High Humidity

[chuckalicious]

Had a good read here but not sure Ive found the answer.

Recently moved into a new house (30 years old) which I have discussed a few times on here with regards to insulating the basement ceiling to improve insulation in the house.

The house has in the past suffered from bad condensation and mold. Since moving in I have now fitted a humidistat controlled extractor in the bathroom and a properly vented cooker hood. No washing has been dried indoors so far.

I just had a Nest thermostat installed and one of the sensors it has is humidity. I was surprised to see a so far constant reading of 60%. I take it this is a little on the high side?

I can't see where the moisture could be coming from. Trickle vents are all open in the windows and kitchen and bathroom doors are closed when in use (and afterwards in the case of the bathroom).

Some other threads have suggested humidity can be coming from moisture below the floor. In my case this would be the basement, which isn't the driest place in the world. Without actually sealing the ceiling in the basement and seeing how the levels in the house go, what else can be done to try and find the moisture source?

I would have fitted a nuaire by now but our hall is small and has lights, smoke detector and a large loft hatch leaving little space to fit the large vent.

Cheers.

 

[ree]

Has any damp proofing work (remedial plastering esp.) taken place?

How much timber framing is present in the construction?

A 30yrs old house with a basement?

A loft hatch in the hall - is this a bungalow?

 

[chuckalicious]

Don't think any extra work has been done other than insulating the loft. The condensation issues could have been before then though - I don't know.

Yes the house is a one off build and due to the layout of the land has a large basement below it.

Yes it is a bungalow.

 

[chuckalicious]

Not sure how much timber is in the house. Roof structure is brick and timber. Walls I think are cavity. Would there be wood in the cavity? Basement is all brick.

 

[ree]

Timber framing refers to the wall construction of many homes over the past 40 years.

You will presumably have cavity walls - cavity insulation can sometimes cause damp cold walls which can "attract" condensation. But you wont know if your walls have been insulated if the previous owners didn't hand on any certificates.

Is the outside rendered? Or can you see a pattern of small filled in holes in the brickwork?

Just noticed that the last house you lived in had similar condensation difficulties (jan 2015 post) - are you still using a dehumidifier instead of ducting your dryer to outside?

 

[chuckalicious]

We used to use a dehumidifier in our utility room to dry clothes on a clothes horse so it didn't cause issues in the rest of the house. The dryer was always externally vented.

House isn't rendered and no sign of cavity work.

 

[AronSearle]

The average outside humidity here was 67% and 18°C, google tells me it will be 81% RH and 15°C tomorrow in Stirling.

So why is an internal humidity of 60% at this time of year surprising or alarming to you?

Typically internal humidity is close to external humidity in warmer months, you have no heating and tend to open windows more.

In winter central heating can create a drying effect, as well as external cold air holding less moisture.

60% humidity would be a concern if you are running the heating and have good ventilation, but if outside temperatures are still warmish then don't expect low internal humidity.

As to sealing the basement, I would be more inclined to insulate it and make it part of the insulated structure, otherwise you need to be careful about ventilation to the basement to protect timbers.

 

[chuckalicious]

I see - if 60% isn't an issue then forget I asked just from my own searching a target of 45-50% seemed to be the norm.

 

[^woody^]

You would be better off ignoring humidity, and working out why condensation is forming in particular places and deal with that.

Humidity is relative so it matters not if it's 40% or 100%, it does not mean that condensation will form or lead to mould

 

[AronSearle]

I see - if 60% isn't an issue then forget I asked just from my own searching a target of 45-50% seemed to be the norm.

That is more for winter.

Outside temperatures will be colder, so outside air will hold less moisture, at this time of year replacing inside air for outside air won't bring the humidity down.

As woody says, it is more important to consider why condensation is happening.

Cold surfaces are bad, insulation is good.

The problem with older houses is that parts of walls can end up being cold enough to cause condensation unless the humidity is really low or you throw lots of heat and ventilation into the mix (uneconomic).

The proper solution is to insulate those walls, and only worry about humidity if that is not possible/practical.

 

[chuckalicious]

Ok. The only option really then is cavity wall insulation. However I note that my outside walls have air bricks, which I assume is for the cavity to breathe? Insulating would stop this wouldn't it and thus cause problems?

 

[AronSearle]

If the walls are brick/block cavity then polystyrene beads are pretty safe.

Cavity wall insulation for brick/block is mostly safe except for high exposure areas where you get lots of wind driven rain.

Timber frame should not have cavity insulation.

 

[chuckalicious]

Right. So far, the issue is only condensation on the windows, which are double glazed units, although I don't know how old they are. They aren't blown with condensation between the panes though. One wall did have condensation when we moved in but this was behind a bookcase and right in a corner. The plasterboard had also been cut to allow speaker cables in and out so there was much more airflow from behind the scenes which I imagine didn't help.

I did notice today that in my boiler cupboard, which has a top and bottom vented door, there is a large vent in the floor which leads directly to the basement. I assume damp air will be getting drawn through this vent? Is it needed if the door is vented?

 

[AronSearle]

But why do you think the basement is a source of damp?

And if this area has damp/high humidity air, it needs to be vented out somwhere, or the source of damp eliminated.

From the information provided it is not an issue of high humidity (again looking at current external conditions), but low surface temperatures.

At 20C and 60% humidity any surface at 12C or less will develop condensation.

Crappy old double glazed windows and parts of uninsulated walls can easily see 12C surface temperatures or less on cold nights (some crap windows might see internal surface temps of 2-6C).

Providing lots of ventillation in the winter will help, because outside cold air can hold little moisture. so a constant flow of fresh cold air heated up, will give you low internal humidity.

As long as you don't mind high energy bills.

At this time of year you get what I would expect, internal humidity close to external humidity (because outside it is still mild), and mild amounts of condensation.

I could be wrong and your basement is a source of high humidity, but nothing you have given indicates that.

 

[chuckalicious]

What you say about low surface temps makes sense especially if indoor humidity follows outdoors at this time of year. That makes sense.

I cannot afford to replace all the windows - there are a lot of them and some are very big.

As the condensation, at the moment at least, is only present on the windows each morning, either I wait and see how bad it gets over the winter or I fit a piv unit in the loft and hope that does the trick as everyone suggests they do.

However on inspection of my walls, there are air bricks on the outside at floor level - would that be to ventialte the floor space? There also seem to be a few higher up which makes me think they are to ventilate the cavity, which is what is putting me off cavity insulation. I assume it isn't a good idea to insulate something that is designed to breathe.