How to prevent water ingress with expanding foam?

Question

I’ve built a Colorbond shed that is in a relatively exposed position. During heavy rain and wind, water can get through the gaps in the ridge capping (see image). I was aiming to inject some low expanding foam to close the gaps. However, as I know expending foam, the canisters need to be used in the vertical position. If I apply from the inside of the shed, the roof will prevent me keeping the canister vertical. Is there a solution for this? I am also open to other DIY solutions for the problem. I would prefer not to apply the foam from the external side of the roof, trying to avoid excess foam from being visible on the outside of the roof.

Assistance from the community would be really appreciated.

MitchellMc · Accepted Answer

Hi @Lawzy,

Ideally, something like this foam corrugation infill should have been installed before the ridge capping was fitted. As the ridge capping is screwed down, it compresses the foam against the sheeting. You might still be able to install the infill strip from the outside. However, the inside looks like the ridges have been crimped to try and prevent water ingress. This might inhibit installation from the inside.

I recommend trying the infill strips before you go ahead with the foam. Expanding foam can be messy, and there is no real way to govern the amount you apply. Either you're going to end up with a big mess on the inside or a big mess on the outside.

Expanding foam canisters come with a flexible nozzle. I think you'll be fine applying the foam from the inside. My preference would be to apply from the outside and cover over that central area to obscure any excess foam. On the inside, you could cut back the excess foam or add timber over that area. If you get expanding foam over the rooftop, it will be harder to hide the mess.

You might also consider installing something like this wall flashing on the exterior. The flat section can be glued and pop-riveted to the ridge capping, and then the corrugated section can be glued down to the roof corrugation. This will form a sealed transition from the flat ridge capping to the profiled roof.

Please let me know if you have any questions.

Mitchell