Sub floor Humidity Issue - Best method to solve?

[GeddyMortgage]

Hi all,

I've been addressing a bunch of issues i've noticed this winter. One of which has been tracking down the source of high humidity (70%+) through the dwelling.

Having setup a bunch of digital temperature / humidity readouts in parallel, i've noticed the highest humidity by some way is down in the crawl space beneath the ground floor. It's at 80%+ (the loft space with vented soffits is 55% comparatively).....anyway i've run a big 400w dehumidifier down there this week, it helped the humidity of the crawl space come down to 60% but within a few days of turning the dehumidifier off its back at 80%+.... i've read online this can be potentially devastating if I leave it so looking to urgently address.

Having crawled around there for most of today (lovely way to spend a Saturday...) I didn't find any leaks or notable dampness which I guess is good. But on the other hand, I also noticed the air down there felt really still and quite musty too, so decided it'd be sensible to investigate the airbricks.

As the property was originally a 1955 bungalow, it has a fairly wide footprint (15m wide, 10m long or so) so I expected to find maybe 2 airbricks on each of the property's faces. But that's not what I found, I only found 5, which I guess isn't the end of the world... but much more concerningly I think only 2 of them are functioning properly either due to not having the appropriate ducting or being bricked over entirely. Photos below.


For ease of reference i've tried to show the positions of the air bricks on the birds eye plan below, along with the rough layout of the walls/honeycomb walls down in the crawl space. I'll show each one (and it's issues) below in numerical order.

AirBrick 1

This one looks as if a front extension was done but no ducting was added, the new extended suspended floor is full of insulation meaning airbrick 1 is never allowing air into the property. I think the solution for this is obvious, needs some ducting, right?




AirBrick 2

This one seemed fine, it's the only airbrick where I could feel a breeze coming through it....and see daylight.... it served as a good barometer for how I expected (and hoped) all the others to be (no such luck)





AirBrick 3

As the block paving slopes up towards the rear of the property this one looks like its been mounted too high? from inside you can see it's only partially visible to the sub floor, also we noticed the way it had been mounted the vents sloped up rather than down. Could it have been mounted upside down? or does this just need a Z vent due to its height? or should we just lower it by a course of brick?





AirBrick 4

The two at the rear of the property (4 and 5) have left me quite concerned. The floor joists run parallel to their openings meaning they're quite obscured, and if that wasn't bad enough, on closer inspection its also obscured by a half brick leaving just 2 small openings for it to vent through.... To fix, shall we remove that half brick and add a Z vent so its vent position will be lower than the floor joist?





Airbrick 5

Same as airbrick 4, couldnt get any closer to get better photos of this one. But the setup looks pretty much the same.




Airbrick 6 & 7

Im assuming the house originally had 2 airbricks down the side here too, as I found what looked like recesses in the inner skin, im wondering if they've just been bricked over by the previous owner..... given the footprint of the property should these be added back in?





Apologies for the long post!... but given the findings above, a few questions in summary.

:- As it stands i don't have any through flow of air....So something needs to be done, right?
:- Are the plans I have for each brick sensible?
:- Given the footprint / subfloor layout of the property, should I add a second air brick on the front?
:- Given what is required to fix the above, would it be better to potentially go with a mechanical / activate ventilation system instead?

Thanks so much, ive no idea what im doing with any of this really so really wanted to make a post. Guidance really appreciated and love to hear any suggestions to help address this as my learnings have all come just from reading stuff online.

thanks again!

Ged

 

[JohnD]

At airbrick 3, there is clearly wet at the junction of wall and paving. Take up some of those stones and see if the drain is blocked or leaking.

The internal pic seems to show water marks on the floor and joist

At vent 5, the joist is a very strange colour, there may have been a long-term leak, probably from the plumbing or something in the room above.

At vent 2, there is efflorescence on the inside wall, or possibly soap deposits as happens when a washing machine waste has been leaking

At vent 1, there is efflorescence on the outside wall near the pillar corner, probably a drain leak.

At vent 4, there is efflorescence by the downpipe, suggesting a drain fault.

There are concrete slabs in odd places, possibly intended to divert water from overflowing drains.

The metal grille gutter against the house suggests there is a known drainage fault, or perhaps the paving has raised the level near the DPC. There are numerous patches of damp and moss at the foot of the walls.

 

[Loofah]

The paving looks high / too close to the dpc so consider lifting the ones against the walls.
I agree on the drainage in general, get it checked out.
For the existing air bricks I'd clear what's in place and add new vents in addition. Wrt 6&7 they were clearly blocked intentionally (one for wiring?! And one possibly to stop cold air freezing the nearby pipes) and need replacing

 

[GeddyMortgage]

At airbrick 3, there is clearly wet at the junction of wall and paving. Take up some of those stones and see if the drain is blocked or leaking.

The internal pic seems to show water marks on the floor and joist

At vent 5, the joist is a very strange colour, there may have been a long-term leak, probably from the plumbing or something in the room above.

At vent 2, there is efflorescence on the inside wall, or possibly soap deposits as happens when a washing machine waste has been leaking

At vent 1, there is efflorescence on the outside wall near the pillar corner, probably a drain leak.

At vent 4, there is efflorescence by the downpipe, suggesting a drain fault.

There are concrete slabs in odd places, possibly intended to divert water from overflowing drains.

The metal grille gutter against the house suggests there is a known drainage fault, or perhaps the paving has raised the level near the DPC. There are numerous patches of damp and moss at the foot of the walls.

Thanks for the detailed response @JohnD, I'm just uploading a video or two now to show my findings off of the back of your helpful reply.

In the meantime, re: joist colour at vent 5, those are all burnt and charred by what looks like an old welding mishap. As alot of the disused copper pipes down there are blackened by fire too.

Concrete slabs were me, I was going to block the airvents for a day or two over the cold snap in winter but never bothered in the end.

Video/s incoming.

 

[GeddyMortgage]

The paving looks high / too close to the dpc so consider lifting the ones against the walls.
I agree on the drainage in general, get it checked out.
For the existing air bricks I'd clear what's in place and add new vents in addition. Wrt 6&7 they were clearly blocked intentionally (one for wiring?! And one possibly to stop cold air freezing the nearby pipes) and need replacing

Yes, thanks, I thought as much re: clearing the airbricks and getting 6 and 7 reinstated. For the partially visible ones (3,4,5) that are mounted so high, they'll need the periscope Z vent things so they can vent properly right? Especially for 4 and 5 due to that big parallel running joist obscuring them.

 

[GeddyMortgage]

@JohnD @Loofah

Thanks for your guidance re: drains. It led me to find some stuff that wasn't even on my radar.

Couple video links below showing the issues I found on vents 1-5, with some questions based on the findings. Especially on the 2nd video.

Air Brick Issues (Vents 1, 2, 3)

Air Brick Issues (Vents 4, 5)

What do you guys think?

Worth mentioning too, after filming, I realised the drain at vent 3 overflowed within maybe 5 seconds of me running the hose down it. So i've got dynarod coming to flush that.

 

[JohnD]

The gullies are all salt-glazed clay. As is usual, they are all cracked and broken and leaking, and have been for years. The cavity is caused by the water turning the soil to mud and washing it away.

No point having them rodded, they all need to be dug up and replaced. You may find the underground drainpipes are also bad.

When digging, you may find the mortar has been eroded between the bricks (this is more common in old houses with lime mortar) and the cavities might have undermined the wall.

While you have your spade out, reduce the ground height against the wall. Finished height, including paving, should be at least two bricks below DPC.

Good luck!


P.s.
Do not allow anyone who sells silicone injections near your house.

 

[GeddyMortgage]

I see. Well, we're due to have a rear extension done in the summer, forcing us to relocate the drains by vent 4 and 5 anyway. In essence as the source of the problem would then be dealt with, would that allow the problem to heal itself?

The drains by 4 and 5 are draining ok so wont rod them, The drain by vent 3 is the one I want rodding as it's overflowing within seconds. That wont be covered by the extension either.

Also regarding the height and location of 4 and 5, should I be getting Z ducts put on them? the periscope type. As it stands even with the extension and the long 100mm ducting theyd add on, they're still badly obscured under the sub floor. So im thinking that needs be addressed too at this stage?

 

[JohnD]

The drains by 4 and 5 are draining ok so wont rod them, The drain by vent 3 is the one I want rodding as it's overflowing within seconds.

It would be optimistic to hope that they are not also broken.

Also regarding the height and location of 4 and 5, should I be getting Z ducts put on them? the periscope type.

Lowering the ground level would be better, but if you need periscopes to clear obstructions, yes. As you already have a damp problem, the more ventilation, the better. One every two metres is not too many.

Near air brick 3 in particular, there is long-term wet, mud, moss and green algae, so I think there is a drain fault. It is not just recent rain. Possibly the paving has an incorrect fall as well. I think the other walls also look damp at the foot.

 

[GeddyMortgage]

It would be optimistic to hope that they are not also broken.

True, but if no water ever runs to those potentially broken drains again from end of April-ish. Eventually the damp wall problem would fix itself wouldnt it as the source of water would cease at the point of when the drains were moved when we extend... Or is that also overly optimistic?

Lowering the ground level would be better, but if you need periscopes to clear obstructions, yes. As you already have a damp problem, the more ventilation, the better. One every two metres is not too many.

Yeah, just thinking again, lowering the ground seems overly involved as its all going to get dug up for the extension anyway. But thinking adding a Z vent now would be sensible as that would stay there for the extension too.


Also is there any point in looking into active / mechanical venting here? Is it generally better than relying on passive venting?

 

[JohnD]

Also is there any point in looking into active / mechanical venting here? Is it generally better than relying on passive venting?

I think if you fix the obvious building faults of bad drainage and ventilation, there will be no need for mechanical devices

You might consider at least removing the paving and digging a trench against the house wall, it will allow it to dry and I think reveal more water problems.

 

[GeddyMortgage]

Yeah fair enough

You might consider at least removing the paving and digging a trench against the house wall, it will allow it to dry and I think reveal more water problems.

Yeah fair enough thanks, cant hurt to dig up a bit.

I think if you fix the obvious building faults of bad drainage and ventilation, there will be no need for mechanical devices

I'm hoping when the vent at the front of the property is properly ducted that will atleast give the sub floor some through draft. Im assuming the drains were leaking for alot longer than when the extension was added to the front, so maybe the through draft was always enough to prevent this getting too bad...until the front extension was added and the front vents were essentially eliminated.

re: mechanical im just thinking maybe adding one mechanical vent will be less work/cost overall, rather than adding z vents to the 2 at the rear and reinstating the 2 on the far right.....Do you only add one mechanical vent if going that route? Or must they work in pairs? (push/pull)?

 

[JohnD]

I have no experience of subfloor mechanical ventilation.

 

[Loofah]

If you fix up all the vents plus add a few then there's no need for mechanical ventilation. It's just something else to go wrong.
With the existing ones as long as you clear them and there's no obstruction then not sure you need to retrofit z ducts either, it's air flow you're after which an unobstructed pathway gives you

 

[GeddyMortgage]

If you fix up all the vents plus add a few then there's no need for mechanical ventilation. It's just something else to go wrong.
With the existing ones as long as you clear them and there's no obstruction then not sure you need to retrofit z ducts either, it's air flow you're after which an unobstructed pathway gives you

Yeah fair enough.

Also trying to balance the coldness of the property though, wondering if mechanical pulling the air exhausting out would cause less drafts through the floor boards etc as I assume the air would be more aggressively guided to the duct rather than up through the ground floor.

Re: z vents - not necessary you think even on 4 and 5 that are obstructed by the parallel running floor joists?

Re: clear the vents - you mean get rid of that half brick blocking them right?