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Garage conversion/workshop fit out

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Garage conversion/workshop fit out

Postby samhay » 11 Jan 2022, 13:50

Hi Folks,
We recently moved and the new place has an external double garage, which will become a workshop.
I could do with some advice. I'll post some photos when I'm able and am happy to make this a WIP if there is any interest.

The garage is only a few years old, built in single skin blocks with pillars. The walls seem to have a damp course between the first and second blocks. It has a flat roof with an RSJ taking the main span - built to a max external height of 2.5m I assume. Joists are, I think 7 x 2" (I can't find my tape measure in all the packing boxes) plus the extra pieces to add a minimal slope for water runoff. The roof is in good condition and, bar any insulation or ceiling looks like a pretty standard cold flat dormer roof construction.

The less good: It's build on a concrete pad that has been widened at some point (i.e. there's a join in the middle of the garage) and the pad extends past the walls on 3 sides. It also currently lacks any doors, so rain can be blown in. The pad/floor is a uneven and slopes towards the back, so there is some water pooling in places, including along the back wall. There is currently a load of junk piled along the outside back wall, which will be removed ASAP, but it looks like there may be water getting under the back wall or through the floor.

The door (double garage door size) is the only opening, so I am toying with the idea of using a UPVC double sliding door unit - i.e. as you might in a garden room - to give plenty of natural light.
I have plenty of driveway, so don't mind losing the option of parking in the garage and I think I can get a door configuration that would allow a 4'+ opening for sheet goods. The space isn't big enough for any monster machinery.
This would also give me the option of building the floor up with some insulation under a wooden floor. I don't have loads of head height, but I could lose 3-4" without too much issue. Whatever I do, the floor needs levelling.

What's the correct order of business - install doors or fix the floor/water ingress?
I will assume the concrete pad does not have a meaningful damp course, so I assume I'll need to add something if I can going to build a floor up from it?

Thanks in advance,
Sam
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Re: Garage conversion/workshop fit out

Postby Lurker » 11 Jan 2022, 14:29

The problem with garage doors is that every time you go in, anyone passing can see what’s worth nicking.

I would put in a side door and fix the garage doors so that they are impossible to open from the outside.
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Re: Garage conversion/workshop fit out

Postby Mike G » 11 Jan 2022, 14:39

Right, Sam, this needs photos. Slabs extending past external walls are a damned awkward feature to deal with, but it is doable.

I don't suppose you're anywhere near Butterton, are you? I'm up there in a couple of weeks and if it's not miles out of the way I could have a quick look.
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Re: Garage conversion/workshop fit out

Postby samhay » 11 Jan 2022, 16:10

I'm the other end of the Peaks I'm afraid Mike. Thanks for the offer though.
I will take some photos as soon as I find myself at home during daylight.

The security issues with garage doors is a good point. It's a quiet road and there will often be a car in front of the garage, so I'm pretty sure I'm happy to take the risk.
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Re: Garage conversion/workshop fit out

Postby AJB Temple » 11 Jan 2022, 17:52

Mike is the total expert on buildings.

But as a workshop if you want machinery in it, I would definitely insulate it, as it will make it much more usable all year round and also cut down a lot of noise. You probably only need one pair of doors 90% of the time, so I would put removable seals on the other pair and removable insulation panels across those too. Get your additional wiring in for plenty of sockets and lights too.
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Re: Garage conversion/workshop fit out

Postby Andyp » 11 Jan 2022, 18:20

samhay wrote: I'm able and am happy to make this a WIP if there is any interest.



there will always be interest in this sort of thing Sam. Always great to see how someone else approaches a task like this.
cheers

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Re: Garage conversion/workshop fit out

Postby samhay » 11 Jan 2022, 22:18

I found my tape measure. The door opening is ca 3.6x2.2m.
I was thinking of putting something like this in it:
Image
It's not terribly pretty, but in keeping with the house and will provide plenty of light.
There will definitely be insulation going in the ceiling, and probably the walls.
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Re: Garage conversion/workshop fit out

Postby samhay » 12 Jan 2022, 16:08

Some photos:
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First job is to clear all the stuff piled against the back wall.
Happy to take more photos if there are specific things to look for.

Thanks,
Sam
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Re: Garage conversion/workshop fit out

Postby 9fingers » 12 Jan 2022, 18:18

I would be really concerned about the security of your door solution especially as it seems to be facing the road/pavement.

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Re: Garage conversion/workshop fit out

Postby Woodbloke » 12 Jan 2022, 18:47

9fingers wrote:I would be really concerned about the security of your door solution especially as it seems to be facing the road/pavement.

Bob

As would I; too much of a temptation. 'Out of sight, out of mind' is one of my mantra's that I've attempted to follow over the years. The door solution looks good, but it's too easy to see all the goodies inside; I'd be tempted to chop a rectangular hole in one of the side walls and fit a smaller, windowless door which is sufficiently wide to allow machinery in and projects out. Mine is just a single door and it's been fine for well over a decade - Rob
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Re: Garage conversion/workshop fit out

Postby Mike G » 12 Jan 2022, 18:50

I think you've got your priorities right in clearing everything away from the walls. I would then make sure your ground level is below slab level all around........and then get some photos of the base of each wall. Also, make sure the roof and gutters are working properly, including standing out there watching carefully next time it rains.
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Re: Garage conversion/workshop fit out

Postby samhay » 12 Jan 2022, 20:17

Thanks Mike. That sounds like this weekend's workout sorted.

Comments on front/doors noted. Knocking a door through on the right hand side is not impossible, but may not pass spousal planning permission.
Any windows in the front will have blinds or shutters, but appreciate that isn't a perfect solution either.
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Re: Garage conversion/workshop fit out

Postby AJB Temple » 12 Jan 2022, 22:50

Clearly the roof drains off to the left (looked at from the front) and should not be too difficult to drain away - does the gutter feed a storm drain - there is a horizontal pipe that runs off somewhere.

It is definitely a big help to have natural daylight and so I would not discount a glazed solution as long as it is made secure.

Steel RSJ's will drip like mad in winter. Insulate.

Looks like a nice size for a workshop. That blockwork could always be rendered and the whole thing softened with some planting.
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Re: Garage conversion/workshop fit out

Postby Lons » 12 Jan 2022, 23:16

I'd agree with the suggestion to render, my first though was that rain will penetrate that block wall especially if wind driven.
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Re: Garage conversion/workshop fit out

Postby samhay » 13 Jan 2022, 13:46

Yes, the roof drains to the left and the gutter seems to work (but I will check properly when we next get rain). The downpipe was draining onto the slab, so I added the piece of gutter as a temporary bodge to get this to drain into the garden below. I don't think there is a drain we can tap into there, but I can add a soakaway. This side is a couple of feet lower than the slab, which is helpful.

I'll have a think about rendering the outside. It's quite possible that we are getting water penetration through the blocks, so that would be a good fix. It would also make it look less like a bunker. I guess the other option would be to paint the outside in a few coats of good masonary paint?

And good point about the RSJ and condensation. I guess a layer of insulation below this would be better than just adding bats between the joists.
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Re: Garage conversion/workshop fit out

Postby AJB Temple » 13 Jan 2022, 14:04

I would run the rainwater to a water butt if you have any gardening aspirations, and drain off overflow to somewhere suitable not adjoining the building.

Painted blockwork always looks like ....painted blockwork. You can buy proofing paints (usually multicoat) but it will look a great deal better if you render it.

Have you eliminated most rainfall splash back from splashing back off the ground onto the building walls?

Mike will advise you on the best way to insulate the roof, and provision of any necessary airgaps. Whilst you are at it you may wish to incorporate wiring in the ceiling from which to dangle a power supply over any machines, provide overhead LED lighting panels and possibly extraction hose brackets, and some hangers for long bits of wood that you will soon have in stock!
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Re: Garage conversion/workshop fit out

Postby 9fingers » 13 Jan 2022, 14:08

I would saturate the inside walls with synthaprufe prior to insulating and cladding with ply

This will control the internal dampness and allow external decoration to the requirements of the domestic authority without the method needing to have perfect sealing.

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Re: Garage conversion/workshop fit out

Postby samhay » Yesterday, 09:52

I've now cleared around the base of the garage and dug it out (only about 2-3") on the side that had grass right up to the edge. I have taken photos around the base.
One observations is that there was heavy duty plastic sheet down along the back. Water was pooling on this and probably penetrating through the bottom of the wall.
I can't dig much deaper on any side as the slab extends out from under the walls in places. To tidy it up, I could put some weed membrane down and an inch or two of pea gravel to keep the weeds at bay. Is that going to be a problem raising the ground back up higher onto the slab?

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Re: Garage conversion/workshop fit out

Postby Mike G » Yesterday, 10:28

Great work Sam. That's done more to dry out your building than anything else you could have done. You should keep the ground level below the slab level all around, and if necessary, organise for any low areas to drain.

Right, the problem of concrete extending outside the walls....... Mortar won't stop water penetration. You'll actually see it run in if there is enough water externally. You should take action externally, not internally. The simplest course of action would be to paint some Black Jack/ Synthapruf over the junction, extending 3 or 4 inches out, and 3 or 4 inches up. It might work. Personally, I would be casting a concrete fillet all around. This would be a sloping concrete shelf a few inches up the wall down to the outside edge of the slab, or at least a foot away from the wall. Then belt-and-braces, you could Synthapruf that. Make sure that this fillet doesn't come within 6 inches of your DPC.

Some might suggest Synthapruf over the junction, then a concrete fillet over that, but I would be worried about the concrete adhering properly to the Synthapruf.

This fillet will almost certainly crack over the years, and you should repair this when that happens.

Rendering the blockwork would be a good solution, but you MUST stop above the DPC. Normally, alternatives would include battening out and applying feather edge boards or proprietry cladding. I don't think FE boards are appropriate in the Peaks, though.

Before you do any work to the blocks and slab, you must thoroughly clean. A pressure washer would be a good starting point. Personally, I think I would be leaving all of this work until the summer, to make sure I started with a completely dry structure. Obviously, any necessary work to the roof, gutters and downpipes can happen as soon as you like, and the sooner the better.

As for lining and insulation.....Yes, you should do it, but you must take care with your choice of insulation. If you use a board such as Celotex, there really should be a ventilated void outside of it if you want to do a proper job. This will mean cutting in airbricks, and spacing the Celotex off the wall. If you use Rockwool or similar, this can be hard up against the blockwork, but you need a greater thickness to achieve the same benefit as Celotex.

If you are going to insulate the roof (you should), then you need to ensure there is airflow across the top of the insulation below the roofing material. That means openings between both ends of each joist pair, and you'll need insect mesh. You can add a layer of Celotex below the rafters, too, and this can make a huge difference.
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Re: Garage conversion/workshop fit out

Postby samhay » Yesterday, 22:54

Thanks Mike, that's all helpful.
I agree that that most of this doesn't make any sense until the Spring when things can dry out. I have a few more questions I'm afraid.

Working down:
Roof - The rafters in the roof are 8"+, so there's plenty of room for 4 or 6" of bats between them and then perhaps a 1" of Celotex below to help with cold bridging from JCB.
Airflow across the top of this should be no problem except there is very little external overhang and and I'm not sure if there is any space for vents under the overhanging roof.
The facia needs to come off as there are several holes in it. Are there vents that can go into the vertical face of this? This also poses a challenge with rendering the walls as the facia will end up flush, or even inset, to the surface of the render if I'm not careful.
The roof is only a couple of years old and is covered in rubber, so I would prefer not to remove it if I don't have to.

Walls - I don't mind losing an extra few inches of floorspace to mineral fibre insulation if I don't have to add ventilation. I assume this still needs a membrane on the warm side and I can batten between the insulation to make fixing easier?

The slab - From the outside, it is quite difficult to see where the slab is in places and I'm not sure what the walls are sitting on in places - I need to dig further down once it dries out a bit. From the shape and state of what I can see, I expect some of the concrete was poured into an earth form (i.e. a hole) back in the day. Painting the junction of the wall and the slab is not going to work as the slab is not in good enough condition.
Internally, the slab slopes to the back with a drop of perhaps 2", so I'll use the DPC as the vertical height to refer off rather than the slab. I can see the sense in casting a fillet and this would also tidy it up nicely. Practically, I can't see much chance of digging below the slab height in a meaningful way in most places, but I could cast a 12" sloping shelf from say 2" below the DPC (it's 4-6" above ground height) with a suitable drop (1/2" enough?) to still give it some height at the outside edge. Back of the envelope calculations says I would need about 1/2 m3 of concrete for this, which is not a major issue.

Internally, the floor will need levelling. Is the best option to pour a thin slab over the top using a fairly small aggregate? Aside from being a little tricky to get level, is this likely to cause problems? I want to keep this fairly minimal so as not to impact head height more than I need to.

Thanks,
Sam
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