DPC and cavity trays

[goodbyegti]

Hello! I'm wondering how to implement the DPC in the attached diagram. The construction is a DPM, with a 150mm slab + 150mm insulation + 75mm screed. The wall is 100mm thermal block on the inner skin, with 100mm insulation, a 25mm SureCav spacer and then 125mm natural stone.

 

Would you normally fit a cavity tray in this instance? And what about the DPC bridging the cavity with no downward slope to the outer skin?

[Reeci]

Only have cavity tray above openings and anything bearing on the structure walls I,e beam or telescopic vent etc. the dpc shouldn’t  bridge the cavity like as water will run along. Dpc top of the brickwork and block work 

[goodbyegti]

Thanks! That's also suggested in the SureCav diagram - makes sense to me.

[Iceverge]

Can you switch to 150mm EPS beads save yourself lots of time money and have a better performing wall? 

 

You can just put a strip of dpm on the outer leaf if the wall, 150mm from the ground then and let the beads go right down to the bottom of the cavity really mitigating any thermal bridge. 

 

 

Edited March 23, 2023 by Iceverge

[Canski]

Are you in a radon zone ?

[Radian]

1 hour ago, Iceverge said:

Can you switch to 150mm EPS beads save yourself lots of time money and have a better performing wall? 

 

You can just put a strip of dpm on the outer leaf if the wall, 150mm from the ground then and let the beads go right down to the bottom of the cavity really mitigating any thermal bridge. 

 

 

+1 for EPS fill, This obviates the need for the SureCav and tricky buisness of fitting PIR and wall ties. Masonry work can just go up quickly and easily then the full width of the cavity is injected once the walls are complete. Ideally the cavity would be widened to at least 200mm.

[Iceverge]

2 hours ago, Canski said:

Are you in a radon zone ?

Yup

[goodbyegti]

Thank you for the insightful comments. As far as the design goes it's too late to change, but good to know for the future.

 

Radon appears to be a moderate risk in north Bristol. To be honest, I hadn't even thought about it.

 

The stone going up on the outer skin is as pictured. I suppose the SureCav at least gives a flat surface to lay it up to.

[ETC]

22 hours ago, goodbyegti said:

Hello! I'm wondering how to implement the DPC in the attached diagram. The construction is a DPM, with a 150mm slab + 150mm insulation + 75mm screed. The wall is 100mm thermal block on the inner skin, with 100mm insulation, a 25mm SureCav spacer and then 125mm natural stone.

 

Would you normally fit a cavity tray in this instance? And what about the DPC bridging the cavity with no downward slope to the outer skin?

Not a great detail. Tricky to get right on site especially if you need radon protection. There are other simpler ways of doing this. Visqueen do a set of details which uses a combined DPM/radon barrier.

[Radian]

1 hour ago, goodbyegti said:

The stone going up on the outer skin is as pictured. I suppose the SureCav at least gives a flat surface to lay it up to.

 

What sort of tolerance is there on your '125mm' stone? If it's regular cropped walling stone it could easily be +/-25mm. Are you laying it yourself or contracting it out?

[goodbyegti]

10 hours ago, Radian said:

What sort of tolerance is there on your '125mm' stone? If it's regular cropped walling stone it could easily be +/-25mm. Are you laying it yourself or contracting it out?

It's been contracted out. The tolerance is much larger than 25mm. It has to match  the stone wall on the existing building.

[Iceverge]

EPS beads or fill fill mineral wool solve a myriad of problem here. 

[goodbyegti]

On 24/03/2023 at 08:41, Iceverge said:

EPS beads or fill fill mineral wool solve a myriad of problem here. 

I can see that now the wall is going up! I have nightmares about mortar droppings.

 

Builder is cracking on at least, and looks good so far. 

[Dave Jones]

surecav doc is wrong they missing a damp and dont show weepers either

 

[TerryE]

We've got an MBC TF with natural stone outer leaf.  We didn't use SureCav as discussed in the following topic, but in our case we had a twinwall TF inner that was structural with the insulation internal to it.  With your block inner and insulation in the void, this might not work for you.

 

Even so I think that the suggested EPC option is a lot simpler, though I would be loath to drop the ties.  The idea of bulging walls in a decade or so is horrifying.  You can get long ties to span the gap and these wouldn't be a problem for the EPC fill. 

 

 

Edited March 31, 2023 by TerryE