Garage ceiling plasterboard and insulation

[gavsw20]

Hi all. I'm looking at plaster-boarding and basic insulating of the garage ceiling this weekend. Room is as follows:
Dimensions = 5.8m * 5.3m
Use = Parking and work on two cars
Note: ceiling is a pitched roof (570mm spaced horizontal rafters) with tiles

Don't want to spend a fortune so will the following suffice please:
- https://www.wickes.co.uk/Knauf-Plast...-2-4m/p/220207
- https://www.wickes.co.uk//Earthwool-...aign=SaleCycle

Some question please:
1) - Is 9.5mm plaster-board OK or should I use 12.5mm
2) - Will that acoustic Earthwool offer basic insulation or am I better off with something like this - https://www.insulation4less.co.uk/rwa45-50mm

I have another thread on dot & dab but makes sense to keep this separate.

[gary1064]

I'm no expert, but aren't there building regs that need to be complied with, something to do with the fire rating if you create a garage ceiling? In our previous house with an integral garage I'm sure there were some restrictions on materials that could be used. Possibly not applicable to a detached garage. But I might be way off beam!

[gavsw20]

I'm no expert, but aren't there building regs that need to be complied with, something to do with the fire rating if you create a garage ceiling? In our previous house with an integral garage I'm sure there were some restrictions on materials that could be used. Possibly not applicable to a detached garage. But I might be way off beam!

Thanks for this.

For clarity, the double-garage is attached to the house (lounge) but has nothing above it.

[Bonzodog]

Building regs for my sons garage was ,two layers of 15mm pb,intumescent mastic the joints and edges.

[gavsw20]

Building regs for my sons garage was ,two layers of 15mm pb,intumescent mastic the joints and edges.

Thanks, was that a garage with a room above it?

[Bonzodog]

Thanks, was that a garage with a room above it?

No,room was next to it.

[adrianw]

not sure about the building regs but wouldn't it be better to use celotex with the foil backing, then board it twice to get the fire rating?

[Jeremy67]

Garages are built to a lower spec, certainly will have been in the past, and can tend to be damp. Plasterboard and damp do not mix.

[Paneraiseeker]

One skin of 15 mm fireboard was enough when I did mine

[gavsw20]

One skin of 15 mm fireboard was enough when I did mine

Thanks for confirming, assume I'll need a a 'fire rated' loft hatch too?

[Mr Nuttington]

Plasterboard thickness depends on the spacing of the rafters you are spanning between: for just under 600mm I would use 12.5mm or a double layer of 9.5mm. As others have said though it's not the best thing for damp garages.

One thing you do need to think about if you are introducing insulation is vapour control. As you have a pitched roof you ideally need a vapour check layer on the warm side of the insulation and a ventilated cavity on the cold side with very regular eaves and possibly ridge vents to give cross-ventilation of the roof-space, all to prevent interstitial condensation forming and rotting your roof structure. If you cant achieve cross-ventilation you would need a fully taped and sealed vapour barrier on the warm side of the insulation to prevent warm vapour from migrating through the insulation.

I would always install a hatch of some sort to give access through the new ceiling to the space above - there's nothing worse that inaccessible voids.

One final thought - if the garage is reasonably new with spindly (50x100mm timber if you are lucky) engineered trusses don't use a sheet material that's too heavy (I'm thinking cement particle boards and some of the higher density plasterboards here) - the trusses wont have been designed to take big loads...

[Mr Nuttington]

I forgot to mention - have a look here to get the low down on building regs fire requirements for dwellings:

https://www.planningportal.co.uk/inf..._-_fire_safety

[Paneraiseeker]

If you use 12.5mm P/B or under with 600mm spaced trusses the plasterboard will sag over time. That's why with trusses you use 15mm board. Or batton the perimeter of each board but that's more costly and time-consuming.

[gavsw20]

Plasterboard thickness depends on the spacing of the rafters you are spanning between: for just under 600mm I would use 12.5mm or a double layer of 9.5mm. As others have said though it's not the best thing for damp garages.

One thing you do need to think about if you are introducing insulation is vapour control. As you have a pitched roof you ideally need a vapour check layer on the warm side of the insulation and a ventilated cavity on the cold side with very regular eaves and possibly ridge vents to give cross-ventilation of the roof-space, all to prevent interstitial condensation forming and rotting your roof structure. If you cant achieve cross-ventilation you would need a fully taped and sealed vapour barrier on the warm side of the insulation to prevent warm vapour from migrating through the insulation.

I would always install a hatch of some sort to give access through the new ceiling to the space above - there's nothing worse that inaccessible voids.

One final thought - if the garage is reasonably new with spindly (50x100mm timber if you are lucky) engineered trusses don't use a sheet material that's too heavy (I'm thinking cement particle boards and some of the higher density plasterboards here) - the trusses wont have been designed to take big loads...

Thanks for this and the PDF link. Although I am still confused with the fire-rating side of this and whether I need it or if can just go with regular 12.5mm plasterboard. I suppose for the sake of an extra £50 I should get it, but that then means a £130 fire-rated hatch.

The garage is pretty sound in terms of damp, it just gets really cold in the winter. when I'm working on my car. The room will not be heated, I was adding the insulation to keep this cold air and draughts out.

Here are images of what I'm working with - the beams I'm looking to affix the plasterboard to are 85mm * 40mm

[ENES]

If you are just lining & insulating a garage ceiling that has no accommodation over (or open to the roof space) - then there is no requirement to provide fire protection.

Roof structure does not require fire protection within a dwelling - floor.structure does.

As stated already - you should be looking to introduce cross ventilation to the roof void above the insulation, unless your roof is already lined with a breathable membrane (Tyvek or similar) beneath the roof tiles.