Acceptable percentage of damp

There should be no dampness in your roof timbers , if there is sufficient air flow in your loft. Damp timbers cause you wood rot.

Wood is a hygroscopic material and will draw in moisture from the surroundings. There will certainly be moisture in a roof space. Construction timbers in a roof space could show readings of say 8% to 14% and be quite normal. So do not be unnecessarily worried The timbers in my roof space are measuring 12% today and it is not a problem – they are dry to the touch and look dry. I am also confident that everything is in order up there. The humidity outside in Lancashire today is 72% (It’s December and it is raining – all day!). The summer months will show a lower moisture content due to a generally lower humidity level, windows open more and clothes dried outside etc A moisture content of 20% and above at any time of the year is indicating that there is a problem developing and would need investigating as this is the range that fungal decay can begin. In the winter months this could be condensation rather than penetrating damp. I use a Protimeter MMS2 and the guidelines are: < 17 Green (dry); ≥ 17 but < 20 Yellow (risk); ≥ 20 Red (Wet) You do not normally need a moisture meter to show you that wood is wet but they can be useful when comparing the differences in moisture content in (say) one area of a loft to another

There should be no condensation at all in your roof space. If you have a soffit climb into you attic space and pull the insulation back from where the roof meets the top of the walls it might be a tight squeeze but sometimes the loft insulation blocks the air flow . If you have no soffit vents then you need to have vents fitted in your roof. You need a specific type to match wether you have slate or a tiled roof. Hope this helps👍

If you are using a damp meter then up to 18% is considered acceptable. Over this figure a problem exists which would require a visit from a damp specialist.