Bagamoya has a flat roof. Technically: three roofs, as the building has three distinct sections, each 1.5m higher from the next. These flat roofs are good in some regards and bad in others.

The good:

Easy construction

Good in high wind

Good for top-floor AC-units, solar panels, rain harvesting etc.

The bad:

Poor drainage

Still requires maintenance

The poor drainage, is due to the relatively slight slope (compared to a pitched roof). This can lead to water pooling and seeping through to the unit below it. Debris can also block the drainage pipes and outlets on the roof, resulting in pooling.

After heavy rains, there usually is some pooling on the roofs. Often, John goes up there with a squeegee to move the water into the corner drains.

Flat roofs are therefore treated with a waterproofing solution. This usually involves:

Removal of the old waterproofing

Adding a membrane (such as bitumen)

Torching on or otherwise getting the membrane to adhere to the roof

Adding “silver coat” and reapplying this on a schedule

Other liquid waterproofing methods can be used for maintenance or touch ups, including types of paint, fibreglass, and others to protect the membrane from the sun and rain.

Note that there are always advances in the products or best ways to replace and repair these things, so it’s worth it to do research each time before work is needed and find something durable.

Lessons learned

Waterproofing (for flat or garage roofs) membranes need to go on the roof, up the sidewall and completely cover the top of the sidewall. Otherwise rain that will fall on the sidewall will just seep in between the membrane and the wall.

Old membranes need to be removed before new ones are added

Membranes need to laid out north-south (not like the current, incorrect east-west layout) due to drainage being on the N and S sides of each roof.

Our roof’s slope is very slight. It might need (costly) screed work, where all membranes are removed and screed/filler is added to create a bigger slope for water to run to the drains. We can discuss this when one section becomes very problematic in future.

The southernmost roof (above Charlie and Werner) only has one drainage pipe (the other have more) and could lead to issues.

We need a schedule to inspect the three roofs and periodically repaint a protective silver layer over the membranes.

The water ingress (above John’s flat, see below) probably seeps to other parts of the roof. The Aug 2024 work was only to repair the section above his living room (not the entire roof) but this will likely need to be done at some stage in future.

If owners make roof-related additions (such as air conditioning, skylights, solar geysers, solar panels), they will need written permission before doing so. Future water damage from this work, will be the responsibility of the owner to solve and pay for.

There are four things we can do with the roof:

Nothing. The dumbest, since it will deteriorate and be costly to fix.

Set a schedule. This is for periodic inspection, maintenance, and repainting, and replacement when needed.

Create an EUA. Rent out the roof to an owner living underneath it. It will be for their exclusive benefit, but will be theirs to maintain (reducing the financial burden on the body corporate).

Expropriate. The body corporate could sell (aka “expropriate”) a section of roof if, say, the unit underneath wanted to buy it to become the legal owner of it, for instance by adding in a staircase from their unit to a rooftop deck or skylight. This could both give the body corporate an injection of capital (if sold at a fair-market price) and all future waterproofing or work, will be the liability of the owner, and could reduce the admin and financial burden on the block.

Issues & timeline

Aug 2024 repairs

Unit 10, John’s, has water damage on the interior, due to water pooling or otherwise seeping down. The BC agreed to get the waterproofing problem (on the roof) fixed and then to pay for the replastering and painting of his ceiling. John got a quote for this with Isaiah / Tho-beka Trading (and was cheaper than the other quotes we got).

Isaiah showed that after a week of no rain, there was i. still water trapped under the top membrane (which they are removing). Also, ii. the membrane that was on the roof (before the current leaky one) wasn’t fully removed, and contributed to the current issues. Lastly, iii. the membrane sheets were laid out east-west (from the front-door to the balcony-side) but since the water drainage points are on the south and northern sides, it should have been laid out N-S.

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Quotes and work documented here⁠

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