Andy Hall wrote:

If you were looking at Building Regulation compliance, it would be a
different story, but for this it's good enough.

Yep.

You may want to think about what temperatures and patterns of use as
well.

If you were constructing the building to meet Building Regulations,
there are guidelines for each element and the approach is called the
elemental method. You can read more about it in the Approved
Document to Part L1 on www.odpm.gov.uk

Basically there are maxima for each component that are allowed if you
are in a situation where the building, by size, location, use etc. is
controlled by the Building Regulations. In that case you would have
had to make an application to the local authority and they would
inspect your work.

If you are not required to work to Building Regulations because the
building is exempt, (you can look on any local authority web site for
information on this or again on the ODPM site), then insulation is up
to you.

Since you are paying, then you have to do the trade off between
insulation capital cost and the cost of running the heating. If you
are using a more expensive fuel like electricity, then you will
probably want to spend more on insulation.

I would sit down and think about expected use patterns the year round
- for example will you want to trudge down there when it is ****ing
with rain horizontally? The go from there.

If in doubr, it probably pays to err towards more insulation now,
because it will be a pain to add later.


The office part of the building will probably be used constantly,
come rain or shine (or snow!), and I can also see me being in there
until late at night on some occassions, such is the nature of the
design business. The workshop part probably won't be used as much...
maybe once or twice a week.

Exactly. You can pick a given size of Celotex and work out the heat
loss for the building at given temperatures.

How does the result of the equation I worked out in my previous post
(1809.2W) indicate which heating solution and output rating I would
need, to maintain the target temperature inside the lodge? I know I
might be jumping the gun a bit here as I have yet to allow for air-
change, but I was just wondering!


One part of the exercise is to ensure that you put in enough heating
to reach the temperatures you want inside for the coldest outside.

The other is to do the cost trade off. To do that one, you can look
at average monthly temperatures, take the predicted use pattern for
that month and hence the energy use and cost based on that outside
temperature. You have to decide on what the pattern of use is,
though.

As above, constant use for the office but not for the workshop.

OK, so you've used 18 degrees as the temperature difference from
inside to outside.

That would mean that if it drops to -3 outside, you would have +15
inside which might be OK for a workshop but a bit chilly for sitting
around.

The typical inside (lounge) temperature used for design purposes is
+21 degrees, so the temperature difference is then 24 degrees.

If you wanted to achieve that, then you would need to multiply your
figure by 24/18 which is approximately 2.4kW

That's where my maths lets me down! I would have recalculated the whole
thing again using the new value of 24°! I assume that multiplying my
result of 1,809.2W by 24/18 saves me doing that and gives me the same
result? (Rhetorical question, as I'll try this offline!).

In other words, when it's -3 outside, a 2.4kW heater would maintain 21
degrees inside.

Ah! So this answers my question above about the relationship between
the result of the calculations and the heating output required? Apart
from factoring in the air-change, of course!

There is also one more component that should be taken into account.
You won't want to have a hermetically sealed box, so some air change
needs to be included.

To calculate this, you need to take the volume in cubic metres and
multiply by 0.33 and the temperature difference again. This would
give you the heat requirement to cover one air change per hour.
However, the normal design criterion for a living room, games room
etc. is 1.5 air changes per hour, so to do the whole lot it would be

Volume x 0.33 x 1.5 x temperature_difference.

Answer again is in Watts and you add that in. It could be as much
heat as for the loss through the walls or even more.

Undertood! I'm not quite sure how to calculate the volume in the roof
space... if the pitch of the roof was 45°, I could just flip one side
through 180° at the apex and treat it as a rectoid (???), but it's not
45°... I'll have to google this one!

Let's say your rafters are 500-600mm apart.

You could cut the Celotex about 3-5mm oversize and it will squash in
with a friction fit. If it's at size or slightly less, you tape them
to the rafters with foil tape.

Yep, a good friend of mine suggested using the tape, even if the
interference fit is right... he said it helps when tacking the walls.


One other thing is to not to forget to put some vents to the outside
from behind the Celotex. When I did my workshop project, I used
soffit vents (round plastic vents with a grille to keep out insects)
that fitted into holes drilled under the eaves, one between every pair
of rafters each side.

You can put them in a different position, but ventilation is
important.

I was wondering what to do about this, there are currently no soffits
in place and the space between the rafters is just open! I was thinking
about sourcing some kind of mesh material that would allow the through-
flow of air, but not insects! Is there a product that you can think of
that would be suitable for this or is the only realistic option to fit
wooden soffits and then cut holes between each rafter and fit soffit
vents? If there was something that I could employ which was already
perforated, then this would save time and a little money! Something like
pegboard, but with smaller holes! Any ideas?


Another thing that I did was to coat the inside wood surfaces with
clear Cuprinol solvent based wood preservative before putting in the
Celotex and covering over.

Were your timbers tannelised? Would you recommend this even if they are?

Also, at this stage, have a think about the electrics.

If you want to hide them and use flush mount fittings, then a good way
is to put in conduits and outlet back boxes and to then run PVC
singles wiring to connect them together.

I went for function over form and used three compartment trunking
everywhere, surface mounted. This allows me to add things as I go
or if necessary move them without disrupting the walls.

That's really the stage I'm at now! I have the cable and the pattress
boxes and I came to an abrupt hault because I obviously need to run a
separate ring main for the electrical heating if that was what I going
to go for! This got me thinking about the heating, and then the
insulation and then hence the start of this thread!

I have recently completed some fairly major renovations to the house, in
that we had the rear left corner of the house removed downstairs, so
that we could extend our tiny kitchen to take up some of the space at
the back of my garage (what a difference it has made, but that's another
story!). One of the things I learnt during this, as I was pretty hands
on with the project, was to set noggins between the studs at a height
which matched the desired position of the wall sockets. The noggins were
set back at such a distance from the front of the studs, so that when
the pattress boxes were attached to the noggins, they would protrude
slightly proud of the innermost face of the studs. This meant that when
the plasterboards were offered up, a swift bash of the boards, around
the area of the pattresses, would result in an impression of the corners
of the wall boxes being left in the back of the plasterboard... the
perfect template! Although you probably know that little trick already!

Anyway, this is what I intend to do in the lodge. I'm just not yet sure
whether to position the mains ring at skirting board height (or just
above) or to run it round at desk height! What did you do? What pros and
cons did you consider? I'm thinking desk height would keep the ring
above any potential dampness and would permit easier access via a cable
tray at the back of the desks or some such device. I did consider the
conduit route, but that proved fairly expensive when I used it at a
previous office premises! Do you think the trunking within the walls
would really be necessary? I know it is probably part of the "perfect
build" which your project sounds like it definitely was, but, while not
wanting to cut too many corners (where it matters), cost is a major
issue for me and I need to save where I can!

On the subject of electrics, I'm still quite unsure of what lighting
fixtures to install in the building. Lighting is, and always has been, a
major issue for me. I have always hated dingy rooms! And I don't want to
end up with a harshly lit space! I want to create some mood lighting
(for the creative looke/feel) and some task lighting for when working on
the computers while referencing paperwork on the desktop. I obviously
want to avoid screen glare and above all, not end up spending an
absolute fortune on the installation, which I am apt to do when it comes
to lighting... it's one of my weaknesses

Have you any experience on this subject? Do you know of any products on
the market that provide multi-tasking lighting solutions? I am
researching this myself but am keen to hear your opinions as you have
already completed a similar project, albeit that you were installing a
workshop which obviously requires a different lighting solution! It's an
awkward one, because I want to be able to install the cabling now that
would be suitable for any lighting installation that will eventually be
chosen and as it's only cable, I'm not too bothered about over-compensating!

Hmm. I think I'd lose patience with that,

I often do

Personally speaking, I am quite left-brained with the exception of
music. Visually, I know what I like and what I don't, and would far
rather see a limited set of choices and work from those than be
bombarded with 20 choices.

Three is usually the number of ideas I put up, and then I have to try
and discourage the client from using an element from each, to create a
hybrid which never hangs together!

Definitely. It doesn't mattter if the odd sheet is slightly dinged,
even. You can cut that out.

I didn't bother because I was able to get a reasonable price for all
the project materials from Jewsons.

Yeah, I suppose it depends on the final price you get for new when
compared to used. I'm quite confident that Magnet will come up trumps as
I have a good contact within that firm and he has assured me that I'd
have to look hard to find a better price for sheet materials as they
have decided to stock them at a ridiculously low price, in order to get
the punters in so they can sell them a kitchen or bedroom! My local
Magnet is currently offering 8x4 sheets of 15mm plasterboard at £3.15
per sheet... that's cheaper than B&Q's price for a sheet half that size!
The sheet price also comes down for bulk orders!

A couple of other questions I have a
As I intend to split the space into two separate areas, should I redo my
previous calculations treating each room completely separately and how
do I factor in the heat-loss of the stud wall between the two spaces?
How would that then affect the heating installation that I opt to go
for? Would it just be a matter of installing a certain wattage of
heater(s) in the office space to meet the optimum temperature of that
environment and then install an arrangement of differently powered
heaters in the workshop to achieve the desired temperature there?

Is there a heating system that would provide both the heating and the
air-change facility that would be required for the building? Maybe
there's a product that does this and also provides air
cooling/conditioning during the summer months! Any pointers would be
appreciated, I don't expect you to all the answers, but as I said, it
appears that you have "been there" as it were!

Also, when estimating the amount of Celotex and plasterboard required,
is there a percentage that I should account for with regards to wastage?
I'm a bit worried about over/under-ordering!

I'd also like to just say thank you at this point, your assistance and
advice is very much appreciated.

rgds

Dean.