Vapour Barrier in internal garage conversion - yes or no?

[Olly80]

First time poster here, but there seems to be a lot of very knowedleg people around and I was hoping to obtain some help. I've had conflicting advice on this issue, and I'm at the stage where I need to push on and either do it, or not... or do whatever else needs to be done to ensure I don't have any problems further down the line.

 

The diagram below should hopefully help explain better, but basically I am converting my integrated garage into a small home cinema/TV room, using a room within a room approach to assist with the decent level of sound isolation I am hoping to achieve. The inner walls and ceiling joists are completely decoupled form the surrounding brickwork, and the outer wall is a separate element, not connected to the inner studwork. Technically, there is some very minor bridging going on with my acoustic baffle boxes, but they are linked with flexible duct sleeve, so it's minimal.

 

There are no windows, as due to planning restrictions, we cannot alter the appearance of the front significantly, so the garage door must stay. However, I am allowed to have air vents in the garage door, and this is how the room will be provided with fresh air (and extracted with a fan) via the acoustic baffle boxes in the the diagram and ducting leading to the vents in the garage door.

 

My question is whether I need a vapour barrier on the inner wall or not? I've read lots of advice on this pertaining to freestanding buildings, sheds etc. but my situation is somewhat different (at least I think it is), so I don't know if the same rules apply? My initial thinking was that I would need one on the inside wall, behind the OSB/Plasterboard. However, I have had some people suggest to me I don't need it. One builders merchant said I should use PIR board on the outer wall on top of OSB, and no need for anything else. I'm not sure if that's correct, but it only added to my confusion.

 

As per the diagram, I don't HAVE to use OSB on the outer wall, it's just what's been suggested, plus I have a load left from lining the inside of the room with it.

 

If anyone could please offer any advice on this it would be very much appreciated. Many thanks.

[A_L]

6 hours ago, Olly80 said:

My question is whether I need a vapour barrier on the inner wall or not?

 

Hello and welcome. As long as the original house remains at normal levels of humidity and the cinema has frost protection levels of temperature then no VCL between them is required.

[scottishjohn]

If you need one in a house --habitable area

-why would you not need one in your new habitable heated area?

I look forward to an experts reply

you have not said what is happening to floor+ ceiling of this garage ---

Is the garage constructed with a cavity wall --or just one layer of brick or block

 

Edited August 23, 2020 by scottishjohn

[Olly80]

2 hours ago, A_L said:

 

Hello and welcome. As long as the original house remains at normal levels of humidity and the cinema has frost protection levels of temperature then no VCL between them is required.

 

I would say the house does remain at normal levels. Generally speaking, it's a very well temperature controlled house, never too hot in summer and retains warmth well in winter, without the need for heating on anything but the coldest of days. As for the garage, have been living here for 3 years up until now, and have never once seen frost in there. So I certainly don't see that being an issue with the new walls, insulation in place.

 

 

1 hour ago, scottishjohn said:

If you need one in a house --habitable area

-why would you not need one in your new habitable heated area?

I look forward to an experts reply

you have not said what is happening to floor+ ceiling of this garage ---

Is the garage constructed with a cavity wall --or just one layer of brick or block

 

 

The floor has already been raised with DPM and insulation to bring it up level with the rest of the house.

 

The original ceiling of the garage is within the house (made of concrete slabs), above which is the kitchen (slightly upside down house). As mentioned, the new room has new joists (with Rockwool slabs in-between) spanning the new stud walls, independent and decoupled of everything else.

 

The block walls are cavity wall on one side (shared with next doors garage), and the other two walls are single block. What can't be seen in the diagram is that there is a bedroom behind the left end wall, and the hallway on the side bottom wall.

Edited August 23, 2020 by Olly80

[Olly80]

Anyone else have any suggestions on this? Thanks.