Christian McArdle wrote:
Anyway I'm not talking about no insulation, I'm talking about doing it
where practical so I will be putting some insulation behind the
dry-lining but not so much that I generate lots of condensation.

Insulation helps prevent condensation. It doesn't cause it.

This group is really good on practical issues but seems to fall over at
least a little (don't want to be too rude) when it comes to theoretical
analysis. Maybe I should try alt.climatechange or something like that,
maybe theres even an alt.thermodynamics group!

If you propose an ELECTRIC underfloor heating system with no insulation in
alt.climatechange, if such a group exists, you are likely to be firebombed
by environmental activists.

Remember in your calculations that your basement floor is (a) at a much
elevated temperature and (b) loses two airsolid interfaces. It is solid
throughout, enabling straight conduction all the way through without having
to swap from solid to air, which provides considerable insulation in its own
right. Typically in an uninsulated floor situation, the floor surface
temperature itself is significantly lower than the room temperature, further
reducing actual heat loss.

Christian.

You're probably right about alt.climatechange! So with your sensible
advice Christian can I make a summary of the sensible points.

1. For efficient heating of the space overall I should stick with
radiators since these are running on gas anyway, therefore I'm
producing less carbon if I run uninsulated on rads rather than pretty
well insulated on the electric UFH.
---This is OK and what I plan to do anyway

2. If I stick with putting in the UFH for comfort heating then I am
wasting my money with the 6mm insulation, since most heat comes from
the rads so payback on the insulation is somewhere well over the
horizon, probably beyond the lifetime of the installation.
---This is OK since I don't have the money or the headroom.

3. For control of the UFH I should use the floor temperature sensor and
set it as low as possible (say 20C) to keep the duy cycle to minimum so
it just does the job of keeping the floor at a comfortable temperature.

Are there any other points I'm missing.

One more area of interest.

The issue with insulating the walls is that it moves the point where
the condensation is generated. Basically uninsulated any condensation
forms on the inside walls of the basement. If I insulate it then forms
on the inside surface of the wall membrane. This is why I didn't follow
the installation advice for the cavity membrane installation. The floor
membrane laps up the walls inside the wall membrane to ensure that
water from the walls (and there is some) drains behind the floor
membrane and ends up in my sub-floor drainage which is pumped away.
They recommend sealing the floor wall joint with waterproof tape. I
couldn't see the point since the top of the membrane is unsealed and so
water vapour can escape at the top anyway (dealt with by heat-recovery
ventilation and dehumidifier if necessary). My thinking was that if I
don't seal the joint then any condensation which forms on the inside of
the wall membrane should (on the whole) run down the gap between the
wall and floor membrane and so end up in the drainage system rather
than on the floor or at the base of dry-lining.

Does this seem sensible. If I'm going to seal the joint now would be
the time as I've put up the stud framework (inside the membrane) but
haven't boarded it yet.

It's been a fun thread!

Fash