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Part garage to utility conversion

Discussion in 'Building Regulations and Planning Permission' started by hfullwood, 27 Jul 2019.

  1. hfullwood

    hfullwood

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    Hello,
    We are currently getting our house extended on the side and have decided to add on converting part of our current garage to a utility room. Our garage is 4 x 8m and we are wanting to convert just the rear section (4 x 3m) into a utility room. The garage is single brick construction so we will insulate the walls and roof. Our building inspector has asked us to add it onto our plans.

    The floor is currently a 6inch concrete slab, 4inch lower than our house floor. We have been told the room needs insulating which we assume includes the floor? It has a damp proof membrane in already which we can prove. Does the floor need insulating too? If so, how do we do this with only 4inch to work with? We aren't planning on heating the utility, as we have a firedoor in place currently from the house to the garage, and only plan to store our washer and dishwasher in there.

    We were going to speak to the building inspector but don't want to make the job more complicated than it needs to be. We will submit the plans and hope for them to be accepted as it is a small portion of work in comparison to the whole extension.

    Thanks in advance
    Hayley
     
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  3. ^woody^

    ^woody^

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    75mm celotext, 22mm chipboard
     
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  4. hfullwood

    hfullwood

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    Thank you for the reply, would we be able to use 75mm celotex, 18mm ply and 6mm cement board instead? Thanks again
     
  5. ^woody^

    ^woody^

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    I can't see why not.
     
  6. mrrusty

    mrrusty

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    I'm surprised that dividing off the back of a garage to house a washer etc makes it a habitable room subject to BC. personally, as utility rooms potentially have water on the floor, I'd rather have the 4" lower concrete floor. Might be worth having another conversation - not to cross your BC officer, but just to confirm his/her thinking. Loads of people have washers and driers in garages. Perhaps it's the dishwasher that makes the difference - it's being treated as a kitchen extension?
     
  7. ^woody^

    ^woody^

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    The OP is extending the house and adding part of the garage to that. A utility is not a habitable room, but is controlled works.
     
  8. mrrusty

    mrrusty

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    yes, exactly, so does he have to insulate the floor then?
     
  9. ^woody^

    ^woody^

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    Same a a kitchen is not a habitable room, nor a bathroom, nor a hallway .......
     
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  11. hfullwood

    hfullwood

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    Thanks for the replies everyone,
    We would like the utility room to be level with the kitchen as the door to the garden from the garage (proposed utility) is 150mm higher at the moment and we would like to tile across and into the utilty room with the same tiles as currently in the kitchen.

    Going back to your post earlier Woody, is the PIR board just fitted tight to the walls on DPM, and then taped and foamed if there are any small gaps? and does the Ply need to be T&G and glued at joints? Does it simply rest ontop of the PIR board or adhesived?

    Our next question would be with regards to insulating the external single walls, (these are in good condition and in a sheltered location away from driving rain and bad weather). From reading through many of the contradicting threads we interperet as...

    DPM or polythene up the walls from bottom of floating floor, taped.
    3 x 2 stud framework not fixed to wall but ceiling and floor
    75mm PIR board inbetween the framework
    25mm PIR fixed to Framework Taped to form vapour barrier
    Mechanically fixed plasterboard on top of this and finally skim?

    Does that sound somehwere along the lines?

    thanks
     
  12. mrrusty

    mrrusty

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    Re single skin walls. You don't want a DPM on the outer cold leaf. As you say build a 2x3 stud framework. Use a breathable membrane on the cavity (cold) side. Insulate between the studs with either PIR or rockwool batts. Now you want a DPM - you could use either thin insulation backed PB which incorporates a DPM, or use foil backed PB. Either way, the DPM goes on the warm side of the insulation.

    This diagram from a timber frame house illustrates perfectly how the inner wall should be constructed https://www.neatwoodhomes.co.uk/TimberFrame&TheBenefits.htm - you don't really need the OSB - the breather membrane is enough to hold the insulation in place, and your timbers won't be structural, but include it if you prefer.
     
  13. hfullwood

    hfullwood

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    Hello, a bit of thread resurrection but we're finally in a position to start on the utility room conversion and had a few questions/ things to confirm.

    The current concrete floor with DPM is 115 to 127mm lower than our intended finish height. With the variations in level we were thinking of self levelling the floor to bring it to the 100mm ish region.

    Are we right in thinking that the floor needs to be first prepped in a mapei primer for concrete before using mapei ultraplan?

    This would then be built up in:
    1. DPM
    2. 75mm PIR board
    3. 18mm T&G chipboard glued together
    4. 6mm Hardiebacker screwed to chip
    5. Tiled to finish on flexible adhesive
    Would we need a "slip" layer between the PIR and the Chipboard or is this not necessary?

    The single skin wall has two courses of blue engineerings that are two courses above current floor height (shown below). Would we have any issues with damp from the wall via this or from the blockwork pier? Would a liquid DPC be of benefit?

    IMG_20200529_155110.jpg

    Part of the utility wall was boarded about 5 years ago and is constructed in:

    1. Studwork screwed straight to brick
    2. PIR between studs
    3. 22mm OSB3
    4. 12.5mm plasterboard to plaster finish
    This has been fine since install but we can appreciate that retrospectively we should have fitted a vapour control layer amongst other changes. Our problem now is that the boiler is fitted to the wall and it would be quite a lot of trouble to take it all off and start again. Will this cause us issues down the line once the area becomes insulated from the cold garage and is warmer?

    With regards to the construction of the new stud partition seperating the utility from the garage and with us building to regs, we were thinking of building the stud wall as follows:

    1. 4" X 2" CLS studding with full fill rockwool
    2. Vapour control layer (polythene?) On utility side
    3. 25mm Insulated plasterboard screwed to studding?
    On the garage side to achieve the fire regs would we be ok to use a single layer of fireboard with taped seams or is it better to use two layers of standard plasterboard with staggered joints and taped seams? This will determine the thickness of the fire door casing.

    For the remaining single skin wall areas are we best to build a stud wall, leaving an air gap of (?) between the brickwork, then fix this to the new chipboard floating floor and pitched ceiling rafters?
    We have a 1m high X 2m wide section that will need creating beneath a window where fixing to the ceiling will not be possible, is there an alternative to this? PIR board glued to the wall perhaps?

    Any help would be fantastic.

    Sorry for the long post.

    Thanks
     
  14. cdbe

    cdbe

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    I don't know how it works with the regs and the insulation, may be some payoff between less on the floor and more on the walls or even a reasonable request to the BCO for such a small area but if I was doing that as a utility with a tiled floor I'd want 50mm celotex and a screed on top. I think layers of celotex, chipboard and cement board with tiles on top is a recipie for disaster - imagine a small leak from the back of the washing machine getting under those tiles and into the chipboard!
     
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  15. hfullwood

    hfullwood

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    Thanks for the reply, just spoke to our BCO and explained that the room will be unheated and we will be going over the recommended amount with all the other insulation and his reply was no.
    Because it might become a habitable room in the future it has to be done to regs.

    Can anyone help with the other questions and room construction?
     
  16. John D v2.0

    John D v2.0

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    Yes the way it was explained to me is they are signing it off based on what they can see but someone else might buy the house and decide to make it into a baby nursery for example, so the ventilation and insulation etc all have to be correct. If you keep the insulated fire door from the main house and lower floor level you could call it part of the garage and leave it uninsulated, but once you lose any of those it's part of the house and needs to be done properly
     
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  17. hfullwood

    hfullwood

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    Thanks for the reply John,

    Can anyone confirm any of the construction methods from the previous post?

    Thanks
     
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