Rusty joist hangers/surface mould on ply

[Jdwood38]

Morning all,

Following on from a separate post about sorting out the insulation in a dormer above a garage, I have now stripped the space back to bare structure. There is a steel in the ridge with roof joists suspended from it with timber infill with plywood making up the flat roof deck . Either through condensation caused by the poor insulation or from water ingress, there is a fair amount of surface rust on both the steel and joist hangers as well as surface mould on the underside of the roof ply. Photos of all attached.

Now I'm not overly concerned about surface rust on the steel as I assume this would take a few hundred years before becoming a problem, but I am surprised by the rust on the joist hangers as these are normally galvanised. So, a couple of questions if I may:

1) Is rust on the hangers a concern?
2) Have we caught the mould on the ply in time that it won't be ruined and require replacing? Can it be cleaned off and treated? We should be fixing any future condensation issues so hopefully there will be nothing further. The image of the mould looks worse under flash than it does in daylight and this is the most significant found in any area.

Apologies that this is a new post but I could not find anything on rusty joist hangers elsewhere in the forums so any responses to this may be easier for someone else to find in future if searching.

Thanks in advance.

 

[catlad]

The gaps around the insulation suggest a don't give a sh't attitude to the construction! token gesture of a vapour barrier! and the rust spots look like cross contamination of metals to me. I would dry the ply out and paint it with some timber preservative.

 

[noseall]

The above is the reason why hybrid roofs are frowned upon unless they are built robustly and conscientiously.

 

[kp00110]

Looks like the vapour barrier was on walls only not ceiling? and not silver tape or foaming joints?

 

[Jdwood38]

The gaps around the insulation suggest a don't give a sh't attitude to the construction! token gesture of a vapour barrier! and the rust spots look like cross contamination of metals to me. I would dry the ply out and paint it with some timber preservative.

Well you’ve pretty much nailed it and that‘s exactly what the approach to doing the insulation appears to have been! It’s even worse in other areas. No vapour barrier at all on the ceiling, pitched roof and whatever the proper name for the ‘dwarf wall‘ in the eaves is.

Thanks for thoughts on the rust and ply; will look at doing as advised on the latter. Should we worry about the metal cross contamination and is there anything we can do to prevent it happening any more?

The above is the reason why hybrid roofs are frowned upon unless they are built robustly and conscientiously.

Grateful if you could elaborate further on what a hybrid roof is? And I assume by conscientiously you mean ensuring things like the insulation is properly fitted, foamed and taped? A ‘hybrid‘ roof can still work successfully if done properly?

Looks like the vapour barrier was on walls only not ceiling? and not silver tape or foaming joints?

It was on some of the walls, here and there; nothing on the ceiling!