Domestic Integrated Garage conversion - seeking advice re. floor (insulation/concrete slab etc.)

[powerbooksub]

Hello everyone

I want to convert my integrated garage (2m x 6m) in to a study and would be grateful for some advice re. the floor before I go out for quotes so I at least appear clued up! I am only worried about the floor at the moment - and will ask the builders later about walls etc.

The local council has confirmed planning permission is not needed, and that I must conform to building regulations. The house was built in 1970.

The plan is to remove the "up and over" garage door and fit an in fill window. Although there is a bedroom above the garage, the very front 1 metre portion of the garage is single storey with a flat roof.

1. So with only a small knee wall, and nothing on top of the proposed window, except a course or two of bricks to make it look pretty and a concrete lintel, I am hoping I won't need a very deep foundation for the very front portion of the study/window?

2. The existing garage floor is a 4" concrete slab which I have started to break out. The level of the existing garage floor is higher than the rest of the house - so it needs to come out. Underneath the concrete slab is rubble/sand/soil. The proposed floor construction will be an insulated concrete slab. Can someone please advise the sequence of construction layers needed - and how deep I must excavate? I have plenty of 100mm Kingspan on site - so will 100mm of Kingspan insulation be OK for building regs?

3. Can the layer of Kingspan sit on top of the new concrete slab - rather than vice versa? I ask this because the intention is to lay underfloor heating (UFH) - and having the Kingspan nearer the surface will help with energy/heating efficiency (i.e. heat reflected back in to the room rather than absorbed by the concrete slab?). The UFH system uses plastic matting which is rolled out - and in to which the plastic pipes snap. This system is low weight/height build up and suits the rest of the ground floor which is suspended timber construction.

4. If the layer of Kingspan insulation CAN go at the top, I don't want to lay my UFH mat directly on top of the Kingspan. I am assuming some form of compactable material needs to go on top of the Kingspan first - perhaps sand? If so, I could then lay T&G Chipboard on top of the sand. Having said that, to save ceiling height could I instead float Chipboard on top of the Kingspan and omit the sand layer?

Thanks for any help and advice - as I am feeling VERY out of my depth with this one!

Thanks

 

[Leofric]

Chipboard on sand - don't think so ! What does the manufacturer of the underfloor heating system recommend ?
' will ask the builders later about walls etc.' -
are builders designing buildings now before they quote on the work ?
The normal procedure is to design the building/conversion, obtain bldg. regs approval and then go to builders for quotations.
The building regs drawings will show the proposed construction and specification including thermal insulation required to comply with bldg. regs.

 

[^woody^]

There are probably 100 threads on garage conversion floors and front walls.

 

[noseall]

1. So with only a small knee wall, and nothing on top of the proposed window, except a course or two of bricks to make it look pretty and a concrete lintel, I am hoping I won't need a very deep foundation for the very front portion of the study/window?

You will need a standard foundation down to good ground. If you are lucky some have a foundations there already.

2. The existing garage floor is a 4" concrete slab which I have started to break out. The level of the existing garage floor is higher than the rest of the house - so it needs to come out. Underneath the concrete slab is rubble/sand/soil. The proposed floor construction will be an insulated concrete slab. Can someone please advise the sequence of construction layers needed - and how deep I must excavate? I have plenty of 100mm Kingspan on site - so will 100mm of Kingspan insulation be OK for building regs?

​

Higher? Trés odd.
Anyhoo you will require....
100mm compacted hard core.
25 - 50mm compacted sand blinding.
DPM
100mm celotex including25mm perimeter insulation.
100mm concrete slab
75mm screed.
There are variations on where to position the insulation as well as variations of how to finish the slab All depends on things like UFH etc.

3. Can the layer of Kingspan sit on top of the new concrete slab - rather than vice versa? I ask this because the intention is to lay underfloor heating (UFH) -

Yes, standard practice. The (wet?) UFH is clipped directly to the insulation.

4. If the layer of Kingspan insulation CAN go at the top, I don't want to lay my UFH mat directly on top of the Kingspan. I am assuming some form of compactable material needs to go on top of the Kingspan first - perhaps sand? If so, I could then lay T&G Chipboard on top of the sand. Having said that, to save ceiling height could I instead float Chipboard on top of the Kingspan and omit the sand layer?

Wet UFH is clipped directly to the insulation and a 75mm s/c screed laid on top.
​

 

[powerbooksub]

Noseall, thank you so much.

Exactly the level of detail I was after.

Thanks again!