Put your hand on the wall behind a wardrobe and it runs colder than the rest of the room. Same at the corner where two walls meet, or where a structural column sits inside the wall. Sometimes a dark stain shows up there. That's not dirt. It's a thermal bridge: a spot where heat gets out faster than it does through the rest of the wall. The HES system that H.0.ME. brings to Italy has a thermal conductivity of 0.048 W/(m·K) (source: HES technical data sheet), and it goes on as one unbroken layer to close off those weak spots.
Heat Always Finds the Shortcut
Heat behaves like water. It looks for the path of least resistance. In a well-insulated wall that path is long and slow, and it takes hours to get through, the time-lag effect we covered in an earlier installment. But a wall is almost never one solid block. Inside it sit concrete columns, ring beams, joists, materials of different densities. Wherever those meet, or wherever the structure punches through the insulating layer, heat finds a shorter route out. That's a thermal bridge.
Don't confuse it with a draft. A draft is air slipping through a gap. A thermal bridge is heat leaving by conduction, through the material itself, and it shows up even in a wall that's sealed tight against air.
Why Junctions Are the Weak Point
In conventional construction the insulation goes on afterward, in rigid boards, over a structure already built from mismatched parts. A board is stiff. It won't mold itself to an irregular surface. Wherever a column or a beam interrupts the wall, the board has to be cut and patched around it. At that cut the insulation thins out, or stops. The inner face of the wall right at the junction stays colder than the rest. Once it drops below the dew point, moisture from the air settles there, and mold follows. We covered how a wall handles vapor in the piece on comfort and humidity.
A Shell That Wraps Around the Structure
The HES system works the other way round. Instead of propping boards against the structure, it wraps the whole thing in one continuous mass of hemp and lime, the same HES mix whose composition we've already described. At the junctions there are no seams. The application method is patent-protected (US 10,266,451 B2, PCT/CH2015/000085), and H.0.ME. has held the Italian license since 2019. Columns and beams stay where they are, and the same unbroken layer covers them, with no gaps for heat to slip through.
On whether it lasts, the evidence comes from a project within the wider HES network, not an H0ME job: at the Fortuny Museum in Venice, a thermal scan taken two years after installation found no detachment and no surface degradation. Credit there belongs to the system we bring to Italy, not to us. But it tells us what matters. A continuous shell holds up over time, and not only on the day it goes on.
H0ME hasn't finished a site of its own with HES yet. The first one is in the works, and it's the journey this series is following.
What This Means at Home
At home it means corners that don't stay cold all winter, and mold that doesn't come back every fall behind furniture pushed against the wall. It also means surface temperatures that hold steady across the whole room, something we measured in the previous installment, comparing three walls side by side. A wall with no shortcuts doesn't leak heat through its hidden spots, and that's heat you stop paying for on your energy bill.
There is a limit, and it's worth stating up front. The continuous shell reduces the wall's own thermal bridges, the structural ones. Windows are a different matter. They need dedicated installation and a purpose-built sub-frame, and wall insulation alone won't cover it.
FAQ
Is a thermal bridge the same thing as a draft?
No. A draft is air coming in through a gap. A thermal bridge is heat leaving by conduction through the material itself, even where there's no gap at all.
Doesn't standard external wall insulation already solve this?
It reduces it. But the seams between boards, the fixing pins that pass straight through, and the cuts made at junctions all leave gaps. A continuous mass of a single material has no seams to begin with.
Do windows create thermal bridges too?
Yes, and the fix there is different: dedicated installation and a purpose-built sub-frame. The wall's insulation alone won't cover it.
The wall-temperature comparison is in the previous installment, "The Night at 38 Degrees: Three Walls Compared" (/la-notte-a-38-gradi-tre-pareti-a-confronto/). Full technical specs for the system are on the Technology page (/tecnologia/). Next up: what it really means for a wall to breathe, with no vapor barriers at all.
Article produced with the support of artificial intelligence and reviewed by the H.0.ME. editorial team.