What is whole-life cost, and why compare houses on it?
Whole-life cost is what a house costs to own: the build, plus every repaint and replacement over the years, plus running bills. A house that is cheaper to build can cost more to keep, so JengaCost shows both and lets you rank on either.
Painted render is repainted every few years; stone or brick facing is not. A sheet roof is renewed long before a tile one. Over twenty or thirty years these add up, and they can turn the cheaper house into the dearer one.
For each house JengaCost lists the parts that wear out, what renewing each one costs, priced from the house's own bill at your county's rates, and how often it falls due. It adds them up over the years you choose, from 10 to 50, together with your monthly power and water bills if you enter them. You can set a discount rate to value money spent later at less than money now; at 0 the costs are simply added up in today's prices.
Where the lifespans come from. No Kenyan table of how long building parts last was found. JengaCost uses manufacturers' warranties where they exist (Mabati Rolling Mills' roof colour warranties, Crown Paints' guidance on repainting), and otherwise InterNACHI's Standard Estimated Life Expectancy Chart for Homes. That chart is American, so the lower end of each range is used, and each such figure is marked as a foreign table. Where there is no figure, the part is listed as not in the total rather than guessed. Change any interval to your fundi's or QS's figure on the cost to own page.