The only trouble with rock wool is that it acts like a sponge if there is any water leak and it won't dry out due restricted air movement so can build up over time without being noticed.

Although not ideal polystyrene is better in this respect and can possibly be done for nothing by collecting sheets or even fragments of PS packaging that can often be found in builders skips. The downside of PS is it is combustible but since a workshop, except in the distant past, is rarely slept in then no problem.

It is amazing what is offered for free on Freecycle sometimes including building materials as some traders would rather give away materials they can't use rather than have to pay for the disposal of trade waste.

CS

I would also add a decent dehumidifier. Get one that has a drain pipe so it can empty under the shed through the floor so you don’t have to empty it every day or two.

I have a wooden garage on a wooden base that I use as a workshop. The floor has a sheet of plastic DPM covered with interlocking rubber matting squares bought from B&Q. The walls have that foil-backed bubble wrap stapled across the main beams, leaving an air gap behind them. On top of this is 18mm or so flakeboard. The building remains dry and I have not experienced any trouble with condensation. There is reasonable ventilation under the eaves.

The roof is currently left as simply the wooden T&G with no cover. Initially, I had polystyrene insulation slabs between the rafters and hardboard over the top, but this caused serious condensation. I removed it about two years ago and have had no trouble since.

James.

Definitely insulate walls and roof with tockwool or gl;ass fibre.

My internal walls are lined with 12 mm ply. and shelf brackets are fixed through the lining to the verticals.

To maximise storage space, being only 10'9" x 6'9" externally, and for security, there are no windows.

ventilation is by a cpule of fixed vents at floor level, and a 6" fan near the ceiling, with a weatherproof hood on the outside.

If you have windows, fix grilles over them, retained by coach bolts, with the domed heads outside and the nuts inside.

The door hinges should be retained in the same way. I made hinge bolts by nturning off the heads of woodscrews and screwing them into the back of the door with a drill chuck, to leave about 25 bmm protruding. trying to cvlose the door marks the p;ost where to mdrill the holes..

In this way with the door closed and locked (The door has a 6 lever mortice lock, although 5 should be adequate ) the hinges cannmot be unmscrewd, and the door cannot be lifted out, even of the hinge pins have been knocked out.

Heating shopuld be dry (NO combustion heaters) If there is a combustion heater, the re must be a flue leading to outside, so that no water vapour can escape to the inside (Also, you don't want to gas yourself) Probably safest all round not have one, in the longer term )

Lighting, LED, lamps or battens, for energy saving and to have plenty of light., particularly over the machines and the fitting bench.

HTH

Howard.

I did go to quite a bit of trouble to ensure good waterproofing; e.g. where plywood sheets met on the walls was sealed, and an outer batten added, as well as regular treatment with one of the waxy water repellent shed finishes.
The one water ingress issue I had was with the roof on one corner.
I made the single pent roof from ¾" shuttering ply, covered and sealed with bituminous paint, and topped with corrugated bituminous sheeting from Wickes, with angled ridge pieces used as seals along the top edge and sides, and a gutter along the front.
Unknown to me, the local squirrel population chewed a hole on one corner, under the bituminous sheet, behind the gutter, but through the wood to make a larder for the peanuts that my neighbour used to leave out for them.

The other issue was a break in attempt one night, where a neighbour's shed had been burgled.
They nicked a cordless drill and 1" tank cutter and chain drilled a hole through ply and plasterboard, big enough to crawl through.
Fortunately they picked a spot immediately behind the pillar of my bench drill and came face to face with a big steel tube, equally fortunately, they didn't realise it wasn't bolted down.

The windows already had steel bars on the outside, and cable gridding (similar to concrete reinforcing weldmesh, but smaller holes) on the inside. The main door was my old house door, with a crossbar of angle iron and a protected padlock; worth having an outward opening door, both for space saving internally, and it's harder to shoulder charge through.
Windows were a pre-made double glazing unit from a local DIY shop, which had been made the wrong size for the customer, so was sold off cheap.
There is now overlapping sheets of weldmesh inside the insulation of the back wall.

I think now, I'd consider Firestone rubber roofing sheets, but they weren't around 35 years ago.

Bill

Edited By peak4 on 09/08/2023 11:38:54

My workshop is mostly a 100mm (or more) cocoon of PU insulation board with edges sealed with tape. It’s built inside a sectional concrete garage. Some of it was built with old garage doors and now with insulation both inside and out. The floor is 100mm (or 150mm) concrete with a damp-proof membrane about 150-200mm below the 50mm screed. It was extended with full sheets of 2400 x 1200mm Recticel (or similar) which, conveniently, fitted just below the roof members. The end , with only insulation, has strips of weld-mesh behind. The inside has been sheeted out with 12mm ply.

Moisture control is by a couple of small dehumidifiers (usually only one running, for up to a couple hours each night) in winter). It is warm in the winter and cool in the summer. Extra warmth is supplied by a chinese diesel air heater and I have installed a CO monitor, for extra safety. I don’t weld or angle grind inside my workshop.

Even the steel door is insulated inside and out. I’ve yet to see the temperature below 4 Celsius and it is usually 6-7 Celsius or above at a relative humidity of 60%ish.

No. 1 action that I found extremely effective, was to cocoon the wooden walled shed in roofing felt so as to exclude rain or snow from accessing the timber walls. Timber is like a sponge. Past experience of a wooden shed with no exterior waterproofing, was a very damp interior and plenty of rust problems. I cut the felt into large squares and nailed it on the outside walls with about a 2" overlap. Felt being heavy but weak and therefore liable to tear away from felt nails, hence using it in squares tends to match the weight of each 'tile' to it's strength. Deal with apex roof in the same way and the door. I did the overlaps so that the top was sort of back to the prevailing winds that drive heavy rain. All still working successfully after several decades. Roof interior filled with polystyrene sheets, mainly ex – packaging. Patches of glue to roof. Walls lined with thin 3ply recovered from elsewhere, voids stuffed with rock wool. Door had a close fitting perimeter frame covered by glued and screwed 3ply and interior voids stuffed with rock wool. Lathe and one bench mill covered in plastic sheeting with a small heater under sheeting. Heat inevitably escapes, warming the rest of the shed, which is 10 x 8ft. Almost no rust and comfortable to use anytime. Interior temperature still goes up and down like a whores drawers. Humidity usually around 60%. Currently growing hedging/ bushes next to South and West walls to keep the sun off the walls as heat is problematical on hot summer days. Location, Brighton, in the 'sunny south.' (Sometimes!)

Edited By DMB on 09/08/2023 19:45:00

I replaced the gently sloping roof of my garages, total 22 x 17 feet asbestos with the cheapest possible roof. Single layer industrial building roofing with two strips of fibreglass, one for each adjacent garage. The consensation was bad until I bought sheets of expanded polystyrene to fit between the joists next to the underside of the roof. There was still some condensation from the translucent fibreglass panels, but 95% had stopped. The modern roofing of this type is usually double skinned with about 75mm of expanded polyurethane and the translucent panels are also double skinned. Cutting and fitting expanded polystyrene, if it is still available, inside the building, even 12 mm thick will provide very good insulation.

My workshop has very little ventilation – i do open the door on occasions. The dehumidifiers sort out that issue – i generally collect little more than 2 litres per month at the most… i expect most of this is wicking in through the concrete floor.

Ventilation is important.

My roof is EPDM rubberover 12 mm plywith glass fibre between the 50mm frame and the internal 12 mm ply ceiling.

The shop itself has no windows, but two small fixed vents at floor level, and a 6" fan with a weatherproof external cowl.

In fine weathger used with the door open, with the door closed, occasionally the fan is switched on.

Heating is by a thermostatically controlled small 2 Kw fan heater.

Since it was built in 2003, just coming up to 20 years ago, no condensation or rust problems

Howard