Insulate or not?

[Bob Minchin]

I have a workshop floor that is 4" concrete on a DPM on hardcore/soil. The plan is to put a wooden floor in to make it more comfortable to stand on for long periods. I don't want to lose too much ceiling height so i was planning to put tiling batten (25mm) down as mini joists with mortar under to adjust the levels and

18mm ply as the floor surface.

Is it worth putting insulation underneath eg 25mm polystyrene or as the space under is not ventilated, would the static air gap underneath be virtually as good as the insulation?

The area is 30 sq metres so I don't want to waste money on polystyrene unless it is going to make a useful difference.

The walls and roof will be insulated for comfort in both Summer and Winter. Depending on how cold it gets and how much I use it in Winter there will be some form of space heating at least to the level to prevent icicles forming on my nose!!

TIA

Bob

[Ian Stirling]

It probably will. Polystyrene conducts at a rate of .04W for a meter cube, with 1C difference on the sides. Divide by .025m, and that's 1.6W/m^2/K. Multiply by 30, and that's 48W/K. For 10K over ambient, that's 480W. ISTR that a gap and a floor is about 4 times that - from some sums I did a while ago. The end result - when the shed is hot for a long time may be different, as the ground underneath will heat up, and then insulate somewhat. But this takes a long time, comparatively.

Do the sums. How long do you use the shed? How hot do you want it.

If you're going to be heating it 8 hours a day, 365 days a year, using electricity, then you probably want to insulate the walls too. If you're going to be using it for an hour every few weeks, it may well be cheaper to simply put in a few heaters.

all the information you need to work it out - there is probably much easier ways.

[John Rumm]

I didn't bother with mine (3/4" ply over 2" high bearers supported on half bricks), and it seems to still be very efficent from a temperature control and heat loss point of view. The air gap under my one is open to the outside as well. The walls and roof are well insulated.

[Bob Minchin]

Thanks Ian,

I'll get my calculator out. I'm not sure how much I will be using the building which will be a hobby woodworking shop for when I retire. I anticipate projects running for some days whilst making the item but then brief daily forrays to apply finish and then to let it dry. I plan two heat sources.

1 a balanced flue domestic gas fire re-jetted to run on propane. 2 a sawdust burner fuelled from the shavings and sawdust from the dust extraction system on the machines.

The latter will be free fuel but I'm not sure how much sawdust it will consume or I will produce and I expect propane will workout dear to run for long periods but convenient for short stays To an extent, I can be flexible when I use the workshop and avoid it in the depths of winter if heating costs are too high.

Bob

[Bob Minchin]

Thanks John, Helpful experience.

Bob

[John Rumm]

One downside of this is the amount of water vapour it will create in the room. Not so good for rust free tool storage.

It might also be worth thinking about some form of frost protection heating to keep it above the dew point in there for the same reason.

I found in my workshop a small wall mounted fan heater on a thermostat set to about 5 degrees does the job nicely. With the amount of insulation in place it does not kick into action often - and when it does only runs for five mins or so.

Nice idea...

Do you have to manually load it with shavings?

(otherwise you may find the place melts when you run a thicknesser for a couple of hours!) ;-)

My one is ok all year round, and will get to comfortable in about 10 mins from its coldest. Note however it is only 1/3rd the floor area of yours.

[Andy Hall]

From having done an exercise of insulating a garage for use as a workshop, the floor is the least worthwhile area to insulate in comparison with the walls, roof and of course the doors.

To give you a rough idea, pre-insulation it would require about

12-15Kw to achieve 15 degrees or so in the winter.

Of that, something like 400-500W was through the floor.

With 50mm of Celotex on walls, roof, doors the heating requirement comes down to about 3-4kW worst case.

I also debated whether or not to implement a wooden floor and didn't a) because of the loss of height and b) to have made it interesting I would have wanted to run extraction ducts under the floor implying at least 180mm as a depth. I did the calculations for either thin Celotex or polystyrene and worked out that there would be a saving of about 300W. In the context of 12kW that is nothing and even compared to 3kW is not a lot when other issues like several hundred W of lighting, plus machinery and so on are accounted for. For comfort I use mats instead.

[Andy Hall]

Is the building reasonably close to the house?

I set up an arrangement with a heat exchanger and secondary circuit run from the CH system in the house. Well insulated pipework runs in an underground duct and there are radiators in the workshop. This is comparatively inexpensive to run.

I'm concerned about the idea of using open flame heating in a woodworking area. While one should try to keep it as dust free as possible, I am concerned about finishes etc.

Although a sawdust or woodburner seems like a good idea, you have to be doing a lot of work that produces shavings and sawdust to keep it going. Really it is only rough preparation work such as planing and thicknessing that produces much of a volume of this.

[Ian Stirling]

[The Natural Philosopher]

I think this is very true...OTOH if you ARE shoving a floor in, and the insulation is cheap, well 300W is 300W.

As the ambient temps rise....right now I guess day/nightime averages are around 8-10C...I have noited that the underfloor heating is simply not coming on..the Aga, a 750W device . plus the usual electricals that run

24x7...freezers and fridges...is capable of heating, with a bit of solar gain, the WHOLE front ground floor of the house...about 1500 sq feet.

and 300W 24x7x52 is 2621 units....a couple of hundred quid at least..

[John Rumm]

Yes - sorry read straight past that without actually seeing it!

[Andy Hall]

That was worst case though -3 outside.

My pattern of use tends to be evenings and weekends, although obviously a retired person or someone using it occupationally might use it all day. I then heat the place to 18 degrees. I have over provisioned the radiators to 6kW output so that it heats quickly. At other times there is a night setback temperature of 10 degrees.

I reckon that the averaged outside temperature over the year is probably closer to 10 degrees. Given that and partial use, I reckon that the averaged heat loss is probably equivalent to 100W or so equivalent. At that point, I don't think it's worth the insulation cost for this depth of floor. If I were going for a deep floor and at least 50mm Celotex, I might consider it, but I rejected that on loss of height grounds, plus the amount of floor support to cope with several tons of machinery.

[Bob Minchin]

Hi John, Andy & others

My experience is that prevention of condensation damage in workshops is best achieved by heating the machines. they only have to be a little warmer than the surrounding air for nothing to condense. In my metalworking shop, I heat the lathe bed, the milling machine, a custom cabinet with a warmed metal sheet in the back and a cast iron surface plate. Each has a number of aluminium clad wirewound resistors powered from 24 volts. Between 3-4 amps total has kept each item completely rust free in an otherwise unheated workshop (apart from when I go in and use a fan heater if needed) The lathe was bought in 1979 and the mill in 1987 and neither have a single rustmark. In the garage, ( my current woodworking shop, a tambour fronted cupboard with two mains lightbulbs in series (for long life & much reduced fire risk) in a metal mesh housing keeps chisels, saw blades, spindle moulder cutters, planes etc rustfree.

The woodburners I've been looking at -

are manual loading.

I may need to supplement the wood supply with a trailer load of broken pallets every now and then and it will possibly burn woody garden waste. I currently save the latter for an annual donation to my employers bonfire party each November but when I'm retired I may burn it myself.

The gas fire as well as being balanced flue has completly enclosed flames behind a glass door with a convector heat exchanger. It is a valor Homeflame I've been offered free originally for spares for the one we have in the lounge.

The workshop is about 100 feet from the house so connecting to the house cental heating is possibly not on.

Bob

[Andy Hall]

Not a bad idea at all. I suspect that metal working equipment is a little easier to keep rust free because generally it doesn't matter if it's oily.

With woodworking equipment, one has to be a bit more careful to avoid contaminants getting onto surfaces to be in contact with wood since some will spoil the surface for certain types of finish.

I haven't had an issue at all since I was able to economically heat the workshop to at least a background 10 degrees. I occasionally run a dehumidifier as well but only on higher humidity days.

For some reason I seem to have quite corrosive finger oils so in any case, I use various preparations according to tool and surface. So for example, planes, chisels and cutting tools get a wipe with camellia oil periodically.

Machinery such as combination machine, bandsaw, wood turning lathe gets a wipe with either Boeshield T9 or Felder Metallglanz for surfaces.

Actually you could if the pipes were well insulated. I covered mine with a substantial foam sleeve and ran them in 160mm soil pipe.

However, if you have a good supply of scrap wood, it could well be a good option.