Insulating a garage ceiling that has a bedroom above

[dotmatrix]

Hello everyone,

We have recently moved into a 1950’s build house with an integrated garage that has a very cold bedroom above it. I have checked the loftspace which has an old loft conversion but has minimal insulation around the pitched part of roof under which the bedroom sits. I am planning on topping this up.

The whole house needed a new heating system, so I have been in the process of replacing all the central heating rads/pipes/boiler, as the new boiler sits in the garage I was asked by the plumber to remove the asbestos ceiling in the garage which is now gone so he could route the pipework through without the dangers of disturbing the asbestos.

Since the ceiling has been taken down I have taken it upon myself to insulate the space between the bedroom my 1 year old sleeps in and the garage below, after lots and lots of research I have decided to use foil faced PIR board 100mm (Ballytherm brand) from the garage ceiling butted up against the floorboards between the joists. There are some areas between the joists that contain cables/pipes that I will be covering with conduit and due to the awkward ness of the space between the joists I will use a rockwool type of insulation. I am then planning to board up with pink fireboard.

My question is, is this the correct way to go about it am I leaving myself open to condensation issues, I’ve been reading about vapour layers and whether I need one. Any help would be appreciated,

 

[^woody^]

My question is, is this the correct way to go about it am I leaving myself open to condensation issues, I’ve been reading about vapour layers and whether I need one. Any help would be appreciated,

None of that applies in this case. Do what you proposed.

Two layers of plasterboard is recommended for garages as this allows joints to be overlapped and protects better from fire or smoke getting through a single joint.

Seal around any joists going into walls to prevent draughts (which is the biggest cause of cold floors and heat loss), and use intumescent seal around the ceiling/wall junction.

 

[JB-BJ]

None of that applies in this case. Do what you proposed.

Two layers of plasterboard is recommended for garages as this allows joints to be overlapped and protects better from fire or smoke getting through a single joint.

Seal around any joists going into walls to prevent draughts (which is the biggest cause of cold floors and heat loss), and use intumescent seal around the ceiling/wall junction.

Why would that not apply in this case?

Also, is it correct to place the insulation up against the floor of the room above, or should it be level with the bottom of the joists of the ceiling below?

 

[^woody^]

There is no condensation risk in a timber floor below a room and above a garage.

Insulate the heated room to keep the warm in, not the cold room

 

[JB-BJ]

There is no condensation risk in a timber floor below a room and above a garage.

Insulate the heated room to keep the warm in, not the cold room

Forgive me for hijacking the thread, but I'd be grateful if you could take a look at a similar thread I recently started. I mention in my thread that there's conflicting advice and that seems the same here!

https://www.diynot.com/diy/threads/garage-ceiling-insulation-struggling-with-requirements.530893/

 

[dotmatrix]

i have spoken to building Regs and Kingspan and neither mention a gap between the floorboard and insulation board. I know what you mean though, the advice out there makes everything more confusing.

@^woody^ how would you hold the board up? or will the friction just hold it?

 

[^woody^]

@^woody^ how would you hold the board up? or will the friction just hold it?

Lath or batten. Either long pieces or 100mm pieces every 500mm or so.