Footings and DPC detail for flush threshold

[matlob]

Hi,

Trying to workout what gound works I need to do and materials I need to order etc

Does this look correct for the slab and dpc layout. The footings are in already

Finished floor level will be the same internally and externally with flush thresholds so there is a double dpc

Am i correct to think that the heavier block should be used below ffl

Thanks in advance for any help

 

[Bonni]

The design I always do is having the DPM's and DPC turned up onto the same brick. Full fill cavity should be banned, you should always have a 50mm clear cavity in my book.

Bridging the DPC across the cavity means you're going over an opening, otherwise, don't do that. The reason why the lean mix is 3 course of brick below DPC is for the mortar snots, your 450 DPC has reduced that to 1 course of brick.

A tent has an outer layer and then you fit an inner layer so you have a cavity. Touch the inside of the outer layer and you get a wet hand. Why on earth people do full cavity fill, or blow cavity insulation in on an older house is beyond belief. On a full cavity filled house, I would place it's valve as £0,00, until it was taken out.

 

[Mr Chibs]

The design I always do is having the DPM's and DPC turned up onto the same brick. Full fill cavity should be banned, you should always have a 50mm clear cavity in my book.

Bonni, I'm curious about this... so can damp travel through full fill cavity batts? I thought these were water repellant.


Matlob, a mate of mine is building an extension and has been advised that 150mm is the 'new' rule for cavity thickness.

 

[noseall]

, a mate of mine is building an extension and has been advised that 150mm is the 'new' rule for cavity thickness.

Not necessarily no. The get-around for ridiculously thick walls, is using bigger-stronger-faster (PIR) cavity insulation, as opposed to regular Dritherm type cavity batts.

bigger-stronger-faster...

 

[matlob]

Thanks Bonni

So run the lower dpm up over the same block as the top one where it meets the dpc?
I assumed the DPC crosses the cavity as the external one needs to be higher up as level threshold, but I understand what you mean about the snots falling in if there is a bridged cavity

Are the block specs correct with 7n being below ffl and lighter ones above

I may go for rigid cavity insulation if full fill is not good and ensure there is a gap on the external

Mr Chibs
The project was submitted and passed off before the changes came into effect so I am on the old rules, I think they do need to be wider now

 

[George_engineer]

You need to do the threshold detail. Away from the threshold drop the ground down 150mm.

 

[matlob]

The internal and external levels are the same. That's why the dpc is how it is as I could just do a standard dpc if the ground was lower so wanted to double check it all looked correct

 

[George_engineer]

Yeah I get the detail it's just why not just drop the ground? It only needs to flush at the threshold so you don't have to carry that level round the rest of building.

Obviously just ignore me if there are other good reasons. But complicated details can go awry.

Agree with the other comments about lapping the dpm (top dpm is just a vcl so you can get a cheaper polythene if wanted). I'd put 7N anywhere there's a possibility of water ingress and think about channel drains or a French drain around the building perimeter.

 

[matlob]

Thanks george. we just want to eliminate any steps ideally. I could fit a slot drain fairly easily as new drainage runs are going around the extension. The ground will also slope away from the house when paved.