Cool (high-reflectance) roof surface

Passive

A roof finished in a material that reflects sunlight and re-radiates what it does absorb, so less of the sun ends up as heat in the rooms below. Costs nothing extra if chosen when a roof is being replaced anyway, which is when it is worth doing.

One of 7 ways to meet Solar gain avoidance / shading (summer). Build 4/7, Upkeep 1/7, Efficiency not rated. Cost, carbon and footprint below are rated against those 7, not in absolute terms.

Cost: Low
Upkeep: None
Skill to build: Specialist
Lifespan: That of the roof covering itself; reflectance drops as the surface weathers and collects dirt, most of it in the first years
Embodied carbon: Low
Space / material use: Low
Output timing: None
Skill to repair: None

What your site needs

Best decided when the roof is being replaced. In a heating-dominated climate the summer gain avoided is partly paid back as winter gain lost, so it is a weaker move here than in a hot one, and local rules on roof colour may settle it anyway.

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, "Cool Roofs and Walls to Reduce Heat Gain" (PNNL / US DOE): a cool roof "utilizes materials with high solar reflectance and thermal emittance to reflect solar energy and reduce heat gain to the home"

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.