Workshop Lag & Clad?

Discussion in 'Carpenters' Talk' started by Sarah Dasdemir, Aug 22, 2020.

  1. Hi Y'all

    Experts, please can you tell me what materials to use to insulate and clad the interior of my wooden workshop including a breathable membrane lining?

    I would like the most reasonable priced but warm in winter range, not the most expensive.

    Thanks :)
  2. ElecCEng

    ElecCEng Screwfix Select

    What is the structure of the workshop? Assuming you will put the insulation between the joists? The depth available will determine what you can do. Mineral wool is cheap but you might not have enough depth without adding timber. PIR boards (Kingspan/Celotex) perform much better and would be adequate if thinner layers are needed. VCL rather than breather membrane. I’d go for OSB to clad as it’s cheap. 12mm would do as 15-18mm might be overkill for a light structure. Most places are doing discounts on insulation right now due to the chaos over the new green homes scheme so shop around.

    OSB should be around £10 a board.
    PIR should be around £15-17 a panel.

    There are places which sell VCL and breather paper by the metre.
  3. Bobby Dazzler

    Bobby Dazzler Active Member

    You don't want a breathable membrane on the inside. That should have gone on the outside underneath any external covering, so that damp cannot get in, and any humidity can get out.
    On the inside you want a vapour proof membrane, VPM, (or vapour control layer, as ElecEng calls it) under whatever cladding you use. The VPM prevents moisture travelling in either direction, and helps to eliminate draughts. (moisture can build up inside, and if it can travel into the insulation, that will become damp and less effective, plus potentially causing rot)
    What space do you have available for insulation? Do you want it only between the wooden structure, or between and over the top of the wooden structure?

    For cost-effectivenes, and price, rockwool between the wooden structure, a VPM over the top of that, then OSB or plyboard over that.

    If you want even more, rockwool or extruded polystyrene (XPS) between the structure, and XPS with a built-in VPM, (silver foil backing, taped for added VPM)) across the top of the wooden structure.

    Edit: Oh well beaten by the fastest fingers first. :oops:
    ElecCEng likes this.
  4. ElecCEng

    ElecCEng Screwfix Select

    Sound advice nonetheless ;)

    Bobby Dazzler likes this.
  5. The structure is apex 10'x16' with 3' veranda, what mm width would you recommend the PIR boards to be please?


    Thank you all for the info xxx
  6. Can I double check: first is the inside of the shed wall, then I put rockwool, then VPM, then osb or plyboard?

    I need to be able to paint the osb or plyboard, which will give the best finish and what paint do I use please?

    Help me out with VPM, I have just looked on this site and have absolutely no idea which one I need as there are so many:

    Also, insulating the roof, do I use the same materials?

    What are your feelings about using plasterboard instead of osb or plyboard?

    Thanks x
  7. Bobby Dazzler

    Bobby Dazzler Active Member

    Yes, from outside layer to inside layer: outside layer, breathable membrane, insulation, vpm/vcl, inside finish layer. The idea is to stop any humidity generated inside from permeating to the insulation.

    Any paint that is suitable for wood. Thus: primer/undercoat, top coat.

    A layer of polythene is fine. As long as it's thick enought to withstand tearing when you're using it.

    That'll be fine.

    In a shed, where damp/humidity is always a risk, plasterboard may disintegrate.

    Your previous question to ElecEng, I'm assuming he was more interested in the dimensions of the wooden structure, i.e the depth available for insulation, e.g. 75mm, 100mm etc.

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