Heat loss: distribution in a typical house

Understanding a typical house's heat loss: what exactly are we talking about?

Heat loss: conduction, air leaks and air renewal

Heat loss is the heat that escapes when the inside is warmer than the outside. It travels by conduction (roof, walls, floors, windows, thermal bridges), but also through air leaks at junctions and around joinery. Then there's air renewal, either intentional via ventilation, or occasional when airing a room. On site, it's often expressed in kWh lost per year, or as "weak zones" identified during inspection.

Thermal distribution: why it changes with the building's age and region

A house built before the first thermal regulations often has a poorly insulated envelope. Roof and walls then carry the most weight. In more recent buildings, conduction losses drop, and the share linked to air (ventilation, airtightness) becomes more visible. The region matters too. In a cold, windy zone, the temperature difference and infiltration increase losses.

Orders of magnitude: what's meant by a "typical house" on site

When we say "typical house", we're often talking about a 90 to 120 m² detached home with a classic layout. In renovation, some benchmarks apply. In a poorly insulated house, the roof can account for around 25 to 30% of heat loss, walls 20 to 25%, air 20 to 25%, windows 10 to 15%, and the ground floor 7 to 10%. These are baselines. The diagnosis or audit gives the real breakdown, particularly for floor heat loss.

Heat loss distribution by zone: where heat most often escapes

Roof and attic: the most common priority

Warm air rises. When the attic is poorly insulated, that's often where the biggest share of heat loss goes. It shows up quickly in older homes, with a cold-ceiling sensation and bills that climb as soon as the wind picks up. A simple check identifies the hatches, downlights, ducts and junctions letting heat escape.

Walls and ground floors: invisible but continuous losses

Walls rarely feel like they're "leaking", yet they dissipate heat continuously. Same logic for a floor over a crawl space, cellar or garage. The result is cold surfaces, discomfort, and a boiler or heat pump that runs longer. Well-designed insulation aims for continuity and avoids gaps.

Joinery and thermal bridges: weak points to treat properly

Windows, doors, roller-shutter boxes and junctions between walls, floors and balconies concentrate leaks. Here, performance depends as much on the product as on the installation. Good caulking, controlled airtightness and treating thermal bridges make the difference, without turning the job into an endless headache.

Air-related heat loss: infiltration, ventilation and installation quality

Air leaks: spotting parasitic air entries (hatches, ductwork, boxing-in)

Air-related heat loss often comes from small holes that add up to big bills. Look around attic hatches, duct and cable runs, recessed downlights, roller-shutter boxes, skirting boards and joinery junctions. Smoke pencils, a thermal camera or a blower door test help prioritise, to limit air leaks.

Ventilation: finding the balance between healthy air and heat loss

Ventilation isn't the enemy. It removes moisture and pollutants. Keep air inlets and grilles clean, and check the settings depending on the system (humidity-controlled mechanical ventilation, heat-recovery ventilation). To reduce losses, insulate ducts in cold attics and avoid overly long duct runs. The goal is healthy air without over-ventilating.

Airtightness: installation practices that change the result

Performance is decided at installation. Ensure the membrane's continuity, tape the overlaps, treat every penetration with suitable sleeves or sealants, and carefully finish joinery junctions with tapes. An insulated, sealed hatch and airtight electrical boxes make the difference. Continuous airtightness delivers on its promises.

Measuring and justifying thermal distribution in 2026: methods and expected evidence

Energy audit and DPE: what they show about heat loss

The DPE gives an overall reading. It flags the items where heat loss dominates (walls, roof, floors, ventilation). The energy audit goes further. It quantifies losses by zone, proposes work scenarios, and helps check that the planned insulation and systems properly address thermal bridges.

Thermography, air-permeability test: when to use them on your jobs

Thermography is useful before works to locate heat leaks, and afterwards to check insulation continuity. The air-permeability test is used when airtightness is a stake (joinery, attic, whole-house renovation). Keep the reports. They're measured evidence in the event of an inspection or dispute.

Traceability in 2026: photos, technical data sheets and thickness consistency

In 2026, incentives and grants require solid traceability. Take dated photos (before, during, after) with a thickness reference. Archive technical data sheets, certificates (ACERMI, CE marking), batch references, quotes and invoices. Consistency between product, surface area, R-value and thickness often makes the difference during inspections.

Turning the analysis into a work plan: reducing heat loss without missing the right package

Prioritise: treat the envelope before sizing the heating

Envelope first. Starting from an energy audit or a DPE, identify where heat is escaping. Prioritise the roof, walls, floors, joinery and airtightness. Less heat loss means a more accurately sized heating system, often less powerful, and a better-controlled budget in 2026.

Coordinate the trades: insulation, ventilation, heating (heat pump)

Key interfaces. Insulation changes air-renewal needs and duct routing. Aligning ventilation (airflow rates, grilles, penetrations) with airtightness at the same time avoids rework. Then size the heat pump on the post-works needs and check compatibility with the emitters.

Common mistakes: insulating without continuity, forgetting thermal bridges, neglecting ventilation

Continuity. Performance gaps mostly come from execution details: untreated thermal bridges.

• Insulation interrupted at junctions, hatches, boxing-in, ducts.
• Untreated thermal bridges, slab edges, window reveals, load-bearing walls.
• Undersized or later-modified ventilation, with moisture risks.