Ground floor for bungalow: joists better than a slab?

[SteamyTea]

7 hours ago, Big Jimbo said:

Please enlighten me, I'm not being a pain, i just dont get it

I kind of get it, but this may help more.

https://www.researchgate.net/post/What_is_the_difference_between_piled_raft_and_pile_group2

[Dreadnaught]

8 hours ago, Big Jimbo said:

The OP said he was having screw piles. How does a passive slab like Harris and Stark have work with screw piles, or any sort of piles in that instance.

 

Yes, @Big Jimbo. Here's how it works:

1. The screw piles are inserted and capped. (Which interestingly does not count as excavation for Party Wall purposes.)
2. Then the EPS is built up as follows:
   1. The lowest level is CellCore HXS, which is a sacrificial honeycomb heave-protection layer (not primarily for insulation). This is in place of a void. 
   2. Then on top of the CellCore goes EPS for insulation forming the usual polystyrene tray with edges in the usual way for a raft.
3. Then rebar and mesh is arranged inside the tray for structural support. (And UFH pipes are attached to the mesh).
4. And then, crucially, the rebar is welded to the top of the screw piles.
5. Then finally concrete is poured in to the correct depth and levelled to form the raft.

Thus the weight of the structure built atop the raft is transmitted through the piles, and not on to the ground surface. Makes sense?

 

The various foundation companies have standard details for this. And interestingly one of the timber-frame companies I contacted was keen to do my build because they hadn't had a chance to use this approach so far, and it was attractive to them because they thought it should have wider applicability than it currently has for sites with difficult soil make-ups.

Edited November 19, 2019 by Dreadnaught

[Patrick]

@Big Jimbo

It s done like this

 

[Big Jimbo]

That's why this site is great. Thanks folks. I get it now. I think screw piles are great, no muck, etc. Its just a shame that they are no cheaper. I think given time, when they become more common the price will drop. In my case, i have good ground, but large, and lots of trees. I am being quoted £1k to bring the kit to site, and £1k a pile going down 7mt. The Piles are not that expensive, and screwing them into the ground can be done with a 3 ton digger and an attachment. Anybody fancy starting a screw pile company with me ?

[Bitpipe]

Typical modest US footprint My sister lives in Austin, not a cheap place (they've been there 25 years). A downtown lakeside house would be mega $$.

 

 

[joth]

2 hours ago, Dreadnaught said:

• Then rebar and mesh is arranged inside the tray for structural support. (And UFH pipes are attached to the mesh).
• And then, crucially, the rebar is welded to the top of the screw piles.

(Presumably the rebar is better welded prior to laying UFH pipes?)

 

To check I understood this, it means it leaves a thermal bridge directly from the UFH pipes/slab through the screw piles and down to earth? 

[Nickfromwales]

10 hours ago, Big Jimbo said:

I have only just picked up on this thread, so apols if i am being a plank. The OP said he was having screw piles. How does a passive slab like Harris and Stark have work with screw piles, or any sort of piles in that instance. I thought that the whole idea of piles was that the load being put on top, had to be spread. Ie: The piles are joined by being linked using a number of methods, for instance, concrete ring beam, steels etc ......How does a passive slab, eps, bit of metal and 4" on concrete link to the piles ??? I thought that with piles, you had to have some form of suspended floor, such as timber, block and beam, metal I beams etc. The whole idea is that the structure, walls, roof, floor, all have to bear on the piles.  Please enlighten me, I'm not being a pain, i just dont get it.......

Read the blogs and you’ll have a much greater understanding   

Jeremys blog for one is very detailed and makes an excellent read.

[Patrick]

1 hour ago, Big Jimbo said:

That's why this site is great. Thanks folks. I get it now. I think screw piles are great, no muck, etc. Its just a shame that they are no cheaper. I think given time, when they become more common the price will drop. In my case, i have good ground, but large, and lots of trees. I am being quoted £1k to bring the kit to site, and £1k a pile going down 7mt. The Piles are not that expensive, and screwing them into the ground can be done with a 3 ton digger and an attachment. Anybody fancy starting a screw pile company with me ?

I looked very long into screw piles. I think the same then you. They might be a decent idea if they where cheaper, but atm in UK they are just silly expensive and your much better off doing driven. Also H&S, plus mortgage/insurance/BC rules mean you need specialist contractor to help drive screw piles in (unlike US, where you can get away with installing them yourself with a 3t digger and a drill attachment). Had a look at ordering the screws themselves and they are fairly reasonable in price. Not much different then driven piles, material wise. But rules and regulations stopped me and when you look for screw pile contractors, you talking BIIIIG £££££.

I also think that driven piles are a bit more solid than screwed, as concrete is much more difficult to fail then metal. I would always trust a RC pile to last 100years over a metal pile.

[Dreadnaught]

2 hours ago, joth said:

Presumably the rebar is better welded prior to laying UFH pipes

 

Yes, in the example I watched welding was indeed prior to UFH-pipe laying.

2 hours ago, joth said:

To check I understood this, it means it leaves a thermal bridge directly from the UFH pipes/slab through the screw piles and down to earth? 

 

Yes. Its modelled thermally so the heat loss is quantified and the piles can be sheathed for their first section if needed.  

 

[Dreadnaught]

1 hour ago, Patrick said:

BIIIIG £££££

 

Oh I suppose it depends on what you consider expensive.

 

The budget estimate provided by the company I will probably use (which I admit is a little old now and needs refreshing) is £12,500 for the design, supply, delivery, plant, installation, and capping detail. This is for a modern bungalow of 125 m². I don't know how many screw piles will be used but I guess it will be between 15 and 25.
 

Edited November 19, 2019 by Dreadnaught

[Patrick]

4 minutes ago, Dreadnaught said:

 

Oh I suppose it depends on what you consider expensive.

 

The budget estimate provided by the company I will probably use (which I admit is a little old now and needs refreshing) is £12,500 for the design, supply, delivery, plant, installation, and capping detail. This is for a modern bungalow of 125 m². I don't know how many screw piles will be used but I guess it will be between 15 and 25.
 

yes, true, but i almost guarantee that a driven pile will be anywhere between 30-50% cheaper. thats what i meant .

[Dreadnaught]

Just now, Patrick said:

yes, true, but i almost guarantee that a driven pile will be anywhere between 30-50% cheaper. thats what i meant .

 

Yes, makes sense. I have protected tree roots under part of my foundations and neighbours close by too so that weighs the decision in favour of screw piles.

 

Indeed, in my case, screw piles were specifically mentioned in our planning application to persuade the tree officer to come on side. And for neighbours, screw piles are quieter and you can side step a Party-Wall agreement too, which is nice.

[Patrick]

7 minutes ago, Dreadnaught said:

 

Yes, makes sense. I have protected tree roots under part of my foundations and neighbours close by too so that weighs the decision in favour of screw piles.

 

Indeed, in my case, screw piles were specifically mentioned in our planning application to persuade the tree officer to come on side. And for neighbours, screw piles are quieter and you can side step a Party-Wall agreement too, which is nice.

Oh yes, there is definetley a case for screwpiles there . Even I have to admit that the cheapest option is NOT ALWAYS the best (it really took something for me to actually write this , you wont here this too often from me_) ?

 

[Adrian Walker]

8 minutes ago, Patrick said:

yes, true, but i almost guarantee that a driven pile will be anywhere between 30-50% cheaper. thats what i meant .

 

Piles are normally used to go down, often a long way, to a solid bedrock.  Screw piles do not go the the bedrock but are held in place by the large surface area acting on the underground material.  As piles are installed the torque is measured to determine the depth that is required.

[Big Jimbo]

1 hour ago, Adrian Walker said:

 

Piles are normally used to go down, often a long way, to a solid bedrock.  Screw piles do not go the the bedrock but are held in place by the large surface area acting on the underground material.  As piles are installed the torque is measured to determine the depth that is required.

Which is exactly why Screw piles should be used more often. Ie; good ground but lots of trees. My point is that down south,( where we always seem to have to pay through the nose) A screw pile at £1k each ! I was told that they cost less than £300 each to buy from the supplier. A contractor told me he could do all 20 of mine in one day. £14k gross profit !!!!!! for a day

[Jeremy Harris]

I went to see a demo of screw piles being put in, as the first plot we looked at needed them to avoid damage to underlying archaeology (strictly speaking, it was a cost mitigation measure).  Very impressive to watch piles being driven in with nothing more than a big hydraulic "screwdriver" fitted to the jib of a digger, in place of the bucket.  It took more time getting the pile set up dead square initially, and in the right spot, than it did to drive it to depth.  IIRC, the initial price we were quoted was way less than £1000 per pile, too, but this was back in 2012.

[Adrian Walker]

8 minutes ago, Big Jimbo said:

Which is exactly why Screw piles should be used more often. Ie; good ground but lots of trees. My point is that down south,( where we always seem to have to pay through the nose) A screw pile at £1k each ! I was told that they cost less than £300 each to buy from the supplier. A contractor told me he could do all 20 of mine in one day. £14k gross profit !!!!!! for a day

 

FYI Attached is the price list from ABC Anchors 

143-SCREW PILE PRICELIST Apr2017 (2).pdf

[Dreadnaught]

To support the point made earlier about other types of pile being cheaper than screw piles, I just had a look through my piling quotes and one company kindly gave prices for multiple systems for the same job, as follows (2018 prices; rough estimates only; only the piles themselves, not installation or other services):

1. Screw piles: £8,400, requiring 30 piles to 4m.
2. Steel cased driven piles: £4,600, requiring 20 piles to 6m. But vibration and noise.
3. Hollow-stem bored grout injection system: £9,000+ and require 20 piles. 

As you can see, screw piles needed more piles as the shaft in comparatively quite slender so can take less of a load.

 

It is also worthy of note that a ground beam, if needed, can cost more than the piles.

[Nickfromwales]

I’ll just say “cold ventilated subfloor under a heated slab?” 
Not in a gazillion years. ?

The direction is forward squire, not reverse !  

[redtop]

we have driven piles, and then steel posts and then steel substructure tying it alll together.  Ground floor will be between .5M and 2.5M above surrounding ground due to slope.  So no choice really over than suspended timber floor.  I agree the exposure to the cold winter air is not great. We will insulate between the 253mm posi joists and then again below them, ventilation gap and then concrete board

[redtop]

6 hours ago, Dreadnaught said:

To support the point made earlier about other types of pile being cheaper than screw piles, I just had a look through my piling quotes and one company kindly gave prices for multiple systems for the same job, as follows (2018 prices; rough estimates only; only the piles themselves, not installation or other services):

1. Screw piles: £8,400, requiring 30 piles to 4m.
2. Steel cased driven piles: £4,600, requiring 20 piles to 6m. But vibration and noise.
3. Hollow-stem bored grout injection system: £9,000+ and require 20 piles. 

As you can see, screw piles needed more piles as the shaft in comparatively quite slender so can take less of a load.

 

It is also worthy of note that a ground beam, if needed, can cost more than the piles.

mine have cost >£20K for 41 220mm driven piles, 3 to 4.5 M steel casing and then 1.5M rock socket, then filled with re-bar and grout