My bungalow has a big sitting room with one wall made of double glazed
panel - the view is fantastic and worth the energy losses, it's good
double glazing though. It also has a 9 foot ceiling, so there is a lot
of air to heat. (House has 300mm loft insulation and cavities filled)

Currently there is an enormous double radiator on the back wall
providing the heating and although we can easily get the room warm the
air flow is the wrong way round. Cold air forms on the windows and runs
down onto the solid concrete (Cork Tiles) floor and then rises from the
radiator to the ceiling. I'd like it to run the other way so that warm
air came over my feet!

It seems to me that the best route to this is to replace the big rad
with a big rad on the floor - I.E. underfloor heating, and a
'conservatory pack' would be about right cost and output-wise to do this.

The trouble is that I don't have much floor 'depth' to play with. The
three brick walls are fine, but there is only about 85mm under the
window. If I put down say, 50mm of insulation there is only room for
30mm of slab. Using just 20mm of insulation doesn't sound very
'building regulation' friendly, in fact neither does 50mm. Any ideas?

R.

Richard Downing wrote:
.....The trouble is that I don't have much floor 'depth' to play with. The
three brick walls are fine, but there is only about 85mm under the
window. If I put down say, 50mm of insulation there is only room for
30mm of slab. Using just 20mm of insulation doesn't sound very
'building regulation' friendly, in fact neither does 50mm. Any ideas?


So presumably you're proposing to raise the existing finished floor
level to allow the insulation and UFH system to be installed on top of
the existing concrete floor? Or have I misunderstood something?

I've recently had a concrete floor removed back to bare earth in order
to install a new slab, 100mm of insulation and an 85mm screed
containing the UFH pipes. From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house. Maybe you could get away with 50mm, but
you'll need a lot more than 30mm for a screed unless you're considering
an electric system. Even then I suspect the screed will need to be a
lot thicker (or otherwise strengthened) because it will be laid on top
of what is basically a fairly flexible material and might otherwise be
prone to cracking. For wet systems I believe the minimum thickness of
screed is closer to 65mm.

Can't comment on what the building regs might require.

Mike

Richard Downing wrote:
My bungalow has a big sitting room with one wall made of double glazed
panel - the view is fantastic and worth the energy losses, it's good
double glazing though. It also has a 9 foot ceiling, so there is a lot
of air to heat. (House has 300mm loft insulation and cavities filled)

Currently there is an enormous double radiator on the back wall
providing the heating and although we can easily get the room warm the
air flow is the wrong way round. Cold air forms on the windows and runs
down onto the solid concrete (Cork Tiles) floor and then rises from the
radiator to the ceiling. I'd like it to run the other way so that warm
air came over my feet!

You've got several options.

Firstly, dig up the existing slab, put in insulation underneath it, and
then re-pour, over UFH pipes.
This is possibly the best way to do UFH - won't move, and a large
thermal mass to buffer the temperature in the room.

You say 'big'. I'm going to take a wild stab in the dark, and assume
6m*6m.
This is about 40m^2.

25mm of kingspan will do .8W/m^2/K.
If the ground is at 20C below the room temp, you're looking at around
1000W over the floor area.
In practice, the ground will also insulate somewhat, so maybe 800W or
so.

Doubling the thickness of kingspan helps quite a lot.

If I Was You.

The easy way.
75-100mm of kingspan, 50mm or so of screed, in which the pipes are in,
10mm of flooring.
At the edge of the room, a 15cm or so strip of 25mm of kingspan, and flooring
over it, with a step down.

Into this 'step' next to the window go concealed uplighters, and maybe a
plant or two, depending on your decor.

'It's not a bug, it's a feature'.

Richard Downing wrote:
My bungalow has a big sitting room with one wall made of double glazed
snip
The trouble is that I don't have much floor 'depth' to play with. The
three brick walls are fine, but there is only about 85mm under the
window. If I put down say, 50mm of insulation there is only room for
30mm of slab. Using just 20mm of insulation doesn't sound very
'building regulation' friendly, in fact neither does 50mm. Any ideas?


Thanks for the replies, they confirm what I thought. I'm now thinking
maybe I could refit the windows 'two bricks' higher (I just looked at
the way they meet the ceiling and this is feasible). This would give me
the depth for a proper insulation layer and thick hot-slab.

SWMBO doesn't like the idea of tubulars or a ceiling fan.

I'll get a quote for someone to dig out the slab and re-lay though, at
my age I don't fancy swinging a pick :-)

As with all my projects, I'll think about it for a few months.... You
might hear about it again.

Thanks once more,

R.

MikeH wrote:
... From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house.

Interestingly, I was chatting to a bloke who specifies UFH the other
day,
and he reckons this conventional wisdom is cobblers.

He reckons that the heat movement through the earth is such that you're
wasting your time insulating: OK, this means you heat the top 30cm or
so of the soil, but once it's up to a reasonable temperature it simply
becomes part of the thermal mass of your home and provides extra temp
stability.

Accordingly, he specifies some edge insulation (so you don't lose heat
to
the ground outside your walls, and recommends nothing under the main
body of the screed.

It all felt a bit wrong to me, but on the other hand the numbers he
showed
me (none of which I can remember) seemed to hang together, and my own
laziness means I want to believe him.

John

wrote:

MikeH wrote:
... From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house.

Interestingly, I was chatting to a bloke who specifies UFH the other
day,
and he reckons this conventional wisdom is cobblers.

He reckons that the heat movement through the earth is such that you're
wasting your time insulating: OK, this means you heat the top 30cm or
so of the soil, but once it's up to a reasonable temperature it simply
becomes part of the thermal mass of your home and provides extra temp
stability.

Accordingly, he specifies some edge insulation (so you don't lose heat
to
the ground outside your walls, and recommends nothing under the main
body of the screed.

It all felt a bit wrong to me, but on the other hand the numbers he
showed
me (none of which I can remember) seemed to hang together, and my own
laziness means I want to believe him.

Well...
There is an unfortunate problem with this.
Namely that it's ********.
The argument that you heat the top 30cm is rubbish.

If you heat a 10m circle (for simplicity) on the ground to 30C, then
what happens?
Assuming that there is uniform sand underneath, with no heat flow.
(the best case).

So, 30cm down, in the middle of the heated patch, the heat just stops?
Of course it doesn't - you end up - over a long period - heating to more
or less the temperature of the slab a sort of squashed hemisphere of
sand, maybe 2-3 meters deep.
This conducts the heat away to the rest of the earth.

Google perimeter/area ratio sand u-value.

Ian Stirling wrote:
wrote:

MikeH wrote:
... From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house.

He reckons that the heat movement through the earth is such that you're
wasting your time insulating: OK, this means you heat the top 30cm or
so of the soil, but once it's up to a reasonable temperature it simply
becomes part of the thermal mass of your home and provides extra temp
stability.

Well...
There is an unfortunate problem with this.
Namely that it's ********.

I didn't say I believed him, just that I wanted to ...

The argument that you heat the top 30cm is rubbish.

So, 30cm down, in the middle of the heated patch, the heat just stops?
Of course it doesn't

Well, no, of course not - I was guilty of over-simplifying.

His argument was that the temperature gradient in the soil would be
such
that you would get a significant temp rise at the top (I think in about
the
top 30 cm or so), tapering to a minimal rise by the time you were a
metre
or two down.

This conducts the heat away to the rest of the earth.

Aye, this is the bit I had difficulty with. I guess his notion is that
there is
no significant heat transmission to the bits of the rest of the earth
that
aren't under your house.

John

wrote:
Ian Stirling wrote:
wrote:

MikeH wrote:
... From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house.

He reckons that the heat movement through the earth is such that you're
wasting your time insulating: OK, this means you heat the top 30cm or
so of the soil, but once it's up to a reasonable temperature it simply
becomes part of the thermal mass of your home and provides extra temp
stability.

Well...
There is an unfortunate problem with this.
Namely that it's ********.

I didn't say I believed him, just that I wanted to ...

The argument that you heat the top 30cm is rubbish.

So, 30cm down, in the middle of the heated patch, the heat just stops?
Of course it doesn't

Well, no, of course not - I was guilty of over-simplifying.

His argument was that the temperature gradient in the soil would be
such
that you would get a significant temp rise at the top (I think in about
the
top 30 cm or so), tapering to a minimal rise by the time you were a
metre
or two down.

Yeah - the problem is - if this is true, you've got 30cm of earth doing
the same job effectively as the insulation in the walls.
Unfortunately - perfectly dry sand - as an example - insulates as well
as 1/10th its thickness of rockwool.
And moist - well, you don't want to go there.

I wish it could be so simple.
I'm in the annoying position of actually having calculated all of this
for my house, in the approved manner, and for the numbers to actually
match my energy bills pretty much.

Annoying - as it means that the 'long pole' in the tent in my case is
the walls, (by a factor of 4) which are really, really annoying to
insulate.

MikeH wrote:
Richard Downing wrote:
.....The trouble is that I don't have much floor 'depth' to play with. The
three brick walls are fine, but there is only about 85mm under the
window. If I put down say, 50mm of insulation there is only room for
30mm of slab. Using just 20mm of insulation doesn't sound very
'building regulation' friendly, in fact neither does 50mm. Any ideas?


So presumably you're proposing to raise the existing finished floor
level to allow the insulation and UFH system to be installed on top of
the existing concrete floor? Or have I misunderstood something?

I've recently had a concrete floor removed back to bare earth in order
to install a new slab, 100mm of insulation and an 85mm screed
containing the UFH pipes. From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house. Maybe you could get away with 50mm, but
you'll need a lot more than 30mm for a screed unless you're considering
an electric system. Even then I suspect the screed will need to be a
lot thicker (or otherwise strengthened) because it will be laid on top
of what is basically a fairly flexible material and might otherwise be
prone to cracking. For wet systems I believe the minimum thickness of
screed is closer to 65mm.

Can't comment on what the building regs might require.


My 2000 system was 50mm poly and 75mm screed. To regs.

My be more these days. Should have gone 100mm insulation.

Mike

Richard Downing wrote:
Richard Downing wrote:
My bungalow has a big sitting room with one wall made of double glazed
snip
The trouble is that I don't have much floor 'depth' to play with. The
three brick walls are fine, but there is only about 85mm under the
window. If I put down say, 50mm of insulation there is only room for
30mm of slab. Using just 20mm of insulation doesn't sound very
'building regulation' friendly, in fact neither does 50mm. Any ideas?


Thanks for the replies, they confirm what I thought. I'm now thinking
maybe I could refit the windows 'two bricks' higher (I just looked at
the way they meet the ceiling and this is feasible). This would give me
the depth for a proper insulation layer and thick hot-slab.

SWMBO doesn't like the idea of tubulars or a ceiling fan.

I'll get a quote for someone to dig out the slab and re-lay though, at
my age I don't fancy swinging a pick :-)

Hire a kango.

As with all my projects, I'll think about it for a few months.... You
might hear about it again.

Thanks once more,

R.

wrote:
MikeH wrote:
... From what I've read, the secret of a
successful UFH installation is the insulation that prevents you heating
up the earth under your house.

Interestingly, I was chatting to a bloke who specifies UFH the other
day,
and he reckons this conventional wisdom is cobblers.

He reckons that the heat movement through the earth is such that you're
wasting your time insulating: OK, this means you heat the top 30cm or
so of the soil, but once it's up to a reasonable temperature it simply
becomes part of the thermal mass of your home and provides extra temp
stability.

Accordingly, he specifies some edge insulation (so you don't lose heat
to
the ground outside your walls, and recommends nothing under the main
body of the screed.


This is to an extent true. The building regs on floor insulation take it
into account.

Sadly in my case it was a suspended concrete floor with a vented airgap
under..and boy does that lose heat on cold windy days.

However just earth alone will not give you the all U values you need,
and it will make for a very long time constant although it does make for
a nice micro climate just outside the walls for tender plants.


It all felt a bit wrong to me, but on the other hand the numbers he
showed
me (none of which I can remember) seemed to hang together, and my own
laziness means I want to believe him.

John