Refurb of old walls - insulate inside or outside?

From a recent thread on rendering:

I'm facing a bunch of this for refurbs over the next couple of years. The main house isn't going to be changed, but I've thin-walled extensions to the rear (pantry etc.) and various sheds that are certainly candidates for adding wall insulation. The rendering, particularly one shed, isn't impressive at present anyway.
So what are my pros and cons for adding insulation to either the inside or outside of the wall?
Thanks
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We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Andy Dingley

Where I've seen external insulation applied it's been quite effective, but it depends on attention to detail to make it work properly. The advantages are mainly; saving of floor space internally, very little internal disruption, the walls inside of the insulation now act as a thermal store. The system I've seen used seemed to be based on something like 50mm Kingspan, covered with mesh then rendered.
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Andy Dingley wrote:

1/. Practicality. It may be more and nastier work to do it outside.. 2/. Wall thickness and where you want it put..this impacts on e.g. windows and doors. interior or exteriors cills, drip beds and the like.. 3/. thermal mass inside the insulation. Or not. Plus loss of room size. Or not.
On 3/. its up to you whether you want fast heat up times or stuff that takes an age to eat and cool.
If the rooms are used only occasionally, insulate inside, but for prime living ares, outside is nicer. Cooler in summer. Stays at even temps in winter.

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Re: Refurb of old walls - insulate inside or outside?
I beleive that if the insulation is at the outside this is best as then the walls will be a heat store and keep the building cool on summer days and warmish on winter nights - but my house is stone clad so i cant insulate the outside of the walls
--

[george]

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wrote:

but won't there be a huge thermal bridge straight down into the earth at the bottom of the wall spoliing any meaningful storage of heat - in other words acting as a constant heatsink - straight into the ground?
Jim
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jim wrote:

some, but you need a bit of integral calculus to calculate it..
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I'd still guess it's a factor big enough to scupper any "thermal mass" usage of existing walls....
I'd be tempted to try and do it from the inside so you are concerned with heating only the air inside the space rather than the ground...
Do the "sheds" have concrete? floors yet? if not you could maybe dig out, insulate with a good slab (100mm?) of kingspan etc (including some insulation upstands along the walls to avoid thermal bridge ;>)) and pour a slab(s) - now that *would* be thermal mass without a heatsink Then line the walls on the inside with insulated plasteboard (say 12.5 pb+ 25mm kingspan) dot and dabbed if poss for speed and space saving over battens etc, do roof as you already plan - can't think what would be much better than that (apart from starting again!)
jim
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We were somewhere around Barstow, on the edge of the desert, when the
saying something like:

Well, just ask somebody who's had it done. From what I heard, it worked well.
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wrote:

I'd like to hear - of course I am happy to be corrected :>)
jim
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Re: Refurb of old walls - insulate inside or outside?
the book i got from leominster library was so good that i bought a copy..
Insulate and Weatherize (Build Like a Pro - Expert Advice from Start to Finish) by Bruce Harley (Paperback - 1 Jun 2008) Buy new: 19.95 15.2523 Used & new from 1.94 Get it by Thursday, Nov 20 if you order in the next 5 hours and choose express delivery. Eligible for FREE Super Saver Delivery.
he recommends insulating on the outside, its a canadian book so they know about cold!
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[george]

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wrote:

Perhaps the OP may like to purchase - on the other hand as you have a copy:-
what does he actually specify to do in this situation?
jim
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the main recommendation in:

is to seal all air leaks and install a mechanical ventilation system which will work the same in windy and still air conditions.
More water gets into a building in small air leaks than through permeable walls and ceilings.
--

[george]


"jim" < snipped-for-privacy@googlemail.com> wrote in message
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Thinking some more along these lines, what do I do about end walls and roof insulation?
My specific case (one of several) is the line of small outhouses pictured in the recent post. There are four of them in a line, the first three of are single pitched roofs, only four feet wide and up to 14' long. The first is a pantry connected to the inside of the house (cold and damp), then an outside toilet, then an old boilerhouse. Beyond that is a workshop, intended for hot working such as welding, smithing and foundrywork (so not much need for insulation!). My plan long-term is to convert the outside toilet into a downstairs inside toilet - obviously this will need decent insulation, particularly for the roof.
If I'm mostly re-working the roof by adding insulation to the inside of it, is there much point insulating the outside of the walls, or should I go for the inside (despite needing every inch of width)? The end wall is also going to be insulated on the inside, as I've length to waste and don't want to put insulation materials on the inside (forge-side) of the smithy building.
Incidentally, I'm also planning a green roof for the smithy, for looks, noise insulation, and because the existing corrugated asbestos is simply too low.
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In message

Having paid the gas bills for the last 13 years, I don't think 25mm was anywhere near enough!
The technique used was to sand/water blast off the exterior water proof paint, secure 25mm Kingspan at 18" centres with vertical battens and re-cover with feather edge boarding (upper part). The lower part was similar except sheets of galvanised expanded metal were nailed to the battens and then rendered.
I don't know where/if a vapour barrier was installed.
The nice thing from your POV is that external render over insulation will give you a drip well clear of the bricks.
regards
--
Tim Lamb

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