Drying and re-insulating a 2.5 year old damp cavity wall

[Adsibob]

For reasons you can read about in the nightmare I reported here, the rear wall of our rear extension that went up 2.5 years ago is very damp and it's likely that the mineral wool fibre that was used to insulate the cavity is also wet. I am considering my options as to how to fix this aspect of the damage (after I have found a solution to fix the parapet wall issue described in the other thread). In an ideal world, the existing insulation just dries out and we can leave it there. But it's not clear to me that is very likely to happen very quickly / at all.

 

It may therefore be the case that we have to open up the cavity by removing every other brick in a row or two, and then pull out the wool fibre. I will check with my main contractor, but from recollection, the wool fibre we used was amongst the cheaper products that pass building control, so it is not rigid and should come out easily. This would then allow us to either inject foam or bead insulation (in fact bead insulation can be injected through a small hole of only 22mm diameter). I'm thinking of something like the bead insulation described here.

 

The majority of the wall is actually glazed, so the cavities are actually quite small:

• a triangle above our sliding doors which is about 5m wide by 1.3m high (at the apex of the triangle); and
• another triangle above our window which is about 3m wide by 1m high (at the highest part of the triangle).

The problem is that the wall will be wet still. It is sealed from the outside (except at the parapet above, where the seal is crap and split/missing in various places) with a brick and mortar sealant and that is likely to impede its ability to dry quickly. So is there an injectable (or pourable) cavity insulation material that performs well in a damp wall and might even assist with drying it out? Sounds like wishful thinking, but I'm hoping some clever company has invented something. The only alternative I can think of is to remove the wet insulation, then try to run some dehumidifying ventilation into the cavity, or remove the wet insulation and live with no insulation until it is dry.

 

Just wondering if anyone has any experience, albeit more likely upgrading a much older wall, not one that was built so recently.

Edited January 3 by Adsibob

[Sparrowhawk]

29 minutes ago, Adsibob said:

The only alternative I can think of is to remove the wet insulation, then try to run some dehumidifying ventilation into the cavity, or remove the wet insulation and live with no insulation until it is dry.

That's the way to do it. Dry it and then put new insulation in.

 

But put mesh over the holes while it's drying, or insert air bricks. You don't want to add an animal problem to your list.

[Mr Punter]

Some mineral wool types, like DriTherm cavity slab, claim to be water repellent. 

 

Maybe get the leaks properly sealed, then do a test hole or 2 to see if it is actually saturated.

[joe90]

Yes I used dritherm and although the outside wall got wet the insulation did not absorb the water 👍. If the insulation has sagged due to water absorption and it looks like you are going to remove the capping can you not drag what insulation you can from above (long stick with a  nail in it?).

[Adsibob]

1 hour ago, Mr Punter said:

Some mineral wool types, like DriTherm cavity slab, claim to be water repellent. 

 

Maybe get the leaks properly sealed, then do a test hole or 2 to see if it is actually saturated.

I think this is a good idea. Thank you. Presumably removing a brick will expose the insulation?

[Adsibob]

19 minutes ago, joe90 said:

If the insulation has sagged due to water absorption and it looks like you are going to remove the capping can you not drag what insulation you can from above (long stick with a  nail in it?).

Not sure it will be that simple, as I think there are structural elements, namely the sloping roof structural bits that will be in the way. But possibly. 

[joe90]

20 minutes ago, Adsibob said:

I think there are structural elements, namely the sloping roof structural bits that will be in the way.

Apart from wall ties I can’t see why anything else should be in a cavity,!

[Adsibob]

1 hour ago, joe90 said:

Apart from wall ties I can’t see why anything else should be in a cavity,!

Yes, you must be right. But I think it will be quite invasive to get through the top, as I think we would need to cut into the membrane and the membrane‘s substrate OSB/plywood. Do able, but then will require call outs from the membrane company to reinstate it, and will complicate the repair as instead of a one tradesman job, it becomes a two tradesman job, which contributed to how I ended up in this mess in the first place. I’m probably not thinking rationally right now though. Waves of anger still permeate through me every few minutes and must be influencing my thinking…

[joe90]

18 minutes ago, Adsibob said:

Waves of anger still permeate through me every few minutes

Time to chill a little if you can, do you have a cross section drawing of that wall etc, it’s difficult to visualise what we are dealing with here.

[TonyT]

Add some retrofit weep vents, you can drill a hole and insert them into the mortar gap

about £15 for 10 from Amazon.

[Adsibob]

3 hours ago, TonyT said:

Add some retrofit weep vents, you can drill a hole and insert them into the mortar gap

about £15 for 10 from Amazon.

Yes these were added to the first row of brickwork immediately above the window two months ago. Is that what you meant, or did you mean to add it to several rows to try to increase ventilation?

[TonyT]

They need to be added to the triangular areas you mention in the first post, at least 2 in each area, high and low level

[Adsibob]

I have the DPM and grips/clamps ready to cover the parapet wall. I was going to do it this weekend, but I’m wondering whether it’s worth leaving it uncovered as we now have a forecast for zero rain over the next 9 days. Obviously the weather could change, but as long as I monitor the forecast daily for any changes, I’m wondering whether it is worth leaving the parapet wall uncovered so that it can get some sunshine which may assist drying, or is it not warm enough for that? Temperature is forecast to fluctuate between 1C and 7C over the next 9 days, but that is taken in the shade and this parapet will get sunshine for half of the day. Or is that not warm enough to assist with drying?

Edited January 6 by Adsibob

[joe90]

58 minutes ago, Adsibob said:

wondering whether it’s worth leaving it uncovered as we now have a forecast for zero rain over the next 9 days.

Yes, definitely will help with the drying out, air movement even with no sunshine will help which will be compromised with the plastic covering it (but stopping more damp in) 👍

[Adsibob]

So I have a few ideas about what is causing the water ingress. I’m 99% confident it’s a poorly specified parapet wall, that, to make matters worse, was built worse than that spec. There were many to be two DPMs but neither travels across the full width of the brick wall, only two thirds of it. Then on top of that, a plastic capping has been laid, but the tiles don’t overlap each other, so there are grout joints between the tiles which have now cracked, allowing water through.

 

Finally, the tile capping doesn’t overhang the brick (let alone have a drip profile.

I keep flip-flopping over what to do (still lots of anger messing with my thoughts).

 

I have 6-9 days of dry weather during which I’m going to let it breathe, but I really need to figure out what the plan is. Long term, i will install an aluminium coping or capping that is properly specified. I may also put in lots of additional weep vents to let more air into the cavity, or swap a couple of bricks with air bricks temporarily.

 

But in the short term, I need to decide which of the following two plans to execute:

 

PLAN A:

Cover the top two or three courses of bricks of the parapet wall (on both sides) with a DPM and clamp it to the parapet with some simple Irwin clamps which I picked up today - this should immediately fix the water ingress (I hope!) but has two potential downsides:

1) it won’t let those rows of bricks breathe, and as these are very damp and quite mouldy, the mould will get worse - I can possibly clean off the mould first, but it is so damp it may just grow back, encouraged by the shade provided by the DPM

2) it is perhaps not going to give me accurate evidence of the exact source of the leak, because several components of the wall will be covered at once; and

3) there is a small chance the clamps could damage the roof membrane which returns up the rear side of the parapet, causing even more problems.

PLAN B

Apply sealant to the cover the cracked joints (and even the ones which don’t look cracked) in the tile capping and also apply sealant all along the small width of brick that is exposed. This should give protection in respect of two of the three concerns about the parapet, but doesn’t solve the lack of overhang issue.

 

The advantage of Plan B is:

1) it gives a more accurate result, as I will know that if this solves the issue for the next few months, we know the exact cause, whereas if it doesn’t then it is some other aspect of the parapet that is causing the leak.
2) it lets the wall breathe

3) no risk of damage to the roof membrane

 

Edited January 6 by Adsibob

[MikeSharp01]

Sounds like you have convinced yourself to have a go at plan B. Your capping idea seems like the most reliable but your idea of finding out if it will work before you part with the money is sound. I think I might make a simple structure with battens that sits, is clamped to, on the wall and is covered by a membrane which would allow the wall to breath but not allow water on top of it. Essentially this is a plastic model of the eventual capping. 

[dpmiller]

might you be able to sneak a camera in to check the cavity tray over the window for gaps or holes too?

[joe90]

If it were mine I would leave for as long as no rain is forecast so it can dry as long as possible, then cover with DPM, clamps don’t need to be very tight and scraps of wood and off cuts of carpet will protect the membrane. Replace the capping with GRP/ali pieces and if possible look at the insulation to assess if it needs replacing whilst the cavity is open. Will you do this yourself of find a builder, which will take time.

[Adsibob]

Thanks guys, all good suggestions. I think I need to get my hands dirty and do this myself. I’ve only used a sealant gun twice before, but both times it was fairly easy, so I reckon I could do Plan B myself. I will mull on this over the next few days of dry period and see if I feel the same way. 
It still beggars belief that of all the professionals involved, they thought this was an acceptable way of leaving the top of a parapet wall:

 

 

This is the apex. Cracked grout between two tiles. Every joint is like that. Two tiles don’t even cover the brick, let alone overhang it. Then membrane does not cover the tiles fully!

 

[joe90]

@Adsibob I am still at odds knowing what exactly you have and how the membrane covers the wall, usually a parapet wall is like this.

 

 

[Adsibob]

It is a bit more complicated. This is a single skin brick parapet wall, because only the outer wall of the cavity wall rises up to form the parapet. In this way, the roof space was maximised to allow more green (seedum) roof. So the membrane which is under the sedum was overlapped up the parapet wall and over the single brick, but not fully over, due to a mistake in my view. Then over that brick that was partially overlapped with membrane, some plastic tiles were layed and over those tiles, another layer of membrane, but again not fully covering the tile. 

Edited January 7 by Adsibob

[joe90]

3 hours ago, Adsibob said:

due to a mistake in my view.

Oh yes, an ally or GRP single skin copping would fix that for sure. First example I found.  https://www.aluminiumrainflow.co.uk/product-page/skyline-91-120mm-wall-width-level-coping-3m-length?gclid=Cj0KCQiAtOmsBhCnARIsAGPa5yY6uN-wvzTSnJtv8_ofO-PsREM2XXOWFL9_3G5VAOwJ8GZ6fHzhYFYaAqTQEALw_wcB

[SteamyTea]

This detail worries me.

 

 

What is to stop water from getting under the tiles when they adhesive/grout fails, and what is to stop water building up and over flowing the top of the flashing when the drain fails?

 

This must be why parapets are so hated.

[joe90]

Sorry @SteamyTea my crayon assisted drawing was only a ref to the coping stone to try and understand the OP,s problem as we have no drawing of what he actually has (a picture speaks a thousand words). @Adsibob actually has no tiles. 

[SteamyTea]

59 minutes ago, joe90 said:

a picture speaks a thousand words

It can, or make for more confusion.

Possibly why I am not sure what is going on in this thread.