What is this Yellow / White stuff on my Rafters in my Loft? Should I be concerned?

[PollyTheDog]

Hello, I've not long moved into my new house and I went up into the loft yesterday to do some cleaning up to prep for adding some soffits and lap vents. While doing so I noticed that a lot of the rafters have some white staining on them, After further inspection I noticed at least one or two of the rafters also have some large yellow staining as seen per photos.

When I had my Survey results, It mentioned High RH, I believe 65-70% which is high, Baring in mind at this point the house was vacant and has been for months. The moisture meter came back at between 12-15% when tested on the rafters also. I've personally tested the Rafters with a moisture meter today and I'm getting between 13-17% depending on the rafter.

When tapping accessible parts of the rafters, They appear relatively solid. Nothing is sopping wet. I've never seen 'Active' condensation up there E.G Water on the bottom side of the felt or any leakages.

What I can't figure out though is what the white staining is, But what concerns me more is the yellow staining that I've yet to see till yesterday.

Can anybody point me in the right direction? Furthermore, How concerned should I be?

I'll be adding Lap vents later in the week, And hopefully be adding some Soffits within the next two weeks. I've not yet been able to reach the yellow staining to wipe it / see the texture properly due to the awkward positioning.

Thanks a lot for any help

 

[Harry Bloomfield]

The moisture meter came back at between 12-15% when tested on the rafters also. I've personally tested the Rafters with a moisture meter today and I'm getting between 13-17% depending on the rafter.

That, is accurate, suggests all is absolutely fine.