Humidity advice..?

[jeds]

If you need to run a dehumidifier to keep RH at a reasonable level, there is something wrong. My advice is look at the basics first; eliminate any true dampness, look at background ventilation and extract ventilation (humidity controlled) for wet rooms, consider levels of insulation and where that can be improved and get the heating working for Autumn/Winter. Houses that have been empty for a period do tend to show higher levels of humidity. I have surveyed dozens of empty houses that show higher than average RH but most tend to stabilise when lived in for a while.

 

[sandman1600]

If you need to run a dehumidifier to keep RH at a reasonable level, there is something wrong. My advice is look at the basics first; eliminate any true dampness, look at background ventilation and extract ventilation (humidity controlled) for wet rooms, consider levels of insulation and where that can be improved and get the heating working for Autumn/Winter. Houses that have been empty for a period do tend to show higher levels of humidity. I have surveyed dozens of empty houses that show higher than average RH but most tend to stabilise when lived in for a while.

Thanks for that. I was really hoping that the humidity would settle when we’d been living here longer (6 months now). The upstairs was really humid at first but that has settled down to reasonable levels since we’ve been here but so has the temperature.

My original feeling was that the humidity was due to the fact that it’s so cold down there. Concrete floors. Roof shaded by trees so little natural sunlight. Because this lower level never really gets to warm up properly, I was assuming that might be the reason for the high humidity lingering.

The walls are all insulated. We can’t really insulate the floor without building it up quite a bit and that’s more work than we really want to take on. So that just leaves the roof space which we’re planning to tackle later this year.

We’re looking at underfloor heating for this whole floor which will add a small layer of insulation on top of the concrete floor and then we’re hoping that the floor becoming a heat source will help balance things out a bit too.

 

[Notch7]

so you have lots of thermal mass on the inside, ie concrete floors and walls and you have no solar gain

so your problem is the temperature stays low

The relative humidity (RH) of the air is an indication of how much water vapour is in the air at a particular temperature compared with how much water vapour the air could actually hold at that temperature.

Air at 100 % relative humidity holds the maximum amount of water possible at that particular temperature and is said to be saturated.

Saturated air at 10 °C holds about 10 grams per cubic metre (g/m3) of moisture;
at 20 °C about 17 g/m3
and at 30 °C more than 30 g/m3.

Put simply, the relative humidity is a measure of the percentage saturation of the air. Therefore air at 50% relative humidity, regardless of temperature, is holding half of its total possible water capacity



If you insulate the floors, walls and ceiling, the building wont absorb the heat from the room as quickly and that will increase its temperature and therefore the amount of vapour the air can hold without feeling damp

 

[sandman1600]

so you have lots of thermal mass on the inside, ie concrete floors and walls and you have no solar gain

so your problem is the temperature stays low

<snip>
If you insulate the floors, walls and ceiling, the building wont absorb the heat from the room as quickly and that will increase its temperature and therefore the amount of vapour the air can hold without feeling damp

Thanks very much. I’ve always felt the temperature was the issue but I don’t know enough about it to say for sure. That’s really helpful.

It’s incredible how different the temperature is between levels and as I said, these rooms never get to heat up like the rest of the house.

 

[Ivor Windybottom]

I don't know whether 1970s floors even had a damp proof membrane. Our 1950s house has them in the walls (bitumen soaked cloth, works very well though), but nothing in the floors.

It may be that water is being wicked up from groundwater by the floor or subfloor, and is evaporating into the air. If that's the case then you could look at perimeter drainage around the building outside, or just accept that running a dehumidifer may just be a fact of life (as it is for us in the winter).

Which rooms have the humidity, the concrete or suspended floors?

 

[sandman1600]

Which rooms have the humidity, the concrete or suspended floors?

It’s the rooms on the lower ground floor that have concrete floors.

The main living space has a suspended wooden floor over a concrete foundation and we’ve not had a humidity issue there.

I’ve attached a plan and an old estate agents photo of the back of the property showing the lower floor to hopefully demonstrate a bit better as it’s an odd property. The lower ground floor rooms (circled red) are offset from the main floor… it’s like a bungalow but the rooms are on two levels.

The area circled blue on the map is where we know there’s a leaking waste pipe.

 

[Ivor Windybottom]

Get that waste pipe fixed before thinking about anything else. Can't see a blue mark though.

I'd try trapping the humidity meter in those rooms and see what happens. Perhaps buy a few more, but decent ones. I bought a load of £3 ones when we moved in, all switched on next to each other they gave wildly different readings. I couldn't rely on them at all so binned them.

I've got some decent ones now, they were within 1% when I checked them together. They were £7.49 each on ebay, so cost more but not exactly expensive.

 

[sandman1600]

Get that waste pipe fixed before thinking about anything else. Can't see a blue mark though.

I'd try trapping the humidity meter in those rooms and see what happens. Perhaps buy a few more, but decent ones. I bought a load of £3 ones when we moved in, all switched on next to each other they gave wildly different readings. I couldn't rely on them at all so binned them.

I've got some decent ones now, they were within 1% when I checked them together. They were £7.49 each on ebay, so cost more but not exactly expensive.

Sorry I must not have saved the blue mark. ‍The leak is under the dining room though.

If this leaking waste pipe was causing or contributing to the humidity, would we not see visible signs of damp somewhere?

The humidity meter was only about £15 from Amazon and the results from that do vary from the Apple HomePod mini readings but it’s usually within 5 degrees and either way, neither of the readings is pleasing.

 

[Ivor Windybottom]

You may not see obvious signs. If it's getting under the slab then it will just be making it generally damp. It's unlikely to be the single cause, but definitely rule out an obvious factor.

I'm having a similar battle here, I've temporarily re-routed the downpipes completely away from the building into the garden, as I suspected the underground pipes might be seeping into the foundations. Old soakaways can be a pain in the arse even without a downpipe, if the ground gets wet then the water can go backwards from wherever the pit is, so they actively extract water from the ground and bring it towards the building. If there's a leaky old pipe then it can seep through the wall and under the floor.

Also check the outside ground levels against the floor level. I've been reducing the garden level in ours, soil tends to naturally get deeper over the decades so sometimes needs a spade depth removing to get things back to where they should be.

My point is that there could be a single issue or a myriad, but you have to approach it scientifically, ruling things out one at a time. Nobody on a forum is going to tell you the cause.

It looks like an interesting house, as it's unique I'd wonder if it was self-build. In which case don't assume that all the standards even of its time were followed.

 

[sandman1600]

You may not see obvious signs. If it's getting under the slab then it will just be making it generally damp. It's unlikely to be the single cause, but definitely rule out an obvious factor.

Thanks for that. The leak is above and behind the bedroom which is the worst of the rooms so that’s definitely a possibility. But it’s also the bedroom that gets the least sunlight and so it’s the coldest room too. We’re waiting for the waste pipe to be fixed under the house insurance right now so it’s not a quick job but hopefully that will be done soon.

It looks like an interesting house, as it's unique I'd wonder if it was self-build. In which case don't assume that all the standards even of its time were followed.

It’s definitely interesting. It’s not self-build though. The estate is all architect designed and I can only imagine the architect was on drugs… we have houses on the estate that are almost like cottages and others that are brutalist cubes. And there’s some questionable design choices in places too so god only knows what surprises await us when the renovation starts.

I really appreciate the advice. I wasn’t expecting a complete diagnosis but there’s definitely food for thought there. Thanks again!

 

[noseall]

I really appreciate the advice.

Put that humidity meter in the drawer with the damp meter and SM gadget (and the bread-maker).

 

[sandman1600]

Put that humidity meter in the drawer with the damp meter and SM gadget (and the bread-maker).

That’s all well and good but we only got it because the place feels damp so ignoring the readings isn’t really addressing the problem.

 

[noseall]

ignoring the readings isn’t really addressing the problem.

Nor is getting that pointless meter out every time there is humidity in the air.

 

[sandman1600]

Nor is getting that pointless meter out every time there is humidity in the air.

I’m not getting it out every time there’s moisture in the air. We suspected there was moisture in the air before we got the meter. The meter is now out all the time keeping an eye on it.

Whether we’re “getting a meter out” or not is absolutely irrelevant. There’s still high humidity whether we’re monitoring it or not.

I was asking for advice about the moisture levels. I’m sorry if that’s offensive or upsetting.

 

[berty3000]

What Woody said at the start is fundamentally true. Cooler air has less moisture-holding capacity, so the same amount of moisture in the air from the various normal sources will cause a higher relative humidity level in a cold room versus a warm room. In this sense, what these RH meters show is only a guide.

The key questions would be: do you have real evidence of high moisture levels or damp? E.g. mould on walls (any house can get this behind units against external walls, but still an indication of excessive moisture as well); damp/musty smell; condensation on windows (this is more normal in winter and doesn't necessarily mean a damp problem, but again, suggests excessive air moisture) - if you don't have these, then you don't really have a problem. If you do, it doesn't necessarily mean there is a serious damp problem, there can be small fixes.

As others have mentioned, do what you can to fix any issues that could cause penetrating moisture (bad drains, etc); maintain ventilation in the home (be willing to have windows on the latch or vents open even if it means losing some heat); and as a precaution, use a dehumidifer in winter. I use a dehumidifier in winter for an hour a day - cheap efficient one and it helps take the edge of moisture levels in a colder house in a very damp climate.