Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




  1.  
    We're at the nearly-moving-in stage and now comes the part where we need to backfill the areas around our house to get the levels up to FFL(ish).

    Due to using a passive slab approach we've now got 500mm of levels to make up all the way around the house which equates to about 50 cubic metres of material in total.

    What does the forum think is the best way to get this done?

    I'm all for using recycled aggregate if it doesn't run the risk of contamination. I'm also not sure what the aggregate size ought to be. We had a thin layer of MOT Type 1 put down over the existing clay before the insulated slab went on, so it seems weird to step up to larger aggregate again for sub-base; but I guess it would be cheaper to do this initially and then put on another layer of type 1 on top?

    Finished surface will be a mix of planted beds and flat slab pavers on sand.
    •  
      CommentAuthordjh
    • CommentTime6 days ago
     
    I wouldn't build up to FFL all around the house. Normal practice is 150 mm below DPC except where you're forming level access. It reduces splashing and the risk of flooding etc. It will also reduce the quantity of material you need. But the levels should have been set so the ground is level when you do that; you don't want a hollow in the ground that will fill up with water.

    We kept a pile of topsoil when we excavated for precisely this purpose, except for a 600 mm wide French drain around the house. That went on top of aggregate. Railway ballast etc is sold sterilised.

    What aggregate to use depends on what load it is going to experience. For flowers and foot traffic, you can use pretty much anything you like; for vehicles then something a bit more standardised is better. The key thing is a graded mix of sizes, and angular pieces rather than rounded, so the whole mix locks together solidly.

    Also may be worth noting that in the current weather, it is quite clear where our llawn is on top of undisturbed clay and where it is on top of replaced topsoil on top of aggregate. The drainage through the aggregate is much better than through the clay, so there's a very sharp line between completely brown grass and mostly brown grass.
    • CommentAuthortony
    • CommentTime6 days ago
     
    I would use subsoil or hogging or selected fill, secret is to compact before you start digging down to same solid undisturbedveverywher. Then compact in 150mm layers, driving a small digger on it is not good enough.

    Ground will still settle probably up to 50mm so over fill is good initially, much harder later on.

    If you can wait til next Easter to do paths patios etc, dig out, membrane hardcore and lay away, if not the lay on lightly reinforced concrete bases 100mm should be OK
  2.  
    Posted By: djhI wouldn't build up to FFL all around the house. Normal practice is 150 mm below DPC except where you're forming level access. It reduces splashing and the risk of flooding etc. It will also reduce the quantity of material you need. But the levels should have been set so the ground is level when you do that; you don't want a hollow in the ground that will fill up with water.

    We kept a pile of topsoil when we excavated for precisely this purpose, except for a 600 mm wide French drain around the house.


    Thanks for the replies

    I don't intend to build all the way to FFL but at the time I researched the standard details for our insulated slab system they effectively showed this approach. You basically have to excavate all round to the underside of below-slab insulation and then build everything up from there, so quite a bit of insulation to cover up wherever you stop and whatever you don't fill is exposed to water/UV instead, so needs a secondary barrier (i.e. render coat).

    We also kept some topsoil/clay for 're-filling' but I reckon this is around 15 cubic metres at best and we probably need 50 or so in total...we just didn't have room to store more at the time and a lot was low quality anyway.

    I've allowed for a perimeter french drain and made sure the levels all slope away from the house. The contractors seem to think clean stone is the way forward for the general fill so that's probably what we'll end up with now. If anything this should drain better than the clay we had before.

    Tony, thanks for the tip on waiting until Easter for paving. We've pretty much run out of money now so lots of the landscape is on hold until then anyway..!
    •  
      CommentAuthordjh
    • CommentTime1 day ago
     
    Posted By: Doubting_ThomasI don't intend to build all the way to FFL but at the time I researched the standard details for our insulated slab system they effectively showed this approach. You basically have to excavate all round to the underside of below-slab insulation and then build everything up from there, so quite a bit of insulation to cover up wherever you stop and whatever you don't fill is exposed to water/UV instead, so needs a secondary barrier (i.e. render coat).

    Yes, we have a passive slab. In our case in addition to the normal concerns we also have to protect our bales against rain splashing up, so the gravel on top of the French drain and the 150+mm upstand are essential. We used paving slabs on edge to protect the exposed sides of the EPS from weather and rodents.

    Clean stone is good stuff for the top surface, but you need to be sure of a mix of sizes and ideally some fines (dust) in the mix to improve the loadbearing capacity. I just spent a lot of money re-laying our drive because we got that wrong the first time.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press