Air / Vapour Barrier in Garage

[benben5555]

Hi,

 

We've got a timber frame house under construction. The garage is attached to the house but has a bedroom above. I'm going to insulate the garage walls to keep it slightly warmer in there, there will be no heating, but our water cylinder will be in there. There will be insulation in the garage ceiling to insulate the floor of the room above. I'm planning on using an airtight paint on the floor of the room above.

 

Do I also need to put an air membrane on the inside of the garage? I was planning on doing this, but now I'm not sure if it is necessary.

 

Thanks

[Nickfromwales]

1 hour ago, benben5555 said:

Do I also need to put an air membrane on the inside of the garage?

This is the correct route, but then you must NOT use the paint as the layers will need to breathe. FYI, putting the AT paint on the floor will be utterly useless and do diddly squat for AT. The AT needs to come past this layer in the garage, and then that membrane gets taped to that layer.

Look at AT as a perfect cube, will all lines, corners etc in contact with one another, as anything less will gives terrible results for a lot of time and money spent.

 

If you can have the cylinder anywhere else, then do so, the garage should be the absolute last option as the heat loss over winter will be significant (albeit a cost / compromise that you may be willing to accept to gain space inside the house).

 

Go way above B Regs levels of insulation in the ceiling of the garage, as this will pay huge dividends over time, that's because the garage will be the coldest draughtiest area in the building so will attract heat loss. You may also need an airtight door separating the garage from the house, or do away with that altogether, IF you want to get a great AT score?

 

You buy insulation once, it lasts a lifetime, but gas and electricity will keep costing you for your lifetime, a cost you need to mitigate against with every effort. The same can be said about the insulation everywhere else, as UK B Regs offers the poorest house you can legally build, and is an utterly dire standard on a very, very good day (and that is the most you can expect if / when the work is executed meticulously by a builder with a conscience which doesn't happen with high frequency btw). 

[markocosic]

AIRTIGHT layer can be anywhere in the buildup

 

VAPOUR RETARDER should be on the warm side (e.g. the floor)

 

https://buildingscience.com/documents/insights/bsi-001-the-perfect-wall

 

What is your plan for the build? Treat the garage as you would the outside world.

 

Seconded on going to town on insulation.