High Humidity in House, Is it the weather?

[Reginalddean]

Hi

i've just moved house, my first job was to dig up the slabs from three sides as they were blocking the vents and breaching the DPC, this is no done.

I am now concerned about the humidity levels throughout the house, this morning at 19 degrees the RH is 81.

Is this due to the wet weather or is it because for the past few years the DPC has been breached? I have a dehumidifier but a friend tells me in this weather it is a waste of time as its so wet?

My daughter has asthma and Im desperate to reduce the humidity levels. Please help.

 

[noseall]

ventillation.

humans breathe out large amounts of water vapour, avoid wet washing or rain soaked clothes indoors etc. in fact read here://wiki.diynot.com/building:condensation_in_houses

 

[JohnD]

An excellent recomendation ventilation will remove the humid air from the house as well as slowly drying out the fabric. I like to open my loft hatch in hot weather to encourage airflow (water vapour is lighter than air so it rises).

Give the airbricks a good poke in case they are clogged with dirt.

We have also recently had posts from people with timber ground floors, where heavy rain has raised the water table and they have water under the floor (as you have recently cleared your airbricks this will help dry it out). can you lift a board, e.g. under the stairs, and see if you have oversite concrete or bare earth, and how wet it is?

 

[Reginalddean]

Thanks for that, we do have the windows open whenever we are in the house. We have two chimney breasts upstairs that are damp, the previous owner told us she had the flashings redone and sealed and they are just drying, they seem to be taking a long time to dryu though, would this be causing the high humidity?

What is the norm for this time of year and weather, does anyone know the RH of their houses?

Thanks again

 

[foxhole]

The chimney breasts should be vented if sealed.

 

[Coniferman]

I monitor the RH in my house and it does vary hugely depending on the weather - I've seen between mid 40's to mid 70's. If it is raining outside then the outside humidity will be in the 90's so not sure venting will help on those days, except for bathroom/cooking.

I think a normal dehumidifer will struggle to make a huge difference unless restricted to a single room with door and windows closed.

It does seem (to me) a bit futile to try to reduce the RH with a dehumidifier for an entire house unless there is a prolonged wet period or an underlying damp issue.

Some of the online weather forecast sites give RH.

 

[Reginalddean]

I agree, I did put the dehumidifier in one bedroom and shut the doors and windows, to start with the RH was high 60's, I then left it running a few hours and the RH dropped to 48. Not long after opening the windows to get some air in the RH was back to 60 .

However, this seemed to make no difference to the moisture in the chimney breasts. Previous owner assures us that the moisture is residual and the flashings have been replaced. How long should it take for a chimney breast to dry out? By the way, they are vented.

Cheers

 

[noseall]

if hygroscopic salts are present within the chimney masonry, then you are likely to have a high moisture reading as these salts attract moisture.
it is common for chimneys to have a high content of hygroscopic salts, owing to their immediate environment, i.e. sulphuric deposits from burning fossil fuels, oil, etc.