Relative Humdity ideal range

Relative Humidity readings are notoriously innacurate, what instrument are you using? Tom

Are you sure? Not usually a problem in summer, when temperature variations between inside and out are small. What are the symptoms?

To reduce cndensation to a mimimum you need to have the temperature of the coldest surface above the dew point, which you can calculate from air temp and RH, but I forget how.. Google?

Use a Psychometric chart? Tom

steamed up windows in the morning but yes only in the winter

"stuart noble"

A fallacious argument, I suggest. The condensation forming on your single glazed windows is only going to remove a small fraction of the water vapour from the air in the room. All other things being equal, whether or not you get condensation forming on the walls isn't going to depend much on whether or not it's forming on the windows. If adding double glazing makes the wall condensation worse it's probably because the new window frames are much more draught-proof and ventilation has been reduced. OTOH better insulation should make the room surfaces warmer and reduce the likelihood of condensation.

Indeed.

The solution too to much moisture in the air is improved ventilation. A kitchen extractor, and a humidstat control bathroom extractor do it for us.

Anyway to answer the original post, isn't the comfortable level of RH about 60%

Just to correct one point I have double glazing, which had the old pipe(hair) draft excluders. When I moved in I replaced them with a newer rubber /plastic type as I could feel air entering from round the windows. Also this greatly reduced the noise levels.

I have an idea this is what caused the problem.

I really dont want to put the old draft excluders back, as the noise/drafts will return.