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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.

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Fundamentals: Mobile home foundation/chassis

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  1.  
    • CommentAuthorstephendv
    • CommentTimeJul 6th 2010 edited
     
    Have some ideas on a base for the 12mx4m mobile home, and would appreciate some comments.
    Thinking of using a steel base with a conventional timber floor layer on top resting on 8 pillars. This would mean that the maximum span will be 3m length wise (4 pillars in 12m) and 4m across the width.

    First layer is a steel frame UPN channel 160mm around the perimeter with 4 internal steel I-beams 120mm. 2 ibeams lengthwise and 2 widthwise.
    On top of this a wooden floor layer composed of 50mm x 100mm beams and trusses. Beams lie directly on the steel perimeter u-beam. 4m trusses on 600mm centres are supported by the steel I-beams so that maximum span is 1.3m.

    - I sort of plucked the steel dimensions out of the air, is anyone able to do a quick calc? If the house is ever moved the crane would lift it using 2 slings, so that would mean 4m spans.
    - Are 50x100 (height) trusses on 600mm centres across a 1.3m span ok?
    - Where the trusses rest on the 2 i-beams, does there need to be something in between? (rubber, glue?)

    Some diagrams to hopefully clarify the ideas here: http://www.casanogaldelasbrujas.com/baseplans.jpg
  2.  
    Where is this being built/placed?

    Why not a timber floor resting on tyres? no metal?

    you got termites where you live?
    • CommentAuthorstephendv
    • CommentTimeJul 7th 2010 edited
     
    Rural land in northern Spain, no termites that I know of. Going pure timber is an option, but I felt that a steel base has a better strength/cost ratio. My biggest concern is if the house is crane lifted with only 2 supports, which means 4m spans.

    I priced up an alternative using purely a wood base of 200x320mm laminated beams on the perimeter and 50x300 floor trusses, worked out about 800 euro's more expensive than the steel + wood combination.

    EDIT: Ok, the above statement was just silly. Comparing apples and oranges, found a table showing glulam equivalents to steel beams, but it doesn't include my beam as it's too thin! Smallest is W8x10, which I believe is 200mm. Equiv pine glulam is 140x240. Doing the adjustments for steel size it brings the costs to roughly the same for glulam vs. steel.
    I've gleaned the above from tables on them intawebs, has anyone built a similar structure or can confirm the rough calcs?
    • CommentAuthorTuna
    • CommentTimeJul 7th 2010 edited
     
    If you put as much effort into your house build as you are into your temporary accommodation, you're going to have a fantastic house... if a little behind schedule :wink:

    From memory (I ought to know, I've been under it enough times), our caravan has four width-ways C beams, about 200mm deep, on top of which are I beams that run the length of the caravan. It's 11m by 3.6m and you can see a bit of the construction here:

    http://bp2.blogger.com/_mI0S6Hpm5No/RursrI8KrcI/AAAAAAAAAEQ/K1nuFUzxPSg/s1600-h/IMG_9780.JPG

    Why not buy a second hand static home, strip off the top part and re-use the base? Or even a lorry base - you should be able to pick one up from a scrap yard at a very good price and you'd have an instant, robust base that is designed to withstand the knocks and bumps of being moved around.

    Building a mobile home from first principles seems to be a waste of a lot of time, money and effort.
    • CommentAuthordickster
    • CommentTimeJul 7th 2010
     
    Just moved our double width mobile to bottom of garden. It's 40 + years old and a lovely build. Floor joists are only 75x12mm the whole thing is built to be lightweight, flexible, but amazingly strong. It weighs 4 ton + when empty, so be careful with your 2 slings!
    • CommentAuthorstephendv
    • CommentTimeJul 7th 2010
     
    Tuna, thanks for the pic our homes will be roughly the same size! (I won't ask what happened to cause the huge hole in the floor...)
    I considered second hand flatbed trailers as they're advertised all over, 2000 Euro for a 12m version vs. 800 Euro to build the frame, so very tempting. BUT yes you are right about the "mobile" requirement being a pain in the 4rse, and perhaps I'm being too pessimistic here. In the best case scenario it won't ever be mobile and will stay just where I build it. In the worst case, it will probably be moved twice in its lifetime. If it just has to survive 4 crane lifts then designing it from the start to be mobile is perhaps over engineering it.

    If instead of the steel frame, I used the laminated beams throughout, then the floor trusses could lie within the base structure and not have to sit on top of it saving some height.
    E.g. 140x280 glulam, 3 of them lengthwise (uninterrupted) and 4 width wise. Then floor trusses on 60cm centers using normal timber 50x120, max span for the trusses would be 2m. ...perhaps I need a structural expert :confused:

    dickster, what is the span of the joists and how far apart are they?
    • CommentAuthordickster
    • CommentTimeJul 7th 2010
     
    Joists approx 600mm apart, longest span 3m. Top skin (floor) only of chipboard. Superstructure in wood, aluminium outer skin, hardboard inner. Roof structure same as floor, but double skinned in hardboard. V strong.

    Each half of the mobile is 3m wide approx. C beam girders every 1.5 metres approx. Joined the units together by putting 75x50mmx 5.1 metre wooden beams into C girder recesses.
    • CommentAuthormarktime
    • CommentTimeJul 7th 2010
     
    Hi Stephen from sunny Tenerife!! A Tenerife that is abuzz with the prospect of tonight's game. Podemos!!!!!!!!

    I bought an old caravan that couldn't pass ITV (MOT equiv.in UK) and so I got it for a song. Shipped it to site (Navarre) on a tow truck, tarted it up and lived in it for over a year. Best bed I ever slept on.

    The lorry idea is also good, a flat-bed comes with wheels so might be easier to move around.
    • CommentAuthorstephendv
    • CommentTimeJul 7th 2010
     
    Hola Marktime, que si podemos! I've seen some 12m flatbeds advertised for 2k euro, so very reasonable compared to building a steel frame (about 1k euro). But given that it may potentially never be moved, I'm leaning towards wood throughout - as long as it can be crane lifted I could always install it onto a flatbed when the need to move arrises.

    Navarra is just around the corner from us, beautiful area.
    • CommentAuthormarktime
    • CommentTimeJul 7th 2010
     
    GOOOOOOOOAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


    Mmmmm....excuse me.

    :shamed:
    • CommentAuthorstephendv
    • CommentTimeJul 7th 2010
     
    Lol. The advantage of being an expat is having more than 1 opportunity for your team to win :bigsmile:

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