Thoughts on insulation (garden building, storage/workshop).

[Chris Bacon]

Yes, it's this again. It does not need to be superinsulated, nor continually heated, just enough so that being in it sometimes when it's winter is reasonable.

It's going to get a rather thin layer of floor insulation - 25mm - under ply, finished with laminate flooring.

The walls are thin concrete slabs, fitted between slotted posts. The posts are thicker than the slabs between, so there's 25mm of "alcove" between posts. The posts will have 2x2 vertically against them, leaving another ~45mm of space to fill with insulation, finished with plasterboard.

Above the plasterboard ceiling, there will be some sort of insulation.

The four doors are another thing; steel frames (square hollow section,

40mm I think), with flat sheets of galvanised attached. They will need some insulation too. Perhaps fit insulation in and board it over with ply.

This all needs to be cheap; best "bang for buck".

So, I ws thinking of laying 25mm EPS floor insulation sheets, fitting further 25mm floor insulation between the posts (as it's non-absorbent re water), inside/over the concrete wall slabs, then having 50mm of rockwool sanswiched between the EPS and plasterboard. Above the ceiling, I could lay ordinary glass fibe or rockwool loft insulation, perhaps

150mm thick. The doors could have 50mm rockwool or similar I suppose.

Any comments on effectiveness, or any cheaper useful insulation, please?

[Brian]

Condensation and other sources of moisture will be a problem with rock wool, it acts like a sponge and concrete tends to allow moisture through- not to mention moisture from inside.

I?d line with something impermeable both sides of the rock wool to keep it dry. I?ve used rock wool ?batts? in the past, they are easier to work with. I think they are intended for cavity walls.

I?ve seen loft insulation which is in a roll but in a huge foil bag - as you roll it out it stays in a roll. You would need to seal it where you cut

- Gaffer tape?

[nothanks]

For cheap insulation:

[Chris Bacon]

Thank you - hence the reason for wanting EPS board on the outer side. The roof overhang is about 130mm. I have run frame sealant long the horizontal joints. The inside (floor, ceiling, walls) will have a layer of Visqueen just behing the finishing surfaces of plasterboard & ply.

For gap sealing, I am thinking "expanding foam".

[John Rumm]

I would do EPS on the floor under the ply, but also stick a layer of visqueen sheet in there to stop an moisture getting through from the hot wet side to the cold side. (EPS alone does not form a perfect vapour barrier).

Foil faced PIR foam boards - either as thick as will fit or you want to spend. IME 2" is fine for this application - you could probably get away with less. Tape up any joints with ali foil tape. You don't necessarily need any timber behind it - you can fix the ply face right through to the concrete. The PIR boards won't crush.

Anything cheap - so rockwool since it does not need to be pretty and you don't care if it takes 8". If it's a "cold deck" roof, then you could use foil backed PB.

25mm PIR boards bonded on with "board fix" PU foam, then ply (also bonded if you want)

Understood, but don't go too cheap since you will be living with this, and are unlikely to want to do it again. Energy costs are unlikely to get cheaper. Also if its a warn dry space that is pleasant to use you will likely get more use out of it since it will be nicer being in there.

My first small workshop I did with 2" EPS all over - it was ok. The current one with 2" PIR foil faced boards, and it is noticeably better.

(I think I paid £300 for a "van load" of boards from our local "seconds" supplier - but that was 12 years ago!).

That did all the walls of the 17x12' space and the complete roof apex and gable ends.

[Theo]

When I looked for that last year, it appeared to be priced at 3x the price of regular rockwool insulation, and unobtainable without lots of faff.

So what I've got is regular rockwool plus this stuff:

a stapler.

Haven't fitted it yet, so don't know how it goes.

(The use case is insulation where I need to regularly move it to access things underneath. Unwrapped rockwool would be a bit of a dustfest)

Theo

[Theo]

Be aware of planning though - if this is under permitted development rules the height is maximum 2.5m. Things get a bit tight when you start adding all the layers.

This guy does really solid garden room builds on Youtube, and has a 'hybrid' roof construction to keep the height down. I'm not completely convinced by his approach because of the cold bridging, but understand it's tricky due to the height restriction. Here's the explanation of his approach:

Seconds and Co is the most well known, but there are other 'seconds' PIR vendors around which might be nearer to you. PIR insulation is basically mostly transport costs, so it could be worth hunting around to see if there's a seconds seller close to you (especially if you have a factory nearby).

Theo

[John Rumm]

I think the building's shell is complete, so this will all be "inside".

Yup the local one in Benfleet was called APCO insulation - but I am not sure if they still exist.

[RJH]

Is plasterboard the best way to go? I'd prefer something that doesn't absorb moisture, provide a decent fixing point for shelves, tool hooks etc., and could take a few knocks - treated OSB probably.

[Brian Gaff (Sofa]

Are there any windows?. I'm thinking of getting a new shed of some kind but a bit out of the loop these days. As I recall draftee doors and windows were the issue with my old wooden one when it was new.

Brian

[Tim Lamb]

In message <sk766a$jrc$ [e-mail]>, Chris Bacon [e-mail] writes

Check the specification buying Rockwool.

Glass fibre manufacturers have re-named their product to confuse. Earthwool etc.:-(

Shuttering ply might be better than plasterboard for your uses.

[The Natural Philosopher]

A couple of my walls are actually MDF - 12 mm I think. Might be 18.

Fantastic surface to mount stuff on.

takes emulsion paint well.

[Chris Bacon]

I'm sure. Marine ply would also be an improvement. However, I can get a sheet of 12.5mm plasterboard for about £7.50. 18mm softwood ply is about £42, 12mm about £33. I'm going to need 14/15 just for the walls.

[Chris Bacon]

No, no windows. Four steel-framed doors along the front, though.... they will need insulating and draught-proofing.

[Chris Bacon]

It's cheap. The building will be dry (I very much hope!). Again, even

9mm OSB, which I would not hang shelves on, is 3x the price. Shelves will be free-standing, with safety retainers if need be.

[Chris Bacon]

Thank you, that is interesting. Looking at the "bays" betwen the posts, it's possible that I could use 75mm thick EPS (~£4215), or 25mm + 50mm EPS (~£397, would be much easier to fit), or 25mm EPS + 50mm Rockwool (~£300). So using rockwool I would save about £100, all else being equal, with not much difference ininsulation value.

Another possible problem is the spacing of the vertical timbers against the posts - they're on (about) 870mm centres, so further studwork to support the plasterboard will interfere with the insulation. Hm.

[Chris Bacon]

That's actually sort-of attractive. Unfortunately, £550 incl. delivery, for 60/65mm boards, or pallets which don't give a very good match. Maybe there's another supplier.

[Andrew]

EPS is 'cheap' but it is 'open cell', so if you use it under the floor it needs to be protected from damp or even water penetration with an effective DPC under the insulation. 'Celotex' and Extruded polystyrene are closed cell. They can go under the DPC.

[Tricky Dicky]

Got to agree about concrete letting moisture in although condensation is your main issue with concrete walls.

If you don?t mind losing a few inches of the room size have you considered building a studded structure around the walls stood off from the concrete to provide an air gap. Depending on how you brace it the structure could be free standing yet strong enough to fix shelves etc. To it. PIR could be pushed in between the studs a vapour barrier on the inside and PB to clad it. For belt and braces a few holes core drilled through the concrete panels would allow ventilation of the air gap. Just remember to stand the frames on a DPC just in case your concrete base does not have a DPM.

Richard

[John Rumm]

Use ply instead of PB and fix through the insulation to the concrete... (will only work on something not easily compressible like Jablite or PIR). No studs needed then (and less thermal bridging)