Garage to Home Office Conversion

bunderoon

Hey all.

We have a late 1970s garage stepped back attached at the gable side of the house. ~12FT x 15FT.
4" cavity walls, insulated with 2-3" foam boards.
Plastered and was plumbed with old rad, not connected anymore and wont be again.
Floor is poured but a few cracks and small poc holes from years of being used as a storage area.
A ~8FT PVC sliding door be installed on a newly laid set 3x4" soap bar block at the opening.

Question is about the floor.
Its always bone dry but a builder suggested ripping it out and going down, installing membrane and putting 4" insulation boards and then screed over. To me, that seems like an awful lot for what it going to be.

My thinking is since the line of blocks will raise the step in level floor up by 3", then simply sort out the cracks and poc holes (they are small), lay membrane, then lay 50mm insulated boards and follow with laminate flooring that will meet the inside frame of the sliding door.
Insulated slabs will be fixed to walls and ceilings. I think the builder is making more out of this job than it needs to be. Power and sockets already out there.

House as recently renovated with complete rewire.

Thoughts on the floor?

Calahonda52

do you intend putting more insulation on the existing?
what do you mean by 4" cavity walls?

bunderoon

Calahonda52 wrote: »

do you intend putting more insulation on the existing?
what do you mean by 4" cavity walls?

Standard 4" double leaf wall. With 4" gap between each leaf. Already insulated. Concrete floor poured when house was built. It had a plastered finish for the time.
Want slab the ceiling joists (6x2s) and walls with 50mm insulated plaster boards.
The ground is always bone dry which makes me think that there is already a membrane down under the floor.

Builder quoting to conversion job is saying to rip the floor up to reinsulate. I'm saying that the new sliding door will be 4" above the ground on new line of blocks ( roller shutter door there at present).

Is laying a new membrane straight into the floor, then insulated board (50mm) then laminate flooring enough or is the done thing to rip up all that concrete and go down further and put more insulation down (100mm).

Calahonda52

The math is simple enough, its the energy saved by having 50mm as opposed to 100mm.
.
For a HO, I would not be inclined to rip it out.
.
The DPC etc detailing with the 4" step will be very important, as well as how it ties in with the under floor membrane
what is the Hamite flrr going to sitting on, concrete or timber ?

depending on your time scale what you could do is put a sheet of plastic on the floor as is and see does it get damp underneath