DPC and Ground Level

[Ed_MK]

HI All,

 

Since the below pic was taken there HAS now been a lot more soil taken from around the trench block to bring it well under by at least 150mm.

I am now working out my drainage ....and it seems the house sits a fair bit LOWER than originally planned...which due my long drainage path
may cause problems for me ....re: getting a good fall from my site to the drain 40m away

 

I was looking at some drawings and as you can see from the picture there is a dampcourse running all around the edge of the connection between
the trench block and the B&B

 

the slab now has a a run of "kicker" bricks around it ...where the timber frame sits (not shown in pic)

 

Now I am presuming that the bricklayer will then build the brick skin on the outside of the Beam and block (on top of the trench block)

 

So what I am wondering is..is there a RELATION to the 2 DPC barriers ...the one the groundworkers put in and the one the bricklayer will put in ?

I mean they are not CONNECTED ..so will be divided by the cavity, as the DPC thats there ...only runs to the edge of the beam(sort of half way across the trench block)

...I presume that is correct?

 

What I am thinking is ...would it be possible to have the DPC on the exterior wall a few course higher?....This of course would have the effect of meaning i get more 
back-fill and a better fall for my drain 

 

I understand the reason for the DPC ...but I guess if i NEED to raise the outside one ...would it affect any damp rising elsewhere, as if i do this ..effective EXTERNAL ground level would then 
be technically OVER the INTERNAL DPC

 

 

hope that made sense

 

 

 

 

[nod]

Your dpc will be separated by a cavity and need to be inline 

The height will be govend by what you are doing inside

If you lay one block on the slab then dpc on top of that Then the internal floor will be filled with insulation and screed to finish flush with dpc

In my case I was still a little tight for drainage fall so I added a course of comon brick Then when we screeded made the difference up with insulation 

 

I spoke to building control at the time and he said add a couple of courses if reguired No need to go back to planing 

[Brickie]

It’s common practice to lay s Dpc under b& b but,confusingly,this isn’t your actual Dpc height. 

Noramally-Dpc will be level with your finished floor. Internally there will be a Dpc under the sole plate of the tf & I’m guessing your membrane will lap into that,creating a continuous barrier. 

Externally,it’s common to have anything between 2-6 courses of face brickwork off your trench block to Dpc. If there is a level threshold detail then additional Dpc will be needed 150mm above,extending 1m past the rise & lapped with the Dpc running right round. Ask your tf supplier for a typical Dpc & membrane detail for the design you have. 

[Ed_MK]

Ok thanks.

Well the frame arrived today and it is FLYING up ...but i did notice they put down boards with dampcourse under them BEFORE they started fixing the panels.

So I am now REALLY confused LOL ...I have dampcourse under the B&B, dampcourse under the TF and no doubt my brickie will put a DPC in the bricks too.

 

Do any of these need to line up or tie together...you know from inside to out ... ?

[Ed_MK]

7 hours ago, nod said:

Your dpc will be separated by a cavity and need to be inline 

The height will be govend by what you are doing inside

If you lay one block on the slab then dpc on top of that Then the internal floor will be filled with insulation and screed to finish flush with dpc

 

 

Initially thats what i was thinking ...."exterior DPC in line with top of B&B"
But today i heard that there is layer of insulation ...which may be 500mm ....and on top of that a screed of at least 500mm ???

...if thats the case and the inside is going to be 10cm higher than beam and block 

and the DPC under that is obviously 165mm below the top 

 

So the DPC on the Trench block ...will be 165+500=665mm below the Finished Floor
So if the ground level needs to be 150mm UNDER the exterior DPC (Trench block top) then the exterior ground level 
will therefor be 665+150=over 800mm below the internal floor ?

 

Am i daft or is that right ?

 

 

 

[Ed_MK]

Below is essentially (forgive the artwork) what I have

 

So I am trying to figure out ...

 

a) If the exterior earthfill needs to be 150mm below a DPC ...which DPC

b) Can you tell where the bricklayer will lay the external DPC course ....and HOW is it possible
afterwards to connect this to an internal one ....or is it not necessary ?

 

 

[RichS]

I think you're confusing 50mm and 500mm, hence your final total ?

[CC45]

Are you going to use a cavity tray?  this should slope down to the external dpc if you are using one.

[PeterW]

Insulation will be min 120mm PIR to get to BRegs with a 65-100mm screed dependant on finish. UFH too ..??

 

If so, count that as 225mm from beam top, so that’s 3 courses of bricks - or one block - high. Assuming these are standard beams then you’ve probably got 140mm depth there, so that is 365mm from the trench block. So you could say your outer DPC is at 4 bricks up, leaving you to have 2 above and 2 below finished ground level. 

 

 

 

Does that help..??

[nod]

4 hours ago, Ed_MK said:

Below is essentially (forgive the artwork) what I have

 

So I am trying to figure out ...

 

a) If the exterior earthfill needs to be 150mm below a DPC ...which DPC

b) Can you tell where the bricklayer will lay the external DPC course ....and HOW is it possible
afterwards to connect this to an internal one ....or is it not necessary ?

 

 

The block and beam will sit on dpc 

But this is not your Dpc heaight 

If you lay one block (225)onto the beam floor then your dpc can go on top of that Which would give you 150 insulation 75 screed If you require more height or just want to add more insulation add a course of brick As I did

If you use a 600 mill highload damp course 100 mill will act as your dpc and 500 mill will be left hanging down onto the B.B. floor

and can be atached to your floor membrane with tape to form a perfect seal prior to laying your insulation It is more exspensive than standard dpc but more of a rubber type material and easy to attached at a later stage

 

Hope the pics help

[Ed_MK]

That looks a cracking job !

I must admit it does look a lot more solid with the block internal walls.

Our timber came yesterday and its flying up ...as you can see from pics below

these guys work like tornado's ...just a blur..makes me tired watching them LOL

 

Going back to DPC ...In the last picture you can see the top of the trench block (with groundworkers DPC)
and the other DPC that was laid under the frame....the "kicker bricks" the block laid directly under the frame was a CUT block
and is about  is around 150mm high

 

I guess i am just nervous about how high I can actually sit gullys currently...and as these will be at exterior ground level
i was trying to get my head around how high they could go and still remain 150mm below the RELEVANT dpc

 

 

 

 

Edited June 5, 2018 by Ed_MK

[Ed_MK]

 

I know I have asked this before ....but I am still not sure ..So please don't flame me

 

I know what the finished floor level (screeded) will be downstairs.

I can see where the DPC was put down for under the Block and Beam 

 

Because my house is sitting a little "lower" than intended ....due in part to me PRESUMING that there would be at least a metre of concrete under there
when in fact there is about 700cm

 

This leaves me 300cm shallower than i wanted to be able to make the longer runs to my manholes and so on to the one 40m away.

 

So where am I confused !! ..Well ...

 

I am thinking is it at all POSSIBLE to have the exterior DPC higher ...(well as high as i can doorframes permitting) ..or is this a bad idea?
This would have the effect of me being able to raise the exterior ground height and hence the gully height and give me more fall to play with

 

Of course this new Brick DPC layer could end up 200cm ABOVE the internal B&B DPC ...But does this matter ? ...they don't "connect"

 

What do you guys suggest?

 

I mean i MIGHT be alright for fall  ...but i hate the word "might" ...as it's usually followed by a "head in hands, elbows on knees, sat against a wall" scenario

Which I am sure we have all been in 

 

 

 

 

[Brickie]

Ok,-forget the Dpc under b&b. 

An argument could be made that it’s unnecessary,but let’s not muddy things further. It’s there as a belt & braces approach,but is NOT & never will be anything to do with what we all refer to as your DPC height. 

Unless there’s a very good reason otherwise,it will be at your FFL. 

End of. 

:))

Edited June 10, 2018 by Brickie
Smiley added

[Ed_MK]

Thanks Brickie.

 

So in my drawing below the brick DPC is too high ?

I need to fit it lower ....in line with screed top ? ...that is FFL ?

 

If that's the case then the earth around the building need to be reduced to stay 150mm below it ..

hence the gullys too  .....ah well

 

CC45 above mentioned "cavity trays " ...this is new to me, as no-one so far has used this term ....is it a necessity, or just desirable 

[Onoff]

I feel your pain! My retrofit included digging down and building back up the bathroom floor. The original dpc, shown blue on the inner brick leaf was nom level with the original ffl and there were some damp issues. 

 

 

I put a dpm about a meter up the wall then came down under the 100mm PIR. The solid grey underneath is 25mm EPS and the dpm is sandwiched between that and the pir. 

 

The corners what with all the folding were a pig as I had to stagger it over footings

 

 

I'd have loved to have had a blank canvas to design this out from the start!

 

Your design above, are there cold bridging issues at the base?

Edited June 11, 2018 by Onoff

[dpmiller]

@Ed_MK is your drawing accurate? I was led to believe TF started at FFL but your kicker is waay lower than that. And is the kicker a standard block or a thermal?

[Brickie]

If the height of the gullets etc is causing you an issue & you need to bring external ground level up to FFL or thereabouts,then you could have a Dpc wraparound detail (standard detail for level thresholds & wheelchair access,etc.)

So,your Dpc goes on level with  ffl as described & you then lay the first 3 courses on to a Dpc left flapping against the building. On top of the 3rd course this Dpc is folded back out onto the brickwork & the work goes up as normal. This gives you a barrier to any rainwater splash ups penetrating inside the building. 

Again,I’d explain your situation to the tf company & ask them to supply you with their standard detail. Level thresholds are commonplace now so by rights they should have one. 

Cavity trays used to be standard on tf,primarily to prevent a build up of mortar droppings around the frame sole plate. Years since I built one (hopefully years till I do again) and back then it was standard for the cavity to be left empty & ventilated. From what I’ve seen on here,that may not be the case now so,again,another one for the tf company to clarify for you. 

Dont feel like you’re being a nuisance to them-for their warranty to be worth anything they need to arm you with all the info necessary for you to build compliant with their system. 

Edited June 11, 2018 by Brickie

[Ed_MK]

On 11/06/2018 at 06:39, dpmiller said:

@Ed_MK is your drawing accurate? I was led to believe TF started at FFL but your kicker is waay lower than that. And is the kicker a standard block or a thermal?

 

 

hmm ...you may be right ..i will check it with a tape and get back to you ....sorry ...i was doing that one above from memory 

[Ed_MK]

On 11/06/2018 at 10:24, Brickie said:

If the height of the gullets etc is causing you an issue & you need to bring external ground level up to FFL or thereabouts,then you could have a Dpc wraparound detail (standard detail for level thresholds & wheelchair access,etc.)

So,your Dpc goes on level with  ffl as described & you then lay the first 3 courses on to a Dpc left flapping against the building. On top of the 3rd course this Dpc is folded back out onto the brickwork & the work goes up as normal. This gives you a barrier to any rainwater splash ups penetrating inside the building. 

Again,I’d explain your situation to the tf company & ask them to supply you with their standard detail. Level thresholds are commonplace now so by rights they should have one. 

Cavity trays used to be standard on tf,primarily to prevent a build up of mortar droppings around the frame sole plate. Years since I built one (hopefully years till I do again) and back then it was standard for the cavity to be left empty & ventilated. From what I’ve seen on here,that may not be the case now so,again,another one for the tf company to clarify for you. 

Dont feel like you’re being a nuisance to them-for their warranty to be worth anything they need to arm you with all the info necessary for you to build compliant with their system. 

 

I have been doing a bit of reading Brickie ... ..especially on cavity trays ....and i am thinking ....would it be a good idea to install cavity tray all around with the top of the tray tucked UNDER the silver breather of the TF?

and then in the same brick course as the trays i could put weeps in every so often

 

does that sound like a plan ? ...I still have to work out my finished ground level for gullies LOL

I guess i have another 2 MINI questions ...

 

a) does an all-round cavity tray effectively REPLACE the brick DPC ....or does this need to be there as well ?

b) would it be a good idea to make sure all courses under the DPC/tray were engineering brick ? 

 

forget the image i did above ...i have just had a peek out there

i only really have about 2 courses on top of the trench block before i am up to the DPC i think ...

 

jesus ..this is confusing !!!!

[Ed_MK]

Well i have took some photos and measurements, what do you guys reckon

 

1. this is the view from INSIDE out through a doorway. the kicker bricks were all CUT with a saw, as i saw them doing it.

they are about 160mm high ...including the bed now from the top of the B&B 

 

2. This is the view from OUTSIDE at the same bit. The B&B must be about 160mm high too as the distance from the Trench block to the top 

of the kicker is around 320mm (note the waste pipe at the bottom)

 

3. I have LOADS of kicker bricks coming loose (see pic) and today and tomorrow I have been re-bedding them and pushing them back
under the TF  ...its like the mortar has turned to dust ...its sooooo flaky. I am no expert ...but i would say they have dried too fast !

but what can we do now  (sigh)

 

[Brickie]

On 16/06/2018 at 19:47, Ed_MK said:

a) does an all-round cavity tray effectively REPLACE the brick DPC ....or does this need to be there as well ?

b) would it be a good idea to make sure all courses under the DPC/tray were engineering brick ? 

A/ it can do but it’s s bit fiddly to get it exactly bedded asyou would a 100mm strip of Dpc so for the sake of it I’d use 100mm too. We used to cut the membrane,slip the tray under & then staple the membrane back. PLEASE get some info from the TF company first before doing any of this though. 

B/ possibly,depends on how tough/frost rated your facing brick above is though. I’d make the muck a bit stronger,or use Sulphate resistant up to dpc. 

With your kickers coming loose,try dipping them in water before bedding them. This should kill the suction & stop them drying out too quick.