Is it possible/cost effective to insulate a prefab garage to use as a workshop?

WIAWSNB

Although natural daylight is wonderful, bear in mind that for much of the time - dull days, evenings, and Winter - you will still need decent artificial lighting. So, yes, I'd personally investigate the option of cutting out the thinner wall sections and inserting windows, but would not consider it end of t'world if it couldn't be done.

You always have the option of a fully glazed entrance - whatever type of garage doors it currently has, this could be framed and glazed and pedestrian-doored very easily.

Work out how much room inside you want as your workshop. If all, that's fine. If less, then decide whether you want this space at the front or back of the garage. And then insulate only that area - leave the rest exactly as it is.

For the floor, a plastic DPM needs to be protected from being punctured, and I understand the usual way is to put down a sand screed to sit it on - this will also get the floor perfectly level. So, an inch of sand screed, levelled and tamped down, DPM laid on top and taken a couple of feet up the wall sides, and then rigid insulation - 2" should be fine - laid directly on top, taped, and then 22mm chipboard flooring laid on top of this, glued T&Gs. Then add the flooring of your choice.

Alternatively, you tanking-slurry the concrete slab, but DPM is much easier.

Walls, adhere insulated p'board directly to the raised rims of the wall sections. Peasy. Consider infilling the central voids first with cheap Jablite insulation.

Ceiling, investigate suspended ceiling panels which use a frame as an easy option, or design one yourself - cables coming from the metal.A-frames and suspending a lightweight frame. 2" rigid insulation sheets on top. A lightweight decorative finish below.

Section62

Sheds are designed to go outside - there's not much point in paying a premium for an outdoor building designed to be weather resisting if it is to be used inside a weather resisting garage. Also, the average reasonable-cost shed won't provide much in the way of insulation and draughtproofing so there will be more cost on top to achieve this. The lack of light, even with windows, will mean a need for artificial lighting.

It would be cheaper to buy a number of 8'x4' OSB boards and 2x2 timber to construct a simple box, although lighting would still be an issue to address.

More fundamentally, keeping fabric outside in an unheated space will lead to it developing an unpleasant smell. To avoid this the space needs to be heated, not just ventilated. And sticking a heater inside an electrically connected wooden box containing flammable materials, inside a garage, is asking for trouble. The risk of fire and means of escape needs to be considered.

I'm all for DIY, but people's health and welfare is too important to risk doing things without giving all the issues proper consideration.

I'd be looking at other options, such as allocating a room in the house for this purpose, or just buying a different house.

jonnydeppiwish!

frame it on the inside with a simple 2 by 4” CLS frame, then infill with insulation slabs. oSB or ply the inside. On the outer edge, damp proof membrane.

If you’re happy with a step up, frame out the floor, starting with DPM, insulation, then 22mm OSB

WIAWSNB

Why bother with the expense and hassle of a timber frame?

Dot and dab. Jobbie jobbed.

KBM68

Is that as easy as it sounds

WIAWSNB

https://forums.moneysavingexpert.com/discussion/comment/81960216#Comment_81960216

Yes :-)

All I can say is, this is what I'd do. I would not bother with the cost and hassle of a timber frame - I just don't see the need.

Insulated p'board is moisture impermeable, so adhering it to the wall slabs should complete the task. If I had any concerns about moisture getting in the joints, or through the actual concrete panels, I'd tank them first.

I'd probably settle for 2" insulation layer - to me the ideal balance between transformative insulation levels, and maintaining max internal space.

teaselMay

I've not done that personally but it's a simple job and I would do it (very cack handed DIYer). Don't be afraid to stretch your DIY, just make sure things are safe (not highly flammable for example)

Bigphil1474

I was considering something similar a few years ago as we were selling a probate house with a similar but smaller garage. Basically a box within the garage.

My plan was to split the garage in two to make a warm workshop at the back and a general store area at the front. I would have built a false wall out of 2x2 and plaster board, space for a door, and fixed it in the middle. This particular garage had a side door half way down. I would then have built 2 sides and a back on that section, with a cut out for the existing window, and a ceiling to close it all off. Fit a couple of ventilation panels, to the inside wall, and fitted a door. Feed lighting wiring in to the new box from above, as either a standard ceiling light or some sort of LED set up. Making the walls and ceiling insulated wouldn't have been hard - plasterboard on inside, some Kingspan in the middle, plasterboard on outside. Or even dispense with the outside plasterboard. That way, when you come to sell the house, the garage hasn't been butchered and you could easily dismantle if required. I remember watching a video on YouTube which showed someone using Kingspan type stuff to insulate the floor as well. By my calcs, a small oil filled radiator would have kept the room warm in winter and cost less than 50p a day.

KBM68

I've learnt so much for all of you - thanks so much

Think I am concerned about:

a) the ceiling, how do I hold the insulation up while the glue sets, should I use that wire they use for false ceilings? Would i be better making a false ceiling (its huge)

Maybe I should pay someone to do that?

b) how do the panels stay on the wall while I dot and dab them? I like the idea of tanking before sticking is that the waterproofing stuff that looks like tar (does it come in white? - I can google) or maybe i can use tape over the joins?

c) the edge of the floor around the doors, will ut be a step? How do I finish it?

Ectophile

What sort of roof do you have; i.e. what are the wriggly roof panels attached to? If it's timber, then the easiest way to attach insulation is to screw it to the roof timbers.

As for the panels on the walls, if you use the right adhesive, they will stick in place pretty quickly. Splodge the adhesive on the wall, push a panel in place, and step back.