Single skin brick garage workshop build

[Matty]

Hi all, I'm starting to convert a double garage to my new workshop tomorrow and would like any advice I can get. The garage is single skin brick and has had an extension built above. One wall is the house which I am not going to do anything with at the moment. the double doors are going to have a lean to timber extension added in the summer, this will be insulated and tale care of that side. The other two are the ones I am going to tackle this week.

When I started clearing the far wall I found that some muppet has built a couple of steps on the outside which are above the dpm, also someone has put earth and patio stones along the back about 400mm above the dpm. I can't tackle digging it out now but will do at a later date as it's clear by looking at the brickwork that its letting moisture in.

My plan is to build a CLS stud wall 38x89mm with an air gap between it and wall. Extend the ring main to add more sockets, insulate stud wall with PIR board then clad with 12mm hardwood ply. I will be using the workshop daily and would like to keep the worst of the cold out in the winter but I want to keep the build costs low as there are a few other things I need to buy for the workshop.

My question is what thickness PIR should I go for, Xtratherm PIR Board 50mm or 70mm? obviously 70 is better but is it overkill and a waste of money. I will put some air bricks into the brick wall when I get around to digging out the earth against it but for now I will put vent holes along the bottom of the stud wall and the top to help ventilate the void.

Any other tips or ideas on workshop building are more than welcome.

Cheers in advance, Matt

 

[Jameshow]

What do you mean by daily 9-5 or 7-9?
if 9-5 then 70mm
If 7-9 then 50mm.

Sounds a plan. Don't forget if a concrete floor you want to insulate that as well.

 

[Lons]

Just to clarify Matty, by single brick do you mean 100mm thick with support piers ( known as 1/2 brick width ) or double skin which is two bricks side by side so around 220mm thick if no cavity?
The reason I ask is that if the former then a habitable, or any extension wouldn't be allowed on top as it couldn't comply with building regs.

 

[robgul]

Just to clarify Matty, by single brick do you mean 100mm thick with support piers ( known as 1/2 brick width ) or double skin which is two bricks side by side so around 220mm thick if no cavity?
The reason I ask is that if the former then a habitable, or any extension wouldn't be allowed on top as it couldn't comply with building regs.

. . . it could be with steels . . . but the issue isn't really relevant to the OP.

Oh, and I'd clad the inside with OSB rather than plywood . . . probably cheaper, and to me a more pleasing appearance.

 

[Matty]

Hi Mate, the extension was already done and signed off prior to the house being bought. It is a single 100mm brick wall supported by piers and a steel over the double garage doors. I'm just looking to keep a bIt of the cold out and use it as a workshop as the car is not parked in there. I'm not touching the wall in any way just building a stud away from the wall and putting ply on it.

 

[Matty]

. . . it could be with steels . . . but the issue isn't really relevant to the OP.

Oh, and I'd clad the inside with OSB rather than plywood . . . probably cheaper, and to me a more pleasing appearance.

I used OSB on my last garage and I didn't think it looked too bad but dust and cobwebs cling to it really badly and I do prefer the look of the ply so I think I will probably end up using ply this time

 

[Matty]

Just to clarify Matty, by single brick do you mean 100mm thick with support piers ( known as 1/2 brick width ) or double skin which is two bricks side by side so around 220mm thick if no cavity?
The reason I ask is that if the former then a habitable, or any extension wouldn't be allowed on top as it couldn't comply with building regs.

It doesn't look like it should have had an extension over it but it was all signed off. Hopefully the stud will add a bit more support!

 

[Lard]

I will be doing something almost identical to yours very soon and over the past few months have gone through numerous plans in my head.....having used it in my bungalow's attic conversion I am leaning toward using multifoil instead of PIR to save a little width. My attic did use a combination of the two but as I don't intend living/sleeping in the garage I'm thinking the multifoil, incl air space both sides, will do for me.

 

[Agent_zed]

why not drywall it, plasterboard is a lot cheaper than ply/osb. It's also reflects light better even unpainted, or a coat of white paint will make it nice and bright.

 

[croft36]

Just to clarify Matty, by single brick do you mean 100mm thick with support piers ( known as 1/2 brick width ) or double skin which is two bricks side by side so around 220mm thick if no cavity?
The reason I ask is that if the former then a habitable, or any extension wouldn't be allowed on top as it couldn't comply with building regs.

Presume regs have changed then, I built over simgle skin garage circa 1970 with full council approval. I used single skin blockwork with hanging tiles.

 

[Lons]

Presume regs have changed then, I built over simgle skin garage circa 1970 with full council approval. I used single skin blockwork with hanging tiles.

It's always possible and slight variations depending on local authorities (though there shouldn't be) but there are 3 main considerations
Structural support and integrity which can be supported with steel
Complying with insulation and U value at the time of building
Whether the existing founds can carry the extra load of the extension / steel / insulation.

The latter was usually the first consideration and in the cases I came across during 19 years of owning a building company I don't remember a single instance where that wasn't required.

 

[Lons]

It doesn't look like it should have had an extension over it but it was all signed off. Hopefully the stud will add a bit more support!

As long as you have the paperwork Matty.

Personally I'd use OSB due to cost savings and paint it white to add light and seal the surface but ply is better if the budget allows.
I'd strongly suggest you fit a breathable membrane which is cheap and belt and braces especially with standard ply, OSB is more resilient and what are you going to do with the floor? Does it have a sound DPM (almost impossible to check.
You need to stop and damp from below DPC tracking across to the bottom timber plate and to the new floor which I presume you'll be fitting, there are several ways to tackle that.

 

[Lons]

. . . it could be with steels . . . but the issue isn't really relevant to the OP.

It might not be relevant to the post question but definitely important to ask in case the extension had been jerry built, most people would want to know that and in any case it's not up to you to police a thread and suggest what should be posted or not., this is an open forum as long as you obey the rules and I haven't broken any.

 

[Matty]

It might not be relevant to the post question but definitely important to ask in case the extension had been jerry built, most people would want to know that and in any case it's not up to you to police a thread and suggest what should be posted or not., this is an open forum as long as you obey the rules and I haven't broken any.

It's all good, it is not how I would want to see it built but it was signed off properly and it was checked over prior to the purchase and no issues came up. Its not my garage either so I'm not going to waste any money digging into the issue, hopefully it won't fall down and kill me , its been up for 7 years so .

I'm not going to insulate it anymore, I think it's probably a waste of money, treated the wall to help prevent damp and now putting up a 2x4 stud wall with ply facing to give me something to fix to and to make it look nice. Will add some vent holes top amd bottom to prevent moisture build up between stud and wall.

 

[Matty]

As long as you have the paperwork Matty.

Personally I'd use OSB due to cost savings and paint it white to add light and seal the surface but ply is better if the budget allows.
I'd strongly suggest you fit a breathable membrane which is cheap and belt and braces especially with standard ply, OSB is more resilient and what are you going to do with the floor? Does it have a sound DPM (almost impossible to check.
You need to stop and damp from below DPC tracking across to the bottom timber plate and to the new floor which I presume you'll be fitting, there are several ways to tackle that.

I've treated the walls directly to keep out the damp. Not going to insulate the walls now as im not going to insulate the floor, just vent the space behind the stud to prevent damp building up from condensation. The DPM on the floor is sound and the concrete is dry, I figure that the garage will be warm enough for 9 months of the year and the cold months I will just heat it with a space heater and man up!

 

[Lons]

I've treated the walls directly to keep out the damp. Not going to insulate the walls now as im not going to insulate the floor, just vent the space behind the stud to prevent damp building up from condensation. The DPM on the floor is sound and the concrete is dry, I figure that the garage will be warm enough for 9 months of the year and the cold months I will just heat it with a space heater and man up!

Sounds like a plan Matty and the stud walls will give you a degree of insulation, maybe some of those interlock mats where you stand will help. You'd need to man up more than a little if you moved up here to the frozen north. Hope the conversion goes well.

 

[MarkAW]

I've got one of these modernish garages pretty much exactly as you describe only mine isn't double size.
Best thing I did was insulate the big drafty steel door with stiff 50mm foil backed insulation. I fitted a pedestrian door, so I was able to seal up the up and over door (whilst still being able to unscrew and get the workbench out if I need)
The second best was boarding the ceiling with plasterboard and laying some rock wool on top.
The door and the ceiling were the worst culprits. It mad a huge difference
I have plans to insulate the walls next when funds and time allow. I'll probably use plasterboard.

 

[joseph67]

I used OSB on my last garage and I didn't think it looked too bad but dust and cobwebs cling to it really badly and I do prefer the look of the ply so I think I will probably end up using ply this time

Is there any surface dust and cobwebs won't cling to?

 

[Matty]

Is there any surface dust and cobwebs won't cling to?

maybe I'll to spray everything with ptfe dry lube and see if the spiders can build on that! lol