Detached garage conversion


Standard Member
Hi All

A long time lurker here. I have started converting a detached single garage in my garden into a movie room and after your views/advice.

The room is 2.5m wide, and about 5.7 long. Its single skin brick, with a concrete floor, and hip roof. Its about 1m from the boundary with my side and rear neighbours so decent sound proofing is fairly important, but i need to keep wall depths to a minimum as its already pretty narrow.

Work proposed is;

Stud work 2x3s at 400m spacing for walls/ceiling, with a 1" gap between outer wall and studs.

Floor to be built from 10mm celotex, on a membrane, and with chipboard on top.

75m R45 equiv Rocksilk insulation inbetween wall and ceiling joists (with additional cheap wickes insulation on top of ceiling joists

Double plasterboard, with all gaps sealed with silicon.

No building regs needed as an exempt building. Considered it but means i need a separate 'means of escape' which messes up the design.

So the questions are;

1) Does the insulation sound adequate? - I am trying to max the acoustic and thermal values

2) Double plasterboarding-How much better is acoustic board? (even if only for one layer).

3)As an alternative to green glue what are thoughts on a) nothing, b)silicon sealant, c) builders caulk

4) The back wall (entrance) will be french doors, and I am proposing black blinds and heavy curtains to help minimise sound escape. Considering a second set of double wooden doors opening inwards, but will be costly as need to get the right size etc. What are your thoughts on sound loss through the french and curtain set-up vs alternative?

5) Probably the wrong section for this question, but to keep it all together; what are your views on projector tech in view of room size etc? Screen will be around 92" diagonal and seats min distance of 10/11ft. There are so many choices with Sony and JVC proprietary tech and the normal DLP vs LCD debate, and prices vary wildly even at the bottom end. I am looking at PJs up to around 3k but in view of screen size etc, what about some of the 1k PJs?

6) Finally, from experience does the overall construction so like it'll do a decent job of cutting down the escaping noise?

Sorry for lots of questions




Active Member
Sounds very similar to what I am doing, only I am building the block shell as well. I'm building the internal stud fixed to the floating floor so there is no connection to the outside wall, I think this will help with sound proofing. I'm doing the same with the ceiling/roof.

I'm going with internal fire doors as well as french doors so in effect the internal room can be closed off completely with no solid fixing to the outside skin.


Standard Member
Sounds very similar - I have built the stud walls to the concrete base of the garage - which may carry some sound i guess, but isnt hugely different to the 'staggered stud approach, so there wont be any direct contact.

Sounds like I am a little way ahead of you as i already have the 'shell' in place. I'll let you know how it works out.

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