On Mon, 25 Oct 2004 23:12:19 +0000 (UTC), DeanoH
wrote:

Andy Hall wrote:

I just posted some information on how I did all of this for somebody
asking about heating for an outbuilding. Use Google Groups and
search backa few days.

Andy, I did read your thread and found it very interesting and
informative. I only wish that my outbuilding was near enough to
feed via a new circuit on the CH system... unfortunately, it's
about 250ft away from the house!

OK. In rough numbers, assuming you didn't insulate the floor, and
your walls are about 2.5m high, if you use 50mm Celotex and divide
equally, you're going to need about 4-5kW in the office bit and 3-4kW
in the workshop bit if you are happy with 16-18 degrees in that part.
These are round numbers based on my own calculations.

It's easy enough to do the sums. Just look up the R value of the
thickness of Celotex that you plan to use and calculate the U value
from the reciprocal of it. Then measure the surfaces in square metres
and multiply these by the U value and the temperature difference
through the walls - usually -3 degrees is used for worst case outside.
This will give you heatlosses in watts. For the floors you can get
figures from radiator calculation programs on the web sites of Barlo
or Myson radiators.

In terms of the heating arrangement, you are presumably going to run
electricity anyway, and with insulation, this is not getting too
outrageous to heat with electricity. Alternatively, if you have
mains gas you could run that and have a small boiler and radiators, or
perhaps LPG into a small boiler. I wouldn't use portable LPG
heaters though because of water vapour that will be produced.




My lodge is made from 4x2" tannelised wood, and dressed with
roofing underlay on the walls, with construction cladding over
the top... the roof is WBP 18mm ply with torch-on felt on top
of that... taking into consideration the ventilation gap behind
the celotex, what thickness board could I go for and would I
need to enlarge the cavity by deepening the joists and studs?

If you look on the Celotex web site there are application notes which
cover the options that you will need closely enough. I assume
where you say 4x2, you mean that the 4" side is the total depth
available? If so, you could perhaps go with 70mm Celotex and have
a 20mm gap behind. You need to check actual measurements.

If you want something fancier with exposed beams in the roof then you
might have to go for something thinner for that - it really depends on
whether you want to clad it. For my workshop I didn't bother because
I actually fitted the Celotex over the rafters leaving the foil
showing. The joists were boarded anyway and the area above is used
for storage so I didn't care about the foil showing.

For a cabin that I completed last year, I did care more about the
appearance, so I put small wooden laths brad nailed to the rafters to
make 20mm spacers, then fitted the Celotex against them. The ceiling
was then clad over the top of the rafters, hiding them and the
Celotex.





Also, do you know of any online suppliers I can get a quote from?


Well, there's the Seconds outfit that Christian mentioned.

Have you bought all the other materials yet? I found that by hawking
a complete project list around the merchants - I faxed each a shopping
list and asked for a quote, it wasn't hard to get reasonable prices.
I just picked the lowest overall quote but one. I didn't trust the
cheapest not to cock up the delivery.




..andy

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