dpc behind skirting?

isnottheword · 28-04-2017 01:30PM #1

Quick query. I have dampness on wall and dampness 40cm into the floor screed (once I lift up the carpet and underlay, I can see this).

It's already been confirmed that there's water coming in via the wall itself. I just want to ensure that there's no rising damp. Someone told me that if I take off the skirting board, then I can determine if there's any rising damp?

Presumably, the DPC is at this level - and it will be dry??...or how can I differentiate between the two types of dampness (IF both exist).

Like I say, one is confirmed, the other (rising damp) I just want to rule out (or in as the case may be).

isnottheword · 28-04-2017 04:04PM

This is a pic of what I'm referring to. Just concerned that the dampness shouldn't extend in to the concrete floor that distance in from the wall if it's just a case of dampness transitioning across the wall itself.....that it may be an issue with the DPC or DPM.

Is it a case that the floor slab would be surrounded by a membrane, and that this would have overlapped the DPC??. Would this then discount water coming across the wall (above dpc level) and reaching the internal floor slab??

isnottheword · 18-05-2017 09:13AM

Done some invasive investigation. I've been trying to find the 'return' or edge of the damp proof membrane.

Open to correction here but according to proper construction detailing and building regs, should it not return up along the edge between floor and wall and meet with the dpc? Is it possible the dpc can be lower than the floor screed and floor insulation??

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chillit · 18-05-2017 04:07PM

I think the important thing is that the dpc is above the OUTSIDE ground level.

bfclancy · 18-05-2017 04:17PM

dpc should be at floor level or there abouts. i can't see in any in your picture you might have to chip more plaster off the wall to find the black strip of dpc. is that an internal or external wall. if its internal then the dpm could be down 225mm from the floor level, if external it should run up to and out under the dpc and form a tray in the cavity by running out under the external block 225mm at least lower than the internal leaf

isnottheword · 18-05-2017 04:48PM

bfclancy wrote: »

if external it should run up to and out under the dpc and form a tray in the cavity by running out under the external block 225mm at least lower than the internal leaf

It's an external wall.

chillit wrote:

I think the important thing is that the dpc is above the OUTSIDE ground level.

Ok, but lets say for whatever reason, there was water coming through the cavity (penetrating damp - NOT rising damp), would it still be important that the dpm runs up the side and under the dpc?...or does that only provide a solution for rising damp rather than penetrating damp?

If a solution was found for the penetrating damp but there was later found to be a penetrating damp issue due to muck/mortar/debris at the bottom of the cavity, would this type of detailing be relevant to penetrating damp then?

isnottheword · 19-05-2017 01:38PM

Ok, some fresh info. I've made an opening in the cavity itself and found this.

You can see the DPC membrane - with a big old chunk of mortar attached to it. Surely that's going to lead to water ingress on an ongoing basis?

mickdw · 19-05-2017 01:50PM

If I'm looking a that right, the mortar is pretty much crossing the cavity due to build up and doing that at a level above the dpc.
What level is that dpc relative to internal finished floor and path level.
Is that the only dpc present? If so it should have clear cavity beneath it and should be continuous with the floor dpm.
How old is the house? It's not obvious that you have a radon detail at all there. Maybe it was build before that requirement came in.

isnottheword · 19-05-2017 02:03PM

@mickdw : I'll have to run a tape measure on it - and see how it compares in terms of level within the cavity and the path level. It's hard to gauge level inside and level in cavity....i've not been able to find the dpc (or the dpm) inside yet...

House was built in 05 - so radon should come into play. Forgive my ignorance but are the membranes not one and the same for radon purposes...just so long as they're continuous??

There is some space below the dpc - but it's not a clean cavity floor. You can see the massive chunk of mortar attached to the upper surface of the dpc membrane - that almost bridges the cavity all on it's own. Surely that will lead to damp floors inside if that's left there?

Metric Tensor · 19-05-2017 04:22PM

You can use a Radon Membrane as a DPM in certain circumstances and provided you use the right kind.

It does not work the other way around - a "standard" DPM has no* radon stopping capabilities.

(* none worth talking about)

mickdw · 19-05-2017 06:09PM

isnottheword wrote: »

@mickdw : I'll have to run a tape measure on it - and see how it compares in terms of level within the cavity and the path level. It's hard to gauge level inside and level in cavity....i've not been able to find the dpc (or the dpm) inside yet...

House was built in 05 - so radon should come into play. Forgive my ignorance but are the membranes not one and the same for radon purposes...just so long as they're continuous??

There is some space below the dpc - but it's not a clean cavity floor. You can see the massive chunk of mortar attached to the upper surface of the dpc membrane - that almost bridges the cavity all on it's own. Surely that will lead to damp floors inside if that's left there?

There is no doubt that if mortar bridged the cavity at that dpc level, it will cause your problem.

Re radon detail, the radon barrier must come out and seal the cavity to prevent gas travelling in the cavity so you should be able to see this membrane at the Base of the cavity if you take out some of the stray mortar.

bfclancy · 20-05-2017 10:59AM

mickdw wrote: »

There is no doubt that if mortar bridged the cavity at that dpc level, it will cause your problem.

Re radon detail, the radon barrier must come out and seal the cavity to prevent gas travelling in the cavity so you should be able to see this membrane at the Base of the cavity if you take out some of the stray mortar.

has to be more than this to cause the dampness, if there is a bridge of mortar above dpc level its not going to bring in dampness from outside and certainly not in any great amount if everything is done correctly outside such as path 6-9 inches below FFL and waterproofer used in the rendering. every house will have a bridge of mortar at some point unfortunately, and it won't bring in dampness. a garage built with 9" hollow blocks properly rendered will have no damp issues and thats basically one complete mortar bridge. your dpm or dpc is the issue

isnottheword · 20-05-2017 06:11PM

mickdw wrote: »

Re radon detail, the radon barrier must come out and seal the cavity to prevent gas travelling in the cavity so you should be able to see this membrane at the Base of the cavity if you take out some of the stray mortar.

I get the need to have a full seal in order to prevent radon getting up & in. However if the cavity is sealed and bridged by the radon barrier membrane - isnt that in and of itself an issue for the transfer of water? Is there a detailing element I'm missing that will prevent any water that hits that radon membrane (at the base of the cavity itself) from getting into the dwelling?

bfclancy wrote:

has to be more than this to cause the dampness

What if the site is very exposed and add the fact that the cavity is filled entirely with polystyrene beads (as opposed to rigid polystyrene boards)?

bfclancy wrote:

if there is a bridge of mortar above dpc level its not going to bring in dampness from outside and certainly not in any great amount if everything is done correctly [..] waterproofer used in the rendering.

What sort of waterproofer? I thought it was a given that masonry walls will absorb moisture - that the whole point of the cavity design was to deal with this?

bfclancy wrote:

every house will have a bridge of mortar at some point unfortunately, and it won't bring in dampness. a garage built with 9" hollow blocks properly rendered will have no damp issues and thats basically one complete mortar bridge.

I get what your saying but then some houses are in more exposed locations than others.

bfclancy wrote:

your dpm or dpc is the issue

Are we not talking in terms of the same thing? i.e. the water going in along the top of the dpc (or radon membrane) - aided and abetted by the large chunks of mortar attached to it that almost close the cavity and the bead insulation that covers the whole cavity also?
...or are you thinking in terms of rising damp from underneath the dpc/dpm?

mickdw · 20-05-2017 06:17PM

The radon detail cannot transfer water to the inside as it is a stepped detail - the barrier is at or near floor level at inside leaf and typically dropped 225mm down along the inner leaf in the cavity before exiting at outer leaf. This stepped radon detail should be continuous with barrier under the entire floor.
All being well this cannot carry water across.

bfclancy · 20-05-2017 09:24PM

yes what i'm saying is moisture is travelling horizontally through to the floor at ground level therefore the tray in the radon is compromised or incorrectly installed. waterproofer is placed in the render to prevent moisture penetrating, it won't prevent it entirely but will for the large part. i assume the bead filling the cavity does not transfer moisture either or what would be the point of it. i would refer to dpc as the strip placed under the leaves of blockwork and the dpm is the layer of plastic or radon barrier under the floor. looks like all the mortar dropings from the blockwork have lodged at the bottom of the cavity as they invariably will and incorrect tray in the radon is allowing moisture to travel horizontally in from outside. or else the blocklayers dropped an awful lot of mortar into the cavity so much in fact that it has filled the tray up above dpc level though this would be very unusual to have that much droppings

isnottheword · 20-05-2017 10:40PM

bfclancy wrote: »

yes what i'm saying is moisture is travelling horizontally through to the floor at ground level therefore the tray in the radon is compromised or incorrectly installed.

You'll have to forgive me - I'm not the sharpest knife in the box by any means! Perhaps we are on the same page? There's water at the base of the cavity and it's running along the membrane horizontally through the wall and into the floor screed?

bfclancy wrote: »

waterproofer is placed in the render to prevent moisture penetrating, it won't prevent it entirely but will for the large part. i assume the bead filling the cavity does not transfer moisture either or what would be the point of it.

Like you say, waterproofer helps but there's nothing that can make a rendered block wall waterproof (and this is a very exposed site). On the cavity fill, It's proving to be pretty controversial - and often leads to the transfer of water from outer to inner leaf - or perhaps allows it to trickle down to the bottom of the cavity?

bfclancy wrote: »

looks like all the mortar dropings from the blockwork have lodged at the bottom of the cavity as they invariably will and incorrect tray in the radon is allowing moisture to travel horizontally in from outside. or else the blocklayers dropped an awful lot of mortar into the cavity so much in fact that it has filled the tray up above dpc level though this would be very unusual to have that much droppings

Again, you'll have to forgive my ignorance but when you refer to the 'tray', you mean that the dpm/radon membrane is stepped across the cavity and that forms the 'tray'?? (or have I misunderstood you completely)?
You can see from that photo that there's a major glob of mortar attached directly to that dpm/radon(?) membrane - that *almost* bridges the cavity completely. There is some space below the membrane but it's not a clean cavity floor by any stretch of the imagination i.e. there's more mortar droppings down there.

As an aside, when the dpm/radon membrane crosses through inner leaf -? cavity -? outer leaf, does it go over or under the dpc membrane?

bfclancy · 20-05-2017 11:04PM

DPM is under the dpc. Looking at your picture either they used 150mm dpc instead of 100 under the block or else laid it off centre. Most of the rain water will run off the plaster and hence the step in at the plinth so it should just drop off onto foot path. I find it hard to believe that much dampness Is being transferred through that lump of mortar unless the foot path is level with the floor. Don't know much about the insulation beads bit if they do transfer water why would anyone use it.

bfclancy · 20-05-2017 11:10PM

What your DPM should be like though it will be often over lapping the block at floor level not as far below as is shown here

isnottheword · 20-05-2017 11:37PM

Was just looking at that very diagram. :-)

Should I not have the expectation of seeing membrane turned upwards abutting the internal side of the inner leaf and the adjoining floor screed/floor insulation? I thought this was part of the regulations?

You raised an interesting point in your pen ultimate post i.e. is it that the dpc is off centre - given that it laps over - yet I can't see any indication of it on the inside of that wall (on the internal blockwork surface - at the base). How big of a deal would this be?

bfclancy · 21-05-2017 11:20AM

That could be a pretty big deal as that would result in rising damp especially if your DPM isn't correct. You need to investigate more. Try to break out a block on external leaf just under the dpc level that should give you a view of the DPM.detail

isnottheword · 25-05-2017 12:48AM

Apologies - I'm coming back to this in dribs n' drabs - time pressured due to other commitments (work, etc.). I've scrapped out the inside opening (space between screed/floor insulation - abutting inside of gable wall) - and taken it down to the bottom of the floor insulation. No sign still of any membrane.

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There's still no sign of a membrane. Is this definitive? i.e. should there be a membrane present immediately underneath the underfloor insulation or could it be further down?
Is it regulation that it should run up along that crevice I've opened up or is my belief misplaced in that respect?

Is it logical to believe that in tandem with what's going on in the cavity itself, that this has to be addressed in order to remediate the problem as a whole?

isnottheword · 26-05-2017 02:02PM

Ok, Ive either found the DPC or DPM => PIC.

Surely regardless of which one it is, there's something wrong here?

i.e. if its the DPC - then surely it shouldn't be below floor screed/floor insulation level?

if its the DPM - then it doesn't seem to be connected to any other membrane going inwards? That seems to be the end of the membrane.

Can anyone offer an opinion on this?

mickdw · 26-05-2017 03:33PM

You need to give us the height this dpc is at relative to path outside.
If it 150mm or more above path, it could still be correct but there would have to be a membrane continuous downward on inside of inner leaf from that dpc or built into wall under that dpc and then down and continuous through the floor.

Check path level and keep digging!

isnottheword · 27-05-2017 04:48PM

mickdw wrote: »

You need to give us the height this dpc is at relative to path outside.
If it 150mm or more above path, it could still be correct but there would have to be a membrane continuous downward on inside of inner leaf from that dpc or built into wall under that dpc and then down and continuous through the floor.

Check path level and keep digging!

Ok, I think I'm beginning to get my head round how this works. It seems there are two ways that the dpm can go in.
1. Could run out at the same level as the DPC.

or

2. Can run out further below that at the 'step' in the raft foundation.

Path to Plinth = 11".
Path to top of skirting = 12" (the skirting being 4.75")
Inside: Top of screed floor finish to DPC = 5"

Cavity Floor* to point at which membrane turns back inward into the inner leaf wall = 4"

* Now I have to qualify what I'm stating here;
1. There's muck on the floor of the cavity - so I doubt I'm measuring from what should be the actual cavity floor.
2. There's muck on the membrane where it turns in - i.e. it may go a bit higher than the 4" measured.

I don't want to knock off those thick chunks of mortar - so that the insurance company have the opportunity to see them for themselves.

Also, with the DPC in the outer leaf, I can only assume it's underneath the big chunks of mortar attached to that wall at that level. I don't want to scrape them off just yet until insurance co. are given an opportunity to view.

So.....

Assuming the DPC/DPM detailing is in order, do I have sufficient grounds to insist that they clean out that cavity floor? Is what's shown in the picture above against building regs?

mickdw · 27-05-2017 06:38PM

So from your dimensions, path to floor level is 7.25 inches
If dpc is 5 inches below floor, that means the dpc is only 2.25 inches above path which is too low - if I understand you right.

isnottheword · 27-05-2017 09:18PM

mickdw wrote: »

So from your dimensions, path to floor level is 7.25 inches

I'm measuring that by taking a spirit level - laying it on top of a corner section of skirting at the back patio door - and checking against path level. There is a bit of a 'step' outside the patio - so having to measure out a bit - but this shouldn't matter much? i.e. even if there is a bit of a taper put on the strip of path around the house (would that be normal?), then I assume that to be negligable?

mickdw wrote: »

If dpc is 5 inches below floor, that means the dpc is only 2.25 inches above path which is too low - if I understand you right.

It's definitely 5" from top of screed floor to dpc.

When you say it's too low, what's liable to happen as a result of this? What's the minimum acceptable level? Is this spelt out in the Building Regs anywhere? If so, was this part of the building regs back in say...2004?

(sorry for all of the questions! ...trying to get to the bottom of this).

Victorian House · 28-05-2017 01:18PM

What is the water level in the area like? It seems like a lot of damage to be accounted by just regular rising damp.

Is there a lot of moisture on the internal face of the external wall? Again, I would be surprised if this moisture could cross the cavity and cause this much damage.

Normally, I would be looking for a leak for this sort of damage - maybe a roof leak travelling down the external face of the internal leaf until it meets the ground level.

isnottheword · 28-05-2017 02:20PM

@Victorian House : An issue has already been identified that pinpoints water being channelled through the wall due to bad workmanship. It's not a roof leak and no issue in terms of water levels (site is raised).

The dampness in the floor was discovered more recently. i had thought that the membranes would prevent water getting onto the floor but it seems that there's no requirement for the membrane to turn up the crevice between screed/floor insulation and wall - to top of floor level (if i've understood that correctly?).
If radon barrier can also act as Damp Proof Membrane, is it ok if it runs at a deeper level in a raft foundation construction (i.e. deeper than screed/floor insulation/d.p.c. level)?
I'm also wondering if what mickdw is pointing out means that the cavity 'floor' isn't sufficiently low enough below the damp proof course?

Victorian House · 28-05-2017 03:28PM

For a raft foundation, my understanding of the typical detail is that the DPM would run along the top of the slab, step down with the slab and run to the edge of the footing. In addition, you would have two DPCs. The first is in the external wall ~150mm above external floor level. The second would be at same level in the internal but, would drape down the outside face of the insulation and wrap on top of the DPM over the foundation footing. The base of the external wall would sit on top of this DPC.

If you search google images for "Detail showing Monarflex membrane and Easi-Load Radon DPC on raft foundation", this is what my understanding of the detail should be. I don't have privileges to post images yet.

mickdw · 28-05-2017 04:33PM

Do you have a raft or a strip footing?

isnottheword · 28-05-2017 05:37PM

mickdw wrote: »

Do you have a raft or a strip footing?

raft.

dpc behind skirting?

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