Foundation ideas

[deuce22]

Hi.

I have just had the strip foundations dug and have poured 750mm of concrete into them.

The issue I have is that the ground was sloping and so I now still have to come up roughly 1700mm to damp course level.

The earth level at the front is roughly 1500/1600mm and 400mm at the back.

The brickie was planning to lay a block flat length ways across the trench for one or two courses and then come up with two blocks and a cavity.

It will take around 2500 blocks just to get to damp and will also take a bit of time.

I would like to know if any of the experienced guy's have a more cost effective way of achieving this.

Cheers.

 

[noseall]

Crikey, thats some slope!

Why is the brickie bothering with blocks laid flat to start with? He may as well crack on with them vertically, unless he needs to make up a specific gap with say one course laid flat, in order to get back to gauge.

I presume you intend showing bricks below dpc (externally) as these will not be rendered?

 

[deuce22]

The ground was pretty soft, so we could not step it.

The concrete company turned up 3 hours late and so we started pouring as it was getting dark, we could hardly see in the trench.

Although we have come up to 750mm with the concrete, it isn't perfectly level, so he will have to lay at least one course flat, to get his levels.

Even if he does do one course flat and then vertical, it still comes to around 2500 blocks.

I just thought that there may be different options that can be done instead that will be more efficient. Would precast concrete panels work in this instance?

One other thing I wanted to clarify was.

I am using block and beam for the oversite. Do I still need to pour a weak mix into the cavity, and if so do I then need to back fill both sides for support.

Thanks.

 

[theoldun]

If we have got a grunter or camels hump any where in founds we cut it out first with two course of brickwork, either laid normal, on edge or splits, whatever the situation dictates. Your bricklayer will not get a 75mm grunt or hump out by laying blocks flat. He will have to cut them.
Regards precast concrete panels, they are definite No NO.
If you are building this unit for your self, then assume you are doing it on NHBC Solo, however do not know whether you are doing B.Regs with NHBC or local BC. Reason for saying this is that NHBC standards to comply with height difference of floor level above external ground still appears to be based on the old approved document Part A 1991 which are different to the latest Part A. As we have no idea what your proposals are for the low ground levels, we would suggest that you read Part A1/2 page 24 very carefully before you start brickwork to footings, as you may find that you have a few problems with regard to the regs.
Thanks very much to you and Hugh for the info on the conveyor trucks. Knew they had them in the States and Europe, but never seen one in this country. Two question. Did the conveyor turn up first and then the 6mc trucks shoot out on to conveyor. Name of company please.
oldun

 

[deuce22]

Hi oldun.

The company I used for the concrete is Minimix.

The conveyor truck turned up first and had 6m3 in his drum. I then had another 4 trucks of various sizes which totalled 26.5m3.

It was £79 per metre and £210 for the conveyer, all plus Vat.

There's no humps or bumps, but it's not perfectly level.

We pegged out the trench for an idea of the level, but as they turned up late you could hardly see in the trench.

I am using local BC and I was told that I don't need NHBC.

The setup I have is.

The architect who we have used for years is also our structural engineer. He has a friend who he works hand in hand with which is the BCO.

We have decided to use them both as they have very good contacts, both private and in the local council and there costs are very competitive.

I am just trying to find out all the different options I have to get me out of the trench and up to damp course.

Cheers.

 

[theoldun]

You are correct, you do not require NHBC Solo. But we would always advise people doing a self build to do so.
Nothing wrong in using private BC providing they are giving the service.
Do not know size of new unit, but feel you must have made a mistake on your block quantities. 2500 blocks on a three bed will give you block cavity block plus partitions for a 2.4 storey height from dpc to 1st floor joists and you will still have approx 50m2 left over. Would suggest you check your figures.
To get to dpc it is either brick or block with filled cavity.
Would also suggest once again that you check with your arch and BCO with regard to BRegs height of floor level in relation to either internal or external ground level You are only allowed 4 times the thickness of wall.
On housing we use block and beam 75% of the time. However as you are insulating above the floor and below the screed you require 300mm split levels dpc between the external and internal dpc. We have our own way of doing it and sealing the dpm at the same time but complicated to explain. Best of luck
oldun

 

[deuce22]

Hi oldun.

Due to the excavator driver removing so much earth I now have to come up around 1.5m high to damp course.

The lineal metre of the foundations is 57m.

It equates to around 1 block flat length ways across the trench (250 blocks), then 6 courses high (double skin = 12 blocks x 127 = 1774).

2500 block was at 1.7m high which is what I was calculating it at originally.

After this I then have to infill the cavity.

What I wanted to know is, am I able to lay a block flat width ways (225mm) across the trench all the way to damp or just below.

I am then laying precast beams, so if I lay the beams on a 100mm bearing it leaves 125mm.

I can then lay the outer skin on the 100mm that is left and lay the inner skin (which is going to be an insulated block) on the beam and block floor.

I realise that it will not be directly above the block below the beam, but would this still be allowed.

I am seeing the architect later, but would like to have an idea before I see him.

Thanks.

 

[theoldun]

With respect your descriptions are very vague and it is difficult to sit here and visualise the unit.
Assume the 57 lin metre of founds includes internal partitions and is not just perimeter. If just perimeter, it is a very big footprint.
Your footings must be the same width as super structure, so you can not go a block flat 215mm wide.
If you want to go solid up for 80% of the height then you can go 440x215x300 trench blocks and then change to 300 cavity wall below block and beam to get your cranked telescopic air vents in.
QUOTE. can then lay the outer skin on the 100mm that is left and lay the inner skin (which is going to be an insulated block) on the beam and block floor.
realise that it will not be directly above the block below the beam, but would this still be allowed.------ NO!!
Will stress again to you for third time. You must sort out with arch and BCO Building Reg A1 /2
oldun

 

[deuce22]

Thanks oldun.

Yes the 57m does include two internal foundations that were needed to support purlins for the roof.

The reason I asked about 225mm wall was because someone I know has done this on the last 3 builds and he has had the loads calculated by an engineer.

He said that as the inner skin is so close to the wall underneath (although it isn't directly above it) the block and beam floor can still support it.

Having said that I am planning on letting these properties out long term, so I want them to be constructed as best as possible.

I've only asked on here to find out as much as I can. I assumed that the reason it cannot be done is due to the internal wall only having the B and B floor for support and this is why (as you said) "Your footings must be the same width as super structure".

I can't see then how he has been allowed to do it.

I have been told that I need a 110mm cavity filled with 60mm insulation. I'm assuming that this extra 10mm won't make much of a difference considering the trench block is only 300mm, or can you buy trench blocks to suit.

I will speak with them tonight about Regs A1/2.

Cheers.

 

[deuce22]

Hi oldun.

I have just finished with the architect/engineer and I have sorted the footings with him.

The wall is a mixture of vertical and flat blocks, which will be 325 wide and I will not need to infill after.

He didn't like the look of what I was told by this guy and said that no decent engineer would allow that.

Thanks very much for your help.