Two 4" blocks on cavity wall - cold bridging issue

Mr.E · 23-01-2023 10:56AM #1

After drilling holes in the walls, we discovered as you can see from the diagram, the builder who constructed the house we purchased placed two 4" blocks to close the cavity. This means we get condensation running down the walls when the heating is on and it is cold outside.

Other than wrapping the house in external insulation, applying insulated slabs on the interior, or dropping the ceiling are there any other solutions?

Thank you

sydthebeat · 24-01-2023 06:59PM

are you sure they used two full 300 x 100 blocks to cover the cavity ??

have you got the space on the outside to cover these two blocks with quilt insulation ie hide this in the eaves?

apart from teh cold bridge issues, you also need to review what and why the water vapour if so high as to cause that level of dampness.

are vents blocked / insufficient or both? do you dry clothes internally in the house? do bathrooms etc have mechanical ventilation with over run settings?

Wildly Boaring · 24-01-2023 07:06PM

Unfortunately this is very common. Had an argument lately with a brickie who still thinks its a good idea. "For strength"

We had similar issues in a house few years ago. Managed to control it by

1. Installing new vent in every bedroom. (Old were blocked up)

2. Purging bedrooms first thing in the morning by opening windows for an hour

3. Running dehumidifier by day in bedrooms when necessary

Once under control removed all poor paint and repainted walls and ceilings.

Calahonda52 · 24-01-2023 07:14PM

The lads and lassies above know a lot more about this than I do, however I see it differently.

Are you 100% sure that its just condensation?.

It looks like water ingress, possibly due to driving rain and roofing felt failure/ bad detailing above the wallplate.

Whats the rest of the house like along this thermal bridge?

sydthebeat · 25-01-2023 06:42PM

https://www.boards.ie/discussion/comment/120152263#Comment_120152263

just to clarify, im not saying its definitely condensation either :D

thats serious level of moisture is worrying, but the OP did say "This means we get condensation running down the walls when the heating is on and it is cold outside."

OP, does that mean you dont get any moisture problems when its mild outside and its pi$$ing rain out?

Mr.E · 27-01-2023 08:34PM

Hey, thanks for all the feedback. The condensation seen in the photo was seen during that week or so of bad frost before Christmas. Usually, there isn't condensation unless there are noticeable decreases in temperature between inside and out.

Some further notes:

You can see from the photos from the thermal camera that there is cold bridging happening roughly 4" down from the wall.

We recently purchased a dehumidifier and once turned on it's in the 80% range and if left on for days it never goes below 62%.

I've been to the attic and there is no evidence of water entering the roof. Also, I've inspected the guttering and there are no issues there.

To answer a few questions you posted:

Whats the rest of the house like along this thermal bridge?

Only in the kitchen but not in the dining room which is on the other end of the open kitchen. One bedroom has condesation marks. That is the spare bedroom that only has heating on with guests present.

To be honest it doesn't really make sense as we have drilled holes even in the rooms with no condensation marks but still found two 4" blocks.

are you sure they used two full 300 x 100 blocks to cover the cavity ??

Yes, holes were drilled below the soffit at different locations around the house, and a solid block was hit but not below 4"

have you got the space on the outside to cover these two blocks with quilt insulation ie hide this in the eaves?

No, unfortunately not it is as per the diagram. . Everything is standard except for the two blocks.

are vents blocked / insufficient or both? do you dry clothes internally in the house? do bathrooms etc have mechanical ventilation with over run settings?

Vents are not blocked, we do dry clothes but in front of the stove and it never creates condensation. Bathrooms are mechanical

C. Eastwood · 27-01-2023 09:47PM

https://www.boards.ie/discussion/comment/120167187#Comment_120167187

Mr.E

You need to retain á Construction Professional for advice, to carry out a survey of your home and make recommendations.

My Professional Advice is to fix 75 mm high density insulation on a Plasterboard slab on to the internal face of the external walls. Fix same in place with metal mushroom fixings. These metal mushrooms should not be fixed within 400 mm of the ceiling.

You will also need to fix approx 45 mm insulation on a slab on to the internal concrete block walls that are built-in to the external walls.

EWI will not solve your problem.

You will also need advice on the type of insulation in the attic, on top of the cavity closing blocks.

MicktheMan · 27-01-2023 10:07PM

Other than wrapping the house in external insulation, applying insulated slabs on the interior, or dropping the ceiling are there any other solutions?

Yes... knowledge & mitigation

Reduce your moisture load ... drying clothes inside by the stove would be first on my list
Improve your heating (maybe by tackling your heat losses) and keep the house warmer
1 & 2 above will then improve your ventilation efficiency and perhaps a cMEV system will bring this further.

we do dry clothes but in front of the stove and it never creates condensation

How do you know this? Where do you think the moisture goes?

To be honest it doesn't really make sense as we have drilled holes even in the rooms with no condensation marks but still found two 4" blocks.

That thermal bridge detail you are seeing at the top of the cavity wall is one of the most common thermal bridges in cavity wall constructions. The presence or not of condensation, discolouration, mould etc is down to the intricacies and interdependence of internal / external conditions (temperature, relative humidity), orientation, room design, occupant behaviour, ventilation efficiency etc. As an example, in many situations, the mere upgrading of an open fire to a stove can inadvertently cause these kind of issues in another part of the house.

Calahonda52 · 28-01-2023 03:39PM

Post 8 should be a sticky

In passing MtM, whats the recommended steady state RH for domestic dwellings😎

Calahonda52 · 28-01-2023 03:52PM

OP, ama bit puzzle here

You are saying the TB is 4 " down from the ceiling, so the suggestion is that the top block is full insulated.

In passing, thermal images should have correct time and date on them

MicktheMan · 29-01-2023 04:48PM

https://www.boards.ie/discussion/comment/120169722#Comment_120169722

The RH% is never really steady state in an occupied house😜

The internal RH% will vary in two ways;

by external temperature on a macro level (i.e. low outdoor temp -> low internal RH% and visa versa)
by occupant behaviour on a micro level.

Overall, internal RH% ranges from low 50's to mid to high 60's% level with the occasional local spike into the 70's & 80's when cooking for instance or taking a shower. The key bit, however, is that the level returns to baseline quickly after the moisture generating activity ceases. Where the RH% lingers longterm north of 70% is a real risk factor for damp (this can occur easily in unused, lower heated spaces on the cooler side of the house).

None of this is applicable, of course, outside the heating season.

MicktheMan · 29-01-2023 05:00PM

My Professional Advice is to fix 75 mm high density insulation on a Plasterboard slab on to the internal face of the external walls. Fix same in place with metal mushroom fixings. These metal mushrooms should not be fixed within 400 mm of the ceiling.

You will also need to fix approx 45 mm insulation on a slab on to the internal concrete block walls that are built-in to the external walls.

EWI will not solve your problem.

OP, it this was my house, I would be very wary of following the advice described above.

Mr.E · 30-01-2023 02:44PM

Thanks for all the feed back .

Micktheman, what I meant by that there is no condensation when we dry clothes - there is no evidence of condensation on the walls. I assume that the correct ventilation is allowing the moisture to escape. In relation to your suggestion on knowledge and mitigation, we do all suggested and the moisture only occurs when there is a dramatic heat change between the inside and outside.

Calahonda52 that diagram doesn't best describe the top block. Here is a photo of the hard insulation running to the block. There is also fg insulation on top of the block. As for the camera, apologies about the date. I got the lend of it.

'You will also need to fix approx 45 mm insulation on a slab on to the internal concrete block walls that are built-in to the external walls.'

What is the rational for this?

Calahonda52 · 30-01-2023 09:05PM

'You will also need to fix approx 45 mm insulation on a slab on to the internal concrete block walls that are built-in to the external walls.'

What is the rational for this?

I believe the thinking is that iff the internal wall is a solid block wall that ties into the inner leaf of the outfall that the internal wall could be a cold bridge.

However as MtM has said, thread very carefully re dry lining in the absence of addressing all the other moisture mitigation measures as you don't want this.

This shows the problem with too much IWI

Two 4" blocks on cavity wall - cold bridging issue

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