Single Skin Garage conversion - Wall system?

[Brian H]

Hi All,

Been lurking on the boards for a good few months now hatching plans to convert my single skin garage to a purpose built workshop.

Broad strokes of my plan will be to install floating floor (DPM, 70mm rigid insulation and 22mm chipboard flooring), frame walls (see attached) and as roof is an 'open gable' I plan to add joists to strengthen as I'll be using for light storage and ceiling system will be 15mm plasterboard, 25mm rigid insulation, 60mm RW3 rock wall and 22mm chipboard floor.

Early days, this past weekend I built a dense concrete block wall covering the up and over door (new development, so rules are I cannot modify appearance so door stayed as false front).

I'm about to start with internally framing and although I have done a fair amount of research but I wanted to check in here as I had read lots of advice and seen some great conversions.

Hopefully my attached picture has worked, I sketched up the wall system I planned to install... any concerns / comments? I'll be installing DPC to the bottom plate and side king studs that make contact with wall and concrete floor.

Any advice is welcome

Thanks
Brian

 

[MikeG.]

Welcome Brian.

Can you tell me what you think are the functions of the breather membrane and the OSB in that build up. Also, if I am reading your drawing correctly, you seem to have an air gap between two pieces of insulation. Could you tell me what the function of that is?

 

[gregmcateer]

MikeG will be along with some first rate advice - just do wot 'e says.

 

[Brian H]

Welcome Brian.

Can you tell me what you think are the functions of the breather membrane and the OSB in that build up. Also, if I am reading your drawing correctly, you seem to have an air gap between two pieces of insulation. Could you tell me what the function of that is?

Hi MikeG,

Great questions, honest answer I'm a lay person playing builder I should note all my 'knowledge' comes via youtube and forums... I'll welcome corrections

Tyvek membrane
I had understood that the breather membrane was there to allow any moisture entering the wall from the warm side of the workshop to escape (assuming that even if I attempt to seal the vapour barrier (rigid insulation) there is still a chance warm moist air might enter the wall system) and secondly it will prevent any moisture entering the wall system from the single skin brick side.

9mm OSB
I had noted whilst 'researching' this seemed common (might be a US thing?) and provided something for the rockwool RW3 to be placed against. Other than that I am unsure as I don't need structural strength...

Air Gaps
I have two voids, firstly I have the whole wall system 'standing off' the brick by 15mm, I had understood this would allow air to pass over the breather membrane wicking away any moisture. Second gap you noted was between rockwall and rigid insulation at around 25mm this is a service void for electrical as I do not want surface mounted trunking etc.

One final note, I'm trying my best to 'sound dampen' as much as I can on a budget... I had hoped that the multiple layers of differing mass would contribute to the wall systems damping effect, but I'm on even thinner ice if thats possible when it comes to my knowledge

Thanks for taking the time to comment and educate

Brian

 

[MikeG.]

OK, let's take a look. For a start, I couldn't see any gap between the Tyvek and the brick (your diagram is tiny, and dark). It would be useful if you have a void. However, to have it up against OSB, which is vapour inpermeable (to all practical intents), renders it pointless. And frankly, I can't see a use for the OSB.

Insulation is a way of trapping air in such a manner as to render it immobile. Moving air is what we are trying to avoid at all costs with insulation. So, there should be no voids within insulation which enable air to eddy around, transferring heat from one place to another. All insulation in any particular build up should therefore be continuous. It's perfectly OK to mix hard and soft insulants as you have here, but there mustn't be a gap between the two.

Moisture transmission through a wall is normally from inside to out. Inside of a building is generally wetter than outside because of heating, and because of human activity inside. Therefore the resistance to moisture entering the wall should be on the warm side of the insulation. So you should have a vapour impermeable barrier on the inside of the wall, and with plasterboard this can be achieved with the use of foil backed stuff. Or, you could line the walls with OSB or ply, which may be more practical in a workshop, and which act as both a vapour barrier and a wall lining.

Finally, half-brick walls (4" brick walls) are frequently damp on the back during heavy rain, as clay absorbs moisture then releases it slowly as it dries. So we need a way of dealing with any moisture that gets through the wall. Ventilation is the answer to many if not most damp problems, so I would suggest creating a ventilated void between your new build-up and the wall, and the best way to do this is by inserting airbricks, and by ensuring that there is a continuous space between the brickwork and the new lining.

So, my suggestion is to start by inserting airbricks at low level at say 1.5m to 1.8m centres around the walls. If the eaves are open you might be able to avoid having them at high level too, by allowing air to enter your new cavity via the eaves. If not then you'll also need high level airbricks. Then build a stud wall of say 2x2s or 3x2s, spaced 25mm off the back of the brickwork, minimum, with a membrane on the back to retain the insulation and allow any moisture out into the void. Sit the studwork on a DPM and with the membrane tucked under the frame at the bottom. Fill the frame with insulation, and plant some more on the surface, but leave no gaps between the layers. Finally fit your plasterboard (foil backed) or OSB over that, and mount your services on the face of the walls internally. Hidden wires in a workshop are a nightmare anyway.....it's much safer to have them surface mounted. The insulation in the roof, whether it is at joist level or follows the lines of the rafter, should meet the insulation in the walls so that there is a continuous envelope of insulation around the workspace. This advice also holds good for the door, which is usually the biggest problem in a garage workshop, and where all the heat goes flooding out.

 

[Brian H]

Hi MikeG,

Many thanks, sorry about the diagram size system may have reduced when I uploaded. I'll look to implement the changes as this tears out necessary costs and sounds like the OSB would be a hinderance rather than anything else!

Cheers
Brian

 

[Peptidoglycan]

Thanks for asking these questions Brian. I am looking at a very similar renovation myself right now. Except that the back wall of my 2-car garage is essentially one giant steel door. Need to think about how I am going to take that out and transition to a new external wall etc. The responses here are really helpful.

 

[Brian H]

Thanks for asking these questions Brian. I am looking at a very similar renovation myself right now. Except that the back wall of my 2-car garage is essentially one giant steel door. Need to think about how I am going to take that out and transition to a new external wall etc. The responses here are really helpful.

I feel your pain, it's exciting to get started but it is only then you realise that you have more questions than answers...

For what it's worth on my single garage I built a block wall, see attached. Never laid a brick in my life so was fun to learn a new 'skill' or at least have a much greater appreciation of the skill that goes into brick laying! Because I am concerned about sound damping to keep good with my nice neighbours I used dense concrete blocks for the mass... boy was this killer to lay but pleased with result.