B&B edge & outer leaf of cavity are not parallel

[Tony L]

Thanks to @Canski for studying a picture in one of my other threads & bringing my attention to this possible defect.  It doesn't look as bad as we feared from the picture on the other thread, but it would be good to receive some comments & advice, please.

 

The builder has started building up the outer leaf of the cavity wall.  This comprises 2 courses of staff blues onto trench blocks, then I've got 2 courses of expensive black bricks (most of which shouldn't even be there, because he was supposed to save those for above ground level - but let's ignore that issue for now).  The outer leaf looks straight, although this far from high quality brick work.  I've taken some pictures showing the variance in the gap from the inside of the inner leaf to the edge of the B&B floor, down one side of the house. 

 

There's a 6"/150mm ruler in each picture.  The ruler measures 159mm, including the clear plastic ends that are of the ends of the measuring part.

 

Picture  1 shows a gap of at least 170mm across the cavity.  The ruler's left edge is resting on a protruding beam.  I don't know why the beam wasn't pushed over, so the extra length hung off the sleeper wall in the middle of the floor, so it wouldn't be seen.  Will the protruding beam be in the way of my trays?  I haven't had time to learn about trays yet.  It looks like the run of blocks into the top corner came up 20mm or so short, & rather than cut 2 blocks to put the corner where it should be, the builder has just left a gap.  Should I insist he re-works this so I have 150mm at the corner?  What's the acceptable tolerance here?  I probably wouldn't even be asking if he'd managed +/-8mm. 

 

Picture 2 is a different view, with the ruler in the same position as picture 1

 

Picture 3 shows the ruler in between the 2 ICs you can see in picture 2. The cavity here is 160mm.

 

Picture 4 shows the ruler just a little further along, by the brick slip you can see in picture 2.  This is close to 150mm.  If the cavity had been built like this all the way along, I'd have been happier.

 

Do I just build on top of what I've got here, & make sure the cavity where the back door goes has parallel sides?

 

If we put a 100mm wide block on the edge of the B&B at the end where the gap is 170mm or more, that would mean the 20mm nearest the centre of the house is not fully supported underneath.

 

 

[Tony L]

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[Tony L]

2  - sorry, the forum software has rotated my portrait picture

[Tony L]

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[Tony L]

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[Canski]

Honestly that's not the end of the world. A 200 mm cavity instead of 150 which is what it looked like from the other photo would have been a problem.

Your cavity trays will be from the top of the first course of block above DPC (+ 225mm ) down to DPC on the outer skin (0.00) Make sure your insulation is in and photographed before these go on. 

 

 

Move on to the next stage.

 

 

Edited December 4 by Canski

[Tony L]

@Canski, that's very reassuring, thank you.

 

I'm printing your last post out to make sure it doesn't get forgotten.

 

Am I right in thinking these cavity trays wouldn't have been required if there had been a cavity (instead of 350mm wide trench blocks) going down below the beams?  If so, I want to think about the additional cost for these cavity trays.  The builder was supposed to be following drawings that show the beams on 100mm wide blocks, with a cavity below.

[twice round the block]

The black bricks the builder is using below ground level.

Are they frost resistant? 

[Tony L]

@twice round the block Thanks for thinking of this.  They're FL, so yes.  Here's the spec'.  Crest Nero Black.

 

 

[Canski]

13 hours ago, Tony L said:

Am I right in thinking these cavity trays wouldn't have been required if there had been a cavity (instead of 350mm wide trench blocks) going down below the beams?  If so, I want to think about the additional cost for these cavity trays.  The builder was supposed to be following drawings that show the beams on 100mm wide blocks, with a cavity below.

Don’t worry about this. You saved having to cavity fill by having the trench blocks to below the beams. Cavity tray is just DPC but wider. It gives you an extra level of damp protection. It’s not expensive and would be installed quicker than cavity filling. You would have to install it over your air bricks anyway so it’s just an extension of this. Get some good tape for the corners though. Start planning the superstructures. 

[Tony L]

Thanks, @Canski.  That's good to know.