Block Reveal - Have I messed this up??

1 Dec 2019
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United Kingdom
I have a large steel to install to the back elevation of the extension. The SE has specified block on side to the internal leaf and standard blockwork on the outer leaf. The extension is of cavity construction formed of dense concrete blocks.

The brickie (after asking me) has formed the reveals by returning the inner skin to the outer rather than using an insulated cavity closer. I found the cavity closers very flimsy when I did the front and the doors being installed here are large, heavy and need decent fixings so I had thought solid dense blockwork piers would be ideal.

I understand the theory behind thermal bridging but given that the rest of my house together with most others of its age were all constructed in solid brick walls so is this any different.

I then worried the BCO would condemn it on this basis but he didn't. Now i am concerned over future issues but am I doing so for no real reason. What is the likely hood of mould/condensation on this reveal in the real world rather than a thermal model?

What would you do?

1) Leave it as it is - it poses limited to no risk
2) Cut out the mortar joint between inner and outer skins and pack with 10mm or so of foam insulation
3) line the inner wall to this reveal in insulated plasterboard

Photo and sketch of what has been installed below any real world advise greatly appreciated;

Block Pier.PNG
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I’d opt for 1, all my walls/doors are like what you have... I have neither condensation/mould... don’t think it’s a worry.
What about the vertical DPC? Are you sure he is a brickie????? Asking the customer how to build the wall, bit strange!
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Sorry forgot to mention there is a vertical dpc between the inner/outer skin.

There is often more than 1 way to build things. I don't see why asking my preference is strange.
If it's problematic or not depends on weather it will be exposed to and what you plan on doing in that room, plus loads of other factors.

I cannot see how it would comply with the limiting value for the individual element. (In approved document C - 0.7W/m2K.)

Adding the 20mm of insulation might just get you there.

Your doors should be able to be fixed into the brick whilst also achieving the required setback over the cavity closer.

You'll also have a much better time fitting the doors if the bricky builds to a template or suitable closers themselves.
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Sorry forgot to mention there is a vertical dpc between the inner/outer skin.

There is often more than 1 way to build things. I don't see why asking my preference is strange.

As the vertical DPC appears to have been pointed in and is not visible I would be more worried about penetrating damp tracking across behind the door jambs. That is probably a far more common cause of damp staining to window and door reveals than cold bridging.

Also as the blocks have been laid flat is the width of the blockwork return 215mm? If so does the vertical DPC cover that entire width?
DPC just popping out of the mortar but cant be seen in the photo. The DPC covers the full width of the return.

I am less concerned about it being compliant with code in regards to heat loss more about potential issues with damp.

Its a 400mm deep block pier which will be rendered and fairly sheltered other than driving rain - surely the risk is minimal and no different from the original solid brick wall that it is replacing?
That is entirely up to you and your attitude to risk. The various standards and regulations have evolved over many years and whilst some of them are a bit dubious, on the whole they are there for a very good reason and have been developed through decades of research and testing. The proprietary insulated cavity closers not only protect against cold bridging at the reveal they also make the vertical DPC detail much more robust and less likely to be compromised by poor workmanship.

The risk of water penetration due to that wall reveal detail might well be minimal but the consequences if it doesn't work will be very expensive and disruptive to fix. I certainly would not risk it but then I am very risk averse. I like following the rules.
as Swwils above, just because one person gets no mould doesn't mean another person won't. It depends entirely on circumstances, air currents, exposure, use of room, and a long list of other factors. Some people get it on one side of the house but not the other, when the construction is identical. You might be ok but there's no guaranteeing. Personally I would have insulated the joint, and if it can reasonably be done now I think it would be worth it.

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