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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
     
  2. ^woody^

    ^woody^

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    75mm celotext, 22mm chipboard
     
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  3. 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
     
  4. ^woody^

    ^woody^

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    I can't see why not.
     
  5. 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?
     
  6. ^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.
     
  7. mrrusty

    mrrusty

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

    ^woody^

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    Same a a kitchen is not a habitable room, nor a bathroom, nor a hallway .......
     
  9. 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
     
  10. 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.
     
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