Builder put 'rockwool' below DPC, I am in flood zone. Fixes or thoughts?

[boxrick]

So in summary... I am renovating my house. My Architect specified that below DPC rigid closed cell insulation to be used. Above DPC we were using full fill and in this case we have specifically used https://www.superglass.co.uk/products/superwall-32-cavity-wall-batt/ For context we were flooded at the start of the year.

I was looking at the cavity of my new porch ( this is the last thing to be built ) and its clear its just full fill with the same material above and below.

So now I am worried about this and would like some advice about how much you guys believe it matters, should I be insisting this is rectified ( given that my entire extension has now been built.

[Redbeard]

If the specification of closed-cell material (XPS, I kind of hope, but OTOH it floats well) was specifically related to knowledge of the flood incident(s?) then it arguably matters a lot. If the builder had the specification it is also arguably their problem. If you expect (at least the possibility of) flooding again then yes, the use of a material which sucks is an issue.

[boxrick]

Hey I appreciate the reply!
 

Just to confirm the specification for closed cell insulation below DPC was definitely due to previous flooding, it has been written in the architect notes because we were flooded earlier this year. There is an entire section on flooding.

The superwall 32 has been used instead both above and below DPC, despite the instructions.
 

Given this how serious an issue am I facing if I leave it as is?

Should I be pushing the builder to put it right even though the extension is finished, this will be a major piece of work?
Does anyone have experience of getting this sort of thing rectified?
Any advice on the best way to handle it would be much appreciated.

For extra context I plan to apply a tanking / heavy waterproofing slurry externally when works are complete.

Edited Thursday at 14:56 by boxrick

[Kelvin]

It’s in the build drawings for a reason. Your builder hasn’t done it to spec. Tell your architect (assuming they are still engaged) Immediately take it up with your builder. Don’t get into a debate where they fob you off with ach it’ll be fine. Do you owe them much money still? 

[boxrick]

15 minutes ago, Kelvin said:

It’s in the build drawings for a reason. Your builder hasn’t done it to spec. Tell your architect (assuming they are still engaged) Immediately take it up with your builder. Don’t get into a debate where they fob you off with ach it’ll be fine. Do you owe them much money still? 

We still have a whole lot of build to finish off. Money is being sent as each bit is completed. My property currently has no roof, so its far from completion. I have been holding back some funds from each payment for 'snagging' on completion

Edited Thursday at 15:20 by boxrick

[kandgmitchell]

Is that a dpc laid flat across the cavity?

[boxrick]

1 minute ago, kandgmitchell said:

Is that a dpc laid flat across the cavity?

Yes thats the DPC

[Redbeard]

26 minutes ago, boxrick said:

Given this how serious an issue am I facing if I leave it as is?

 

You have already answered your own question. XPS (I assume) was spec'd so that it would not become a wet sponge if flooding happened again. It has not been used. A dry sponge has, and a dry sponge will get wet in a flood. Obviously tricky as you say most of it is completed, but you did not fail to follow the spec.

[boxrick]

[kandgmitchell]

1 minute ago, boxrick said:

Yes thats the DPC

So it's a tray dpc then where the inner leaf level is higher than the outer leaf level so as to direct any water ingress to the cavity out to the external leaf (and thence via weepholes). It's just that in the photo the dpc looks flat across the cavity rather than sloping as per the drawn detail - although even that doesn't have the 150mm min drop from the inner leaf dpc to the tray as per Approved Document C diagram 9(b).

[boxrick]

22 minutes ago, kandgmitchell said:

So it's a tray dpc then where the inner leaf level is higher than the outer leaf level so as to direct any water ingress to the cavity out to the external leaf (and thence via weepholes). It's just that in the photo the dpc looks flat across the cavity rather than sloping as per the drawn detail - although even that doesn't have the 150mm min drop from the inner leaf dpc to the tray as per Approved Document C diagram 9(b).

Can you clarify?
Here are a couple of pictures from about a month ago when the cavity was exposed as it was built up. It looks like there was a slope towards to external wall.



 

[Nickfromwales]

@all

If the Super wall 32 gets immersed, will it dry back out again quickly, and without degradation? There are other threads on here stating folk tested this in buckets of water/other and the product seemed to just shake it off.

 

If the op has this in the walls already, then getting this swapped out may be a complete nightmare.

[nod]

His mistake But your probably going to have to live with it 

[Kelvin]

1 hour ago, Nickfromwales said:

@all

If the Super wall 32 gets immersed, will it dry back out again quickly, and without degradation? There are other threads on here stating folk tested this in buckets of water/other and the product seemed to just shake it off.

 

If the op has this in the walls already, then getting this swapped out may be a complete nightmare.

I went to a builders merchants and it was all sitting outside with some vague tarp over it. I asked them about it and they said it dries out eventually but that will be sitting in free air. How likely is it to dry out inside a wall. That said if you get flooded that badly everything is soaking for a long time anyway. 
 

He could always stick a few moisture probes into this area in a few places. 

[Andehh]

How often do you get flooded? During those circumstances I'd imagine you're gunna have bigger worries to work through!!! 

[Spinny]

I think you need to talk to the architect. This an unauthorised deviation. Consideration needs to be given to the possible options to remedy the situation. Replacing it would be one, but there may be other options, the obvious one being to up specify the external waterproofing so that water cannot get into the cavity. (presumably the flood waters don't reach the DPC height)

 

I only have experience of one extension build so am biased by that, but I'd say you cannot trust builders or tradespeople, you have to start by assuming that everything has to be checked until they show that to be unnecessary by their own conscientious actions. Builders don't necessarily even read the architects spec. The problem with building is that once a mistake is missed when it occurs it becomes very costly to put right later.

[Roger440]

4 hours ago, boxrick said:

Hey I appreciate the reply!
 

Just to confirm the specification for closed cell insulation below DPC was definitely due to previous flooding, it has been written in the architect notes because we were flooded earlier this year. There is an entire section on flooding.

The superwall 32 has been used instead both above and below DPC, despite the instructions.
 

Given this how serious an issue am I facing if I leave it as is?

Should I be pushing the builder to put it right even though the extension is finished, this will be a major piece of work?
Does anyone have experience of getting this sort of thing rectified?
Any advice on the best way to handle it would be much appreciated.

For extra context I plan to apply a tanking / heavy waterproofing slurry externally when works are complete.

 

Ref your last paragraph, I'd suggest you don't do that. In the event if a flood, your wall will never be able to dry out. So you will have damp inside.

 

Any suggestions or ideas that you can keep water out to the extent the structure stays dry is a fantasy. Water will get in, and definitely into the cavity.

 

I speak from experience.

 

Personally, I'd have had no insulation at all below dpc level in a flood prone situation.

[boxrick]

So now the question is what to do.

 

Leave it in or get them to rip it out and then look at replacement with something like blown bead

 

OR if / when we do flood again we do it at that point.

 

I'm guessing to remove it all will mean a brick removed every meter or so and it all pulled out.

 

The cavity has no weep vents anywhere right now.

Edited Friday at 09:47 by boxrick

[kandgmitchell]

17 hours ago, boxrick said:

Can you clarify?
Here are a couple of pictures from about a month ago when the cavity was exposed as it was built up. It looks like there was a slope towards to external wall.

I'm not trying to add to your woes but take yourself on line to the Planning Portal and look up Approved Document C and go to page 30 and look at Diagram 9(b), does your arrangement look like that? A tray should have a significant slope outwards to prevent water reaching the inner leaf. It should definately have weepholes otherwise water can't drain away.

[torre]

I'd echo @kandgmitchell's point. You either have a tray with significant slope plus weep holes, or separate DPMs on inner and outer leaf. None of this is easy to correct retrospectively.

 

I've seen similar insulation float around quite happily for weeks but it's not designed for total immersion and is bound to hold a lot of moisture afterwards for considerable time and I'd also be concerned it will slump down to the bottom of the cavity after flooding and leave a cold bridge between it and the batts above.

[boxrick]

My architect seems to think that we should just leave it at this point. I may float the idea of removal to my builder and gauge his reaction. Given its all fresh bricks and currently dry, removal wouldn't be *that* hard.

My feelings are, if / when we flood again ( maybe it will never happen ? ). Just cut into the walls then and rip it all out and replace with blown bead. We could even do a moisture test, its going to be no more expensive that it would be to do it right now?

[ADLIan]

If it’s superglass insulation phone their technical department and get their advice

[SteamyTea]

20 hours ago, ADLIan said:

If it’s superglass insulation phone their technical department and get their advice

Good idea.

Fibres can be coated with hydrophobic molecules, this is why some wool type insulation can be used to fully fill the cavity.

 

@boxrick

I may not fully understand your drawing, but I would be concerned about solid insulation below the DPM floating upwards in a flood situation.

It is likely to cause other issues above it.

I would raise concerns with the Architect before talking to the builder, though you may need to mention that work in that area will have to stop.