. The plaster under the kitchen window is a different temperature to the plaster a metre along the worktop wall. After a wet west wind the old concrete holds a tea-coloured puddle against the new cream. That puddle is the quote that stopped at the elevation and never asked about the shelf.

Point at the ledge

You cannot diagnose a sill from the footpath if the wrap looks complete. Finished is a paint word.

A surveyor looks at the ledge. Does the new coat meet the frame with an extended sill, or does the original thin slab still stick out like a tray the wrap refused to wear? Is there an overhang and a drip, or a birdbath? Is the interior stripe under the glass, on the horizontal, or is it the vertical corner of a reveal you already read about?

Designing Buildings’ note on thermal bridging is the grown-up sentence for this line: heat prefers the short, dense path. The old sill is that path. A thermal camera is a belt-detector. The field is dark. Every window wears a glowing ruler. Guessing from the cream is how the original ledge survived a grant.

Point at the sill. Not the reveal. Not the meter box. Not the flue. Those essays exist. This one is the shelf.

If the person quoting you will not look at the sills, they are quoting a field. A field is not a house. A house is a field plus every ledge the rain still uses.

The money, without folklore

These figures are fixed by house type, not a percentage of a quote, and they are not a prize for wrapping a field and leaving a belt of original wall under every window.

The wrap is €3,000 for an apartment, €3,500 for a mid-terrace, €6,000 for a semi-detached or end-of-terrace, and up to €8,000 for a detached house. Internal lining, if that is the other conversation, is €1,500 / €2,000 / €3,500 / €4,500 across those same four types. Cavity wall insulation for a detached house is €1,800: that is the other wall costume, a hopper job, not this essay. None of those numbers is a you-pay band for a wrap. We do not invent one.

SEAI does not pay for a feature wall. The whole-surface rule is the rule. A wrap that quits at every sill is still a coat with a belt of original wall. The grant is for a coat, not for a cream photograph with 1976 shelves.

The house has to have been built and occupied before 2011. Approval comes before work. If work starts before SEAI says yes, the grant is gone. If SEAI does not approve, no work starts, and you pay nothing. That is the grant guarantee as Retrofit Dublin runs it. Retrofit Dublin is SEAI-registered. The phone is 01-233-7477. The 15-year guarantee is on the insulation, not on the folklore that a cream elevation is a finished sill.

Passive House Plus has spent years on Irish junctions: the boring drawings where the coat actually meets the frame. The Irish Times on the heating bill you can cut without folklore still starts with the fabric you already own. RTÉ’s report on the January retrofit package put the wall money in the same announcement as the rest of the 2026 push. None of them will write you a hymn about a puddle on a 1976 ledge. That is our job.

Finish the coat, then argue about the machine

A whole-home energy strategy is an order of operations. You stop the leaks. Then you change how you make the heat. The cheapest first move in most Dublin houses is still the hat. Then the walls, including the sills. Cavity if the camera says the gap is clean, dry, empty. A wrap if the cavity is the wrong job: boards to the frame, new extended sill, rain thrown past the coat. Then the machines.

Retrofit Dublin does home energy upgrades in that order on purpose: fabric, then systems. A heat pump behind a cream wall and a glowing ruler under every window is a very efficient device heating a shelf. Do not buy an expensive machine to feed a belt you refused to finish.

If the wrap still quits at the sill and the kitchen plaster is still a cold stripe, Claim Your Grants.