The cheapest house to build is not always the cheapest to own
When people compare houses they compare what each costs to build. But a house is paid for again and again after it is finished: the outside is repainted, gutters rust through, doors and taps wear out, and one day the roof is renewed. Over twenty or thirty years these costs can be a large share of what the house cost to build, and they differ from one house to the next.
Cost to build and cost to own
Quantity surveyors call it whole-life cost or life-cycle cost: the build, plus everything the house costs to keep over the years you plan to own it. In today's prices it is:
- the build, including the plot works;
- every repaint and replacement that falls due;
- running bills for power and water, if you count them.
Some choices shift money from the build to the years after it, and others the other way round. A painted render is cheaper to put up than a stone or brick facing, but it is repainted every few years. A sheet roof costs less than tiles, but it is renewed sooner. A flat concrete roof needs its waterproofing redone. Two houses that cost the same to build can cost quite different amounts to own.
| To build, with plot works | KES 4,593,163 |
| Year 7: repaint outside walls (110 m²) | KES 34,923 |
| Year 10: repaint inside walls (265 m²) | KES 83,889 |
| Year 14: repaint outside walls (110 m²) | KES 34,923 |
| Year 20: replace fascia and gutters | KES 56,232 |
| Year 20: repaint inside walls (265 m²) | KES 83,889 |
| Year 20: replace internal doors | KES 118,800 |
| Year 21: repaint outside walls (110 m²) | KES 34,923 |
| Year 28: repaint outside walls (110 m²) | KES 34,923 |
| To own over 30 years, before running bills | KES 5,075,664 |
That is 11% on top of the build, in today's prices. Some parts have no published lifespan yet and are not in the figure: windows, taps and cistern fittings, septic tank desludging. See it year by year, with the source of every figure.
Among JengaCost's 3-bedroom designs today, the differences in upkeep are smaller than the differences in build cost, so the house that is cheapest to build is also the cheapest to own over 30 years. That changes when you choose different finishes, a different roof, or a longer horizon, which is exactly what comparing on cost to own is for.
How long do the parts of a house last?
This is the hard part, and it is worth being honest about. We found no Kenyan table of how long building parts last. What exists:
- Manufacturers' warranties. Mabati Rolling Mills gives fade-free colour warranties of 5 to 15 years, depending on the paint system. Crown Paints says ordinary paints need repainting every 3 to 4 years, and offers silicone systems that last longer.
- Published tables from abroad. InterNACHI's Standard Estimated Life Expectancy Chart for Homes is the most widely used. It puts exterior paint at 7 to 10 years, interior paint at 10 to 15, galvanised gutters at 20, interior hollow-core doors at 20 to 30, metal roofing at 40 to 80, and clay or concrete tiles at over 100.
The American figures assume a temperate climate and roofing heavier than 30-gauge sheet, so JengaCost uses the lower end of each range and marks every such figure as a foreign table. Where there is no figure, as for steel casement windows or septic desludging, the part is listed as not in the total rather than guessed. Any interval can be replaced with your fundi's or quantity surveyor's figure.
How to use it
- On the compare page, pick the years you plan to own the house (10, 20, 30 or 50) and, if you want, your monthly power and water bills.
- Set Lowest cost to own as one of your priorities. Each house then shows its cost to own beside its cost to build, and the ranking takes both into account.
- Open cost to own for any house to see what falls due in which year, and change any lifespan you know better.
A discount rate lets you value money spent in twenty years at less than money spent today. At 0, the costs are simply added up in today's prices, which is the plainest way to compare.