New Garage Workshop Advice Needed

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Lung

Member
Joined
5 May 2024
Messages
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Location
Devon
I'm nearing the end of my garage rebuild and need advice on various aspects as I'm completely clueless about them as the internet is full of contradictory info.

For background, I had a 1930s detached garage that was damp and dangerous as the walls were bowing outwards, plus cracks were opening on both long walls due to the slope and lack of foundations. I've had it knocked down, but due to its location on our property it had to be rebuilt to the same size and shape or it would have needed full planning permission and a pre-application visit made it clear it would be a nightmare to get through.

The roof was completed this week, and the builders only have some rendering to finish off and the doors to fit and we'll be left with a new garage to use. The inside is up to me to sort, and that's where i'm having problems making decisions. The garage is approx. 7.2m long and 2.7m wide (external), with a double pitched roof and walls made of single skin block. It is divided into 2 sections internally:
One is approx 1.8m x 2.5m (internal), with a single door into the garden and no window. Right hand wall is a party wall with neighbour's garage and has a pier to support the roof, which is double pitched. Consumer unit is also on this wall, which we had fitted 3 or 4 years ago. This will be my wife's section, used for gardening tools, washing supplies, kids toys etc.
The other is approx. 5m x 2.5m (internal), with a door into the garden and another door into the lane, the latter being a 1100 width door to get my motorbike in and out. There's no up and over door, but there's a 1.5 x 0.9 window on the garden-side wall. Internally there are piers next to each door, and another on the end wall to support the ridge. Slab is new, with a new DPC underneath, but due to the slope it's only at external ground level at one end. This is nominally my area, and when we contracted the builders the plan was just for it to be for my bike and general garage storage/small working area for a vice/airbrush etc., so we didn't consider insulating it.

Since the build started, my wife decided she'd quite like my 3D printers to be moved from the dining room into the garage, which is fair enough, but they are quite cold sensitive so having bare block walls and no insulation feels like it's going to be completely unsuitable. I've spent ages looking at how to insulate it and due to the piers I had decided to build insulated frames so each section between the piers would be "50mm airgap, 50mm insulation, vapour barrier, 18mm OSB". Hoever, I recently read a thread on this forum which suggests this plan won't work as there's nowhere for the air in the gap to go as i can't see any ventilation in the roof.

So, question 1: is there a way to insulate this with no ventilation, or is there a different solution to keep the temp reasonable for both my use during winter but also my printers running in the cold?

The next area i'm unsure on is the external finish. It's been rendered with sand and cement, and i'd planned to use a waterproofing treatment on it to prevent as much moisture ingress as possible, but now I'm worried about the lack of ventilation and am wondering it leaving the render alone might promote some small level of breathability and enable the interior to stay more dry.

Question 2 is therefore: what should I do to the external walls to give the best solution for keeping the inside warm and dry?

The next area is the issue of the DPC and internal floor being level with the external floor at one end. I'm going to have a french drain installed externally along the wall to try and reduce the opportunity for water to pool and soak into the wall at that point. I'm also intending to paint Black Jack on the internal wall/floor corner to a minimum of 150mm on both surfaces.

Question 3: do these sound like reasonable mitigations to keep the floor dry?

The final area I'd love some input on is power. We have a consumer unit fitted, but it's single phase and I can't afford to have 3 phase fitted. I'd like to be able to install various tools in the future, and don't want to be limited if possible.

Final question: Is there anything else I could do to maximise the tools I could use in the garage (16 amp circuit maybe?), or should I just get used to only looking at single phase tools or fitting invertors/convertors?

As you can see, there's a ton of things going on that I really am struggling to make decisions on, so I'd appreciate any input on these aspects, plus anything else people can suggest that I probably haven't considered.

Bonus last question! Should I rescue the Union Jubilee my neighbour is getting rid of, even though my wife has given me strict instructions to only put things in the garage I will use? I used to do tons of woodturning as a kid, but haven't touched a lathe in 30 years.
 
Some images to put it all in context:
PXL_20240214_110358007.MP.jpg

PXL_20240225_173418529.jpg
PXL_20240424_182656194.jpg
Screenshot 2024-05-07 172043.jpg
Internal plan.jpg
 
Bonus last question! Should I rescue the Union Jubilee my neighbour is getting rid of, even though my wife has given me strict instructions to only put things in the garage I will use? I used to do tons of woodturning as a kid, but haven't touched a lathe in 30 years.
Yes, take it. Then make something your wife will enjoy. For example: a fruit bowl, coasters, pepper grinder. After that it’s classed as a useful tool, even if you don’t turn it on again for years.
 
I am not a qualified electrician so take everything here appropriately.

Re power; Don't worry about the single phase/three phase issue, my take would be there are very few if any normal 'hobby' size tools you'd put in a garage that would absolutely require 3-phase power without any single phase alternative available. The issue you might have is how much power is available in terms of kW in the garage. If you want to install a 3 phase machine, you will need to go down the 1PH->3PH converter route. Do you have something specific in mind that is 3PH?

You say you have a CU in the garage, that's fine but how big in terms of size and where does it run, will determine current carrying capacity in the circuit/cable running (from the house?) to that CU? That may be the limiting factor for you. If it's on a single circuit in the main house CU then what's the size of the breaker and the cable in that circuit? Remember, the breaker in the CU is primarily there to protect the cable on that circuit from overload, it's the fuse in the plug that protects the tool - and in their own ways they both protect you.

(Oh, and if you're adding a completely new circuit to the existing supply for power to the rebuilt garage CU then I'm sorry but my understanding is that's notifiable under Building Regs and will need certification, which realistically means getting a qualified sparky involved. Not necessarily as bad as it sounds, but do get multiple quotes, I just had to get some new work done and the quotes varied by more than five times! Shop around.) Getting quotes from several sparkies will also get some advice on how best to do it.

16A circuit? What do you plan to have that needs that much power <i>on a continuous basis</i>? Remember, assuming we're talking normal 230V AC, power and current can be thought of as effectively equivalent for any single item since it's simply Power = Current x Voltage (with a few wrinkles I'll get to). 13A current through a 13A plug will give you near as makes no difference 3kW. Do you have plan to have anything that will draw more than that that much power?

The sorts of things that might are stuff like welders, and you'd need to check the spec of the welder to be sure and that means checking the manufacturer's spec . Hydraulic lift motors can have a high power draw as well. I don't know what your 3D printers draw but if they're in the dining room atm they must be less than that if they're running off a 13A socket.

If you do need a 16A supply to something, then you need a suitable socket plug combo (blue commando socket and plug for 16A @230V) not an ordinary 13A socket/plug and it should probably have it's own circuit back to the CU ' again discuss it with a proper sparky

The next thing to consider is how many things will you have running simultaneously and hence what will be the worst case continuous power draw? In planning my own workshop for example, I don't expect my lathe and milling machine ever to be working simultaneously, but lathe, bandsaw and air compressor, very possibly. And since a garage CU will be supplying multiple circuits, e.g. tools and lights, you need to think about draw per circuit as well as total, though tbh if you go with modern LED lighting you'd really struggle to have a problem overloading a lighting ciruit in a garage!

The main other wrinkle is about high transient power draw when a something like an industrial motor or a welding arc starts up. The breaker in the CU is designed to trip at the rated current as a continuous load but for a brief period it will stand a much higher current, how high and for how long depends on the spec of the breaker.

If you want to learn more about the issues, I would thoroughly recommend the videos on YouTube from John Ward as a starting point.

Finally, should you take a free power tool? You have to ask? Really?
 
I think your over thinking the damp issue. You gave render on the outside, Osb on the inside, so, so long as it's not on a Welsh peninsula facing south east and your not drying wet clothes inside it you won't have a issue of damp? To could leave the tops open to the roof space by saying a cm for added ventilation ?
I'd go for 75mm insulation too. Also so multi foil over the pillars for added insulation.
 
the original looked like it had been rendered in cement, no wonder it was damp, you could have knocked off the cement render and seen if it would have improved things but it's obviously too late now.
 
This is a very interesting and timely thread as I am in the process of sorting out the garage here too as the flat bitumen roof is leaking and have been for some time (we have just moved into the property in mid July). We are having a warm roof installed to help with insulation and obviously get it the interior weather proof. The interior will need remedial repair and we are in the process of receiving quotes. I am going for a click board floor I think it’s called. Also need to work out how to arrange the workshop effectively.
 

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