Cupped floorboards - Source of moisture above or below floor?

[NewbieHouseGuy]

The issue
I have a 1970s house that I moved into 9 months ago. The floorboards in all rooms upstairs squeak and are all cupped, apart from one which is crowned. Some (but not all) of the stairs floorboards are NOT cupped or crowned.

There is moisture in the house
However I know that the rooms (rather than under the floor) in the house are too humid. Humidity in all upstairs rooms consistently ranges from 50-75%. On cold days there is some condensation on windows. The radiators at front of house (which is north facing) are weak so those rooms are colder. There is no extractor fan in bathroom or kitchen (though we open windows).

I’ve read that cupping comes from too much moisture from UNDER the floor.

Questions
I would really appreciate your thoughts on the following:

• How do I find out whether the issue that damaged the floorboards is a) generally too much moisture in house OR b) moisture UNDER the floorboards. Would it help to take a moisture reading under the floorboards?
• 2 clues - directly beneath the bathroom the ceiling shows clear marks of a flood (perhaps 1ft x 1ft). This has been painted over. Also the ceiling below one of radiators has same thing but 6in x 6in. Might this have caused the issue?
• Any prospect of drying out cupped floorboards and them returning to normal? They may have been like this for 10-20 years, so my guess would be that they are not repairable.
• What kind of professional do I need to call in to get guidance?

 

[Deleted member 174758]

Wood fibres tend to swell on the moist side and shrink on the dry side. The grain (cut) makes a difference (look at the rings on the end of a board) - "smiley" ring boards are more likely to cup over time, "frowny" ring boards are more likely to crown across the width - all depending on how near to the relative humidity of the house they were dried to.

Once a board has cupped it can be dried out, but it will always be slightly cupped, unfortunately

 

[foxhole]

Just about every home with floor boards has cupped or crowned boards .

 

[NewbieHouseGuy]

Just about every home with floor boards has cupped or crowned boards .

Thanks foxhole, that's reassuring. From the answers here I'm thinking I should check the moisture levels below the floorboards to ensure there's not currently excessive moisture, screw the boards down to stop squeaking and then sand the cupped boards to level. In your opinion would that be a sensible way forward?

 

[foxhole]

Only sand if you want the boards on display or no point .

 

[NewbieHouseGuy]

Only sand if you want the boards on display or no point .

Thanks foxhole, but the cupping is so bad that you can see the floorboards through the carpet and can feel with your feet. Maybe I just need thicker, better quality carpets!

 

[foxhole]

Boards should be overboarded with hardboard to avoid seeing floorboards , which can happen even if they are flat .

 

[NewbieHouseGuy]

Boards should be overboarded with hardboard to avoid seeing floorboards , which can happen even if they are flat .

Ahhhh! You learn something new every day! I'm actually learning 20 new things every day... thank you, I'll look into overboarding. I'd probably get someone in to do it. Would a joiner be the right person to screw down the floorboards and overboard everything?

 

[foxhole]

General handyman could do it , safer to lift a few boards to check wiring and pipe location before driving screws in.

 

[NewbieHouseGuy]

General handyman could do it , safer to lift a few boards to check wiring and pipe location before driving screws in.

I guess that this means that all your doors have to come off and be shortened?

 

[foxhole]

Depends on what existing space under door you have .

 

[tel765]

Damp causes cupping - over boarding will do nothing for damp, in fact it might increase the risk.
Presumably you have GF suspended floors?

Your problem is damp - damp from a variety of sources.
Powerful Extractors are a must in bathrooms and kitchens.
The heating system must be able to operate at its full capacity when needed.
Trickle heating with trickle venting is often successful with condensation.
Through ventilation below any suspended G/floors is needed.
Clothes dryer to vent externally.

 

[foxhole]

Damp causes cupping - over boarding will do nothing for damp, in fact it might increase the risk.
Presumably you have GF suspended floors?

Your problem is damp - damp from a variety of sources.
Powerful Extractors are a must in bathrooms and kitchens.
The heating system must be able to operate at its full capacity when needed.
Trickle heating with trickle venting is often successful with condensation.
Through ventilation below any suspended G/floors is needed.
Clothes dryer to vent externally.

He has no damp problems, read the post, ground floor is fine .

 

[Nige F]

Your problem is damp - damp from a variety of sources.
.

I don't think it is ted, and how can stairs cup ? I think an experienced woodworker will give an accurate answer soon. Keep taking the meds ted.

 

[tel765]

What do you think causes cupped floor boards?

Most of the OP's original post was concerned with damp. eg "the rooms in the house are too humid"
Humid air rises - hence loft ventilation requirements.
There are cupped boards on the stairs.
The OP describes upstairs conditions that are ripe for excessive humidity.

We have no pics of the cupping so we dont know how"cupped" the boards are.
Cupped T&G can be well serious enough to show thro or distort floor coverings.
Doing as i suggested for say 6 months or so will be less disruption than raising the FFL.(what thickness hardboard were you proposing?).
Perhaps, as you suggested, sanding will be a future possibility depending on the seriousness of the cupping.