First question - my first stopping place for insulation u values was
the DIY Wiki. They don't seem to be there which surprised me - or
should I have looked elsewhere other than in the obvious place
'Insulation' ?

The reason for the calculations is convincing a disbeliever that he
should insulate his workshop. Single brick structure, to be lined
with OSB on a 75mm framing. But how do I calculate the heatloss
across such a 75mm cavity without any insulation - do I need to take
into account convection ?

Any helpers please

Thanks
Rob

On Dec 17, 10:14*pm, robgraham wrote:
convincing a disbeliever that he should insulate his workshop.
Single brick structure

Hahaha... leave it one winter...
1 - Insulate walls AND ceiling AND floor
2 - Not insulating the floor gets calf muscle ache all night long
3 - Vapour barrier is important

U value of wall...
- Find the R value for 1 brick
- Find the R value for various insulation types of various thicknesses
- U = 1 / (R1+R2)

So 20mm marmox (R= 0.60) on uninsulated cavity wall (R=0.73) gives a
combined U of 0.75. An uninsulated cavity wall on its own is 1.37 so
nearly halves the heat loss. Makes warm up very fast, plus when cavity
wall later insulated it jumps further. No point using plaster anymore
on external walls, Marmox is quicker and almost anyone can skim 3mm
with a bit of effort... belt sander... angle grinder... expanding
foam.

Actual wattage differences, for 21oC internal temperature...
- Calculate wall surface area
- Calculate U value of wall
- Heat Loss = Area * U * 21 = Watts

So for example a 5.31m^2 wall with 50mm celotex (U=0.40) has heat loss
is 45W, without the celotex a solid 9" brick wall is 235W. That shows
how even a little insulation helps hugely - consider four such walls
and you've 1kW heat loss BEFORE considering your door, draughts,
windows, floor & ceiling. Doing 50mm celotex on those four walls saves
0.8kW.

Do a Google for "R value" and look for single brick.
You have to do an estimate for the studding re "cold bridging".
Simplest is to stick a piece of 25mm XPS over the studs before the
final plywood or hardboard. B&Q do lots of cheap(ish) insulation at
the moment.

On 17 Dec, 23:05, "js.b1" wrote:
On Dec 17, 10:14*pm, robgraham wrote:

convincing a disbeliever that he should insulate his workshop.
Single brick structure

Hahaha... leave it one winter...
1 - Insulate walls AND ceiling AND floor
2 - Not insulating the floor gets calf muscle ache all night long
3 - Vapour barrier is important

U value of wall...
- Find the R value for 1 brick
- Find the R value for various insulation types of various thicknesses
- U = 1 / (R1+R2)

So 20mm marmox (R= 0.60) on uninsulated cavity wall (R=0.73) gives a
combined U of 0.75. An uninsulated cavity wall on its own is 1.37 so
nearly halves the heat loss. Makes warm up very fast, plus when cavity
wall later insulated it jumps further. No point using plaster anymore
on external walls, Marmox is quicker and almost anyone can skim 3mm
with a bit of effort... belt sander... angle grinder... expanding
foam.

Actual wattage differences, for 21oC internal temperature...
- Calculate wall surface area
- Calculate U value of wall
- Heat Loss = Area * U * 21 = Watts

So for example a 5.31m^2 wall with 50mm celotex (U=0.40) has heat loss
is 45W, without the celotex a solid 9" brick wall is 235W. That shows
how even a little insulation helps hugely - consider four such walls
and you've 1kW heat loss BEFORE considering your door, draughts,
windows, floor & ceiling. Doing 50mm celotex on those four walls saves
0.8kW.

Do a Google for "R value" and look for single brick.
You have to do an estimate for the studding re "cold bridging".
Simplest is to stick a piece of 25mm XPS over the studs before the
final plywood or hardboard. B&Q do lots of cheap(ish) insulation at
the moment.

Thanks John, for the pointer - as you say there ought to be one on the
'Insulation' page.

js - I take it that what you are saying is that a single brick, 75mm
stud wall with OSB facing is going to have the same insulation value
as a single brick wall with no lining at all ?

I don't believe that. And what's more that's not going to help my
discussion with the 'Disbeliever' who is expecting figures from me to
satisfy the argument.

Rob

robgraham wrote:
First question - my first stopping place for insulation u values was
the DIY Wiki. They don't seem to be there which surprised me - or
should I have looked elsewhere other than in the obvious place
'Insulation' ?

The reason for the calculations is convincing a disbeliever that he
should insulate his workshop. Single brick structure, to be lined
with OSB on a 75mm framing. But how do I calculate the heatloss
across such a 75mm cavity without any insulation - do I need to take
into account convection ?


Not really. single brick is about 7 U valeue wise. insulation should
bring it down to 0.5. Even with windows and a door, overall value should
be no worse than one or two. Probably at a rough guess from 200W/sq
meter floor area in winter to 50W/sq meter.


Any helpers please

Thanks
Rob

robgraham wrote:
On 17 Dec, 23:05, "js.b1" wrote:
On Dec 17, 10:14 pm, robgraham wrote:

convincing a disbeliever that he should insulate his workshop.
Single brick structure
Hahaha... leave it one winter...
1 - Insulate walls AND ceiling AND floor
2 - Not insulating the floor gets calf muscle ache all night long
3 - Vapour barrier is important

U value of wall...
- Find the R value for 1 brick
- Find the R value for various insulation types of various thicknesses
- U = 1 / (R1+R2)

So 20mm marmox (R= 0.60) on uninsulated cavity wall (R=0.73) gives a
combined U of 0.75. An uninsulated cavity wall on its own is 1.37 so
nearly halves the heat loss. Makes warm up very fast, plus when cavity
wall later insulated it jumps further. No point using plaster anymore
on external walls, Marmox is quicker and almost anyone can skim 3mm
with a bit of effort... belt sander... angle grinder... expanding
foam.

Actual wattage differences, for 21oC internal temperature...
- Calculate wall surface area
- Calculate U value of wall
- Heat Loss = Area * U * 21 = Watts

So for example a 5.31m^2 wall with 50mm celotex (U=0.40) has heat loss
is 45W, without the celotex a solid 9" brick wall is 235W. That shows
how even a little insulation helps hugely - consider four such walls
and you've 1kW heat loss BEFORE considering your door, draughts,
windows, floor & ceiling. Doing 50mm celotex on those four walls saves
0.8kW.

Do a Google for "R value" and look for single brick.
You have to do an estimate for the studding re "cold bridging".
Simplest is to stick a piece of 25mm XPS over the studs before the
final plywood or hardboard. B&Q do lots of cheap(ish) insulation at
the moment.

Thanks John, for the pointer - as you say there ought to be one on the
'Insulation' page.

js - I take it that what you are saying is that a single brick, 75mm
stud wall with OSB facing is going to have the same insulation value
as a single brick wall with no lining at all ?


No. a single sheet of plasterboard makes a lot of difference.


Cant be arsed to work it out, but likley a 50% reduction in U value. I
lived in a single brick plus 2" rockwool and plasterboard, and that is
pretty good.

Old cottage I rented, 3mm of oak tiles on exterior kitchen wall
completely stopped condensation. single brick is DIRE - almost anything
makes it better.

Out of interest, I calculated the thickness of a stone castle wall
needed to reach modern U values. It was either 3 meters or 6 meters.

Those ice age people who lived in long barrows, weren't stupid, it
seems. Nor are castles necessarily the cold places we think they might
have been.

On Dec 17, 11:42*pm, robgraham wrote:
js - I take it that what you are saying is that a single brick, 75mm
stud wall with OSB facing is going to have the same insulation value
as a single brick wall with no lining at all ?

No, it will be better, just nothing like as good as with insulation.

You NEED to check the following R values, grabbed off Google.

Uninsulated Brick + Cavity + OSB..
- Single brick - R = 0.12
- Unventilated Cavity - R = 0.18
- 18mm Plywood - R = 0.70
- Combined R = 0.12+0.18+0.70 = 1.00
- Effective U = 1/R = 1/1 = 1.0

Four wall surface area = 4x 3 x 2.3 = 27.6m^2
- U value of uninsulated wall = 1.0
- Internal temperature = 21oC
- Heat Loss = Area * U * 21 = 27.6*1*21 = 579 Watts


Insulated Brick + 50mm Celotex + OSB...
- Single brick - R = 0.12
- 50mm Celotex - R = 2.63
- 18mm Plywood - R = 0.70
- Combined R = 0.12+2.63+0.70 = 3.45
- Effective U = 1/R = 1/3.45 = 0.29

Four wall surface area = 4x 3 x 2.3 = 27.6m^2
- U value of insulated wall = 0.29
- Internal temperature = 21oC
- Heat Loss = Area * U * 21 = 27.6*0.29*21 = 168 Watts


Assume perfectly insulated floor, ceiling & windows.
- Uninsulated - 579W = 7p/hr cost
- Insulated - 168W = 2p/hr cost

Assume 100 day winter, 2hrs/day
- Uninsulated = £14 cost
- Uninsulated = £4 cost

Assume 100 day winter, 8hrs/day
- Uninsulated = £64 cost
- Uninsulated = £16 cost

The reality is uninsulated will not have perfectly insulated floor,
ceiling & windows.
- 2hrs/day becomes £42 v £12
- 8hrs/day becomes £192 v £48

Additionally, overnight heating re frost & condensation may be
required.
- It is here that uninsulated becomes a money pit
- You are background heating for 22/16hrs a day which adds up


One other comment re insulation on the inside:
- Insulation on the inside = fast warm up, no thermal mass
- Insulation on the outside = slow warm up, high thermal mass

For a workshop insulation on the inside is probably best.
- Background heating - tube heater on Smiths Plug-In Thermostat
- Boost heating - wall mounted FX20VL fan heater (thermostat), floor
industrial jobbie etc

That way it gets warm very quickly indeed.

Typo...

Assume perfectly insulated floor, ceiling & windows.
- Uninsulated - 579W = 7p/hr cost
- Insulated - 168W = 2p/hr cost

Assume 100 day winter, 2hrs/day
- Uninsulated = £14 cost
- Insulated = £4 cost

Assume 100 day winter, 8hrs/day
- Uninsulated = £64 cost
- Insulated = £16 cost

The reality is uninsulated will not have perfectly insulated floor,
ceiling & windows.
- 2hrs/day becomes £42 v £12 insulated
- 8hrs/day becomes £192 v £48 insulated

Typical figures re wall 30% of heat loss, uninsulated floor/ceiling/
window and insulated floor/ceiling/window to equivalent of 50mm
celotex. It comes down to how often it is used (2hrs/day or 8hrs/day)
and whether frost protection is required (which really costs with
uninsulated).
Assuming walls are roughly 30% of heat loss and insulated example
copies the 50mm celotex (or equivalent).

On 18 Dec, 01:31, "js.b1" wrote:
Typo...

Assume perfectly insulated floor, ceiling & windows.
- Uninsulated - 579W = 7p/hr cost
- Insulated - 168W = 2p/hr cost

Assume 100 day winter, 2hrs/day
- Uninsulated = £14 cost
- Insulated = £4 cost

Assume 100 day winter, 8hrs/day
- Uninsulated = £64 cost
- Insulated = £16 cost

The reality is uninsulated will not have perfectly insulated floor,
ceiling & windows.
- 2hrs/day becomes £42 v £12 insulated
- 8hrs/day becomes £192 v £48 insulated

Typical figures re wall 30% of heat loss, uninsulated floor/ceiling/
window and insulated floor/ceiling/window to equivalent of 50mm
celotex. It comes down to how often it is used (2hrs/day or 8hrs/day)
and whether frost protection is required (which really costs with
uninsulated).
Assuming walls are roughly 30% of heat loss and insulated example
copies the 50mm celotex (or equivalent).

Many thanks js - that's a tour de force. If that doesn't convince my
mate, then he deserves to freeze to death !!

I'll just punt that across to him as it stands; no point in me doing
the work again - I'm really grateful.

Rob