Foundations/rising wall help

[Vijay]

Got a slight snag with the foundation depth after clearing all the topsoil from the plot. My rising walls will be Polarwall ICF for the external walls and foundation blocks for the internal and sleeper walls. My external walls will also be in Polarwall ICF. I've done some quick drawings to show my issue.

 

The structural engineer says the important thing that he is concerned about is the distance from the bottom of the mass concrete footing to finished ground level has to be 1200/1500 (depending on where abouts it is).

 

I've wondered why I need so much rising wall out of my footings before I sit the beam and block floor. On the architects drawing, it shows 450mm which is 1.5 x Polarwall panels. This gives me 900 from FFL to top of concrete or 1350/1650 from FGL to bottom of concrete.

 

 

 

 

For ease of installion, the floor beams really need to sit on top of a Polarwall Panel so I looked at doing this. The B&B now sits on top of 2 x Polarwall panels and give me 1050 from FFL to top of concrete or 1500/1800 from FGL to bottom of concrete.

 

 

 

 

 

 

Now, this is what I think makes sense as it saves digging out, mucking away and loses a course of Polarwall ICF and now gives me 750 from FFL to top of concrete or 1200/1500 from FGL to bottom of concrete which is exactly what the SE specified.

 

So can anyone think of any reason why this wouldn't work? Someone suggested frost but the rising wall is still 600 from FGL. I should also mention that I've assumed that FGL is exactly that, the FINISHED ground level once landscaping and everything else is done, as it will obviously be lower that the moment with topsoil removed.

 

Cheers for any help and sorry for the long post

 

Vijay

Edited February 23, 2017 by Vijay

[RichS]

Surely if what you are achieving with your last sketch is what the SE is asking for there is no problem. As long as the ground at that depth is solid enough to take it then why bother digging out another 300mm?

[Mr Punter]

Why are you using the Polarwall below ground?  Why not just us concrete blocks?  I assume the void is vented, so you won't gain from insulation.

[Vijay]

1 hour ago, RichS said:

Surely if what you are achieving with your last sketch is what the SE is asking for there is no problem. As long as the ground at that depth is solid enough to take it then why bother digging out another 300mm?

 

That's exactly what I thought but wondered if there would be a reason it was done like that.

SE has replied saying as long as the measurements from FGL to bottom of concrete footing is 1200/1500 it is fine

[jamiehamy]

1 hour ago, Mr Punter said:

Why are you using the Polarwall below ground?  Why not just us concrete blocks?  I assume the void is vented, so you won't gain from insulation.

 

I suspect to provide a cold bridge free join between the founds, external wall and floor

[Vijay]

1 hour ago, Mr Punter said:

Why are you using the Polarwall below ground?  Why not just us concrete blocks?  I assume the void is vented, so you won't gain from insulation.

 

Just a personal choice really and also to keep the materials the same, as it makes sense to carry on with concrete  from the footings upwards rather than have concrete footings, then block and then concrete in the ICF,

 

Yes it's vented with telescopic vents and I would rather have some insulation rather than none

[Mr Punter]

1 hour ago, jamiehamy said:

 

I suspect to provide a cold bridge free join between the founds, external wall and floor

No it won't.  Polarwall is just concrete between 2 sheets of 50mm XPS, so the concrete will connect the foundation and the floor / wall.  Also, the vented void means outside air to the underside of the floor.

 

Using it for a single course, getting it perfectly level and filling with concrete will be a real PITA and pretty expensive.

 

[jamiehamy]

16 minutes ago, Mr Punter said:

No it won't.  Polarwall is just concrete between 2 sheets of 50mm XPS, so the concrete will connect the foundation and the floor / wall.  Also, the vented void means outside air to the underside of the floor.

 

Using it for a single course, getting it perfectly level and filling with concrete will be a real PITA and pretty expensive.

 

Okay - you're partially right.  Using ICF  for the below ground won't eliminate cold bridging,  but it will reduce it significantly or eliminate depending on how you view it. 

 

- I've done a rough sketch to show. @Vijay. This is not based on yours per se just an aside to show what is possible although I think yours will be like this from looking at it? 

 

 

[Jeremy Harris]

11 minutes ago, jamiehamy said:

Using ICF  for the below ground won't eliminate cold bridging,  but it will reduce it significantly or eliminate depending on how you view it. 

 

 

You're spot on, Jamie, if you continue wing insulation down to a couple of feet below ground level, even with a vertical thermal bridge up through the the core, the net effect is to significantly reduce the overall thermal bridge at this point.

 

There was some work done on using below ground peripheral insulation to reduce thermal bridging in refurbs, where taking the floor up to add under floor insulation was impractical, and it is a pretty good mitigation measure.  By significantly reducing outward, horizontal, heat transfer, the heat loss path is forced to be vertical, and even though soil isn't that good an insulator, with a deep layer of buried peripheral insulation you can create a deep enough layer of soil under the floor to be a reasonably effective insulator.

Edited February 23, 2017 by JSHarris

[Vijay]

43 minutes ago, jamiehamy said:

Okay - you're partially right.  Using ICF  for the below ground won't eliminate cold bridging,  but it will reduce it significantly or eliminate depending on how you view it. 

 

- I've done a rough sketch to show. @Vijay. This is not based on yours per se just an aside to show what is possible although I think yours will be like this from looking at it? 

 

 

 

 

That's pretty spot on to what I'll be doing, except the Polarwall inner panel will come down to and in between the floor beams - so they kind of encapsulate the beam. It's more work cutting them to fit but Alan has said if I get him the exact measurements' he'll cut the fillets to fit for me  

[PeterW]

1 hour ago, Vijay said:

That's pretty spot on to what I'll be doing, except the Polarwall inner panel will come down to and in between the floor beams - so they kind of encapsulate the beam. It's more work cutting them to fit but Alan has said if I get him the exact measurements' he'll cut the fillets to fit for me

 

Check with SE and beam supplier on that - the strength in a BB floor comes from the blocks and the beams and you're not supposed to leave voids unless absolutely necessary (soil stack etc) or as agreed with the supplier. 

[Vijay]

I'll have to advise the floor beam supplier anyway or they'll try and sell me their slips anyway for those gaps

[jamiehamy]

14 minutes ago, PeterW said:

 

Check with SE and beam supplier on that - the strength in a BB floor comes from the blocks and the beams and you're not supposed to leave voids unless absolutely necessary (soil stack etc) or as agreed with the supplier. 

Not strictly true I'm afraid - Tetris flooring has no blocks at all - and is basically just XPS wedged in the middle as @Vijay is doing. 

 

I'd still go with Tetris @Vijay    but I think you've finalised this anyway? How many blocks will you have to fit in between the beams?! It's going to be in the thousands I'm guessing?

[PeterW]

2 minutes ago, jamiehamy said:

Not strictly true I'm afraid - Tetris flooring has no blocks at all - and is basically just XPS wedged in the middle as @Vijay is doing. 

 

My understanding is that Tetris has to be complete too - it gains strength from the whole structure so the XPS works as the blocks. 

 

As I said - just worth checking with a manufacturer before modifying a significant structural element ..! 

[Vijay]

7 minutes ago, jamiehamy said:

Not strictly true I'm afraid - Tetris flooring has no blocks at all - and is basically just XPS wedged in the middle as @Vijay is doing. 

 

I'd still go with Tetris @Vijay    but I think you've finalised this anyway? How many blocks will you have to fit in between the beams?! It's going to be in the thousands I'm guessing?

Pretty finalised as I need to make decisions and stick to them otherwise I'll keep changing forever and never actually get it done! lol

 

I think there'll be a fair few blocks  but I don't mind fitting them all myself (and a couple of mates if they can help) - It's a good workout!

[jamiehamy]

2 minutes ago, Vijay said:

Pretty finalised as I need to make decisions and stick to them otherwise I'll keep changing forever and never actually get it done! lol

 

I think there'll be a fair few blocks  but I don't mind fitting them all myself (and a couple of mates if they can help) - It's a good workout!

I know. ? As you were :-) 

[Mr Punter]

18 hours ago, JSHarris said:

There was some work done on using below ground peripheral insulation to reduce thermal bridging in refurbs, where taking the floor up to add under floor insulation was impractical, and it is a pretty good mitigation measure.  By significantly reducing outward, horizontal, heat transfer, the heat loss path is forced to be vertical, and even though soil isn't that good an insulator, with a deep layer of buried peripheral insulation you can create a deep enough layer of soil under the floor to be a reasonably effective insulator.

 

Trouble is there is a ventilated void underneath the beam and block.

[Jeremy Harris]

8 minutes ago, Mr Punter said:

 

Trouble is there is a ventilated void underneath the beam and block.

 

Yes, it's not applicable to this specific case, I was referring specifically to cases where there wasn't a suspended floor, hence the reference to refurbs.

 

There's a more general question here, though, why do we still consider having a suspended ground floor with a cold void underneath?  It needs a great deal more insulation than a ground floor that doesn't have a void underneath, to achieve the same thermal performance, and, given that insulation can be load bearing and rest on the ground I wonder just how cost-effective a suspended floor is in the long term, say through the life of the building.

[TerryE]

4 hours ago, JSHarris said:

Why do we still consider having a suspended ground floor with a cold void underneath?

 

So the timber floor board don't rot!   Hang on a  sec.  What timber floor boards? 

[Vijay]

Decided to call the building control company and the inspector is popping around Monday to confirm he's happy with the depth of the footings so far. My digger mate doesn't really want to go over the same part again and again as the front of the house has a few recesses where the ground is bound to collapse if the digger goes over it too many times.

[Russell griffiths]

Get some ply sheeting in to hold the corners. 

If you lose a corner it will take ages to clean it out and more cost in concrete. 

[Vijay]

Already lost a few corners so will definitely have to board up some corners to save concrete

[PeterW]

2 hours ago, Vijay said:

Already lost a few corners so will definitely have to board up some corners to save concrete

 

Just double check before you do just how much you will lose - I've done the same today and looked at a couple of corners but I worked out that I would only save £40 worth of concrete with £55 worth of OSB and that's at zero labour cost ...

[Vijay]

12 hours ago, PeterW said:

 

Just double check before you do just how much you will lose - I've done the same today and looked at a couple of corners but I worked out that I would only save £40 worth of concrete with £55 worth of OSB and that's at zero labour cost ...

 

I did wonder that but it was also for neatness too.

 

Any ideas the cheapest material I could use for shoring the corners? I wondered if I could just use very thin 3 or 5mm ply/hardboard and just back fill with earth to take out the majority of the collapsed corner

[PeterW]

If you use 6mm then it won't come out when you're done - what sort of damage is there ..? Back filling can be a challenge as there is nothing for the shuttering to brace against.