A Parametric, Geometry-Aware Residential Construction Cost Estimation Model for Ghana: Design, Validation, and the "Completeness Gap" in Informal Contractor Quotes

2026-03-22

AI Summary

This study addresses the pervasive “completeness gap” in self-built housing in Ghana, where informal contractors commonly quote a uniform per-square-meter rate that systematically omits critical items such as reinforcement, plastering, screeding, and ancillary works, often leading to project abandonment. To counter this, the authors propose GHP—the first parametric cost estimation model integrating geometric information—implemented within the GhanaHousePlanner platform. GHP generates code-compliant bills of quantities across seven key modules, including foundations, masonry, and structural steel. Validated through three case studies, GHP estimates (ranging from 519,000 to 1,398,000 Ghanaian cedis) exceed informal quotations by 29% to 98%, exposing significant underestimation. The model establishes a novel, auditable, transparent, and standardized paradigm for construction cost estimation in sub-Saharan Africa.

Technology Category

• Intelligent Robots: State Estimation
• Cognitive Modeling & Cognitive Systems: (Computational) Cognitive Architectures
• Machine Learning: Feature Construction/Reformulation

Application Category

• Economics, Online Markets and Human Computation: Cost models of using LLMs in production systems
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

Ghana faces a residential housing deficit of two million units. A key driver of project failure is the "completeness gap", a systematic discrepancy between informal contractor quotes and actual costs. Informal estimates often use flat per-square-metre pricing that omits essential structural and finishing components, leading to project abandonment mid-construction. This paper validates a parametric, geometry-aware cost estimation model via the GhanaHousePlanner (GHP) platform. The model provides self-builders with itemised bills of quantities (BoQ) reflecting the true cost of code-compliant construction in Ghana. The GHP model uses seven calculation modules: foundation, blockwork, cement, structural steel, roofing, plumbing, and electrical. It features a primary geometry-based mode and a formula-based fallback. Accuracy was tested using three case studies (75, 120, and 200 per-square-metre homes) benchmarked against February 2026 market prices in Greater Accra.GHP estimates (GHS 519,000 to GHS 1,398,000) were 29 to 98 per cent higher than typical informal quotes. This gap arises from the omission of structural steel (Y16 rebar), plastering, floor screed, and full services in informal estimates. Findings confirm that per-square-metre rates rarely cover the requirements for a fully completed, code-compliant building. The GHP model offers a transparent, auditable alternative to informal quoting. Despite material price volatility and labour market informality, the tool provides a framework for improving cost predictability and reducing project stalling in the sub-Saharan African housing market.

Problem

• completeness gap
• residential construction cost estimation
• informal contractor quotes
• housing deficit
• code-compliant construction

Innovation

• parametric cost estimation
• geometry-aware modeling
• completeness gap
• bill of quantities
• informal construction market