DPC - Recognised Construction Details

[Jammy5]

Hi there, I'm hoping people on here can solve a really bad head. I'm not getting much joy out of my contracted architect, so thought I'd see if anyone is able to help as I'm really going round in circles with this one.

 

I received my SAP calculation package and within it, it states that "Recognised Construction Details (RCD) for Masonary Construction to be used and followed" as per the following: www.recognisedconstructiondetails.co.uk/walls/masonry-cavity-wall-partial-fill-insulation

 

The specific area thats causing me a problem is the detail regarding the DPC/DPM which is:-

MPF-150-E5-12-Ground bearing slab_ insulation above

 

In addition to this, I also must install a gas membrane that spans the cavity.

 

The finished floor level (patio) along the back edge of the house (9.5m wide) will be level with the internal finished floor level. This will then slope from front to back (13m long) to ensure the front face of the house is 150mm below the internal finished floor level. Obviously the issue being that I do not have a DPC 150mm above ground level.

 

I plan on installing an ACO Slot Drain along the full back edge of the house (this elevation has a single 6m wide bi-fold door) but this leaves the two sides non-compliant with a slope running from +0 to -150mm below along a 13m length.

 

The below are my thoughts on how I could achieve the Recognised Construction Details:-

 

Figure 1

 

 

 

 

Figure 2

 

 

 

Figure 1 has the DPC at ground level on the whole rear elevation and less than 150mm along the side elevations.

To combat this I’ve added a second DPC (shown in red) a block above.

 

Figure 2 is as per the recognised construction details but I’ve simply raised the DPC up by a block on the inner and outer leaf. This would mean the internal is 450mm above my internal finished floor level but I would achieve a minimum 225mm above external finished floor level (with it being 300mm on the front elevation).

 

I also plan on installing on standard DPM under the slab and bringing that up to the top of the second block on the inner leaf (finished floor level).

 

Which of the two is the best option?

 

 

 

An architect I know, really dislikes the Recognised Construction Details. Their opinion is the DPC should be flush with finished floor level and should not run down the inside of the inner leaf, above the skirting board. He is arguing that in practice there will be mortar droppings into the bottom of the cavity tray which will block the weep holes, and water will rise up the cavity tray and eventually lead to damp down the internal wall.

 

As a compromise, he has recommended a different detail which wraps a block on the inner leaf.

 

The purple is DPC, the red is the gas membrane and the blue is a normal DPM. There will also be a vapour barrier installed as standard above the insulation which isn’t shown. The detail is shown below:-

Figure 3

My main issue with this, is I am already two blocks high, above the trench blocks, and would mean removal of a course of blocks or three bricks to install the gas membrane. I also wouldn’t be able to complete the full fill insulation as detailed and in theory isn't following the recognised construction details.

 

Are the recognised construction details really that bad if I follow them as per one of my two details above?

 

Sorry for the length of this, but hopefully I've explained it well enough.

 

Many thanks.

 

 

[ETC]

Draw what you have built to-date and post it here.

The details do not look practical to build.

[Jammy5]

I'll post shortly but I've basically built two trench blocks and two blocks up (both inner and outer leaf) on the drawings above. I've also laid and compacted hardcore ready for a blinding of sand

[Gus Potter]

Have you had an SE input yet?

 

SE's can help smooth things out.. if you are willing to pay for a fair days work.

 

 

 

 

[Jammy5]

13 minutes ago, Gus Potter said:

Have you had an SE input yet?

 

SE's can help smooth things out.. if you are willing to pay for a fair days work.

 

 

 

 

A structural engineer has had input. No mention about DPC or anything as such in his details. Is it a structural engineer that would advise on these things?

 

Sorry for all the questions

[Gus Potter]

7 minutes ago, Jammy5 said:

A structural engineer has had input. No mention about DPC or anything as such in his details. Is it a structural engineer that would advise on these things?

All the members of your design team have a responsibility. The big problem that a lot of them will have is that you are not paying one of them enough to coordinate it all.

 

If this was happening you would not be asking these questions on BH.

 

It's that simple!

 

 

Edited Friday at 20:31 by Gus Potter

[Jammy5]

3 minutes ago, Gus Potter said:

All the members of your design team have a responsibility. The big problem that a lot of them will have is that you are not paying one of them enough to coordinate it all.

 

If this was happening you would not be asking these questions on BH.

 

It's that simple!

 

 

Ok, I understand what you're saying. Everything was paid for via my architect, so he was the one co-ordinating it all, but he's barely communicating. It took me two weeks of chasing to get electronic versions of the drawings out of him.

 

I just feel quite stuck with this one at such as important stage really.

[ETC]

Post your architect’s and SE drawings.

[Gus Potter]

2 minutes ago, ETC said:

Post your architect’s and SE drawings.

@ETC I don't always agree but on this point good advice.

[ADLIan]

I wouldn't get too hung up on the position of DPC/DPM in these details. Their primary function is to show the geometry of junctions (with all adjacent materials and physical properties) in order to arrive at the Psi-value - the DPM/DPC has no effect here.

[Gus Potter]

11 minutes ago, ADLIan said:

I wouldn't get too hung up on the position of DPC/DPM in these details. Their primary function is to show the geometry of junctions (with all adjacent materials and physical properties) in order to arrive at the Psi-value - the DPM/DPC has no effect here.

Architecturally..but can you explain how that is going to work structurally when the SE has to then fix the stuff that you should know about!

 

You can go chucking in DPC's, rocker bearings,  thermal breaks at will!

 

If you want to profess about changing stuff them maybe go onto explian how it impacts on the structure.

 

Yes, I know life has got harder for Architects and the thermal regs but the same applies to SE's.. strart collaborating and learning.

 

 

 

Edited Friday at 21:05 by Gus Potter

[Jammy5]

I'm on my mobile or I'd have looked to remove names etc from the drawing and then post. The two details attached are from the architect (mentioning DPC) and the structural engineer which is void of any mention of DPC or detail.

 

The only difference is I've gone with a traditional slab and the external ground floor is as mentioned above.

[ETC]

38 minutes ago, ADLIan said:

I wouldn't get too hung up on the position of DPC/DPM in these details. Their primary function is to show the geometry of junctions (with all adjacent materials and physical properties) in order to arrive at the Psi-value - the DPM/DPC has no effect here.

Er…..I think the gas barrier, DPC and DPM positions are critical…..so I’m told…..

[ETC]

What’s the difference between FGL and FFL?

My advice would be to separate the radon barrier from the DPM and have the radon barrier below the slab - makes life easy for putting in the DPM which should go above the slab.

DPC in the inner leaf at slab level.

DPC in the outer leaf at 150mm above FGL.

[ETC]

Might work……

[ETC]

Radon can be 225mm below FGL….

[Jammy5]

Thank you for the reply.

 

You have shown FFL at the correct height but FGL1 is the same level as FFL (needs raised 1 block). 

 

Unfortunately, I have already installed two blocks above the trench blocks (up to FFL) and the compacted hardcore is already in place.

 

I have also gone for a traditional slab rather than block and beam.

 

Sorry if I wasn't clear above

 

 

 

 

 

[ETC]

Might be worth giving your local friendly Visqueen rep a call…..they’ll do a detail……mine could be a bit contrived.

Continuous radon/DPM/VCL above a ground bearing slab sealed to a radon proof DPC that rises through the cavity to the top of the first block above FFL. A stepped radon proof DPC sealed above stepping down through the cavity to FGL. An additional DPC minimum 150mm (shown 225mm) above FGL.

Edited Friday at 22:42 by ETC

[Jammy5]

20 minutes ago, ETC said:

Might be worth giving your local friendly Visqueen rep a call…..they’ll do a detail……mine could be a bit contrived.

Continuous radon/DPM/VCL above a ground bearing slab sealed to a radon proof DPC that rises through the cavity to the top of the first block above FFL. A stepped radon proof DPC sealed above stepping down through the cavity to FGL. An additional DPC minimum 150mm (shown 225mm) above FGL.

Thanks so much. In fairness that's very similar to what the guy I know is recommending.

 

Just a couple of questions please.

 

What's the vertical yellow line? And what are the lines above the screed? Is this just showing the flooring finish and skirting?

 

I'm assuming the red is the gas membrane and there's no additional DPM needed anywhere?

 

I've been recommended to run a belt and braces, standard DPM above the ground floor slab (below insulation) which would finish to the top edge of the second block (inner leaf only). Would this be required?

 

I'll give my visqueen rep a call. I really do appreciate the help with this one. 

[ADLIan]

3 hours ago, ETC said:

Er…..I think the gas barrier, DPC and DPM positions are critical…..so I’m told…..

Not to the Psi-value (the heat loss at a junction) which is all the RCDs are looking at. They cannot cover every scenario of floor level, external levels, DPM/DPC positions etc

[ETC]

5 hours ago, Jammy5 said:

Thanks so much. In fairness that's very similar to what the guy I know is recommending.

 

Just a couple of questions please.

 

What's the vertical yellow line? Internal plaster And what are the lines above the screed? Is this just showing the flooring finish and skirting?correct

 

I'm assuming the red is the gas membrane and there's no additional DPM needed anywhere? Correct. You’ll need to seal everything. 

 

I've been recommended to run a belt and braces, standard DPM above the ground floor slab (below insulation) which would finish to the top edge of the second block (inner leaf only). Would this be required? My solution is having a radon barrier used as a DPM as well as a gas barrier and when placed above the insulation will also act as a VCL - needs verified by Visqueen though.

 

I'll give my visqueen rep a call. I really do appreciate the help with this one. NB.

 

[ETC]

[ETC]

I’m not sure how this will work at a door threshold….Visqueen rep will advise on everything. Give him/her a call.

Oh and by the way - try and course everything - makes life easier.

Edited Saturday at 05:02 by ETC