I've got a shed built of big solid concrete blocks, that also has a concrete floor. I want to insulate the whole lot so it can be fit for human habitation – so I need to insulate the floor, walls and ceiling (which is currently just corrugated metal). The question is, what type of insulation to use, and how? I need to try and save space, so I want to avoid leaving an air gap between the concrete and the insulation. I suppose I need something that can cope with getting wet – I'm assuming I will get condensation etc. on the inside of the blocks. So not too deep, no air gap (or very little), can cope with damp. I'm assuming wood wall batons and something – foil perhaps? I'll be covering the insulation with timber tongue and groove. It's not huge, so I don't mind if it's a bit more expensive. There's such a myriad of options and kinds, I just don't know where to start, except that I doubt I can use rolls of rock wool or thick glass fibre stuff just due to the depth etc. (the ceiling especially is not very high!). Any help with this will be really appreciated.

  • Put the insulation on the outside so the concrete thermal mass works in your favor instead of against you. It also does not impinge on living space. Jun 4, 2017 at 22:38
  • hey that's an interesting idea i hadn't thought of!
    – Luke Smith
    Jun 4, 2017 at 22:40
  • It's a key strategy in passive solar design for instance. Jun 4, 2017 at 23:33

1 Answer 1


The most efficient (highest R-value for the least cost) is batt insulation.

For the walls, You say, "solid block wall", so I presume it's not hollow blocks. So, installing rigid insulation boards on the exterior and then covering it with a moisture barrier (building paper, peel-and-stick membrane, etc.) and then covering it with, as you say, "timber tongue n groove" will give you both the insulation you need and the waterproofing you need. This can be done using wood stripping installed the opposite direction you're going to install the "timber tongue n groove". (Placing the insulation on the exterior will help with the size of the spaces too.) The thickness of the rigid insulation depends on the thickness of the stripping and how much you can afford...generally R-21 is recommended. The stripping should be easy to install if the blocks are solid and not hollow.

For the ceiling, providing a pitched roof with R-38 batt insulation is recommended for your location. Be sure to vent the attic to prevent condensation and ruining the insulation.

For the floor, we don't worry so much about concrete slabs on grade. The cost is too great compared to the benefit of adding perimeter insulation.

  • That's brilliant Lee thankyou. One question if you can - so i've fixed batons to the outside. Is my rigid insulation going in between the batons, or am I leaving an air gap and fixing the insulation on top of the batons? Does the exterior of the concrete need some space for moisture to collect and run off into the ground- prevent the damp accumulating? Also much appreciate the advice re internal floor thanks.
    – Luke Smith
    Jun 5, 2017 at 6:12
  • No, you do not want an air space in the wall system. I'd install the stripping (batons) just far enough apart so you don't have to cut the rigid insulation. If you completely fill the void, there will not be any condensation and thus no need to vent. You can use EPS, ICO or XPS boards, which is made to mastic or epoxy directly to the wall. I would not use styrofoam. We worry about warm vapor from inside the house entering the wall and hitting the dew point in the insulation. However, with your wall system, you will not have this problem. The only other moisture
    – Lee Sam
    Jun 5, 2017 at 6:45
  • To worry about is rain/snow and you should have a moisture barrier under your siding. (We don't worry about that moisture hitting the dew point, because it's not warm air (vapor) moving towards cool air. However, the attic will need to be vented properly with "cross ventilation".
    – Lee Sam
    Jun 5, 2017 at 6:51
  • Brilliant info Lee thankyou. so moisture barrier on top of insulation fixed to the wall- and my final layer of wood on that. Fanstastic just what i needed to know, much appreciated.
    – Luke Smith
    Jun 5, 2017 at 8:23

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