Rethinking Roofs: Cooling Homes in Informal Settlements with What Already Exists

In Kroo Bay, Freetown, 91% of homes have corrugated zinc or metal roofs. On a hot afternoon, those roofs turn living spaces into ovens — temperatures inside can exceed outdoor air temperatures by several degrees. The people most affected are women and young children, who spend the most time indoors.

We entered the Rethinking Roofs global competition — organised by SDI (Shack/Slum Dwellers International) and IIED — with a simple premise: don't replace what people have. Work with it.

Stage 2 Submission

The Toolkit

Together with architect Rayane Djaffafla, we designed three complementary strategies that communities can choose from based on their structure, ownership status, and available space.

Alt 1 — Layered Cooling Roof

A shading mat sits above the existing metal roof, held by ballast (no drilling, no damage). A 150–300mm ventilated air gap lets hot air escape before it radiates into the room below. Blocks 60–80% of direct solar load. Best for owner-occupied homes with solid structures. Cost: ~$750/dwelling.

Alt 2 — Suspended Cooling Ceiling

A woven panel suspended below the metal roof creates a thermal buffer entirely inside the room. No work on the roof at all — ideal for renters or fragile structures where adding roof weight is a risk. Installed room by room. Cost: ~$450/dwelling.

Alt 3 — Detached Canopy

A community-owned shade structure for courtyards and shared spaces, anchored with gabions (wire mesh filled with local stone) — no foundations, no land title required. Can carry solar panels. Cost: ~$650 serving 3–6 dwellings.

All three are lightweight, relocatable, and designed for incremental rollout so households can spread costs over time.

Choosing the Right Intervention

A decision framework matches each household's context — structural capacity, tenure status, space type — to the right alternative. No field expertise required to use it.

Climate Context

The three cities were chosen to represent different climate stress profiles across sub-Saharan Africa. The charts below show annual distributions of dry bulb temperature, relative humidity, solar radiation, and wind speed — the four variables that drive how much heat a roof absorbs and how much it can shed.

Freetown, Sierra Leone — Hot and persistently humid year-round. High solar radiation combined with near-constant humidity means little relief overnight. Metal roofs stay hot.

Accra, Ghana — Similar temperatures but slightly drier, with two distinct wet seasons. The radiation load is comparable to Freetown but wind speed is more variable, which matters for ventilation-based solutions.

Addis Ababa, Ethiopia — Cooler and at altitude, but with very high solar radiation intensities during the dry season. Lower absolute temperatures mean the delta from a cooling intervention feels larger relative to comfort thresholds.

Impact

Climate simulations across three cities — Kroo Bay (Freetown), Alogboshie-Achimota (Accra), and Kirkos (Addis Ababa) — point to 3–5°C reductions in peak indoor temperature. That gap is the difference between sleeping and not sleeping, between a child being able to study and not being able to.

Beyond thermal comfort: the interventions also address fire risk (covering exposed metal edges), pest control (mesh vents block rodents and insects), and create visible value in roof infrastructure that shifts community behaviour around maintenance.

Decision Labs' Role

Our contribution sat at the intersection of geomatics and systems design. We ran climate baseline analysis across all three cities using local weather data, used Geobase to process satellite and aerial imagery of each settlement, and modelled thermal performance with EnergyPlus to stress-test the temperature reduction claims before they went into the submission.

We also built the decision framework above — the logic that matches a household's structural capacity, tenure, and space type to the right intervention — and documented it as a reusable toolkit that any community organiser or architect can apply without us in the room.

Where It Stands

We submitted Stage 1 in January 2026 and were invited to Stage 2, which we submitted in April 2026. Winning entries will be showcased at the World Urban Forum and published in an e-book by the competition organisers.

The work was done in collaboration with practitioners from IIED, SDI Kenya, and SDI — whose field knowledge shaped every design decision from the start.