# Forum Home Renovation Sub Flooring  Excavating under the house.  Please Share your experience,suggestions..

## Yande

We bought the house, (South Coast NSW) and then wanted to move our business to home.  The Garage was cramped, and there was some storage space via a full sized door, to under the house.  So....., I started digging into this horrible shale material. 
Fortunately my best mate is a (retired) brickie, and I have a great neighbor, (practicing) carpenter, and then I discovered renovateforum!  BeeUTee!!  
So initially, I wanted to take one (1) pier out, and was instructed on how to do that, then I thought, well, we are only going to get one chance at this, so why not take two (2) piers out.
Now looking at a space of 3.6m x 6m.
Figuring as it is only going to be used for some storage, and a work bench, am thinking 75mm (3") thickness 20 MPA concrete, and what do you guys (and girls) think?  Worth putting reo in or not?   
I would be, what you call, a jack of all trades, master of none.  Am comfortable swinging a mattock, or installing a mother board.  I'm the CEO and the toilet cleaner. 
So in the meantime of me submitting more photos, any ideas, links, leads, suggestions regarding, laying plastic, reo, drainage, (ag pipe?) would be appreciated.  It's pretty dry down there.  Can feel the moisture during a wet period, with just a tiny evidence of water on the ground during our wettest period. 
Photo below shows my initial plan, after I had moved everything, stacked up left over brinks etc, to only think, why stop at one pier, two would be make more sense, hence those bricks, and a lot of other (valuable) junk will have to be moved, again!!  :Cry:    
Thanks for reading, any tips would be greatly appreciated.

----------


## paddyjoy

Have a look in the go to whoa section if you haven't already, there are a few excavation projects in there that will help you out. 
I wouldn't skimp on the REO and waterproofing, it might be dry now but if you get a big spell of rain who knows. Our place has a partial excavation with a diy slab, it's a disaster, slab has cracked and during extended periods of rain water makes its way in through the concrete. You don't want to go there.

----------


## SirMe

Hi, 
Im cureently looking at this as well. 
Some great tips on this forum and look at these threads....  http://www.renovateforum.com/f176/un...vation-109833/  http://www.renovateforum.com/f176/man-cave-construction-sub-floor-excavation-112896/ 
EDIT: You might need an engineer and think about when you sell the place if new owners will ask for permits etc.... 
Good Luck and keep us posted.

----------


## Yande

So just an update..  Have kept on digging, and decided to take another pier out whilst doing the job.  Thought being, if you are going to do it, might as well make the most of it.  Will get some more pics together soon whilst I wait for the 2 (190mm x 75mm x 3.9m) hardwood beams to arrive.  A lead time of 2 weeks as they have to be sawn.  My builder believes that shrinkage will not be a problem, as they will be bolted to the original beams that will remain in position.  Priced steel, Merbau, Kiln dried, though at $100 each, these work out not only cheaper, but structurally sound as well.. 
Pics to come 
Paddyboy... Your advice has been taken on.  Thanks
SirMe..  Thanks

----------


## SirMe

> So just an update..  Have kept on digging, and decided to take another pier out whilst doing the job.  Thought being, if you are going to do it, might as well make the most of it.  Will get some more pics together soon whilst I wait for the 2 (190mm x 75mm x 3.9m) hardwood beams to arrive.  A lead time of 2 weeks as they have to be sawn.  My builder believes that shrinkage will not be a problem, as they will be bolted to the original beams that will remain in position.  Priced steel, Merbau, Kiln dried, though at $100 each, these work out not only cheaper, but structurally sound as well.. 
> Pics to come 
> Paddyboy... Your advice has been taken on.  Thanks
> SirMe..  Thanks

  
Looking forward to the pics.... 
Good luck with your project.

----------


## Yande

Some pics I have taken this evening.. Still awaiting my beams, (bearers) to arrive. 
This one shows the excavation, with a mattock and shovel..  Fortunately, did not hit any major rock, until the last little bit in the corner.  Mostly light shale. 1.2m in depth..  
Total floor space will be 6m x 3.6m.   
Next pic shows the two piers I will be taking out, and on the right, (mid) some of the fill I have deposited there.  Plan is, when we lay the slab, boxing out a small retaining wall, perhaps .6m high, along the back of the slab, and along the left side of the slab. From there up, either using brick or timber to enclose the area, leaving access via a door.  So far, I have increased the depth of the footing along this wall be an inch.  will be using reo, and bars into the retaining wall.   
When my beams arrive, they will be bolted to the existing bearers, resting on the pier behind, and the wall in front.  Wall in front (through a doorway) lies my garage.   It's a strange build, and one we haven't definitely worked out why.     
This is the wall that my new bearers will rest on.  As you can see, the remains of some bearers I am removing. We figure they once went across to the outer wall of the house.  Now, (as they have been cut off, the garage has double ceiling height.  The lounge is directly above where I am standing, so we could quite easily, put another ceiling on the garage, and extend the lounge out over it.  It is a strange thing..   
This shows it best..   
So if anyone has any tips, ideas.  I'm all ears.  Fortunately my very friendly and obliging neighbor is a builder, so he has been providing technical advice.

----------


## phild01

The first photo with the 1.2m measure, looks as though the pier is at the edge of the excavation.  How will you be shoring this up?  Essentially I suggest a retaining wall that can withstand the lateral load of the pier.

----------


## Yande

Yes, I think the same.  Sort of made mention of this when I sated that I was going to incorporate into the slab a retaining wall, tied in, and yes, perhaps (now that you have pointed it out) the .6 m wall may need to be a little stronger/higher here.  i just pulled the .6 m measurement out of the air, and this section I have no specific plans for yet.   But initially, I was just going to lay a slab, and then, brick.  My dad suggested that I needed a concrete retainer (tied into the slab) to secure such eventualities.  This is why I am posting here.  Thanks again for your suggestions.  Advice even. 
(On the other hand, looking at the photo, it looks critical, though in reality, the thought of it caving away, really never crossed my mind.)  But, I do get what you are saying.

----------


## phild01

Yes, don't underestimate this.  I have seen subsidence occur in less dramatic excavations with piers on edge.
Can I also suggest that the slab should be tanked in combination with an integrated retaining wall, also appropriate drainage.
You will end up with a useful and worthwhile space.  For it to be somewhat habitable you gotta do the planning well to avoid damp and flooding issues, or walls breaking under the strain..

----------


## Yande

Thanks phild01 for your input.  It is like buying tools, "buy right, but once!" Or something like that.  Though perhaps in this situation, it is a lot easier to pop down and replace a dud tool!  
Build right, rest and forget!!  
Beams are arriving tomorrow, should have them in in a day or two, and then will concentrate on getting the details of the slab finalised. 
Shoring up the pier edges.  Tanking, in one form or another, and drainage...  A little bit of levelling, and then some sand, plastic.... 
Getting the water out, if it ever comes in...  Needs a plan... 
Will get back as everything evolves... 
Thanks 
Mark

----------


## SirMe

Nice work so far.......   :Smilie:  :2thumbsup:

----------


## SirMe

> Yes, don't underestimate this.  I have seen subsidence occur in less dramatic excavations with piers on edge.
> Can I also suggest that the slab should be tanked in combination with an integrated retaining wall, also appropriate drainage.
> You will end up with a useful and worthwhile space.  For it to be somewhat habitable you gotta do the planning well to avoid damp and flooding issues, or walls breaking under the strain..

  Phil are you saying tank the base of teh slab before pouring and after its has been poured?

----------


## phild01

> Phil are you saying tank the base of teh slab before pouring and after its has been poured?

  When I did similar, I had continuous moisture barrier under the slab that continued up the walled areas.  But this is just a barrier and if it is totally sealed then it is effectively tanked.  But I had moisture flow and necessitated a proper drainage system behind this.  So ag lines, that can be washed out, were created under the slab and geo type matting behind the walls like this:NuDrainâ¢ Sheet Drains | Nilex
So the drainage system is set up first and then the moisture barrier over the lot, pour the slab and starter bars to do the walls a bit later.  It could be a total concrete pour for walls and slab but this might be more difficult handling the form-work. 
Careful considerations like this gave me a perfectly damp free dry area, and I can see the ag lines draining during heavy rain.

----------


## Yande

Well digging is all done, (well still planning drainage) piers have been taken out and re-inforced bearers have been installed.  I'm getting there.  Main problem now to solve is drainage.  As there is no external outlet available, perhaps a simple solution will be an ag drain leading to an open sump, as if any water gets in, there is no way to find an outlet for it.  Concrete outside all round.  There is a corner, near the door, perhaps that could work?   We've been here for 12 months and have seen no moisture, but I want to be sure, to be sure, to be sure... 
Here's some updated pics..  (second pic is after wetting down..)   
Thanks Phil for your input.  Plan now is to lay the slab, (after sand, moisture barrier, steel) and place steel for the future retaining wall, and even completely concrete in the exposed pier(s) to stop subsidence.  Now thinking of then taking the slab back a meter or three, (no more major excavating) at around 1.2 meters above the initial slab, It's just too good a storage area to wall off.  Perhaps put a timber frame back there to close it all off then.  Hehe, my wife is Chinese, and I know what she is thinking, but...  I'm not sharing that here, and it is NOT GOING TO HAPPEN!! 
So drainage solutions are the main conundrum at the moment...    And to tell you the truth, I'm excited...  I have Sh*8 everywhere, and now I have a work space coming to fruition, seem to be collecting more and more tools...

----------


## phild01

If you can set up some ag lines to the pit, and later discover a drainage problem, you can then set up a pump-out from the pit.  Might be worth investigating how this can be set up now so to make any future solution easy.

----------


## Yande

> If you can set up some ag lines to the pit, and later discover a drainage problem, you can then set up a pump-out from the pit.  Might be worth investigating how this can be set up now so to make any future solution easy.

  Yes, that is the plan..  Once slab is in, difficulties arise....
I was thinking of setting up a small plastic bucket beside the pit!   :Smilie:   As usual, I will resource any suggestions you give. 
Thanks mate!

----------


## SirMe

Just out of interest what is teh netting next to your bearers? GaragewallIMG_2275_zps66db92b1.jpg Photo by yande2536 | Photobucket

----------


## phild01

> Just out of interest what is teh netting next to your bearers? GaragewallIMG_2275_zps66db92b1.jpg Photo by yande2536 | Photobucket

  Do you mean the vermin wire.

----------


## SirMe

> Do you mean the vermin wire.

  Is that what it is? 
Does that have some kind of backing?

----------


## Yande

> Just out of interest what is teh netting next to your bearers? GaragewallIMG_2275_zps66db92b1.jpg Photo by yande2536 | Photobucket

  It is a really strange build.. (I tried to explain it, but...  a picture is worth.....)  
 Through the door on the right of the pic below is where my excavation is going...  Behind the 30cm chipboard strip above the door is the "vermin" wire.  Putting both pics together, taking in the double ceiling height in the garage...  Yep, we are still attempting to work out what happened.  They had the bearers there, but chopped them off.  But then, the span would have been too big...  And yet, they sheeted it etc.,  Even section for the window.  But in future, we have tons of options..  Extend the lounge room, Mezzanine the garage..  etc etc...     
The bearer(s) below has been cut, Previously we assume they spanned out over the garage..       
Have had a little hold up thinking about drainage options, plus life..

----------


## phild01

> Is that what it is? 
> Does that have some kind of backing?

  Vermin wire is embedded into the brick course work and tacked to the walls bottom plate and continuous for the whole house to keep mice etc out of the wall cavity.

----------


## Yande

So another update... 
I procrastinated about completion.  Friends were saying, "Oh, it's so dry down there..  You don't have to worry about drainage.."
Phild01 comments were consistently in my mind, ..... drainage was severely needed... 
Eventually, I was in two minds, though thankfully, my nature is not as a risk taker.  Again fortunately, I had a Skin Cancer cut out of my arm and that delayed the concrete pour preparations, and then yesterday the heavens opened up after a very prolonged period of dry came to an end. 
Initially all was well, (that is, dry), this morning, when I went down to check, my slab area was swimming, though fortunately, the water was still contained to the initial excavations of my proposed drains. Water was seeping in below the surface level.  Worryingly around the piers that are exposed..   I set up a siphon, and that is still running as we speak. 
I was so lucky, for I nearly "just poured," Now, I know much better. 
 You can see the seepage (mostly) from the left of this pic, just under the exposed pier footing....  
 This is where I am presently removing the water from.  Future plans are for drainage to go out through the wall, underneath the path outside, at this corner...   
So, now waiting for the rain to stop.  Dry things out.  Fit out an appropriate drainage system, and pour that slab..  Then shore up the exposed pier footings..

----------


## phild01

Yes, my underneath area always seemed dry until the torrential rains would expose ground drainage.  Glad you got to see this before you pressed forward.
It is useful to have the drain ag lines set up so they can be washed out.  Also separate your walls from the excavated area by tanking as you don't want rising damp issues.

----------


## Yande

> When I did similar,.............the drainage system is set up first and then the moisture barrier over the lot, pour the slab and starter bars to do the walls a bit later.

   

> It is useful to have the drain ag lines set up so they can be washed out.

  I'm heading in your direction Phil.  Just wondering if you could describe how you access your Ag Drains once you poured over the top..  I think I get it, but just not sure..

----------


## phild01

> I'm heading in your direction Phil.  Just wondering if you could describe how you access your Ag Drains once you poured over the top..  I think I get it, but just not sure..

   My area, while dug out, was still above ground level at the front.  So ag lines are exposed to view and accessible in this area.  If your area is fully under normal ground level with no access to drains, then you would need a pit with an automatic pump out.  Not my area of experience but expect it would be done this way.

----------


## SirMe

Just be careful about a pump if power goes out and itsw raining heavy how will you get the water out?

----------

