Another workshop insulation question

Quite a range of ideas here but something has to be better than nothing as most people report satisfaction with their scheme. The horror stories of walls filling with condensation probably relate to a domestic situation where multiple occupants are breathing, cooking, bathing and showering and not ventilating the house. In our workshops we are usually sole workers and the shop is probably empty the majority of the time. Rapid changes of temperature and humidity seem to be the greatest enemy to our machinery so controlling the rate of temperature change and humidity are helpful. The other issue is making the workshop comfortable to work in and this will probably need some heat in the winter. Insulation goes a long way to help with temp.stability and make heating more economical. You probably can’t have too much insulation but too little will not work as well as the optimum amount. Working out the optimum amount must be possible as there are figures available for types of construction and insulation values but I gave up trying and are just going to fit what goes in easily. So far I insulated the roof with 2” of polystyrene and it is surprising how much cooler it is in the summer but still b cold in winter. THe vapour barrier thing seems complex to me, it seems that a temperature differential across the insulation forces moisture from one side to the other and it condenses as it cools so a barrier on the warm side prevents the transfer but in Britain the warm side will be inside in the winter but could be outside in the summer, it probably all works out because the dew point in the summer won’t be an issue.

Mike

Ian,

New sectional wooden buildings when tongue and groove type are made from freshly treated timber and therefore quite wet when delivered. Expensive ones are no different either. It's best to let them dry out for a few weeks before insulating them.

Foam insulation boards are quite strong and only need the odd block every 2ft or so to space them off the walls.

My last workshop was a tin shed and it would rain inside with condensation, simple old 2nd hand suspended ceiling sheets stopped that and thereafter the roof was dry.

PS you will soon see how useful Fan heaters are at keeping you warm.

Edited By Dave Halford on 19/09/2018 19:10:48

Thanks again guys, the comments are of real value to my thinking. As regards budget, I am relatively lucky in that I am spending part of an inheritance (which also funded in part the move to this house with more land and facilities except my workshop). I just hope that Roderick is also gaining the information he also needs to answer his problems. I didn't mean to hi jack.. My previous proper workshop (not the temporary one for the last 18months) was a sectional concrete garage with a corrugated fibre cement sheet roof. The condensation problems were horrific until one winter I installed a pot bellied stove to burn timber. Even then in use most days the condensation would show up as thoroughly damp patches on the inside of the concrete sections and the roof would drip in the worst of the cold.. Hence this time it was imperative that I return to wooden buildings. As a lot of my stuff is still packed and stored in the conservatory an indoor workshop is shall we say out of the question. I have checked out this modern PIR board to day at the builders merchants, Dave and yes I am surprised at how rigid it is. the idea of short spacing blocks appeals from the work load point of view as well.

regards

Ian.

Ian,

No problem at all. My moving situation is very similar to yours. I just managed to take some pics of the garage before the removal guys filled it with my stuff. I'm doing some comparative U value calcs at the moment - I'll report back in due course.

Cheers,

Rod

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Rod,

To completely cover all the walls and ceiling, of your garage, with 100mm polyurethane insulation board (similar to celotex but secondhand, and likely without a covering like celotex), could have cost me less than £200, at the hammer.

That would be including covering the doors and windows! Celotex/Recticel new would be a horrendous cost, in comparison. Mine came as 1200 x 1200mm and 1200 x 600mm pieces, but there were piles with larger pieces on offer when I bought mine at a regular dispersal sale.

I could not get any larger bits into/onto my car. To cover your garage walls and ceiling would have required five of my totally crammed (overloaded, maybe) car loads, so a Luton van full, probably.

I acquired mine because the guy who bought the rest of the lots (yes, a large lorry load) wanted one less lot than knocked down to him. I paid £46 + commission, I think. The bulk of his lots were twice the height as the one I went home with and probably much larger sheets. so his cost/unit area was much less than half of mine. That means I could have bought enough insulation to cover your garage for far less than £200 - possibly as little as £100.

Most on here would, undoubtably, source it new from Jewson, Wickes or elsewhere. New is easier to fix, but the far more expensive route for the same insulation material....

Your looking at a linear 49 sq/m will be a lot more in reality.

Biggest problem with mine is concrete floor where the cold travels up your bones. Best cure lasts about 3 yrs the cheap 3mm rubbed rubber matting.

Mine has apex roof exposed to the roof. At first i just boarded underside up with 3/16" plywood, massive benefit. Years later decided on chipboard interlocking on top of the rafters together with 4" rockwool in fill = little gain just worth while.

Best bang for buck is the interlocking chipboards think 2.44m tall x 605mm, easy and quick to install on to battens. Mine has no infill just air space so its not a direct transfer of cold and what counts, battens might have been 3 x 1 1/2"?
Would need 33 boards (linear) at £11 each + min 52 battons £2.3 ea + screws etc all in approx £500 plus roof.
Beauty is you can make up and or bolt racking and shelving to it = no lost space and it keeps the noise down substantially.

If use cellotex or similar you have nothing more than a pin board for £612 min unless its covered over.

Even with all that having been through it your biggest source of cold will be from them garage doors and the gaps.
I did at one point Cellotex 2" over the door, made virtually no impact so installed a painting sheet across the width, that cured it temporary. Then i partitioned it off with that chipboard that cured it, really really cold the other side with cellotex lined door, 5 mins your out of there.
All i have now is a puny 1kw oil filled rad only ever left on lowest setting and on thermostat, takes 1 1/2hrs to warm in the coldest of winter. To speed up i do use a calor gas heater from 7.30am ish.

5M X 5M is a fairly large space to warm up quick or even keep it relatively warm enough to work in. Dependant upon what you need i would think about partitioning off which could double the wall space.

By the way tools never oiled and coolant used daily.

I can't change my original post but several people have posted corrections so the newer values are available to readers. I got my figures a decade ago and was remiss in not keeping up with changes. Closed cell EPS used to be rated better than open cell PUR and both way better than the very open fibreglass structure due to convection contributions.

I did at one point Cellotex 2" over the door, made virtually no impact so installed a painting sheet across the width, that cured it temporary. Then i partitioned it off with that chipboard that cured it, really really cold the other side with cellotex lined door, 5 mins your out of there.

This sound very like a draft issue Jon.

OK. I've done some sums. Celotex/Kingspan is certainly the way forward. Concrete block / 50mm Kingspan / 11mm OSB gives me a U of 0.4 which is poor compared with a new build wall requirement of 0.16 but not too bad compared to a refurbishment which the regs seem to allow to be 0.3 to 0.55 (if I understand it correctly).

I've bought a pallet (25 sheets) of 50mm Kingspan seconds from these people **LINK** for £432 delivered which should do the job. I'll keep you posted.

Rod

Rod if using seconds and relying on the foil for your vapour barrier then buy an extra roll of ali tape so any small holes can be sealed and not just the joints. If you also want to calculate where the "dew point" is within that construction you will find it's in the insulation so any moist air getting to that point will condensate out within the insulation so best to seal so that can't happen.

My shop is small, 3 x 2 m internally. three walls and the roof are insulated with 50mm glassfibre, the wall with the fire door with 6 lever lock has 100mm, because of the weight of the door called for heavier timber to support it. The sloping roof is now covered with a one piece EPDM rubber membrane.

The floor is 3/4 (or the metric equivalent) ply, on 8 x 2 bearers; on top of this, in the central walking area, are rigid, openwork, plastic mats. The back wall is close to a high fence, and the far end is partially sheltered by a bay tree.

The door end is barely two metres from the back of the house.

When cold, (East Anglia).a thermostatically controlled 2Kw fan heater runs for about 10% of the time. When the ambient temperature dips to 5'C or less, a 60W tubular heater under a bench is switched on and this keeps the temperature just high enough to prevent rust problems, (Being a steel bench - well cluttered, this slightly helps to radiate the heat).

I feel that ventilation is important, to get rid of the water vapour that we exude in our breath and perspiration. Any form of combustion heater is a No No in my view for this reason.

Ventilation is provided by two small fixed vents in the back wall, and a 6 inch fan high on the back wall, with intake through a weatherproof cowl. Unless it is raining, or it is cold, I often work with the door open, so the fan does not see a lot of use. Rust problems are almost non existent.

Howard

Jason, thanks, I hadn't considered that. And thank you everybody else for your experiences. It all helps balance the cost/effort/effectiveness equation in this benign ( if possibly slightly salty) climate down here on the south coast.

Cheers,

Rod

Rod, just a thought but I prefer WBP ply over OSB sheet as it gives you a smooth surface, you can get OSB with a smooth side but it is more expensive. I dont think the cost difference between WBP and standard OSB is that much.

Ron

Jason I take on board very much the comments concerning the dew point position within the layers of material and the sealing up of all holes and seams. However a little further information might be useful to all of us in this discussion. This concerns wiring and the power distribution within the workshop. I had thought of running the ring main in the air gap/vapour barrier and pulling the cables through the insulation and through a fixed mounting board across frame members on which the relevant electrical items are mounted.

If the problems that have been mentioned are so critical then perhaps the other option is to surface wire throughout after all the insulation and inner cladding have been completed. Not a major problem for me as I like my power points high up, minimising trailing cables. I would then run the ring main at about eaves level on the surface of the inner cladding but pinned into the structural framework. There would then be no compromise of the insulation/vapour barriers except at one position in the building, that being being the main power entry point which in my case is in cable terms 41 metres from the supply so has to come in from outside.

regards

Ian

Don't pin (clip)your cables on the surface run them in conduit and/or trunking for physical protection down to metclad boxes. Workshops fall under part P so you won't get it signed off unless it is protected and it is just good practice due to the risk of things getting knocked. Also makes it relatively easy if you want to add more drops.

On the subject of metclad, MK do double socket outlets with the rocker switches at the ends rather than between the sockets which makes it easier to use if you have gloves on or are just blessed with fat fingers.

Definitely don't hide cables in the wall. Any future changes or additions will become more difficult. Go with Jason's surface mounted conduit, better still use surface mounted trunking for all the cables and sockets. Such as this from *** TLC *** very neat. All the wiring can be concealed and the only extra cabling is for the lighting circuit.

John

Yes thank you guys for the cabling information. I have always had a bit of a thing about hidden cables, i.e not really liking it so I think I will add in the necessary, surface wiring with conduit or trunking.

regards

Ian

A timely thread for me, having just moved house and setting up the workshop again in a sub-basement.
The external wall is concrete block lined with 20mm EPS and faced with 10mm plasterboard which obviously won't be much good for hanging shelves and tooling, etc, on. Will need to panel it with something more substantial.
Looking on Castorama website, equivalent to B&Q, it looks like a choice between
MDF 25mm / Green MDF 18mm / Green chipboard 28mm / OSB 22mm or Hardwood Ply 18mm.
All except the OSB have a smooth/faced finish. What would seem to be the best choice ?
TIA
DaveD