Thermal Bridge T/F

Which of the following statements concerning Thermal Bridges are correct?

Thermal bridge free construction is achieved if a Psi-value of 0.006 Btu/hr.ft.F or less is achieved 

True

Thermal-bridge-free is a defined performance level: Ψ ≤ 0.006 Btu/(hr·ft·°F), which is 0.01 W/(m·K) — the figure PHI publishes, with the IP number as its conversion. The companion limit for point bridges is ΔU ≤ 0.0018 Btu/(hr·ft²·°F), or 0.010 W/(m²·K). Be clear about what kind of number this is, because it is routinely over-read. It is not a pass mark: the building criteria set no limit on Ψ at all, and what they require is that an unavoidable bridge have its Ψ verified and computed on exterior dimensions. Meeting 0.006 everywhere earns a modeling permission — you may drop the thermal-bridge surcharge from the calculation entirely — while a junction at 0.008 does not fail certification, its loss simply has to be counted.

So-called ‘geometric’ thermal bridges arise where there is more than a 60° change in insulation orientation

True

the 60° is a real threshold rather than a rough figure — a change of direction has to exceed about 60° to count as a geometric bridge, so gentle bends do not qualify. The external corner of a wall is the standard case. What makes a corner a bridge is geometry alone, not any fault in the construction: a small interior surface has to give up its heat across a larger exterior surface, so the flow concentrates and the inside corner runs colder than the flat wall beside it. That is why corners show up first on a thermal camera and why mold appears in them. At an internal corner the geometry reverses and the surface runs slightly warmer. Geometric bridges are one of three families, alongside constructional bridges, where something pierces the insulation, and repeating ones such as studs and wall ties.

In hot climates thermal bridges help to reduce cooling demand

False

they increase it. A thermal bridge is a shortcut through the insulation and it conducts in whichever direction the temperature difference points. In summer, with the outside hotter than the inside, that means heat flowing in, so the same defect that cost heating energy in winter now costs cooling energy, and the peak load rises along with the annual demand. Two things follow. Thermal bridges are not a cold-climate concern to be relaxed in the south — the physics is symmetrical, and in a cooling-dominated climate they work against you through the longest, hottest part of the year. And the surface-temperature consequence changes sign rather than disappearing: a bridge that showed as a cold patch in winter shows as a warm one in summer, so the local discomfort remains.

Thermal bridges arise primarily due to using wrong insulation types

False

A thermal bridge is defined by an interruption of the insulation layer, not by the choice of insulation filling it. Trace the insulation line around a section with a pencil: wherever you have to lift the pencil, or wherever something crosses the line, that is where a bridge is. A balcony slab, a steel lintel, a foundation wall, a stud — those create bridges regardless of what product sits between them. The type of insulation matters for how much you need to reach a given U-value, and for whether it can take load or moisture, but it does not create or prevent the bridge. This is worth being firm about because it points at the fix: bridges are designed out through geometry and detailing, not chosen away at the specification stage.

Step-free balconies extending from interior concrete floors are impossible to use in a Passive House project

False

The difficulty is real but it is not a prohibition. A concrete floor slab continuing outward as a balcony is close to the worst case in the catalog — an uninterrupted, highly conductive element crossing the full insulation thickness over a long line — but structural thermal breaks exist precisely for it: proprietary connectors that carry the moment and shear across the joint through stainless steel bars set in an insulating body. There are other routes too, and often better ones. Support the balcony on its own columns so it never touches the floor slab, or hang it off the facade on point fixings, which converts a long linear bridge into a few point ones. What is not acceptable is running the slab straight through and leaving the Ψ uncalculated.

Considering point thermal bridges, it is better to use stainless steel fixings than mild-steel

True

Stainless steel conducts at roughly 17 W/(m·K) against about 50 for mild steel, so swapping the material cuts the heat flow through a fixing by around two thirds for the same geometry. That matters because point bridges are penalized by concentration rather than by length: a bracket or a bolt gathers heat from all around it. Two caveats worth carrying. Stainless is better than mild steel but far worse than almost anything non-metallic — a laminated-veneer post or a foam-glass block beats both, so use steel only where the structure genuinely demands it. And the same reasoning drives the choice of wall ties and cladding clips, which are repeating point bridges: enough of them, and their combined effect is folded into the assembly U-value rather than counted one by one.

Thermal bridges affect not just energy flows but also health and well-being of the occupants

True

the health consequence is the more serious of the two. A bridge does two things: it adds heat loss, and it lowers the interior surface temperature at the junction. The energy cost is usually a small number. The surface cost is what damages buildings and the people in them — a strip that falls below about 54 °F holds surface humidity above 80 percent, which is where mold begins, and near 49 °F it reaches the dew point and condenses liquid water. Mold spores affect respiratory health and allergies, and once established in a wall build-up they are expensive to remove. That is the reason to think of thermal bridging as a moisture and health question first and an energy question second, and why the surface-temperature check sits alongside the Ψ threshold.

Heat loss from point thermal bridges are typically less significant than from linear thermal bridges

True

the reason is arithmetic rather than physics. A single point bridge can be severe, but a building has relatively few of them, while linear bridges run along every junction in the enclosure: every corner, every eaves line, every window perimeter, every slab edge. Multiply a modest Ψ by a very long total length and the linear entries dominate. Two qualifications matter. It is a generalization, and a building with many cantilevered steel brackets or a heavily fixed rainscreen can invert it. And point bridges that repeat at regular intervals — wall ties, cladding clips — are not entered as individual χ values at all; they are folded into the assembly U-value, which is why they can be significant without ever appearing in the thermal-bridge list

Negative thermal bridges improve the energy balance of Passive House buildings

True

A negative Ψ reduces the modeled heat loss, so it improves the energy balance directly. The mechanism is the exterior-dimension convention: PHPP measures the building on its outside faces, which deliberately overstates the envelope area at a corner, and the negative value is the correction that hands the surplus back — think of it as undoing a double count rather than as the building gaining heat. A clean external corner runs about −0.036 Btu/(hr·ft·°F). One rule attaches to it, and it is what keeps the accounting straight: you may take credit for the negative bridges only if you have calculated all of the thermal bridges, positive ones included. Claiming the corners while ignoring the balconies is exactly what that rule exists to prevent.