Part garage conversion

[david3456]

We have a double garage that is quarter integral with the house. The idea is to convert the bit under the house to a utility room. There is a pillar in the middle of the garage which holds up the corner of the house so it is a matter of closing off two openings and cutting a door through from the hallway.

My idea is to put up studs and to use plywood on the garage side, plasterboard on the house side and insulation between. I just want to check that there are no regulations that might disapprove of this.

If this is ok, I notice studs are 89mm wide but insulation is in multiples of 25mm. Would I leave the air gap garage side or house side? Is there any issue between choosing celotex or polystyrene?

 

[david3456]

Perhaps the first question should have been, do I need to register/get permission for change of use?

 

[^woody^]

I just want to check that there are no regulations that might disapprove of this.

The wall needs to have 30 minutes fire resistance, and your proposal won't.

It will also need to be insulated to the standard of an external wall.

Ventilation, electrics and any drainage will also need to be approved under building regulations.

There is no change of use, but you will need to check with the council planning dept, that there is no planning condition requiring the garage to be kept as a garage

 

[david3456]

I just want to check that there are no regulations that might disapprove of this.

The wall needs to have 30 minutes fire resistance, and your proposal won't.

Hmmm. I thought plasterboard was a fire-break. At the moment the only barrier is a sheet of plasterboard under the bedroom floor joists. That's how the house was built 40 years ago. Have the rules changed?

What would I need to add to make it sufficient?

 

[noseall]

My idea is to put up studs and to use plywood on the garage side

Hmmm. I thought plasterboard was a fire-break.

Plasterboard is but ply wood isn't. There would be nothing stopping you putting a layer of ply beneath the plasterboard or fill out with ply between studs, if you are looking for a solid fixing arrangement.
The wall will also need to comply thermally also. Here is a recent spec' for a wall separating habitable from a garage/store.
INSULATED WALL BETWEEN WC AND STORE: TO STORE SIDE, 2 LAYERS 12.5MM FOIL-BACKED PLASTERBOARD WITH STAGGERED JOINTS AND PLASTER SKIM ON 100MM X 50MM TIMBER OR METAL STUDDING WITH 100MM CELOTEX FULL-FILL INSULATION., FINISH WITH 37.5MM CELOTEX PL4000.

 

[david3456]

My idea is to put up studs and to use plywood on the garage side

Hmmm. I thought plasterboard was a fire-break.

Plasterboard is but ply wood isn't. There would be nothing stopping you putting a layer of ply beneath the plasterboard or fill out with ply between studs, if you are looking for a solid fixing arrangement.
The wall will also need to comply thermally also. Here is a recent spec' for a wall separating habitable from a garage/store.
INSULATED WALL BETWEEN WC AND STORE: TO STORE SIDE, 2 LAYERS 12.5MM FOIL-BACKED PLASTERBOARD WITH STAGGERED JOINTS AND PLASTER SKIM ON 100MM X 50MM TIMBER OR METAL STUDDING WITH 100MM CELOTEX FULL-FILL INSULATION., FINISH WITH 37.5MM CELOTEX PL4000.

The idea is the plywood forms the outer mechanical barrier on the garage side. There wouldn't be much point putting it under plasterboard! So it appears that stagger and pl4000 means 3 layers of pb, whatever.

Useful information.

 

[chappers]

From memory the bottom 100mm of the wall will also have to be masonry to comply with fire regs, unless the garage has the prescribed fall in the floor to the front (sorry can't remember the required gradient).

 

[^woody^]

From memory the bottom 100mm of the wall will also have to be masonry to comply with fire regs

You've got dodgy memory.

What happens to stud walls upstairs?

 

[^woody^]

At the moment the only barrier is a sheet of plasterboard under the bedroom floor joists. That's how the house was built 40 years ago. Have the rules changed?

No, its still the same for floors.

And still the same for walls too. You could have just one sheet of plasterboard and skim if you knew which side of the wall the fire would start.

 

[chappers]

From memory the bottom 100mm of the wall will also have to be masonry to comply with fire regs

You've got dodgy memory.

What happens to stud walls upstairs?

It's not just to do with the spread of fire it's to do with the potential leak of flammable liquids from the garage, there must either be a 100mm step impervious to flammable liquids or the floor must fall away towards the garage door.

 

[david3456]

Useful additional responses. I intended to put a run of bricks down anyway so I that can hose down the garage floor. Interesting about skimmed plasterboard. It seems that retardant plasterboard with filled gaps should do the same job. Any other cover would improve on it.