Detached garage / workshop wall insulation

[stanleyfromspa]

Hello group,

I'm planning the upgrade to my garage to make it a more pleasant (=warm) place to work on the car. It will not be habitable space.

The garage construction is fully detached from the house and built as follows:

Walls - 215mm solid wall of 102mm facing brick tied to 100mm block work
Floor - 125mm concrete over a polythene DPM

Having insulated and draught proofed the roof, doors and windows I would like to insulate the walls and plan on the following final layers:

Outside
215mm solid wall
- 102mm facing brick
- 100mm block work
25mm timber battens
65mm Kingspan / Celotex insulation
Plasterboard / interior timber cladding
Inside

So my questions are:

• Where should the vapour protection be installed?
• Do I need a vapour permeable membrane and a vapour barrier in different parts of the wall, if so where for each?
• When battening should my lowest horizontal batten be above the DPC in the wall? (i.e. not bridge across the DPC)
• Should I also fill the voids between battens with insulation or leave for services?

Apologies for the basic questions but I'm finding the information on the web confusing and in some cases conflicting.

Thanks in advance

 

[John D v2.0]

Vapour barrier needs to be warm side of the insulation.
Although my concern is whether you'll have enough ventilation if you're working on car stuff. If you're not generating much moisture, you might not need to worry, as only the battens would be moisture sensitive

 

[^woody^]

You don't need a vapour barrier. They are for timber frames.

Stop the battens above DPC.

 

[stanleyfromspa]

Thanks for the speedy responses and information chaps. If I understand correctly this means the following:

Outside
215mm solid wall
- 102mm facing brick
- 100mm block work
25mm timber battens
65mm Kingspan / Celotex insulation
Vapour control layer
Plasterboard / interior timber cladding
Inside

Thanks again

 

[stanleyfromspa]

Vapour barrier needs to be warm side of the insulation.
Although my concern is whether you'll have enough ventilation if you're working on car stuff. If you're not generating much moisture, you might not need to worry, as only the battens would be moisture sensitive

Hi John D, I'm not planning on painting or running vehicles in the workshop so there shouldn't be an issue with ventilation. Thanks

 

[JohnD]

beware putting the car into the garage when it is wet with rain, this causes a blast of moisture which can cause tools etc to rust.

unheated sheds and garages are prone to condensation as the temperature fluctuates. Ventilation doesn't seem to help much. Yours sounds substantial and well-insulated so will not suffer as much most.