Hi Arthur, not here I'm afraid. U-values improve with the thickness of a particular insulation [or other material] The U-value also varies with the thermal conductivity of the insulant [k or lambda value] These values are derived from laboratory tests and are published by manufacturers [and elsewhere] Not sure if there is a comprehensive list here either as there are so many different materials.

There is however a u-value Ready Reckonner in the Green Building Bible Vol 2 which allows you to assess exactly what you are after.

Thanks Mike, that was the sort of thing I was looking for.

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

gives some other k values.

Get the U-value by dividing the k value by the thickness in metres.

E.g., the k value of rock wool insulation is given as 0.045. If you have 200 mm of it (0.2 m) you'd get a U-value of 0.045 / 0.2 = 0.225.

Often, though, quoted R values are in American units (using furlongs and fortnights or something). Sometimes people call them RSI values when they're in units consistent with what Mike up North said. Convert American R values to rest-of-the-world R values (RSI) by dividing them by about 5.7.

The advantage of using R values is that you can add up the values for the different layers of the wall. However, when you then want to calculate the heat loss for the the wall you need the U value to multiply by the area.

So

Not confusing or difficult to get your head around at all then!

The main problem I found was calculating U values for actual bits of my house. For example:

tiled roof, flamed (mortar on back of tiles), 50mm air gap, 50mm kingspan between rafters, rafters 50*100mm with (on average!!!! - actually each rafter follows a uniquely twisty, turney path) 325mm space between, 25mm kingspan + 12.5 mm plasterboard over the top.

The other main problem was real world performance a slab of PUR foam in a foil sandwich is going to work better than any open celled stuff (thermafleece for the rich, rockwool for normals) in draughty conditions. This makes U values rather academic (if they were not academic enough in the first place).

It is worth remembering that it is actually not physically possible (or at all practical) to get to building regs levels of insulation let alone passive house in a lot of the existing housing stock. I is however extremely desirable to get some insulation in where there is none. I've lent my BGG to a neighbor but I thing the first few 10's of mm give a very big return over nothing. I am a little weary of the 'unless you are getting to passive house standards, it's not worth it' attitude.

I know I and others have posted the next bit in one colour or another many times but it is worth re stating:

Passive houses are all very well and if you are one of the vanishingly insignificant number of people who live in one or who are going to live in one in your lifetime you can choose to be smug or otherwise. Most of us live in houses drawn from the existing stock and will continue to do so, as will our children and theirs. It is the existing stock which is the most important element to address.

It's sunny here today!!!

S.

Yes, I agree Skywalker. Its easy to lose a sense of priority reading forums like this because so many people are involved in dream new-builds.

Thank you, Skywalker!

from the national statistics site:

"There are a total of 22,539,000 households in England and Wales. 21,660,000 of these are occupied (20,451,000 in England and 1,209,000 in Wales), 727,000 are vacant (676,000 in England and 51,000 in Wales) and 151,000 are second homes or holiday accommodation (135,000 in England and 16,000 in Wales)."


I would stab a guess that at least 25% the 22.5 million are not sensibly/ upgradeable to current building regs without stripping down and refitting (probably having to use the very best materials such as aerogel). Another 50% would require major re fits like mine. Using my small house as a guide this would cost around £15-20k minimum (roof off, plaster and lath down, upstairs and downstairs floors up infiltration sorted and & replaced) using professionals. The remaining 25% would be 'easy' £10k on average to do.

There is then the small matter of the 880,000 mainly vacant properties.

I suppose the 60 or 70 passive houses are really helping then!

Flipin' 'eck

S.

I was responding to your post rather than the jist/original hijack of this thread!

Uptake has been low because it is :

a. voluntary (never a good thing).
b. administered and run by the power companies who have little or no interest in doing it (generally speaking).
c. does not apply to hard to do/difficult (expensive) situations.

Of course few want to spend £20k (or several months DIY living in dust like my family) on their house. Even less will wear knocking down their Tudor/Jacobean other old timber frame property 'cos it is a bit drafty.

The fact is that massive energy savings are to be had for much smaller levels of investment if carried out accross the board. We talked this through before I'll have a look for the thread.

But we are wondering off the point I was making here - stated U values mean very little, current building regs are very difficult to meet in a lot of the existing stock and passive house standards all but unreachable except for a very few.

S.

Skywalker, thanks for the link. It's an interesting subject but I don't see how to get people to improve their properties. I'm amazed at the number of people I've spoken to who don't believe insulation has any effect. One person had his house cavity wall filled and loft insulated but said it hadn't made any difference to his bills. I then found out he likes his windows open all year round. A friend who converted a barn only installed the minimum insulation because he had to for building regs. There's a lot of education needed on this matter and it will be interesting what effect the latest government push has for installing insulation.

Marktime

Sensible comment, my last post was a bit harsh in the that the hotbox method does the job on getting a sliding scale of how well each for of insulation may be performed when compared to another in the same conditions.

I'm not sure about the rest of your comment. When I think of the millions of lofts with rock wool type products in them where a gale blows as well. No one has failed there, correct installation, as per manufacturers instructions, widely accepted practice. Does it give the specified U value - does it tomatoes.

I have also yet to see a report of a process real world monitoring using random sampling of fabric elements of actual dwellings (not special stuff like PH's, 'example dwellings, or BRE lab rats) in terms of comparing design limits to actual performance over time (your Wimpey/Barrett stuff).

I'll bet all my tandems & my skateboard there will be (statistically) none which meet them even if they have be built by one of the very many good builders.

S.

Regarding u-values v real life performance in general, have a look at this http://www.lmu.ac.uk/as/cebe/projects/stamford/index.htm

Regarding settlement of some compressive insulation it can and does occur. I have seen it on site many times and I have also seen research which highlights it as a problem. It can and does affect the conductivity significantly. I'll try and remember where the report on this is.

Marktime, can you point me to a citation which discusses the boundary conditions you mention that are factored into the u-value of mineral wool. The only hot plate test I am aware of which factors in any level of air movement is one recently conducted by the NPL in their investigation of multifoil http://publications.npl.co.uk/dbtw-wpd/exec/dbtwpub.dll?&QB0=AND&QF0=ID&QI0=%204835%20&TN=NPLPUBS&RF=WFullRecordDetails&DL=0&RL=0&NP=4&AC=QBE_QUERY certainly not the norm

Marktime,

The stamford link concludes I believe that there is a difference between predicted steady state u-values and real life performance.

There is nothing about settling in the Stamford report - that is in a different publication, the one I am going to try to find. Hopefully someone else here has seen it and can point us to it. I do not know what makes the insulation settle for sure - gravity? But I do know that it does - I have seen it in lofts and I have also seen it in the cheek walls of dormer walls. The dormer walls were full of flies by the way. Other lodgers in the loft included many wasp nests and at least a pair of bats - who knows if they have something to do with it.

Presumably the boundary conditions you refer to are what I would call Ri and Ro: Resistance of the surface inside and outside respectively. In my opinion these do not accurately take account of the passage of air in a cold loft, or any other such construction where air can be funneled through part or all of a construction, such as above insulation fitted between rafters; or in a ventilated cavity. I believe it is for this reason that NPL introduced a new methodology to their hot box testing. If you read their report you will see that this is indicated as being the case. Indeed there is an acknowledgement that u-values do not take account of either air infiltration or solar gain.

Very interesting stuff - my bikes are safe.

"The actual thermal bridging through linear junctions was higher than predicted and the true U-values of the floors, walls and ceilings as constructed was higher than calculated"

So on a careful new build, where you would expect at or near design limits to have been met the insulation does not do what it says on the tin!

" Analysis of the experimental data has shown that the mechanism for heat loss via the party wall is driven by upwards air movement in the cavity. This air movement is generated by thermal stack effects and by pressure differences caused by the action of wind moving across the dwelling. Heat transfer from the internal conditioned spaces occurs by conduction through the single leaves of the party wall into the party wall cavity. The heat is then lost via bulk air movement upwards in the cavity and then by conduction and air movement into the loft space."

Probably still good houses though.

I really do not think that it should be a surprise, or a subject for too much heated debate (sorry!) that lab results differ from the real world - they nearly always do. Tests/controlled experiments give us models which can be applied in/to the real world; but they are only models.

I think the issue with insulation is that it appears to have all been worked out very carefully to several decimal places and gives the impression that this can be transfered to the real world without too much thought/further transformation. This is probably expecting too much.

All I'm left with is a much warmer/more energy efficient house, which can't be bad. I just don't know how much warmer/energy efficient, which is annoying 'cos it has been and is hard work.

S.

This is why the tests demonstrated that these developers were not delivering what was written on the tin and confirms what I posted for goodness sake.

Quote <In addition to losses attributed to ventilated party walls ....

35. Other possible explanations for the remaining unaccounted for difference between measured and predicted heat loss are as follows:

a) The U-values of the various construction elements may not have been achieved in practice due to quality or technical problems during construction.

b) The values for linear thermal bridging obtained by thermal modelling and used in parametric SAP may have been unrealistic due to either quality or technical issues during construction.

c) The air permeability of the test dwellings may have increased significantly during the test due to the high thermal stresses imposed on the building fabric, joints and junctions.

d) There may be other, as yet unidentified heat loss mechanisms, which are not included in the parametric SAP model. > End quote.

The next time you cross a bridge you want to hope that the construction has met the design criteria and that no waivers on quality have been allowed so that at least you, like the proverbial chicken, will get to the other side.

The science is out there, why do you need to second guess it?