Ventilation under floorboards

[Burnerman]

I'm somewhat unsettled by the arrogance of the previous post......after all, this is a forum hopefully designed to help and educate people, not to lock horns with those who are trying to help.
I fail to see how an underfloor inspection can take place without lifting floor boards......we have no indication of how deep the 'crawl space' is, and for sure the depth will vary according to the slope of the land involved.
As for an access hatch under the stairs.....the verdict is open on that one.
Anyway, back to the original help request, hopefully!
It would be excellent to find that any rising moisture is being kept in check by appropriate DPC......finding wet wall plates or joists isn't desirable.
Air exchange needs to be maximised......there are other methods to allow air in, without major surgery. Unfortunately, the neighbours may not be aware or even care about potential problems......out of sight, out of mind etc.
At the end of the day, any damp smell can be kept out by sealing any cracks / gaps in flooring / skirting and so on. That's fair enough, so long as there aren't any nasties taking place below!
Have a good evening everyone
John

 

[ree]

Its arrogant to post ignorant and misleading and possibly expensive information when you are supposed to: "help & educate".

Its arrogance in your case to pretentiously pretend to knowledge that you dont have such as the blather about a Victorian property having a concrete raft with a polythene vapour barrier: "that you wont see whether its there or not." Rather like a description of ghosts dont you think?
Rafts were certainly not used by the Victorians - rafts typically are 200mm min deep with re-bar reinforcement.
Neither was polythene.
Neither were vapour barriers.
A vapour barrier would go on top of any surface material not below it.
Membranes go below concrete but, in your arrogant wisdom, you have replaced the DPC from under the joists with what you call a membrane.

"light through the bricks" - do you mean a honeycombed wall?

"we have no indication of how deep the crawl space is" - wrong, we have an exact indication to within an inch or so. Count the bricks.


You too, like the other ignoramus, would: "like to see a few boards come up" presumably because "the verdict is open on" the position of an access hatch.
I notice that the OP has now indicated that the access hatch is alive and well under the stairs. Go figure?

What is it with you guys - If in doubt, tear up a bit of flooring?

With help such as you two are offering the OP will eventually sit down and weep.

 

[ree]

OP,

Thank you for the further pics.

You are now going to bring a builder in - to do what?
You've previously had a "damp survey" - by whom for what (besides the PIV system)?

If you mark the external pics with a line indicating the interior FFL it would help to accurately "place" the correct air brick positions?

The external render is touching the ground and should be cut back by 50mm to break capillary contact.
Could the external gravel have possibly been laid as a kind of French drain to deter damp penetration of the wall. Then again, it might merely be a gravel path. How deep does it go?

Something for you to consider: now a rendered wall is shown, and given the probability of a solid wall, your troubles might possibly be moisture penetrating through the wall along with rising damp from a bridged DPC?

Something for someone to check is the material that was used to re-plaster the interior, & the skirting, where the previous damp work took place.
Note that, externally, any injected remedial DPC holes have been bridged by the render.

So, if indeed you do have a built-in mechanical DPC, and an injected chemical DPC, then both have been bridged and damp is bypassing them.

It just occurred to me: does the chimney breast(s) in your flat have a fire opening or a vent? When was it last swept. Is it on an internal or external wall?

 

[drpepe]

you describe a similar situation to our house - blocked vents, elevated outside ground level and blocked up crawl space. Although in our case the crawl space is too small to crawl in and was full virtually to the floorboards with wet rubble! Our downstairs stunk of stale damp.

With advice from this board and others, we added and exposed vents, dug out the sub floor and dug a narrow, shallow, trench outside to lower the ground level see album

The smell has gone and further damage to the joists and other woodwork has been prevented.

 

[Burnerman]

It seems that I must be a complete ignoramus as you say, Mr Ree.
I'm fully aware of building construction - Victorian or otherwise....I appreciate my terminology isn't 100 percent but my intention was to help the OP to understand what's actually going on under her floor rather than to baffle her.
Granted, it's now possible to determine how deep the underfloor void is to some extent, at least in one area.
For sure, I wouldn't like to crawl or work down there - although I have done so (family building firm, 1921 / 1985) - and I doubt if there would be a queue of people wanting to do so.
John

 

[Burnerman]

you describe a similar situation to our house - blocked vents, elevated outside ground level and blocked up crawl space. Although in our case the crawl space is too small to crawl in and was full virtually to the floorboards with wet rubble! Our downstairs stunk of stale damp.

With advice from this board and others, we added and exposed vents, dug out the sub floor and dug a narrow, shallow, trench outside to lower the ground level see album

The smell has gone and further damage to the joists and other woodwork has been prevented.

I did something very similar to my holiday cottage last year, Dr.P......where you have gravel, I've just left things open but covered the trench with mesh, just to keep the leaves out. It's worked well, and there wasn't many options anyway. I keep a couple of floorboards loose inside, just to keep an eye on things, but no drama so far!
John

 

[drpepe]

you describe a similar situation to our house - blocked vents, elevated outside ground level and blocked up crawl space. Although in our case the crawl space is too small to crawl in and was full virtually to the floorboards with wet rubble! Our downstairs stunk of stale damp.

With advice from this board and others, we added and exposed vents, dug out the sub floor and dug a narrow, shallow, trench outside to lower the ground level see album

The smell has gone and further damage to the joists and other woodwork has been prevented.

I did something very similar to my holiday cottage last year, Dr.P......where you have gravel, I've just left things open but covered the trench with mesh, just to keep the leaves out. It's worked well, and there wasn't many options anyway. I keep a couple of floorboards loose inside, just to keep an eye on things, but no drama so far!
John

The trench isn't finished yet, and I am certainly open to ideas to prevent leaves (I have previous posted about it).

I thought a good solution was large pebbles so there would be air gaps, but leaves could easily be swept off...

Now a trip to the beach required!

 

[jezztri]

Thank you, for everyone's replies. It has been very useful. I'll check the vents at the weekend, dig around and see what I can find.

In terms of the render being too low - I literally just got the entire property re-rendered just before Christmas, so not sure I want to raise anything at this stage!

I did mention to the plasterers to replace some vents but for some reason they did not. The reason I did this was because I was getting penetrating damp above the DPC level. All have dried except the one in the sitting room, which has the bay window seen in the pic.

I do have an internal chimney and certainly there is a smell coming from that one but not the same smell and probably do need to get it swept.

The first pic in the more vents albums shows the side room and then the second pic shows the front vents. As you can see, there is a sort of ditch slope down from the front. My entrance level is the same level as the level of those vents in the first pic if that makes sense

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• jezztri
• 29 Jan 2015
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• jezztri
• 29 Jan 2015
• 1

 

[jezztri]

I've just checked my neighbours and they have done something similar to what you have done Drpepe.

 

[Burnerman]

Traditionally with hard cast render a lip is formed just to cast the run off water clear.
The only thing I can see there is that the path is a bit on the high side, and any rain splash could bounce a bit higher than is desirable.
The air vent number seems ok, so long as they are clear.
Dr P's route could be worth considering, especially if it has benefitted your neighbour.
Concerning the internal chimney, there will always be a bit of damp on the concrete hearth as it would be poured directly onto the ground..... That never mattered because the fire kept the damp down.
John

 

[ree]

OP,

Are your walls are solid?

Covering a channel with wire mesh looks terrible - surely your idea is to improve the appearance?

"raise" the render? The idea is simply to remove the bottom 50mm of render where it contacts the ground. At the moment it will be sucking moisture up past any DPC. If you are serious, then it must be hacked off. It would take about two hours.


The black lower band of render looks to be the original rough'ish render, esp. as they have left the S&C plinth in place. The new, upper white render is well done.

OP, there are still a number of my earlier questions outstanding. I'd appreciate your answers.

 

[goldeagle]

Apologies somewhat off topic...but just been reading this thread and amazed at some of the content of ree's posts. But then saw his location and that explained a few things...

 

[Burnerman]

Anyway jezztri you'll probably be wondering where to go from here......!
From what you have shown us from your underfloor pictures, I would say that things are in good order......obviously we can't see everything. The more ventilation in the underfloor void, the better!
I don't know how easy or possible it is, but it's best if any pipes are lagged, and are not in contact with the floor base.
Outside, the more space between the air bricks and the ground the better. Any rain running down the render should drop clear of the DPC.
So....the original problem! Can you feel a draught coming up through gaps in the floorboards? If you can, you'll get the pong - harmless though it is.
The answer would be tight fitting carpets and skirting boards, to keep the draught at bay. If there's a black edge to your carpets where they meet the skirtings, that's the common tell tale for draught.
Maybe there's food for thought there.
Regards
John

 

[jeds]

Cross flow of air is important. You really want the air to enter vents on one side of the house an exit on the other. As john said, there will be a sleeper wall somewhere across the house, these can sometimes be blocked off by debris, or even deliberately, preventing cross flow. The only route for the air then is upwards through your floor. Can you crawl under your floor and have a look - apparently there's loads of space.

 

[ree]

goldeagle,

Perhaps you would care to give a couple of examples of what seems to amaze you?

We are not discussing Planning Dept's or BCO's so how does a location "explain a few things"?

The principles of sound building activity are global - have you found flaws in these desirable principles? Which ones - gravity, right angled triangles, capillary action - perhaps they dont operate round your way?