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Insulate the roof, or the attic floor if the attic stays unheated

Roof insulation is usually the first and most effective insulation step; with an unheated attic, insulating the attic floor is cheaper and simpler.

Do it yourself

Sources checked on .

Large impactUp to 910 kg CO₂ a year · 85×treesInsulationLevel 4 · RenovationCost: €2,500–25,000A few days

A pitched roof needs three layers: a windproof underlay, insulation that completely fills the space between the rafters, and an airtight vapour barrier on the inside that keeps moisture out of the insulation.

If the space under the roof stays unheated, insulate the attic floor instead. It saves energy, material and work, and it is easier to do yourself than the roof slopes.

Aim well above the legal minimum: a common Flemish target is a thermal resistance (R) of about 4.2 m²K/W, which takes roughly 10 to 16 cm of insulation depending on the material. Premiums and their conditions change, so check the current ones before you start; in Flanders, your Energiehuis can tell you.

Details

ImpactLarge · Up to 30% of a home's heat loss can go through an uninsulated roof, which is up to about 4,500 kWh a year in an average Flemish house (15,000 kWh for heating). How we rate impact
CO₂ savedUp to about 910 kg of CO₂ a year, roughly the yearly uptake of 85 forest trees. How we count CO₂
Estimated savingFluvius estimates that up to 30% of a home's heat loss can go through an uninsulated roof. (confidence: medium)
Who actsYou (owner)
Needs landlord's agreementNo
TypeAction
Constant or subject to changeConstant · Good practice that barely changes with new laws, prices or services.

Do this together with

Sources

  1. Dakisolatie (in Dutch) · Vlaamse overheid (vlaanderen.be) (official source) · checked on
    Backs: the three layers of a pitched roof; insulate the attic floor when the attic is unheated
    Where: sections 'Hellend dak isoleren' and 'Onverwarmde zolder? Isoleer de zoldervloer'
  2. Energie besparen met je woning: isoleren en BENOveren (in Dutch) · Fluvius (official source) · checked on
    Backs: up to 30% of heat loss through the roof
    Where: section 'Je dak isoleren'
  3. Dakisolatie (techbib energieloket) (in Dutch) · Kamp C, provinciaal centrum voor duurzaam bouwen (via Stad Mechelen) (official source) · checked on
    Backs: target R 4.2 m²K/W (about 10 to 16 cm); attic floor is easier to do yourself
    Where: sections 'Streef naar minimaal de BENOveer-norm' and 'Zoldervloer of plafond isoleren'
  4. Dakisolatie is verplicht (in Dutch) · Vlaamse overheid (vlaanderen.be) (official source) · checked on
    Backs: a legal minimum for roof insulation exists, and an insulated attic floor counts as an insulated roof
    Where: section 'Minimumnorm voor dakisolatie'

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