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Underfloor Insulation Queries.

  • 14-07-2009 1:05pm
    #1
    iamlegend2008
    Closed Accounts Posts: 92 ✭✭


    Hi

    Im just about to start laying 50mm of underfloor insulation prior to screeding. There is no underfloor heating. My questions are:

    (a) How smooth/clean does the subfloor need to be. I have swept it etc but am wondering if anythings else needs to be done (ie does it need to be scaped of any mortar etc)

    (b)How should pipes be treated. The pipes are already lagged. if there is a 1 inch gap between pipes does any insulation need to go here

    (c) I spoke to a couple of local people and one person recommended a damp proof membrane underneath the insulation and another said to apply plastic on top of the insulation so Im very confused.

    Any help would be appreciated.

    Cheers


Comments

  • #2
    Quazzie
    Registered Users, Registered Users 2 Posts: 29,309 ✭✭✭✭Quazzie


    It depend what type of insulation you are using and also the set-up of the subfloor.

    It is advisable to put a radon barrier membrane underneath the insulation, but you also might require a slipping sheet seperating the insulation on the screed depending on the type of insulation you intend on using.


  • #3
    iamlegend2008
    Closed Accounts Posts: 92 ✭✭iamlegend2008


    Hi Quazzie

    Im using the xtratherm XT/UF 8ft by 4ft sheets.

    There is a radon barrier already under the subfloor.

    I also have a bundle of Xtratherm permiter strips but I cant see how to use them since the external walls already have 50mm insulated slabs applied.

    Cheers


  • #4
    Quazzie
    Registered Users, Registered Users 2 Posts: 29,309 ✭✭✭✭Quazzie


    iamlegend2008 wrote: »
    Hi Quazzie

    Im using the xtratherm XT/UF 8ft by 4ft sheets.

    There is a radon barrier already under the subfloor.

    Xtratherm XT/UF has a foil backing on them, and from my understanding they react badly with the heat caused during the setting of the screed, thus a slipping sheet (1200 gauge polythene should be fine) is advisable to prevent this and also prevent further damage to your insulation.
    iamlegend2008 wrote: »
    I also have a bundle of Xtratherm permiter strips but I cant see how to use them since the external walls already have 50mm insulated slabs applied.

    Do you have the slabs on the wall all the way down to the subfloor? If so I think that presents a problem.


  • #5
    iamlegend2008
    Closed Accounts Posts: 92 ✭✭iamlegend2008


    Hi

    The boards have just arrived and are marked quintherm so I guess a substitution was made by the builders providers. The quinn boards are also 8fy by 4ft and foil lined.

    My insulated slabs do go almost all the way to the ground (pehaps a 1 inch gap).

    Can I not just lay the perimiter slips facing upwards and butut the floor insulation upto them. Since they are 6 inches high they will be 2 inches higher than the screed once its applied and can be cut off.

    From further reading, I believe that I do need to apply 500 guage plastic beneath the floor slabs.

    Cheers

    Cheers


  • #6
    iamlegend2008
    Closed Accounts Posts: 92 ✭✭iamlegend2008


    ...and according to the home bond manual it recommends putting plastic on top of the insulated slabs also :confused:

    So in summary it looks like I will have (top to bottom)

    (a) Screed
    (b) Layer of 500 gauge plastic to prevent screed seeping under underfloor insulation
    (c) Quintherm underfloor insulation
    (d) Layer of 500 gauge plastic
    (e) Subfloor
    (f) Radon barrier

    For (c) where the slabs meet the external walls, perimeter strips will be used (perimeter strips will stand on subfloor and floor slabs will butt up against them.

    Does this look right ?

    Sorry, it seems a simple thing but I seem to be having a problem with it.

    Cheers


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