New Garage Workshop Advice Needed

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5 May 2024
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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:

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.