1960's House Should I be Concerned with these Seemingly Damp Trusses

[steveoelliott]

Hi Folks,

 

I have a 1960's house with concrete roof tiles with recently rebedded ridge caps (2022). All roof tiles are in place from the outside and nothing obvious from visual inspection.

 

Whilst in the loft I noticed what is obviously the result of dampness to a some rafters on the north facing side. They don't feel damp to the touch but are cold to touch (unsurprisingly). I have a cheap moisture meter with prongs I got from Amazon and that is reading the moisture level between 25-33%. Other rafters in the same loft space range from 11 to 16%.

 

There is no evidence of water ingress and the loft is mostly boarded with lots of cardboard boxes etc. up there. It would be very obvious if something had been leaking, especially with recent weather. I took some pictures of the worst truss and the nail thing that holds it down has clearly suffered from corrosion as a result of the doubt (I don't know what these fixings are called) but I just can't see how these trusses have come to be wet. There is sarking behind the trusses so even if there were a loose tile or water blowing underneath, the sarking would prevent it coming into contact with the truss.

 

I could just be worrying too much and perhaps this is the result of humidity within the loft space but it just doesn't seem that damp in there.

 

Thanks...

 

 

[SteamyTea]

13 hours ago, steveoelliott said:

I have a cheap moisture meter with prongs I got from Amazon and that is reading the moisture level between 25-33%. Other rafters in the same loft space range from 11 to 16%.

They seem low readings, but I very much doubt they are in the danger zone.

 

As the building is quite old, there is almost certainly no vapour control layer between the living area and the loft.  This will allow higher humidity air to migrate into the colder loft and condense, the formula is simple.

T_{(dew point)} = T_(air) - 100-RH_(air) / 5

 

 

[steveoelliott]

1 hour ago, SteamyTea said:

They seem low readings, but I very much doubt they are in the danger zone.

 

As the building is quite old, there is almost certainly no vapour control layer between the living area and the loft.  This will allow higher humidity air to migrate into the colder loft and condense, the formula is simple.

T_{(dew point)} = T_(air) - 100-RH_(air) / 5

 

 

Thanks. Those are readings from pushing prongs into the timber rafters. However, they don’t look or feel damp.

[SteamyTea]

5 minutes ago, steveoelliott said:

However, they don’t look or feel damp

That is because we don't have receptors to feel moisture in out fingers, all we feel is temperature and surface texture, then out brains fill in the rest from past experienced.

 

As long as your loft is properly ventilated, I doubt you will have a problem.

[steveoelliott]

20 minutes ago, SteamyTea said:

That is because we don't have receptors to feel moisture in out fingers, all we feel is temperature and surface texture, then out brains fill in the rest from past experienced.

 

As long as your loft is properly ventilated, I doubt you will have a problem.

Thanks…
 

It is breezy up there and the roof doesn’t sweat like it used to in our old 90s build. Probably just being paranoid.