Energy and insulation - advice sought

I’m about to start a conversion of part of a fairly large barn into a residential space and I’m particularly interested in advice around the central issues of energy and insulation. Rather, I’m hoping for more than this: advice is always very welcome but I’d really like the opportunity to visit sites where I can be shown what has worked (and what hasn’t!).

My barn is of a very simple construction with stone walls to the N,W & E, and an open (or simply shuttered with timber) side on the south. Openings in these timber planks will hold windows. All the windows will be on the south wall. The roof will all be replaced. So I’m looking at the best ways to insulate the building and also the possibility of using the large south facing roof area to generate electricity and hot water.

Heating the house: I’m inclined to fit a wood burning stove as I have a plentiful supply of wood. But advice is sought on what type (In a different building I fitted a jotul and was rather underwhelmed with performance/cost ratio - and very poor back-up service from the supplier).

The house I’m currently selling has had its energy reports (B&D) and I was surprised to see how much heat was lost through the walls even though they’re between 60cm and 100cm thick. So advice on internal wall insulation would be helpful.

I’m reasonably experienced in renovating old buildings but in the past my thing has always been to use re-claimed and period fittings. I’ve felt this was appropriate for various reasons, from the “green” aspects of re-using things to the aesthetic ones of respecting a buildings history. It’s also where much of my knowledge lies - I’m a brocanteur. However this barn conversion is in places more like a new-build; something I’m not familiar with at all. So, although I wish to retain the external look of the building, my main questions here are chiefly centred around efficiency.

Is there anyone out there who can offer advice - and, hopefully, give me a chance to see the work?

Also, if anyone is thinking of fitting a geothermic underfloor heating system and wants to ask about them or see one I’m very happy to help.

We have had a geothermic heating and hot water system since 2005. The ground floor has underfloor heating, which is great in winter, barefoot in the morning on warm tiles, mmmmm.

We needed to replace all the ground flooring, so it allowed us to insulate it properly. The two upper floors are heated by radiators, and as eeh water temperature is only 46-48 degrees, we have much fatter radiators than usuall, so that they can pump out more heat.

We live in a house built in 1700, we have fitted double glazing, as mentioned the ground floor is insulated and when roof was replaced, we had a composite material placed on top of battons on sheets of aglo, then batons, then slates.

The walls are not insulated

We also have a wood burner, and when the wood burner heats up the room, the thermostat cuts out the geothermic heating.

We also have an additional heating element in the hot water tank which will aloow us to heat it with solar panels. Which is my next project.

We specified a bigger pump than perhaps nescessary as we have another builing we would like to use it for.

I have two compressors, one which comes on when the air temp is below 5 degrees, we have three phase elec, as 320 volts is more efficient ( uses less elec) for pumps

I also plan to have a small petrol generator to run the solar panel pump during power cuts.

Then in power cuts we can have hot water and use the wood burner for heat.


We used a company miles away from us, and they charge us a fortune for maintainnce. There are alot more installers these days, so get one neareby.

Nowadays more people are having the same systems as us with airothermy, which takes heat from the air, This avoids all the digging up of the garden.

and leroy merlin sell a choice of 6 backboiling wood/pellet stoves…some are cookers too…mmmm lovely!

Steve I was browsing for some pipe for my woodstoves and discovered lots of stoves with back boilers…

here’s some more,bouilleur,foyers,chaudieres-fr.html

and from the UK!…

these look rather beautiful and I’d consider being an agent to sell them… yummy!…

plus these kits look interesting and seem reasonably priced,eau,solaire-fr.html

and they also do a combined woodstove and hot-water solar panel kit,solaire,bois-fr.html

PS I don’t know about water panel degradation times but I do know that the 1990 generation of PV’s were recently applauded for being efficient for far longer than expected. 25 years instead of 10, on average.

Good luck with it then, cant wait to hear more…

I saw a water heater panel in Brico Depot yesterday for 375 euro…I’ve not seen more than 2 of these on any house so far and they are pretty efficient. Tonnes of french fitters exist and if you plan to DIY, Germany is the biggest user of all the renewables in europe so far, tho I hearSPain is also quite advanced with water and PV panels.
I dont think they’re too complex, especially if its from scratch. there are lots of free designs on the web. and some excellent books. I shall try post some more of my links up soon…there are also some on the energy discussion page in this renovation section. We’re planning a trip down south to work late in June so if you’re home would love to drop by for a nose…thanks…ps if anyone wants a laugh I shall also post some photos of my own solar shower…its made from an old radiator and sits on my caravan at my workshop. It cost me 50 euros!

ooh thanks Jo, so that doens’t sound as expensive as I was expecting to be honest. I think my hubby will be very interested to find out more. We’re in Languedoc between Beziers and Montpellier. If we ever hear back about our mortgage then I’ll post about our project on my blog including all the green ideas we have.

Hi Jo,
Thanks for the reply.
I’m very interested in these water solar heat exchangers - and how they can be linked to a wood-burner/back boiler. I’m also interested in the PV panels and selling back to the EDF: love to hear anyone’s real experience of it - and if efficiency remains constant over time or if the panels degrade.

I’m in the Gers; probably four or five hours south of you. You’re very welcome to visit.

(Off subject: I used to have a contemporary art gallery, “the living room” in London and was involved in various scrap schemes. Let me know how your ideas are progressing on this.)

Hello Steve. About the woodburning questions. The jotul problems sound as if you’re right i.e.caused by chimney, positioning etc, as they are usually quite reliable. Historically, Godins, Devilles, Rosieres are the Mercedes, BMW and SAABs of the french stove world but I dont know much about modern ones.(I restore antique, usually enamelled ones)

@ Suzanne, if a stove is too hot it’s really only due to putting too much fuel in, and then opening air flow/running it up too fast. The KW rating refers to the average and highest output possible for the model and it’s always possible to burn a smaller amount of fuel inside the box if the box is too big.

I think a largish (8kw upwards) woodstove will heat a whole house efficiently if fitted with a water back boiler and if the chimney is used wisely i.e. fit air bricks and insulation to divert the heat back into upstairs rooms. There should be no need for electric radiators and only ever a temporary need for an emersion heater. (in fact I think they are pointless in a woodburner setting)

Re. renewables, the most efficient cost effective return for an investment is by insulating properly, for example; secondary glazing if its too expensive for double glazing will return in 4-8 years, double-glazing in 5-10. then after 10 years, double-glazing reaps its rewards in bigger savings.

Re; energy production, using water solar heat exchangers are by far the best investment (Solar Water Collectors/panels NOT PV = Photovoltaics, which generate electricity.) Sorry Suzanne, but it’s true… For an investment of £5000 for water heat exchanging panels you can provide 40% of the heat for a 3 bed house, IN WINTER… IN THE UK! So ALL hot water needs for all summer, and 40% MINIMUM all year round. That includes radiators.

What I’m saying generally is that if you combine a water panel system with a woodburner/backboiler you can heat a whole home and only use a minimum of electricity, which then can EASILY be provided with an average array of PV panels. (smaller than 21m)

There will be much too much electric in summer, and EDF will buy it back, although the rate of tax breaks on renewables have just been cut (cheers Sarkozy, you idiot)

Even at the current rate of tax, a self-build £25,00 euro investment in PV panels will make a profit after 10 years and should give 80 square metres of PV production, with an income of 4-5000 euros per annum. Most home projects are 21 square meteres, which is enough to supply a 3-bed efficient home.

For all Solar projects The roof must be facing south or south east or the panels installed elswhere, but in the right direction. (i.e. a shed or on the ground even) PV panels are more expensive to buy but about the same cost to instal as Water panels.

I’d love to see more of both projetcs…where are you ? We’re in the Vienne near Poitiers.

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Steve, thanks that was really useful. Our project (if it ever comes off - still keeping my fingers crossed) would be a complete renovation including new concrete then tiled floors on 4 levels and we’d be ripping out the old fireplaces (not nice anyway). We’d sell the tommettes (not my style, I prefer stone but I’m sure someone else will be very happy with them). We would also be replacing all windows & doors and probably going triple glazed with a metal coating for efficency, we currently have double glazed which were hand-made but I think the next project needs to be even more efficient as it will be our long term home.

We fully insulated our current home (which has thick stone walls) and we’re happy that the insulation works well but I’d want more in the roof as it’s not thick enough for me. The roofing here in the Languedoc is ‘special’, the tiles basically sit on top of each other and move a bit in strong winds or mini tornados! I don’t want to hear the wind in the next house (I don’t like the noise of the wind as it whistles through the village - we’re on a hill and I find it eery).

Interesting point about EDF and needing 50kw, we kept having problems with our electricity at first & discovered we were only on 9kw about enough for a kettle and a toaster! Big houses are expensive to heat of course so we want to invest in the energy efficient means now in order to save in the future, part of our problem is working out the long term cost/savings as loads of people are quick to say ‘oh green energy is a waste of time, you’ll never recover your money’. Like you though I think it is probably decades but for a long term home I think it may be worth it. Luckily my uncle is an energy specialist (runs a company called Envantage specialising in energy saving for commerce) so I’m hoping to get him to do all the maths - not that he knows it yet but I do enough french trouble shooting for his maison secondaire I’m sure he will be happy to return the favour).

We’re currently in an apartment with underfloor heating & it’s fab, you are so right, the kids love it and if we had a dog (our long term plan once we have done this project) then I’m sure the future dog would love it too.

I’m sure my hubby will be very interested in your post and may have some questions for you, I’ll be back to you in the future I’m sure :slight_smile:

Great post - thanks Steve.

This is largely in response to Suzanne’s comment regarding a geothermic system.

It’s really nice living in a house with underfloor heating. The house is warm without any cold spots and the air is dry.

Would I install a similar system again? I’m not sure. Or, to qualify this, probably in a complete new build and probably not in a renovation.

About nine years ago I installed a geothermic underfloor heating system in a large 15thC building. After some teething difficulties it has worked well and is relatively cheap to run. But to retrospectively install such a system is difficult, time-consuming and expensive. There are also fairly complicated issues to resolve around value, pay-back, and environmental damage.

The basic principle of my system is that I’m able to take “free” heat from the ground, increase that heat through pressure and then allow it to be slowly released into my house. The pressure is created by an electric heat pump or compressor. This electricity use is the main running cost of the system.

Like many of us, I’ve done a lot of renovation work myself and employed specialists for specific jobs. A heating system like mine, in a building like mine, involves five distinct skills: demolition and earth moving, concrete laying, plumbing, electricity and tiling. A general building company may take all this on but I, for reasons of interest and cost, tried to do everything but the plumbing and electricity. This was done by a specialist with an excellent reputation (they’d done the heating in the Pic de Midi observatory and a massive chai at Chateau Montus). This seperation of responsibilities suited me, wouldn’t suit everyone, and I think possibly has implications if there was ever a need to make an insurance claim.

The first part of the work is fairly easy technically but very hard physically and at times quite alarming. You need to destroy the inside of your house. I had to break through modernish concrete tiles set upon a reinforced conrete slab. In a couple of rooms I was able to save 19thC encaustic tiles and 18thC hexagonal tommettes to re-use later. Digging out over two hundred sq m to a depth of 30 or 40cm poses real problems. First of all you need a mini-digger which is powerful enough to do the job yet small enough to get through the doorways. You’ll need a powerful hand-held breaker for detailed work around fire-places. And then you need lots of strong arms and backs and wheelbarrows to get everything out. And somewhere to put it all. Whilst doing this (when not utterly exhausted) it’s possible to start feeling a tiny bit alarmed. Not the daily “What the hell am I doing?” stuff, but the implications of no foundations. OK, so the house has sat four square for hundreds of years without movement, yet to see it now, apparently unchanged on the outside, but from the inside perched on the very edge of an exposed earthen rim was quite a nervy time. Especially as the internal walls, load-bearing and at times only 40cm thick, were sat on equally exposed earth now cut to exactly the width of the walls. Better get pouring concrete quickly! (Actually before the concrete went down I dug further trenches and set drains for loos, bathrooms and kitchen. Then sand went down, then a plastic membrane. Then little concrete piers to support the metal reinforcing grills. Then tons of conrete.)

Once this huge slab was done there was a real sense of relief: there is a floor to walk on! Sort of.

The next part was fairly easy. It involved fitting large polystyrene (?) panels all over the floor. They were each about one metre sq and had regular bobbles all over one side and interlocking ridges along the edges. These, when connected, created a uniform, insulated surface covering the entire floor. Along the edges of each wall a band of polystyrene (?) was fixed - this to provide space for the expansion and contraction of the next concrete slab. At a fairly central point in the house a manifold was fitted just above the final floor height. This accepted a flow and return pipe from the heat pump - which needed to be installed away from the main living parts of the house because its quite noisy when working. From the manifold a single plastic pipe was taken into each room, coiled from the outside walls to the centre and then coiled back, within the existing coil, and out of the room back to the manifold. The pipes were pushed between the bobbles on the upper side of the polystrene sheets which hold them in place. It can be quite tricky to design all this for the aim is to have all the pipes set equidistantly, never have them crossing, and ensuring that the pipe can get back to the manifold without a join (potential leaks!). This was also the time when I put the electrical and phone cables in place. Once all the pipes were connected to the manifold they were filled under pressure (I think it was about 16bar) and left for a week. There must be no drop in pressure - evidence of a leak. Whilst under pressure the next concrete slab is poured, again with metal reinforcement throughout. And again this is very hard work for although I used retardents and had a very slippy liquid mix, its difficult getting the stuff around a house, through doorways, whilst maintaing a good level.

Whilst all this was going on I was organising the trenches outside and the specialist heating company was installing the heat pump, the heat exchange unit and an automated system to be able to flip between phases in the three phase electrical supply. There are different ways of getting the initial “free” heat: air, water and ground - with ground sourced heat being vertical or horizontal. We were recommended to install a horizontal heat capture system. This involved trenches being dug, three metres apart and two metres deep over quite a large area. A plastic pipe which holds a refrigerant was put in the bottom of the trench, the trench was back-filled to a depth of one metre and then the tube was brought back along the same trench to another large manifold. This trench was then filled in completely. This was repeated over a dozen times - there is now over 2.5km of plastic pipe sitting one or two metres underground outside my house!

At one metre down there is a constant temperature of +14°C. As the refrigerant is slowly pumped around underground and then up to the compressor near the house we see the geothermic gain. We already have 14° of heat. Within the pompe de challeur, or heat pump, the temperature is raised to about 40°. This is the average temperature that the refrigerant under the house slowly circulates at. It leaves the heat pump at 42° and slowly ciculates. When the return temperature is 38° the compressor(s) kick in again and push the temperature to 42°. Once the floor is heated through this gives an ambient air temperature of around 20°. This works best in a sealed system: open doors, draughts, poor insulation will all make the pump work harder, ie the compressors will be on more of the time - the fall in temp from 42° to 38° will occur quicker and the increase in temp from 38 to 42 will take longer. The heat pump I have (CIAT) has two compressors; one running at about 14kw the other 26kw. Nearly all the time (I think all the time this year) only the first, small, compressor has been called upon. In very cold weather the second one kicks in as well - this uses a lot of power.

So, after that just the tiling.

I chose this system because it seemed the most effective and efficient at the time. It doesn’t seem too expensive to run (about 2000€ per year for a large house - over 400sqm heated, each room nearly 4m high); or rather, of course it’s expensive but nowhere near as bad as gas or oil. But is it worth the cost and effort of installation? Probably if seen over a very long time scale - decades rather than years.

What have I learnt from the experience? I think it’s ideal for many new build properties where a huge slab of concrete is going to be set anyway. It doesn’t really go with open fireplaces (I have five on the ground floor), nor ill-fitting 18thC doors and windows, nor 2 or 3mm old glass. But imagine how efficient it could be in a modern, well insulated, house. Or how expensive my life would be here without it. There are issues about heating the floors above the ground floor - I can go into this if anyone is interested. Because there is the need for occasional very high electricity consumption I need a high supply (50kw) to the house - which means a high standing order whether I use any electricity or not. The frequent short term power cuts we get in this area have no bearing on the heat of the house - the heat in the slab takes a long time to dissipate. Some pieces of very old furniture which have lived for centuries in damp local houses have not liked the transition to my dry warm environment. The children love being barefoot. The dogs like sleeping on the floor. I don’t know how long things last - for instance one of the cheapest parts - the plastic tubing - had a twenty year guarantee. Yet to replace it would involve breaking one of the most expensive parts -a large concrete slab covered with over 200sqm of 18thC tommettes (small quantities of old floor tiles are fairly inexpensive - they can be very expensive when you’re looking for very large quantities of matching tiles). For the first winter after installation we had frequent power cuts. The EDF were adamant it was the fault of our new heating system. The heating engineers came out every few days for several months - they were equally adamant the problem lay with the EDF - but changed and re-tested every electrical part of the pump and the three-phase switch that they could. Eventually the problem was resolved by an EDF engineer changing the connections behind the EDF meter where my bit of the installation connected with theirs! This part of the job had been done by another electrician some months earlier when the EDF demanded that I put a meter on the edge of my land rather than in my house where it had sat before. I never discovered whether the fault lay with my first electrician or a part of the EDF box. Over the last eight years there has not been another problem.

I don’t know if this helps anyone make a decision about this sort of heating - hopefully it highlights some of the issues. Feel free to get in touch if there’s anything you’d like to know more about.

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Thanks for all the quick responses: people do read this!

Christine, I find the idea of strawbale construction to be very attractive in many circumstances but I don’t think it will work for me on this renovation. Three walls are already built in stone and the fourth (south facing) will be mainly glazed. Between the windows I’ll need insulation behind the timber planks (and a vapour barrier) but hope to keep the wall’s depth to around 20cm - so not enough for a straw bale. Also these areas of infill between the windows are quite small - so timber frame, LdV and placo looks likely.
Ian and Kate: I think I’m with you on LdV, for roof insulation especially, but I’m interested in hearing about/seeing other options. I’ve read about using hemp as an internal wall insulation (then rendered with lime). I’d like to hear from anyone who’s done this. Similarly I’d like to see costings and ease of use for different roof structures. The insulated plaques which fit between newly posed chevrons look interesting (quick to do and reasonable internal finish) - but does this justify changing perfectly good (but old and irregular) chevrons? On another roof I used insulated aluminium rolls. It was quick, easy and initially seemed very effective (but expensive). However the stipulated joining tape continually failed - I had to get into the roof void each year to re-tape it.
I’m also fairly sceptical about these energy reports for old buildings - the standard forms used don’t seem to recognise their inevitable complexities or idiosyncrasies. Mine referred to “thermal ruptures” at the corners of the building - yet this is where the walls are thickest. However the barn project has fairly thin stone walls (30cm) and I feel extra insulation would be beneficial. I don’t wish to alter the exterior so it will be interior insulation. Dry-lining packed with LdV is the common french way (and one I’ve done on other projects) but I’m not really happy with it for this barn - not keen on the regularity it leaves and don’t really like the finish of un-skimmed plasterboard (but I may do it because it’s easy and it works!). So, back to other possibilities. Any suggestions?

Suzanne, I’m probably being unfair to my jotul. I bought it because friends recommended them and they’ve been very happy. However I’ve never been really satisfied with it (it’s in the gite so often not used, so not really a problem): it only seems to work really well when on full blast and a door is left open allowing lots of air into the room. I have real difficulties damping it down without it smoking and struggle to keep it going over night. I’m aware that these problems might be caused by other things like height and quality of the chimney, prevailing winds and the “shadow” cast by the large building near to the gite. But this is my problem; the stove was too expensive an item to go through a trial and error period and the back-up from the suppliers was non-existent. Too many possible varients have meant my problems with use have proved impossible to overcome. Anyhow, I’d welcome any other comments on good makes and suppliers.

Kids bedtime now; I’ll write about geothermic heating later.


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Hi Steve

Had a look at your website - love that chateau (if only we had 650k lying around we’d snap it up!) and that car - first thought was: cool! and then : how do you keep it clean?

Regarding stone walls, we think they should be insulated - they’re cold in winter and warm in summer - they conduct heat too well and make too good a bridge to the outside. We’re renovating a 1000m2 building and turning it into apartments. We overlaid the thick stone walls with stud and put on placo and laine de verre insulation inside (and the electrics) and put in double glazing. We’ve found that this system together with lots of Laine De Verre in the attic and between floors (lowered ceilings to put 300mm min LDV up there) has meant that the electric radiators need to do very little (if anything - especially in kitchens, hallways, bedrooms etc).

When we eventually get our own barn to convert, we’ll go for a decent woodburner in living room and then electric rad points dotted around and then add the rads when and where needed - and lots of insulation of course!.



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The house I’m currently selling has had its energy reports (B&D) and I was surprised to see how much heat was lost through the >walls even though they’re between 60cm and 100cm thick. So advice on internal wall insulation would be helpful.

Steve, I’ve read doubts being cast on the applicability of energy reports in respect of thick stone walls. I believe that such a wall in its un-insulated state has a lot to offer in terms of energy storage by virtue of its mass and insulation by virtue of its thickness. Quick fixes like “doublage” applied to the internal walls may improve the apparent insulation but it deprives the house of its “storage heater” effect and leaves a cold and damp wall to the outside. Leave a door open and all your heat disappears - with bare stone walls it will take days for the temperature gradient across the wall to be altered to any significant extent.
Needless to say my house has such walls and I’d be very reluctant to cover them - but what I have done is to put as much “laine de verre” in the “combles” as I can.
Not an answer to your query but a point to consider….

Have you thought about strawbale construction ? Environmentally friendly, economic and very very good insulation. can be used to build or to renovate by insulating on the outside. Can’t offer you a site to visit I’m afraid, but check out books by Barbara Jones in English and André de Bouter in French or visit French websites : or

christine hooper

Hi Steve,

If our next project ever comes off we will be in a similar position to you, we’re interested in fitting underfloor heating (by taking advantage of the garden), using solar tiles for heating water & a pool (the electricity generating type) and having thermally efficient windows. We did a renovation of an old place in France before but just went with what the builder said and have ended up with a nice house but it doesn’t tick all our green & long term boxes. We asked about underfloor heating & the architect said it wasn’t possible. In fact “ce n’est pas possible” became a phrase we heard a lot when we asked for anything green or luxury end of the spectrum. It’s probably because it’s not something they do very often here (solar panels aside) so you may have to use companies further afield to achieve what you want. That is a lesson we learnt - local isn’t always the right answer for all aspects of your project especially if you are going niche on a few areas of requirements.

We’re going to the Grand Designs show in a early May to pick up some contacts as we know there will be German suppliers there, I have no problem with this after all we are in Europe!

On the woodburner - we have a Jotul and it’s excellent, in fact it’s too hot (probably too big for our room). It does burn through wood if I leave it up too high once it’s got going but we’ve found once it gets to the stage where it burns the gases then we can turn it right down and it heats the whole house. In fact, we regretted putting in electric radiators as we’ve hardly used them & have taken most of them off in fact. We have reversible air conditioning/heating for the bedrooms which works really well in normal weather (struggles a bit in minus temperatures).

If you find a decent supplier in France for your geothermic underfloor heating can you post about it, as we’d be really interested.