Thermal insultion for a shed block wall

[David]

We have just cleared a run of cupboards and shelving from along half the back wall of the shed. The wall is south facing and getting full sun at the moment, and the top is over 30C although the bottom is a much more reasonable 17C.

Anyway, it looks like a good time to get some insulation on there. We have a stock of OSB of various thicknesses so the obvious way (I think) is to get some PIR or similar insulation and fasten that to the wall using screws through the OSB.

Which brings me to bangs per buck.

I am guessing that "as thick as possible" is the starting point but I was wondering what the minimum might be to upgrade a single block wall made from concrete blocks.

The blocks are about 10mm thick.

[In hindsight I should have built with the much lighter thermal blocks then rendered them. Lesson learned but I am unlikely to build another shed.]

I am assuming that it is cheaper to buy Celotex or Kingspan or similar than to buy a composite board made from wood and insulation.

Thinner is cheaper but too thick could be diminishing returns.

Any insulation to avoid (bearing in mind possible flammability)?

Wall is roughly 2080 mm high and 3500 mm long. Might leave a bit of a gap at the bottom. Also, is it worth having a membrane down the back for waterproofing?

Cheers

Dave R

[The Natural Philosopher]

even an 18" of cork makes a serious difference. beyind 6" of cxelotex its diminishing returms so somewhere in the middle

??? Remind me not to visit!

polystyrene. cheap but flammable

TBH ;d stud the thing out and use rock wool and plaster board

you need that for vapour barrier with rockwool - celotex has its own foil barrier

Or you might use foil backed plasterboard

[Harry Bloomfield, Esq.]

The Natural Philosopher has brought this to us :

They offer a flame retardant version.

[Harry Bloomfield, Esq.]

Really???

[Brian Gaff (Sofa]

If its a wooden shed with hindsight on my older shed, I'd have made the concrete plinth bigger and tried to guard against any water collecting near the wood at all, especially in the corners or other uprights as its there where they tend to rot first!

Brian

[Brian Gaff (Sofa]

I never had much luck with block built sheds in one way and another, always seemed to be dank. Brian

[Steve Walker]

For a wooden shed, I'd have the whole shed raised on bearers, so it is not in contact with the plinth, and make the plinth as *small* as possible, so that there is no exposed plinth-top for water to collect on and run under the shed.

[RobH]

My wooden shed is on wood rails wrapped in dpc.

[Tim Lamb]

In message [e-mail]>, David [e-mail] writes

Celotex 80mm, 12mm ply OSB etc. and use *distance screws* for your fixings. Clearance hole through ply. Masonry drill for fixing plug though ply,insulation and into wall. Start plug on the screw end and tap gently into hole. Screw tight once seated. Works best with flangeless plugs.

[The Natural Philosopher]

Or build a one or two or three course brick wall and pop the shed on that.

[David]

A slim chance the units are wrong. :-)

[David]

It is, though, built from concrete blocks. Although 10mm or 10 cm not 10 mm.

Cheers

Dave R

[David]

Thanks. Today's prize for the most useful answer. :-)

Cheers

Dave R

[John Rumm]

You have to consider how much space you want to lose as well...

That's thin... :-)

100mm perhaps?

Yup. However look for one of the less well known brands - and possibly a supplier of "seconds" - you often find the price is a third of that the builders merchants will want for the branded option.

You want a vapour barrier that will stop warm wet air from getting into cold spaces. With foil faced boards that typically just means taping all the joints with a self adhesive ali tape.

As a frame of reference, I used 50mm PIR boards behind (cheap) ply for my workshop, and it works very well - however I did not only the walls, but the internal face of the roof as well to create a complete thermal envelope. It keeps it cool in the summer, and is very quick and easy to heat when you want to work in there.

[John Rumm]

ISTR doing similar - with a long multi material bit on the drill - drilled through the board, insulation, and foam, and then use a single brown plug on the end of a 5.25" screew. Tapped it into the hole and tightened. IIRC did about 6 or 8 per board.

(for the ceiling vault I screwed the insulation straight to the rafters, using long strips of ply to act as big washers since there is no cladding on the ceiling on mine)

[David]

Thanks. I recall you posting about it.

The roof is flat(ish) steel and the spaces between the joists are filled with fibreglass roll insulation (it was cheap at the time) and that seems to work very well summer and winter. Plasterboard ceiling.

As you suggest, I am struggling to balance loss of internal space with better insulation. Board also gives me a space to e.g. hang tools (in an outline) and easily run electrical cable.

I am making an allowance in my head for insulated board for a floor some time in the future. Floor is a deep concrete slab.

Many years back this NG gave me a lot of assistance in building the Mother of All Sheds (MOAS) and I am now finally getting around to some fitting out work.

Electricity is in. Main drainage and water are laid up to the edge of the shed. I have a cable run (plastic drain pipe) intended for Cat5E but haven't dared to try and pull the initial cord through yet in case it breaks.

One day it may have a WHB. Perhaps even a toilet and shower.

Anyway, weather is lovely so I should be out there working.

Cheers

Dave R

[David]

Argh!!!

100 mm. Do I have an issue with the "0" key???

[John Rumm]

I think you need to make the trade off in light of how you use the building. In my case I needed enough insulation such that it made the building feel *much* better (none of that cold / damp feel that outbuildings usually radiate at you!), and also enough to make it quick and easy to heat to a good working temperature when needed.

However I am not living in it, and only need it at comfortable working temperature for what amounts to a small number of days/year. The rest of the time, I just want enough low level heat for frost protection and to keep the content above the dew point to stop everything rusting.

So 2" PIR was around a 10x reduction in heat loss over the single block plus render wall building.

Yup it is nice having walls you can readily fix anything to.

(and one slight benefit with not having massive depths of insulation is that you can still easily enough fix through to the masonry if you have to fix something very heavy)

You could lay PIR boards on that, and then pour a 2" slab on top of them.

Yup, I remember it well :-) Full width of the garden and with a pent roof...

The longer you leave it the more likely it is to break! :-)

(having said that, pulling or blowing a new one is not usually that difficult)

Yup I would like that in my next workshop when I get round to building it.

I would probably stick an unvented cylinder in there heated with an immersion or two.

Yup!

[David]

<snip>

<snip?

I don't think I have the headroom for PIR then a 2" slab. I was thinking more of thin PIR and OSB on top. However I will bear this in mind, as always.

Cheers

Dave R

[alan_m]

Friends of mine have used an plastic grid which takes gravel under a shed with a wooden floor (on bearers)

Something similar to

completely filled with larger size gravel