Keeping an outdoor workshop dry

Hello, I'm a newbie here so please don't jump down my throat. Now that I'm retired I want to set up a dedicated workshop. The Management says I
can't have any more hobby space indoors, so my options are either to use my single brick build garage or erect a wooden shed. Having a car that is too big to fit the garage, I'm inclined to make use of this 'spare' building. However, not being connected to the house and being of single leaf brick construction with a corrugated asbestos roof, it is inclined to be damp, even though the concrete floor and walls have a DPM.
Thermal calculations based on U values from domestic heating design websites suggest I would need 68 watts of heat input for each degree Celsius I wanted to keep the garage above ambient, even if I carefully insulated it. Electric heating to 16 or 18C would cost several hundred pounds a year, which is more than I can thoil.
My guess is that there are lots of members of this newsgroup who have outdoor workshops and have solved the problem of damp at a reasonable cost. Please can you share your experiences? Can I make use of this garage or would I be (much) better off with a new wooden shed? Oh, and I should admit right away that once this is solved I will have a ton more questions about lathes and milling machines...
Thanks,
Alan
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I would improve the insulation and use background electrical heating. Avoid paraffin heaters like the plague.
I am just going through a similar exercise with my garage; I have insulated the ceiling with glass wool and plasterboard, and am planning to insulate the metal door with expanded foam sheets (and possibly a large curtain). I am fortunate in that the garage is attached to the house and built of aerated concrete blocks rendered externally, so I have head start over you. I am planning to use electric wall heaters like those sold by Machine Mart.
Which domestic heating design website did you use (save me looking for one) as I would like to do a similar calculation.
David
--
David Littlewood

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if going for a wooden shed ..
dig a hole 1 foot deep ..........fill with chippings ............
lead drainage trench off ...to lower ground
set concrete blocks roughly 1 blocks length apart ...spaced over the chippings ...and level
build shed with dpm under the floor between the rafters and floor boards
make floorboards at least 7/8 thick and rafters 2x4..........and you got a shed that will support half ton machines.
the insulation is up to you ...you can buy the stiff stuff with silver foil backing in sheets of 8 x4
these... you can saw through easily and fit between the roof rafters and wall uprights noggins ..and the other... whatever they are called.
concrete ..............here's how mine was built ...the dpm does not add much to the price ...i only wish that i had put cavity walls in though ...
http://smg.photobucket.com/albums/v190/aboard_epsilon/workshop /
my roof was lined with double layer of acoustic suspended ceiling tiles ..........i caught a building firm tearing down a supermarket ...and i got them for free....they made a hell of a difference to the noise levels in there ...........and altered heating it ...26x 26 in very cold weather...........from 8500 watts to 3500 watts....calcs based on any heat input.
all the best.markj
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I use a cheapo dehumidifier which I bought from BeanQueue - has the dual advantages of drying the air as well as raising the ambient temperature. If you do go down this route then be sure to get one which can be connected to a pipe to the outside world so as to avoid having to empty the thing every week.
--
Boo

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One area commonly overlooked id draught proofing, in a building like your garage it will account for most of the heat loss. Air is a lousy conductor (after all all most insulation works by traping air) and takes an awfull lot to heat it. If that nice warm air is then replaced with cold air from outside you are on a hide into nothing.
My suggestion for your garage would be to line the walls with a vapour barrier, this used to be tarred paper but is a horrible fire hazard. there a plenty of high tech solutions out there but plastic sheeting works well for me. Hold this on with wooden battens say 2" x 2" then cover this in whatever takes your fancy for a wall covering. 1/4" ply works well. You want to pack the spaces with insulation.
Depending on your situation you can treat the roof the same or you can put in a ceiling.
Don't forgrt the floor, I assume your garage has a congrete floor. I'd suggest the vapur barrier followed by insulation, either polystyrene or dense minerarl wool topped off with chipboard flooring.
And finaly the door, if it is an up and over type it is well woth insulating and draught proofing, if wooden doors draught proofing should do it.
I have followed the above on several occasions and been very happy with the results, even my wife doesn't complain about the heating bill (one small oil filled radiator on a thermostat)
Regards
James
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The message

James, I thought the vapour barrier was intended to keep the moisture, generated inside the building, from condensing on the cold outer walls and causing problems there. Bill Lamond

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Hi Bill,
It's a long time since I worked in a design office but if I recal the way it works is that the vapour barrier in this case keeps the moisure out from the damp walls. The internal ply will be at the same temperature as the room so no condensation.
It's a departure from the norm but when I was an apprentice we did model this for my fathers workshop, the theory worked out then (30 years ago) and it's proved pretty sound as he is still using the workshop today. I don't think there is a perfect answer, even the professionals get it wrong. I worked on a job last year where all the ceilings were brought down due to excessive condensation caused by a very high tech heat recovery system.
The calculations we ran took us a couple of days in the pre-computer days but I'm afraid lack of use has faded them into obscurity. I now write about the finished product and don't get involved with the design.
On the tack of design be carful of these online heat loss calculators. Most assume that the building complies with current building regs which an old garage clearly doesn't. Damp and air changes and insulation will be totally different and give very misleading results.
James
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The message

Hi James, Thanks for the reply. I have no real knowledge of the building business and I was thinking of a conventional house wall where, hopefully, it is unlikely for moisture to come from the outside. However, I have had a pile of new wood that ended up with dry rot because I had allowed it to sit on a damp floor with no ventilation. Ever since then I have been wary of moisture getting onto wood where there is no ventilation. Hope this explains my comments. Bill
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Hi Bill, no offense taken, it never even crossed my mind. I've been working in the Building Services Industry all my working life, but I certainly wouldn't claim to know everything - very far from it. Sometimes it's just common sense - isulation keeps you warm etc. but when it comes to condensation you get into dew point calculations which can get realy rather interesting. The trouble with the industry is that things have moved on with building regs requiring excellent insulation and draught proofing and everyone using computers to calculate heat losses and gains. Now we have no one in the industry who know the basic principles and can cope with older buildings. Still it keeps old phogeys like me employed. - James
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In article

I just did an approximate calculation on my garage as part of my preparation for putting a lathe in there. It's about 4.2m x 2.8m, 3m high, 1 outside wall of 8" Celcon block, rendered externally, 2 walls back on to house, 1 7'6" x 7' steel up & over door, roof of 3/4" ply and 3-layer felting, with 100mm of fibreglass and plasterboard within.
The results surprised me: very nearly half the conduction heat loss went through the steel door. Losses through the floor and the 2 walls backing the house were negligible. I knew I needed to insulate the door, but didn't realise how important it was until I had done this.
David
--
David Littlewood

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writes

like
lousy
vapour
hazard.
sheeting
then
ply
can
flooring.
walls
and
went
backing
..yep - and the roller shutter in my new workshop is about 15' square - definately the biggest loss of heat
AWEM
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Blimey, I never expected this level of detailed and thoroughly researched help. Thank you gents. I'll just go ahead and copy James' proven recipe. Mind you, I don't expect SWMBO not to complain: she's a Chartered Accountant and nickel and dimes me to death on all my other profligate hobbies :-)
Regards,
Alan
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