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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentTimeSep 10th 2014
    I have a feeling I may be starting a series of threads that all look the same ... but this one is about the best way to build my ground floor.

    The structural ground floor is a concrete slab, sitting on a big bunch of EPS. The slab isn't perfectly level or smooth - perhaps up to 10 mm max variation - though it is reasonably flat. I also need to build it up by 65-75 mm to finished floor level. (The height difference is the threshold height of a lift-and-slide door and the desire to achieve level thresholds). So my problem and question is what is the best way to build up the floor level?

    'Best' may mean cheapest, or perhaps there's some other criterion like buildability to be taken into account.

    I think there are two fundamental ways to build up the level - screeding or battens. But there are lots of options - sand and cement screed or self-levelling? And is the self-levelling a thin layer plus battens on top or is it full height. Finished floor will be a mixture of some or all of these surfaces: carpet, lino, tiles, engineered timber, cork, bamboo. They all have different thicknesses and strengths/requirements for support. One room will be a shower wet room. Others are kitchen, utility, dining, living and a bedroom.

    I'm not sure how much I should care about introducing thermal resistance between the slab and the floor surface, nor even certain whether more resistance is good or bad. I'm not planning on UFH.

    I think the way to go is separate floors in each room. This allows for different build ups for the different surfaces, and will be easier to build I suspect.

    But what do you think? What options should I be considering?
    Consider Gypsum self levelling screed if you are happy with a single level - requiring all finished to be the same thickness - doesn't seem like that's an option from what you say.

    This being the case sand and cement screed with variable thicknesses to suit floor finish above is the only way to go.

    Thermal resistance is irrelevant in my view in your case
    • CommentAuthorEd Davies
    • CommentTimeSep 10th 2014
    Does the desirable thermal resistance depend on the desired temperature profile?

    AIUI, this is a “forever house” and likely to be occupied a lot of the time therefore more thermal inertia is good so lower thermal resistance is desirable, I'd have thought.
    • CommentAuthortony
    • CommentTimeSep 10th 2014
    I would make life easy and perfect and go pumped screed perfectly level, fast and no hassle, they can do the shower room to falls into a wet room gulley.

    Second choice is a good floor screeder with tradition sharp sand and cement.
    Are you getting in a specialist to do your wet room Dave?

    Personally I wouldn't do the wet room at the same time as the rest of the house.

    To determine the right level for your raised threshold in the wet room you will need to know precisely your finished floor level outside the wet room door otherwise you risk having the threshold too high or too low.

    If you are getting in someone to do your wet room then it should be part of their duty to get all the falls correct into your floor drain so I would not split that responsibility to your screeding contractor as it will invariably result in buck passing if the job doesn't turn out right.
    • CommentTimeSep 11th 2014
    Interesting. Everybody is talking about screeds. As far as I can tell the sand and cement solution is about twice the price of timber battens, with 'cleverer' screeds more expensive, so why does everybody recommend/assume a screed solution?

    And what is the floor build up that gives me a level finished floor with different thicknesses of finish (e.g. lino versus timber)?

    I tend to agree with Mike that the thermal resistance isn't hugely important, but I'd like more evidence one way or the other. I think the time constant of the house will be long enough to prevent massive swings through the day, but I don't have a good feel for it.

    I haven't thought whether I'll need a specialist for the wetroom(s) (there might be another upstairs as well but that's a different engineering problem). What you say makes sense, Gordon, making things wheelchair accessible does seem to complicate them quite a lot!
    Posted By: djhI haven't thought whether I'll need a specialist for the wetroom(s) (there might be another upstairs as well but that's a different engineering problem). What you say makes sense, Gordon, making things wheelchair accessible does seem to complicate them quite a lot!
    As you know I prepared our wet rooms myself but to be honest it is not something I would jump at doing again. You need to be a cheapskate like me and it helps to be a gluten for punishment as it's a messy, tedious and time consuming job.

    I also had the benefit of being able to give my drawings to the supplier and have them calculate exactly what I needed and then have two friends in the trade give me practical advise on many critical steps of the process. Without that I am not sure that the job would have turned out the success that it did.

    The actual levelling of the floors to create the correct falls was done by one of my mates as I was not confident to take on that part of the job myself.

    What floor finish will you have outside the wet room? Will the door open in or out? There are various raised thresholds available off the shelf here for wet room application, not sure if they are readily available in the UK. However the style that is used where there is wood flooring outside the room I would not be confident of being robust enough for use with a wheelchair as the raised lip is quite narrow.

    I can't remember if it is 10mm or 15mm but the door threshold needs to be a minimum of one of those amounts above the top of the floor drain (at least according to the rules here). Given that you have 75mm to play with rather than having a raised threshold across the door you may be able to form a slight ramp down from the door which will serve the same purpose (of not letting an overflow flow out of the wet room) and be a lot easier to navigate in a wheelchair. I'm sure the wheelchair association must have resources available for advising on such.
    • CommentAuthorShevek
    • CommentTimeSep 12th 2014 edited
    Given the choice I'd be going for timber battens. For wet rooms I'd go with the likes of XPS:

    All you do with the Marmox board is screw fix and tape it. No tanking liquid required.
    • CommentTimeSep 12th 2014 edited
    Posted By: Chris P Baconnot letting an overflow flow out of the wet room

    You can also get linear drains that you put across the door I believe. Same as the drain for the shower itself.

    As you know I prepared our wet rooms myself but to be honest it is not something I would jump at doing again.

    Thanks for alerting me to the probable need to find a specific subcontractor for the wetroom
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