I have at long last decided to do something about insulating the 2 ft thick rubble filled stone walls of my house and sought advice from the Wiki on what had previously proved a stumbling block in calculating radiator sizes, etc. ? what is the U value of such a wall. I thought I was onto a winner when I found under Heat Loss:
?Computing U values for more complex walls
When dealing with complicated wall constructions it can be handy calculate a U value by taking into account the properties of several layers of different materials.
See an example for a Rubble Filled Wall?
But unfortunately following the link merely gives rise to a 502 error which claims to be temporary but has persisted for weeks as far as I am concerned.
So is this just me (or Firefox) or is there really a problem with this link? Either way how do I get round it to see this example?
It's a link to google groups archive of a thread titled "Insulation u value wanted" from this group, probably they've b0rked their URLs, here's a working link ...
Thanks for that. It looks useful. I have the same problem as Rob in that my walls are sandstone rather than limestone but like him I don't expect it makes much of a difference even if I can't find a U value for sandstone.
Unfortunately my talents do not stretch to modifying the wiki.
For those who don't want to work through the whole thread the relevant bit is as follows:
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From the top of my head:
Outside surface resistance = 0.04m^K/W Limestone: conductivity = 1.13W/mK; divide the thickness by this value to give resistance. Mortar (and presumably loose fill): conductivity = 0.84W/mK [1] Rockwool: conductivity = 0.05m/0.038W/mK = 1.32m^K/W [2] Plasterboard resistance = 0.06m^K/W. Inner surface resistance = 0.13m^K/W
Add up all the resistances, then take the reciprocal to give your U-value.
[1] It depends on the proportions of wall to rubble-fill, but I would have thought about 75% stone to 25% mortar and crap, which gives an average conductivity of about 1.04W/mK.
[2] If you want a precise figure, you should also include for the studs in the dry-lining.
R = 0.04 + 0.56/1.04 + 1.32 + 0.06 + 0.13 = 2.09m^2K/W. Therefore U-value = 1/2.09 = 0.48W/m^2K. To work out heating, probably best to use 0.6-0.8 unless you can put actual values to the thicknesses of the leaves of the wall.
Hugo Nebula
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A feature of rubble filled walls, or at least my walls, is that the width of the rubble infill varies from next to nothing to upwards of two thirds of the thickness of the wall and there are also voids where the fill has slumped and occasional rows of stone 'throughs' that tie (not always successfully) the two leaves together.
Solid masonry walls? I think you can safely assume the thermal resistance i s negligible.
I've converted a chapel with 12-15" solid (no cavity) brick and sandstone w alls. Installed double glazing - negligible effect (well, kept the rain out ). Lined all outside walls with 100mm PIR/Kingspan/Celotex - building trans formed into an easy-and-cheap(ish)-to-heat place.
What I'm saying is don't get hung-up on calculations for your existing wall s that aren't of much value. Likewise with heating calculations, if you spe nd a little more than strictly necessary, have a bit more insulation and sl ightly more heating system capacity - you have a good outcome.
Precise calculations are only really of value for housing developers that w ant to trim every last ounce of cost away whilst trying to meet the minimum standards of building regs.
When I lived in such a building, (2 foot 6 inches thick, slate faced walls, rubble core, internal plasterwork) I found that once it had been warmed up, it was as warm and easy to heat as the fully insulated 1930s house I own at the moment.
The only downsides were the draughts due to the ventilation needed to run the fire and the Aga, and the way that all the heat vanished through the roof until I had it reslated, this time *with* sarking under the slates. Oh, and the cost of warming it up from cold every time I visited. It took about 3 days of a roaring fire to get it warm, after which, it was like living inside a huge storage heater.
If I were living there now, just for fun, I might point an IR camera at it to check where the heat was leaving.
Which more or less mirrors what I found in the 1970s conversion of a Victorian Kingdom Hall I lived in for a while with 9" brick walls and no loft insulation. The new windows did stop most of the draughts, though.
I would have thought (without doing the calculations) that my rubble filled walls are at least the equal of 11" brick cavity walls which apparently have an U value less than half that of 9" solid brick.
I wanted to do the heat calculations for two reasons. The first to see what size radiators I really need and second to see what is the smallest boiler I can get away with. Since my 22 year old boiler will need replacing shortly now seems the sensible time to do it in conjunction with extra insulation. Having excess capacity on a condensing boiler boiler is not good if the end result is that it is not as efficient as it could be.
On 31/08/2013 11:22, snipped-for-privacy@gglz.com wrote: ...
Also useful if you have limited space to fit radiators and you need to know whether what you can easily fit in will do the job, or you need to find a different solution.
The 11" wall will have a 2" air gap and that will allow a small skin of stationary air to form and insulate it. Adding insulation will make it an ~2" layer of still air which will insulate better.
I would have thought that for a really thick rubble wall the U value would be about the same as a solid concrete floor.
It would be quite good to externally insulate them as that would allow them to store and release energy and keep the internal temperature more constant.
Insulate the walls on both sides and use them as a thermal store?
It's all rather academic as there are other factors that hugely effect this sort of wall. Eg, if it is damp, the latent heat taken up by the moisture as it evaporates is huge. Your occupancy of the building and its thermal mass. The type and distribution of the heating.
You won't get an accurate "U" figure anyway as you don't know the exact construction of the wall and it will likely vary in different places. So to calculate your insulation, best thing is to ignore the wall. Also determine if there is dampness and what you are going to do about it first (ie before you insulate it).
I have this number BTW for a free government insulation scheme, dunno if it's viable in your area.
But the rubble filling is anything but solid. The air filled voids provide insulation and the actual contact paths that the heat conduction has to follow are not straight lines and the paths themselves are constricted at every rubble/rubble boundary as uneven lumps of rubble will tend to have mainly small contact patches.
That would materially change the appearance of the property, and not for the better. As it is there will still be 2 internal transverse walls and the wall that separates the house from the barn (which will be insulated barnside to avoid making a narrow room even narrower) to act as heat sinks.
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And how would you propose I warm them up in the first place and extract the stored heat in the second place?
Rubble walls are like single-skin brick in terms of heat loss - ie, bugger all use. Once the heat starts travelling through it, it just keeps going to the outside.
If brick had a K value of 0.75 and stone 1.5 then a 24" thick solid stone wall would be marginally better than a 9" thick solid brick wall but the rubble fill confers some benefit, the problem is how much.
Hugo took the fill as largely solid - "It depends on the proportions of wall to rubble-fill, but I would have thought about 75% stone to 25% mortar and crap, which gives an average conductivity of about 1.04W/mK"
I am not sure whether that is directed at the wall as a whole or just the rubble fit but my rubble filled walls have unmortared rubble and some dust with plenty of voids so potentially at least the rubble should have a much better K value even if not down to that for dry sand (0.15 -
0.25) but below that for stone chippings of 0.96.
Incidentally there seems to be some dispute about stone K values. Hugo quotes 1.13 for limestone, the Wiki lists 1.5 and the linked list 1.26 -
1.33. For sandstone the Wiki lists 1.3 and the linked list 1.7. Has the Wiki listed limestone and sandstone the wrong way round?
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