I intend to insulation my timber framed shed/workshop with rockwool insulation and would like to know if I should put a vapour barrier between the insulation and the interior panelling, which will most likely be plywood?
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Yes. However, do make sure that the space behind is ventilated and that the outer layer isn't allowing rain to penetrate first.
A hose and sprinkler played on the outside wall are helpful to determine this.
Thanks for the quick reply....This is a new build but I will check for "leaks".
What should the thickness should the membrane be...can I use polythene dust sheets, or should a get the "proper stuff" ?
Get proper Damp Proofing Membrane - and plan for some left over, for it's handy stuff to have around.
The polythene dust sheets that I've seen are pretty thin, so I would err towards the correct material - it's not expensive.
Alternatively, if you use Celotex/Kingspan rather than Rockwool, it has a foil barrier anyway.
Be and queue sell varying thicknesses of plastic sheets and they are all cheaper than the damp proof stuff they sell (its about £3 for a fairly thick sheet i think)
I was discussing shed insulation with a mate last night. Can you use polystyrene sheets as insulation as surely they are cheaper than anything else - and does polystyrene work well?
In message , at 09:48:31 on Sun, 11 Mar 2007, Lawrence Zarb wibbled
Plywood is unlikely be hfrshy as a vapour barrier.
The panelling will be plywood not the vapour barrier!
I wouldn't use B&Q as a price guide for anything. An enquiry to a heavy side builders merchant should give more realistic prices.
You can use expanded polystyrene sheets, although there is the question of fire risk. Vapour barrier is still needed.
The second point is that Celotex has almost twice the insulating property for a given thickness as compared with Jablite (polystyrene normally used under floors)
I did the calculations for this when insulating my garage for use as a workshop and the insulating property of the sheet material is the major determinant in the amount of heat required to maintain a given temperature.
Take a look at this document
If you were to use this method of construction, with all of these components, you would end up with a U value (reciprocal of the sum of the R values) of better than 0.25 (design goal for a house).
However, the point is clearly that the insulation is almost the sole determinant.
However, for the application, I was not setting out to achieve house values (it's not habitable space) and I was also looking at costs of materials and running and also space taken up by the material itself, which I wanted to mimimise.
I did some calculations based on using 50mm Celotex (R value is 2.15) and worked out that I could reduce the heat requirement to around
2-3kW worst case from 12kW as it had been without insulation. A huge difference. Reducing it further from that to under 2kW wasn't worth it given the costs and pattern of use.I also looked at the Jablite web site and to achieve the same insulating property, one would need just under 100mm thick material. I didn't want to waste that much space and I did feel that with the convenience of built in vapour barrier, the Celotex was worth the investment.
The short answer is that polystyrene can work well... it depends a bit on what you are aiming to achieve.
As Andy said, the PIR foam (Celotex etc) will give better insulation, however the importance of that will vary with the size of the building and the amount of use you plan to make of it. So if you heating requirement with jablite is 1kW spending the extra to reduce it to 600W may not be worth it in a building for occasional use.
(Having said that, since I built the workshop I have found a local source of PIR foam at the same price as I paid the builders merchant for jablite - so in that sense using the better stuff becomes a no brainer)
When I built my workshop (8' x 14'>10') I used 50mm jablite in the walls and the roof. I had decent quality 3/4" shiplap on the outside, and relied on the jablite as a vapour barrier as well. I left a 1" airgap (although I placed this on the inside so that it left a convienient wiring cavity), and then lined the inside with 1/" ply.
I have been pleasantly surprised just how thermally efficient it is. I have a wall mounted fan heater in there controlled by a thermostat. I leave the fan heater set to its lowest power (800W) and the stat set to about 5 just to keep any moisture and frost at bay. It very rarely kicks in. When working in there in most weathers, I can have it a reasonable temperature in under 10 mins just by turning the stat up and not bothering to increase the power on the heater.
Some piccies here:
The message from "Lawrence Zarb" contains these words:
I'd stick it outside the insulation.
Vapour barriers should be between the insulation and the warm damp air. There's probably not much point putting it inside the interior panelling however so between the interior panelling and the insulation would be favourite.
On Sun, 11 Mar 2007 17:55:03 GMT, Guy King wrote in :
Nuh-uh. Probably not a real consideration here where the outside temp is above freezing much of the year, but at Mawson in '80 the insulation in the dongas was about 75% ice, in the outside layer, after years of water vapour diffusing through the styrofoam and freezing when it got to the outer bits. The one night we hit -33 C all the nailheads in the wall of my donga sprouted flowers of hoarfrost because the ice had reached the level of the tips of the nails. The new buildings that were being built had vapour barriers over the insulation to prevent this.
words:
rockwool
barrier
Collaboration,
40-1-B12, CERNGlad to see you are taking note of the experiences of my forebear Sir Douglas
There is a webcam at Mawson Sound so you can see for yourself how taxing the weather is.
A W E Mawson
Dr Ivan D. Reid took things to extremes as usual:
This moose suspects it all deep ends on the tempera chewers on the two sides of the wall. We insulated our rifle range and put a vapour barrier (molished of cut-up dustbin bags stapled to the timber) on the outer wall (where rain was otherwise likely to blow in, it being ancient and very terrible overlapping planks), supported the insulation with stapled-up string, then added a liner of marine 3-ply on the inside. It jbexed very well, until the local scrotes burned the place down one night.....
It depends on where the vapour is coming from, and on if it can evaporate from the insulation without waterlogging it.
Cadbury Moose.
On Sun, 11 Mar 2007 19:44:29 -0000, Andrew Mawson wrote in :
The Home of the Blizzard.
Not sure if Mawson Sound is at Mawson Base or at Commonwealth Bay where the original Mawson Expedition huts are -- Google finds very few references. I was at Mawson Base which is nearly as windy as Commonwealth Bay -- our average wind speed was around 33 knots so the monthly wind run would have circumnavigated the Equator!
Is your nickname "Shock and"? ;-)
freezing
nailheads
Commonwealth
Collaboration,
40-1-B12, CERNWhat has all this got to do with inserting a vapour barrier in a shed?
The message from "Lawrence Zarb" contains these words:
You're the one who crossposted to the shed. What did you expect, on-topic answers? (insert smiley of choice here)
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