Top 5 Roofing Mistakes Kenyan Builders Make (And How to Avoid Them)
Top 5 Roofing Mistakes Kenyan Builders Make (And How to Avoid Them) Roofing is one of those stages of construction where the mistakes you make aren’t always immediately obvious – but they will find you. Usually on a Tuesday night in the middle of the long rains, with a bucket on your living room floor and your fundi’s phone going to voicemail.
At Builder Choice Mabati, we’ve seen the same roofing mistakes repeated across Kenya – from Westlands to Wote, from Eldoret to the coast. They’re avoidable. Here are the five most common ones, and exactly how to make sure they don’t happen on your build.
Mistake 1 – Buying the wrong gauge (and not knowing it)
This is probably the most common mistake, and it happens in two ways. Either the homeowner picks G30 when their roof structure actually needs G28, or – worse – they pay for G28 and receive underweight G30 from a supplier who knows they won’t check.
Why it happens:
Many buyers just go with whatever the hardware or stockist recommends. If the person behind the counter has a stack of thin sheets they need to move, guess what they’re going to recommend?
How to avoid it:
- Know your purlin spacing before you buy. Standard residential spacing (600–900mm) is fine for G30. Wider spans need G28.
- Buy factory-direct from a KEBS-certified manufacturer. Builder Choice Mabati is certified and cuts to your specification – what you order is what you get.
- If in doubt, get your structural engineer or experienced fundi to specify the gauge before you order.
Builder Choice Mabati G30 starts from KSh 480/m. G28 is KSh 670/m. The KSh 90–100/m difference is worth paying when your roof genuinely needs it – but don’t pay G28 prices for G30 sheets.
Mistake 2 – Ignoring rubber washers (or using the wrong ones)
This one is almost criminal in how common it is. Every roofing nail that goes through a mabati sheet creates a hole. That hole, without a rubber washer under the nail head, is a guaranteed entry point for water.
Why it happens:
Some fundis skip washers to save time or because the client didn’t buy enough. Some homeowners don’t know washers are a separate line item. Either way, the result is the same – slow leaks that appear months later, often after the fundi has long moved to another job.
How to avoid it:
- Buy rubber washers before the fundi starts. Budget KSh 140 per pack from Builder Choice Mabati.
- Rule of thumb: one washer per nail, every nail. No exceptions.
- Check that the washer is correctly seated flat under the nail head – a tilted washer doesn’t seal properly.
- For ridge cap and valley sections, double-check that the lap joints are properly sealed too.
Mistake 3 – Under-ordering and making emergency top-up purchases
This one hurts the budget in two ways: the cost of the extra delivery or transport, and the risk that the top-up sheets are from a different batch and don’t match the colour or finish of what’s already on the roof.
Why it happens:
Buyers estimate roughly instead of measuring properly. Or they measure the floor area of the house instead of the actual sloped roof area (the slope is always longer than the wall height). Or they forget to account for overlaps.
How to avoid it:
Always measure the slope length (rafter length), not the wall height. Add 10–15% to your calculated area to account for side and end overlaps. Include accessories in your initial order – ridge cap, valleys, barge boards. Send your measurements to Builder Choice Mabati and get a free quote with exact quantities before you order. We do this for free.Mistake 4 – Wrong purlin spacing
The purlin is the horizontal timber or steel member that the mabati is nailed to. The spacing between purlins is critical – too wide, and even a quality G30 sheet will sag, rattle in the wind, and eventually fatigue at the fixing points.
The correct spacing:
- G30 sheets: maximum purlin spacing of 900mm for corrugated, 1200mm for box profile under normal conditions
- G28 sheets: can handle slightly wider spans, but still follow manufacturer guidelines
- Low-pitch roofs: use closer spacing – water sits longer on shallow-pitch roofs, adding load
Why it happens:
Timber is expensive and some builders stretch the spacing to cut costs on purlins. This is a false economy – the mabati wears out faster, and the roof may require earlier replacement.
How to avoid it:
- Get your carpenter or fundi to confirm purlin spacing before sheeting begins.
- If you’re inheriting an existing roof structure, measure the spacing before deciding on gauge.
Mistake 5 – Buying cheap mabati to save money (and paying twice)
We’re not being self-serving here – this is a documented pattern we see constantly. A homeowner buys the cheapest sheets available, they look fine going up, and two to three rainy seasons later the roof is rusting at the cut edges, the colour has faded badly, and there are small leaks at the fixing points.
The real maths:
Let’s say cheap G30 mabati costs KSh 350/m vs Builder Choice G30 at KSh 570/m. On a 200-metre job, that’s a saving of KSh 44,000. Sounds good. But if that roof needs replacing or patching in 5 years, and your quality roof would last 15+ years, you’ve effectively paid for two roofs in the time a quality roof would have needed zero attention.
KSh 44,000 saved upfront vs KSh 100,000+ in early replacement, leak damage, and disruption. The maths don’t lie.
What to look for in quality mabati:
- KEBS certification – Kenya Bureau of Standards certified manufacturer
- Accurate gauge – ask for the gauge in millimetre thickness, not just the G-number
- Colour-retention coating – ask specifically about the coating system (polyester, PVDF, or equivalent)
- Factory-direct pricing – buying direct removes the middleman markup that funds cheap-looking “discounts”
- Warranty – Builder Choice Mabati backs its products. Ask any supplier what their warranty covers.
Build it right the first time
Call / WhatsApp: 0722 818 240
www.builderchoicemabati.co.ke
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