Advice wanted: filling gaps between roof ribs when fitting vent or hatch

S

seth

New Member
Can anyone give advice based on experience please?

I plan to fit a small roof vent in a T5. The roof has shallow ribs, with the low section wide enough for the cutout for the vent. But the cowling is wider, so it needs to fit on top of the ribs. This means that I need to fill and seal between the ribs in order to provide a wide enough flat surface. I want to avoid any risk of water leaking in.

Does doing something fairly crude to full the gap between ribs with Sikaflex work well?

I'm not familiar with Sikaflex so find it difficult to guess how well it'd cope with the amount of the flex there will be in the roof without ending up with hairline cracks at the joint with the metal/paintwork.

I tried making a perspex spacer as an experiment, thinking this could then be bonded neatly in the channel between the ribs (the vent base screws to the perspex). But maybe the thinner layer of adhesive would be at least as liable to developing hairline cracks at the joins? Being bonded to 3 sides of minutely flexing steel panels seems more likely to fail than something bonded to a flat surface.


So any real world experience from fitting a vent or roof hatch which spans the ribs on the roof would be welcome. Thanks!
 
Watching with interest I'm hoping to attempt the same job over Christmas. I found a company in Germany that sell an insert that goes between the ridges thus making a flat surface
 
That's a neat (if pricey!) insert.

I was using some low profile mushroom style vents designed for boat decks (round things just big enough to build very quiet computer cooling fans in underneath) - kept it below the magic 2 metre height!

I made some perspex discs which matched the base, but trimmed straight edges on two side and chamfered them, so they neatly filler the 'gully' between the ribs, with enough depth plus space at the side for the recommended depth of sikaflex. The depth of the ribs is about 7 or 8mm, and I used 3mm thick perspex. £5.46 for two from eBay. I made a protoype from 5mm perspex (another £2.64 - we're talking big R&D budget here...) before settling on 3mm as giving the ideal depth of Skialfex (according to the data sheet) given how it fitted in practice. I used Sikaflex 521V (black) which I'd also used to bond the solar panels on. Amazing stuff.

I bonded the perspex on, creating a flat surface to then fix the base to. These were designed to fit with 3 stainless steel screws. I was able to line these up and drill pilot holes in the perspex then use very short screws, but I think the sikaflas on its own would have been fine. I added a bit more sikaflex around the bases to make a sound looking fillet. I smoothed sikaflex into the inside of the 'chimney' so created from inside the van.

The roof was exposed to a lot of pretty severe weather over several months before the inside before the roof liner finally covered these vents. There was never the slightest hint of leaking (unlike pretty much everything that had come out of the factory!). The sikaflex is solid but has a tiny bit of rubbery give. I'm very confident of the seal given how it's worked out.
 
All the heki's I've seen look too chunky for my liking though .
Never seen anything flat enough to not stand out like a sore thumb (other than a glass sun roof)
 
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