A properly detailed walk on installation does not leak. What makes it demanding is that the waterproofing detail is buried under a terrace, so it cannot be inspected, adjusted or patched afterwards without lifting the surface. It has to be right the first time, and that is a different discipline from an ordinary rooflight sitting proud on a roof.
How a flat roof rooflight leaks generally
The mechanism, and the kerb reasoning, is on do flat roof rooflights leak.
What follows is what changes when the whole detail is under a walked on surface.
The buried kerb
The defining difficulty.
On a normal roof the upstand stands above the covering where it can be seen. Under a terrace it is beneath paving, insulation and a drainage layer.
Nobody will look at it again.
Why that changes the standard
Because there is no second chance.
A detail that is nearly right on an exposed roof gets noticed and corrected. The same detail under a terrace shows up as a wet ceiling two years later.
Standing water
The condition the detail lives in.
A terrace surface holds water briefly after rain, and the waterproofing beneath it can hold water for longer, so the junction is wet far more of the time than a roof detail is.
The perimeter channel
What keeps water off the junction.
A drainage channel around the panel collects surface water and takes it away before it reaches the frame, and it is a designed component rather than a gap.
Keeping the channel clear
The one piece of maintenance that matters.
Leaf litter and grit fill a perimeter channel, and once it is blocked the water sits exactly where the design was keeping it away from.
The fall of the terrace
Designed rather than assumed.
Water has to be taken to an outlet, and a terrace laid flat with the expectation that it will drain somehow is where these installations go wrong.
The general point is on what is the minimum fall for a flat roof with a rooflight.
Pedestal paving and drainage
A helpful combination.
Paving on pedestals lets water pass through to the waterproofing below and run to an outlet, so the surface stays level while the layer beneath does the draining.
The upstand height
Measured from the waterproofing, not the paving.
The kerb has to stand proud of the waterproofing layer by a proper margin, which under a terrace is easy to lose sight of because the paving hides everything.
The requirement is on how high should a rooflight kerb be.
The termination under the frame
The critical lap. The waterproofing runs up the upstand and terminates under the frame, so anything reaching the top of the kerb is already outside the building.
What happens if the lap is short
Water behind the membrane. A termination that stops short lets water past the top of the waterproofing, and under a terrace that water has nowhere to go but into the structure.
Movement in a trafficked floor
An additional demand. A terrace flexes slightly under load, and the waterproofing detail at the frame has to tolerate that movement without working itself loose.
The frame seal
Compressed and gasketed rather than sealed. The glass to frame joint on a walk on panel is a designed weathering detail with gaskets and drainage, and it is engineered for the traffic rather than sealed against it.
Why sealant is not the answer
Because it is being walked on. A bead of sealant in a floor takes foot traffic, grit and cleaning, and it is the least suitable place in a building to rely on adhesive.
The general principle is on can a leaking rooflight be resealed.
Where the frame is set too low
The mistake made in pursuit of flush.
Setting the panel down to match the paving without keeping the upstand height beneath it produces a beautiful terrace and an installation with no margin at all.
Where the fault usually shows
At a corner, in heavy rain. Corners are where the waterproofing is most worked and where a channel most often blocks, and that is generally where the first stain appears below.
Diagnosing one
Harder than on an ordinary roof. Nothing is visible, so the investigation starts with the drainage and the surface, and lifting paving is the next step rather than the first.
The method is on why is water coming in around my rooflight.
Condensation mistaken for a leak
Possible, and less common here. A walk on assembly is a great deal of glass, so its inner surface is generally warmer than a standard unit and it condenses less readily.
What a good installation looks like
Boring, and it stays that way. A properly built upstand, a continuous waterproofing termination, a drained perimeter and paving that carries water away is an installation nobody thinks about again.
Who should build the kerb
Whoever is responsible for the terrace. The waterproofing and the upstand are one piece of work, and splitting them between two trades is how a termination ends up nobody’s responsibility.
What to ask for in writing
Who owns the junction. One question, agreed before anybody starts, prevents the single most common cause of trouble on a walk on installation.
What we take on walk on glass
We take responsibility for the junction between the waterproofing and the frame in writing, because under a terrace there is no way to correct it later and no way to argue about it usefully.
The whole picture is on the walk on rooflight installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.