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Housing - New Build: Constructing a basement in a limestone area

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  1.  
    • CommentAuthorTriassic
    • CommentTimeApr 17th 2013
     
    Has anyone got any experience of building a basement in a limestone area?

    I'm planning to construct a full footprint basement on a sloping site, open on the downhill side and full cover at the rear (north side). Anyone got any advice on most cost effective construction method / spec, how difficult is it to excavate limestone (maybe 1.5m worth), likelyhood of ground water.

    I'm thinkling of constructing a 1 1/2 storey bungalow over the basement. Is it best to have block and beam floor over the beasement to provide fire protection?

    I was also thinking of a solor heat sink under the basement - any suggestions?
  2.  
    Can't offer you any practical experience but when I was previously considering building a basement I was leaning towards using ICF's.

    Having said that I subsequently saw a TV programme (Grand designs I think) where they used ICF's and had problems with moisture coming in at the level of the concrete pours, I think they had done two pours to fill the full depth. They had to then tank the basement from the inside which IMO is never the best solution, so if I were going to do a basement in the future I would definitely take the trouble to tank the outside as it was being built as a precaution.

    Where you are on a slope you should find it easier to address any moisture problems as you will have the possibility to form a drain at the base of the wall buried in the slope and drain off any water to the front of the house.
  3.  
    What they tend to do here is dig out with a JCB (with a JCB mounted jack hammer if really solid) then shutter the internal dimension, use the natural surface for the outside and then pour concrete (having placed rebar as appropriate).
    • CommentAuthorPaulJ
    • CommentTimeApr 17th 2013
     
    I have done a basement with ICF, with timber floor and timber frame above.

    A good soils report is essential from the outset. Don't try to save on this. It will inform the type of waterproofing required, the ease of excavation, radon / contamination, requirements for temporary works and structural design of the retaining walls.

    You also MUST employ an engineer to do the structural design. Use one who is well used to basements and the build system you decide on and they should be able to provide you with the most economical solution.

    If you are using a warranty company like NHBC they prefer to see a type C (internal drained cavity) waterproofing, because it carries the least risk.
    • CommentAuthortony
    • CommentTimeApr 17th 2013
     
    I wouldn't expect ground water, lay some land drains under it and round the back, no waterproofing necessary I can give more details of how this works if you like.
    • CommentAuthorTriassic
    • CommentTimeApr 18th 2013 edited
     
    Posted By: PaulJI have done a basement with ICF

    Which ICF system did you use and why did you go with ICF? Also where did you place the waterproof layer?

    Any thoughts on the cost of the basement - I'm trying to put together an initial budget for a self build project.
    • CommentAuthorPaulJ
    • CommentTimeApr 18th 2013
     
    We used Polarwall, which is like shuttering but made of XPS. Simple to construct. I don't think they currently have a BBA cert though they are in the process of getting one.

    We used an internal cavity membrane system for the waterproofing, where you form a channel around the perimeter of the slab, leading to a sump which is fitted with a pump. Walls and floor are covered in membrane which is a bit like big bubblewrap.

    You may be able to have a much simpler setup as Tony suggests, although I can't work out how you can exclude all waterproofing?

    Budget about the same as the above ground per metre (£1500?), with additional allowance if you have difficult ground conditions or are on a confined site.
    • CommentAuthortony
    • CommentTimeApr 18th 2013
     
    It is easy to exclude all waterproofing!

    It is impossible to include it! whatever you will fail one day

    If there isnt any then it cant fail, I am sitting in my basement now which is warm 20C with no heating in the house at all and it is dry
    •  
      CommentAuthorfostertom
    • CommentTimeApr 18th 2013
     
    Cos limestone is free-draining so no water table causing hydrostatic pressure - however there may well be horizontal watercourses aka springs but a large flow can be piped away and a french drain around shd deal with any dispersed flow. Big problem tho if you reach the bottom of the limestone and find something less permeable - will find lots of water there.

    If it really is dry (no water table) limestone, then you have a rare, ideal opportunity to do interseasonal storage of copious summer solar heat just dumped into the uninsulated ground under and around an uninsulated slab/basement walls in gd thermal contact with the subsoil. Search on here and google for AGS and PAHS.
  10.  
    <blockquote><cite>Posted By: PaulJ</cite>We used Polarwall, which is like shuttering but made of XPS. Simple to construct. I don't think they currently have a BBA cert though they are in the process of getting one.

    We used an internal cavity membrane system for the waterproofing, where you form a channel around the perimeter of the slab, leading to a sump which is fitted with a pump. Walls and floor are covered in membrane which is a bit like big bubblewrap.

    You may be able to have a much simpler setup as Tony suggests, although I can't work out how you can exclude all waterproofing?
    Budget about the same as the above ground per metre (£1500?), with additional allowance if you have difficult ground conditions or are on a confined site.</blockquote>


    I don't understand how you filled the Polarwall so badly that you had enough water coming in to warrant a full internal drainage membrane setup. Why didn't you take the Polarwall off the inside and repair the leaks in the concrete? Even non-waterproofed concrete is quite water resistant if the work was done well.

    Limestone can be tricky but it can also be sold on. One of my customers drilled through the base of his old quarry and the water table came through in winter.

    Use the slope if you can to drain all the water externally to below the basement. Your contributor who suggested if there is no water you cannot have a leak was quite right.

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