Garage Conversion - Best way to raise concrete floor level 35-38mm including a DPM

Discussion in 'Builders' Talk' started by Rebpro, Feb 1, 2021.

  1. Rebpro

    Rebpro New Member

    Hi there,
    have started the process of an integral garage conversion. Have had BC out to have a look and have been advised because the current concrete floor is not far off the level of rest of the house, I do not have to insulate it; but must add insulation elsewhere to make up for it (walls and ceiling).

    I do however have to add a DPM. I also want to raise the height of one half of the room to the same level of the kitchen as I wish to lay laminate flowing through from the kitchen into what will be a new utility room - 35-38mm.

    I am wondering what is the best and most cost effective way raise the floor to match up to the existing kitchen concrete floor level?

    I am also installing a stud partition in the conversion, and I am wondering if I install this before or after I have laid a sheet of DPM? Obviously if I install it after, I pierce the DPM screwing the soleplate down. If I installed it before, do I lap DPM up the partition walls? (Didn't have the sense to ask BC man when he came)!

    He did suggest to just install T+G Floating on DPM to raise the height a bit, but did not give me definitive answer how I could match them up completely!

    Any help on this greatly appreciated!
  2. rogerk101

    rogerk101 Screwfix Select

    Insulation, insulation, insulation.
    You make it up with 15mm insulation plus 22mm chipboard = 37mm height gain.
    You'll NEVER regret having put in insulation, and your feet will thank you for it in the winter ... every winter.
    FWIW, I was disappointed that I was only able to fit 40mm of insulation under my 22mm chipboard flooring during my garage to grannyflat conversion, but I'm grateful that it was more than 15mm, and even more grateful that it was not 0mm.
    Last edited: Feb 1, 2021
    Rebpro likes this.
  3. Shanebo

    Shanebo Member

    As above celotex of similar insulation, chipboard, underlay and flooring. You'll need to work out depths.

    Tongue and groove generally come in 18-22mm
    Laminate is about 5mm
    Underlay I'm not sure of, but you should be able to make it work
    Rebpro likes this.
  4. jimoz

    jimoz Screwfix Select

    Insulated tile backer board? I used it in my porch with a click vinyl over. Probably not designed for such a lightweight floorcover due to durability though
  5. Have you checked how thick your garage floor slab is? Mine was only about 50mm and it broke out easily. I was then able to put in a dpm and a hefty layer of cellotex and then screed to the level of the house.
    rogerk101 likes this.
  6. Rebpro

    Rebpro New Member

    Hi guys, thank you for the replies on this!
    I think Roger's suggestion of fitting in some thin insulation actually makes sense. I can't think of another way to raise the height apart from SLC; and that doesn't offer what a thin bit of insulation could.. not to mention the cost comparison! One thing I am concerned about going this route with a floating floor; I have to match the existing kitchen floor pretty closely for the laminate to not have any issues going from one floor to another.. I don't think you can use SLC on top of a floating chipboard floor?!

    The bungalow is 1970's and has no insulation underneath the rest of the house, so I do not see the point of going crazy and digging up 100mm of the floor to get some decent insulation down unfortunately.. Although I understand the benefits! My cavity walls pass for the regs as they are fully filled with candy floss foam stuff, but they requested extra there as digging up the floor would be a pain!

    Can anyone help me with the DPM under a stud partition? What's the usual way of putting it down when you're dividing a room... Just lap the whole room up as normal, blobs of silicone where you fix the soleplate etc?

    Thanks again!
  7. How do you know it's 100mm? Have you checked?
    You know what assume does?
  8. Rebpro

    Rebpro New Member

    Hi NoOhm. I only know it’s approx 100mm from having to chisel/break out a bit of it digging down for foundation under the old garage door for new wall... could literally see from a side on view. Cheers for the help and advice tho :rolleyes:

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