Raft foundations are necessary when ground conditions are poor (such as made-up ground or old coal mine areas) or when the water table is high, as they distribute building loads across a wide area rather than concentrating them at specific points like strip footings; while more expensive due to additional mesh reinforcement and concrete volume, they prevent structural movement and cracking in brickwork, making them more cost-effective than deep excavation when solid ground is several meters below the surface.
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Deep Dive
OVER ENGINEERED FOUNDATONS - 30+ Tons of CONCRETE #constructionAdded:
Hello, welcome back to the channel. Now, today we are starting a brand new extension. You can see behind me.
>> Yesterday we started taking down the conservatory that is now gone and we filled the skip. And today is a fun demolition day with me and the boys dropping this small extension. We've already capped off all the gas and water and electric.
I can't breathe.
>> We need to get rid of the old boiler, strip the roof structure off, and then that is pretty much going to be today sorted. This extension, we're going to be having a really cool goalpost steel system. So, if you come in this pillar here and the pillar on the other side of the property, that's going to be removed. We're having a steel go all the way down to the footings, coming all the way up to joist level, and then we're having a massive 8 m steel go across the entire back of the house, landing on the old goal post system. But that's not for a little while. So, what we need to do is start dropping this.
So, we're going to get stuck in and get absolutely ventilated.
Very chaotic in there.
Not as chaotic as I was here.
>> This is surprisingly easy. My fun hammer. Say again.
>> Yeah.
just excess use. I imagine there's nothing to it for taking down the hat.
>> Yeah. Green boy.
Really funny.
I tell you what, right. Well, I think we might put some of these to a side cuz we're going to be using the same thing.
So, we may as well use them like down the gable end.
Oh.
>> Oh, great word.
It's all right, Jack.
>> You You deserve a break. It's a big paw.
>> M.
Now, a lot's changed on this job since we were last here. As you can see, we have now dug the raft foundation, which is going to be poured at a later date.
And today we're going to be pouring this foundation up against the house. So we've got about four and a half cube of concrete coming. We're going to get everything set up ready for the big pour. And then in a couple of days time we're going to be putting our DP MADAN mesh and then pouring the raft foundation. I will come back to you in a little bit when I know why we're having two concrete balls.
Very nice.
All right.
Heat.
Heat.
Heat.
Hi, we are back on the extension over in Sheffield. Last time we were here, which was last Friday, we poured three and a half, four cube of concrete in this footing here. And then today we have a another wagon of concrete coming a cube to pour a big raft foundation. So, the structural engineer suggested pouring a concrete foundation up against the house so that when we put our eight cube concrete raft in that is below the raft balancing out all the ground. Um, so there's not loads of weight pushing up against the house from the raft. Don't really understand his thinking.
Surely the concrete's pushing up against the house as well, which makes no sense.
We're all a bit >> We're all a bit perplexed.
>> Yeah.
>> Um so yeah, that's the reason we've got two concrete balls. Now, like I said, we have HQ coming today. We've got a pump.
We've got a load of mesh to put in the footing. So you American viewers will like that. Follow me. So this is all the mesh that's going to be going in the footing. The reason we are using a raft foundation rather than strip footings is because all of this ground has been made up and the original house foundations are way over 2 m deep because the ground is so poor around here. So using a raft with meshing distributes all of the weight from the new block work and brick work and it's not going to put a direct load on the ground below. So that's the reasoning. So we've got to do some prep.
We've got BPM. We've got all the mesh to go down that to sort out. So, yes, we'll catch up in a little bit. There we go.
Right. So, we've just got all of the grand whacker just to compact everything. Next stage of putting in this raft foundation is a DPM membrane.
So, this is our DPM or damp proof membrane. It's just to stop water coming up. Basically, we're creating a fully tank system. Bit like a paddling pool.
You can see here on the original house property, they also have a raft. Exactly what we're going to do. But you can also see how they have a DPM. So that's all we're doing right now. Get this rolled out and start on the mesh.
Nice.
So these are the castles that are going to be sitting in between the mesh here.
And that allows it to sit off the ground so the concrete can flow under it and on top of it. So, we're going to get all that sorted.
>> I don't know why you're patting yourself on the back so much.
I saw that comment.
>> People just love to do some extreme work. He >> is going to hate.
>> Right. Let's go.
>> Nice.
>> Fantastic. Lower your side down for me.
>> I have that. Yeah.
>> Down.
>> Yeah. You want me to go that side?
>> Yeah.
It's tremendous.
Tremendous.
And it would be to slide it under that pipe.
Damn. So, uh, all the mesh is down.
Plenty of overlap. We're just waiting on some wire to tie everything together.
The next step for us here is to put these things on. Don't know what they're called. Uh, they're going to go on just like that. We're going to tie them with the wire to the current mesh. And then on top of that is going to go the next layer of mesh. We've got two layers of this mesh. Um, and we've got about a 350 mil concrete pour going in and around them and on top. So hopefully this slab never moves. Um, yes. Yes. So most of the time when we do extensions here in England, 90% of the time you'll see us do a strip footing. Most of the houses around England also on strip footings.
all the strip foot in this dig a one meter trench 600 mil wide mass fill it with concrete and then you build your block work brick work on top of that and it goes all the way up. Now there's some pros and cons to that. Couple of pros really quick, really easy, a lot more cost effective than upper methods. On the other hand, we have raft foundations which is what this house and all the houses on this estate are built on and also what our new extension is going to be built on. Again, there's a couple pros, couple cons. We'll start with the cons first. It costs a lot more because there's a lot more prep work. There's mesh that goes in. There's a lot more concrete that goes in compared to a normal strip footing. Um, what else? You also have to have a structural engineer do the full design for you. So, there's an extra cost as well. But the positives, it spreads the load a lot more. So, you can use a raft foundation where you've got perhaps coal on your ground. So, if there's been a coal mine, the ground's pretty poor, we'll often use a raft foundation. And again, uh what else? It also helps if the water table's really high. And it also stops cracking and movement in brick work and your extension, which is a real good thing. But most of the time, it's a lot more expensive and it's quite rare we use it. In this case, today we are using it because the ground has been made up by couple of meters. So, the ground here is really, really poor. So, it's more cost effective in this case to actually use a raft foundation than strip foots.
Otherwise, we'll be digging down about 3 meters to hit solid ground and that just doesn't make sense.
>> Easy.
>> Okay, cool.
title for now.
>> I love that. Um, last time we was here, we were about to pour this concrete.
However, the building inspector came to inspect all the work we did and we had a little bit of push back. He wanted to see the structural engineers designed that our architect had provided even though our structural engineer was chartered. Um there was just a lot of push back from him. So he wanted to fully examine all of the floor prep we did and our drawings to make sure that we were still adhering to everything that the building control wanted ticked off. Basically a load of nonsense and politics. However, the concrete did get poured. Unfortunately, we weren't here for it. So, we had to cancel the pump.
We had to cancel the concrete on the day. So, it was all a bit hectic. Either way, the concrete base is in. 8 and 1/2 cube of concrete in. Yes. So, next time we'll be here, we'll be setting this out. So, thank you very much for watching. Apologies for not showing at that stage. Don't.
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