Attic radiant barrier

Passive

Reflective foil fixed under the roof deck or hung from the rafters, facing an air gap, so heat radiated down from a hot roof is turned back before it reaches the insulation. It must face a gap to work at all, and it is not insulation: it blocks radiated heat, not conducted heat.

One of 7 ways to meet Solar gain avoidance / shading (summer). Build 2/7, Upkeep 2/7, Efficiency not rated. Cost, carbon and footprint below are rated against those 7, not in absolute terms.

Cost: Low
Upkeep: None
Skill to build: Basic
Lifespan: Indefinite where it faces an air gap; laid flat on insulation it silts up with dust and stops reflecting, which is why that position is not recommended
Embodied carbon: Low
Space / material use: Low
Output timing: None
Skill to repair: Basic

What your site needs

An accessible roof space with room for an air gap in front of the foil. The source is explicit that where summer heat gain through the attic is small the benefit shrinks with it, which is the case in a mild oceanic summer.

Inputs

none

Outputs

none

Ranking in its sub-function out of 7 alternatives

Every option in this sub-function, with the value on each axis and a note on what drives it (this solution highlighted):

Solution	Build skill	Upkeep burden	Efficiency
Fixed horizontal overhangs (south)	None	0	N/A
Adjustable brise-soleil / shutters (east-west)	Basic	4	N/A
Deciduous vegetation shading	Basic	3	N/A
DIY shade-sail window screen	Basic	2	N/A
Cool (high-reflectance) roof surface	Specialist	0	N/A
Attic radiant barrier	Basic	1	N/A
Vented roof / attic assembly	Intermediate	2	N/A

Build skill and upkeep burden are proxies (lower burden = simpler to maintain); the efficiency column is this sub-function’s ranking, 1 = best. “N/A” where an axis isn’t rated here.

Sources

Building America Solution Center, "Attic Radiant Barriers" (PNNL / US DOE): "a layer of reflective aluminum foil material placed in the attic next to an air space to block radiant heat transfer"

Tutorials

No build tutorial recorded yet.

What this page does not tell you

No sizing or quantities: how much a technique yields, and how much a household needs, both depend on the build and the people, so the catalogue compares options rather than dimensioning them. It carries no bill of materials and no build sequence, and it is written for an oceanic, clay-soil climate (Normandy, France). Regulatory notes are indicative and need confirming locally.