Leak in roof can’t figure out

[Sean foley]

My garden roof roof is leaking , the roof consists of plywood sheets over the joists, the roofing felt over the plywood , then the galvanised metal sheets are fixed , I’ve been up on the roof and can’t figure out how water is getting trough, I was thinking it might be condensation under the metal sheets but it only leaks in heavy rainfalls, 

[ProDave]

Thread moved to the roofing section.

 

Your issue is most likely the fixing bolts are in the trough of the corrugations where lots of water runs down.  They are usually in the peaks, where there won't be flowing water so less likely to leak.

 

Take each bolt out one at a time, apply lots of waterproof sealant and re fit. 

[joe90]

21 minutes ago, ProDave said:

the fixing bolts are in the trough of the corrugations where lots of water runs down.  They are usually in the peaks

Not always, my box roofing on my workshop had fixings in the trough as specified (they are not long enough elsewhere) and had rubber sealing washers. I agree that the old nail through fixings for corrugated roofing were used at the peaks.

 

 

[Conor]

What's the fall? Looks a bit flat.

[Sean foley]

There’s a decent fall on the roof , could condensation forming under the metal sheets be the issue as I use a electric heater inside the garden room , 

[joe90]

17 minutes ago, Sean foley said:

could condensation forming under the metal sheets be the issue

I would have thought the underfelt would have dealt with that, that’s what I did with my workshop roof and no condensation.

[ProDave]

41 minutes ago, joe90 said:

Not always, my box roofing on my workshop had fixings in the trough as specified (they are not long enough elsewhere) and had rubber sealing washers. I agree that the old nail through fixings for corrugated roofing were used at the peaks.

 

 

It must depend on the material, my box profile roofing and my cheap corrugated shed roofing are both fixed with longer screws through the tops.  Some very soft materials may not be suitable for that. 

[saveasteading]

Bolts would go through the crowns, but screws usually go through the bottom to clamp it tight.

Silicon will suffice but make sure it is external quality. Its use is usually as a bodge.

For a better job get the best screws. They are designed do that the seal is along  the thread. The rest of the washer to cladding interface is for pressure not a seal, although ig helps.

You should  get them from a fixings specialist.

If the hole has ended up too big, use a wider diameter.

So choose big names like hilti and pay 3 times as much.