If it was my house before start thinking about heating systems I would see how best I could insulate the walls. Regardless of how efficient HP are, they still use energy which needs paying for despite RHI payment. The smaller your HP needed the better. Bore holes are expensive ASHP noisy if not sited properly. What scope have you to insulate the walls internally or externally and what about the floors. I think to take a fabric first approach (Insulation, elimination of cold bridges and elimination of air leakage) is where I would start. Spending money on these areas is there for ever, a once off cost, whereas any heating system requires repair, maintenance etc and the smaller and simpler the better. Once you have worked out what you can achieve with this approach go back to the calculation to see how much energy is needed to heat the house.

Posted By: lookseehearDoing some calculations on the heat loss calculator ( https://www.resurgence.org/resources/heac.html ) seems to indicate that the total heat lost during a typical year might be in the region of 35,000 kWh

Hmm, that calculator says the heat loss from my house is 14,888 kWh per year. PHPP says it is a maximum of 2,160 kWh, and it's much closer to the truth. I was pleasantly surprised that it allowed me to say my house was built from straw bales but not so pleased by its reluctance to let me enter triple glazing, or underfloor insulation or even 450 mm of roof insulation. So I'd take everything it says with a big pinch of salt.

IMHO, a better approach would be to ask the vendor for a copy of their heating bills, and some idea of how warm they keep the house. Given the time of year and where you are in the house-move cycle, I would suggest the following plan:

(1) Get to completion on the transaction and move in
(2) Try to enjoy Christmas
(3) Sort out whatever turn out to be the most urgent deficiencies of the house
(3a) Hopefully not the oil heating
(4) Subscribe to PH+ magazine - the current issue has a good Enerphit refurb

Meanwhile, and while waiting for an end to the covid confusion:
(1) Get or make some accurate floor plans and elevations of the house and make several copies
(2) Decide on how you will plan to install some ventilation (preferably MVHR)
(3) Decide on your airtightness strategy
(4) You can start on the MVHR and airtightness anytime after this
(5) Decide on your goal (PH, Enerphit, AECB Gold, Silver etc etc)
(6) Decide details of your insulation plan
(7) Only after the previous step will you be able to work out how much heat you will need and start to think about how you might obtain it
(8) Decide how to implement all the plans
(9) Do it

Hi all,

Thank you so much for all your input so far. I'm definitely getting that insulation is preferable, there are a few reasons why we aren't massively keen which I'll try to set out below, but they focus around the fact that this is an old house (here it is https://www.rightmove.co.uk/property-for-sale/property-84497702.html).

From what I've read about internally insulating stone houses, by creating a warm box inside a cold house, the external walls are much less likely to dry out properly after cold wet weather, and that can cause accelerated damage to the fabric of the walls (freeze/thaw when sub zero and the walls have no chance to dry out between wet weather) and also damp issues (regardless of breathable materials). I can't remember the source for this, but I remember reading that you are encouraged to use the walls as a heat sink in order to help the drying out process. Also, unless we are going to internally insulate everywhere, we'll end up with some very comfortable rooms and some very cold rooms. Insulating all rooms internally would be a huge disruption to family life, so I expect it wouldn't be something we would 'get around to' in the first year or two.

External insulation seems to be the 'right' thing to do to drastically improve the performance of a building. There are a few issues with this. The main one is altering the appearance (see Rightmove link above). It isn't the most beautiful building in the world, but we're quite keen on the natural stone as well as the foliage (although currently it needs some work cutting back and tidying up). The next issue again relates to the breathability of the walls, as we're quite nervous about getting this right in terms of using sensitive materials and preventing damp, both from inside the house and soaking up into the walls from the ground. I know that external insulation is also an expensive option with no RHI to help pay for it (and it doesn't look like many people are having much luck with the GHG either - I wouldn't be confident in finding a contractor and getting the works booked in before it expires in March next year). Also this link (https://www.engineshed.scot/building-advice/common-problems/how-to-insulate-stone-walls/#external-wall-insulation) seems to indicate that EWI might only be suitable for a harled or rendered finish, as well as the need for planning permission.

The final reason why we've invested a lot of time researching ground source/air source heat pumps is that the boiler needs replacing relatively soon. It may be an old workhorse that will continue to function, but the vendors (who have been looking after the house for nearly two years - sadly it's a probate sale) told us that the boiler is 'intermittent' despite recently being serviced with comments from the engineer that it's functioning well at the moment. It's also not a condensing boiler, so less efficient than newer models. We know that given the size and structure of the house we won't be able to heat it up in an hour or two if it's a cold evening, so we're expecting to be keeping the heating on pretty consistently over winter.

We're quite desperate not to put in another oil boiler. If we do that we know it's likely to be in there for the next 20 years or more and we have an opportunity to do a good thing and avoid burning a lot of oil. We know that either way we look at it, it isn't going to be a cheap house to heat, but a heat pump and a green electricity supplier will put our conscience to rest at least.

All this said, I'm leaning towards DJH's suggestion of getting in and acquainted with the house before doing anything significant (boiler-allowing). We have a few other priorities (levels are too high, so french drains required on the perimeter and repointing of stonework in hot lime mortar to correct previous cementicious pointing applied, as well as aformentioned loft insulation).

It is a very nice looking house plenty of character so can understand why you would not want to mess around too much with it. I note it has a poor EPC is there a requirement to have a good EPC rating for RHI ? I do not know much about HP and RHI but I know you needed a C for FIT for solar PV.

I know Carlingcott, lived in Peasedown, architected around Bath for years, and IMHO would not hesitate to EWI this house.

As you say "It isn't the most beautiful building in the world" but could become so because EWI is a great opportunity to modify elevational appearence, get rid of what's crude, improve window design/material/proportions and end up with a seriously handsome house, such as the attached (rear elevation, farmhouse nr Glasto, v beautiful Georgian front, crude Victorian rear).

Of course this is a major project, new windows, extending the eaves/verges, but after thorough insulation incl roof you'd barely need a heating system, maybe let the old boiler struggle on, for the few days it's needed, feeding a few retained rads. You woudn't need to disturb the ground floor to insulate it, if the EWI is carried down into the ground, to base of founds if modern, or as a horizontal sub-surface 'wing' if founds are shallow (or on bedrock), forming a 'coffer dam' of insulation around the ground floor perimeter. The building fabric will thrive, mould disappear, any rising damp too, with good EWI.

Apart from loft insulation there isn't much insulation / thermal improvements that actually have a decent ROI. I would still go for EWI if you can. The improvements to the internal thermal stability both summer and winter - especially with stone walls are a great advantage and v. difficult to put a monetary value on that advantage. And of course any chance of mould in corners or behind wardrobes will be banished. In fact wot fostertom said above +1.

Think carefully about changing to an upside down house. It might sound appealing but the amount of times you will be going up and down the stairs will IMO soon get tiring and everything needed for living (shopping etc.) needs to be carried upstairs. Do a proper count of how often you all go in and out of the front / back door (which will mean an up and down the stairs) especially now the kids are 6 and 3 and want to play outside and have friends around and for a few years yet they will need a level of supervision when in the garden, difficult when you are 'upstairs'

For thermal calculations I use https://www.ubakus.de/en/r-value-calculator/?
My 500mm basalt walls come in at a u value of 3. With 100mm of EPS EWI the u value goes to 0.31 and the difference to the internal environment summer and winter has been worth the expense.

Your edges do not have to be that hard even with rigid boards. You can rasp reveals etc instead of using angle beads, and you can wrestle thinner boards round curves and build them up. Have a look at luneretrofit.com for sprayed Diathonite (though not sure if that was internal).

Udireco is good for uneven walls, as you say.

Thanks LSH

Posted By: lookseeheardue to the lack of breathability

No no - only the cellular plastic insulations are unbreatheable; EPS, wood fibre etc are fully breatheable.

Stone may be underestimated for insulation, but 1-1.5 is stiil v poor (whereas cob BTW is about 0.7 or better, even in RdSAP). Any room that's not strongly heated (e.g. turned off when not occupied) soon feels stone-cold clammy - it's all the cold radiation.

Posted By: fostertomNo no... EPS... [is] fully breatheable.

No No it isn't.

A typical water vapour diffusion resistance coefficient (µ-value) for EPS is around 60 (though it can be significantly more or less, depending on density). Which is certainly better than XPS (typically around 150)

For comparison:
solid wood - around 50;
expanded cork - around 25 (but can vary significantly by brand);
wood fibre insulation - around 10 (similar to plasterboard);
mineral wool - 1.

Personally I'd consider EPS adequately breathable in new build, but would avoid it for insulating an old stone-walled building.

All values are from my own notes...

All I can do is recount my own experience.

I have a stone wall property, 500mm basalt stone with rubble infill with no render on the outside. The property is 36M long and 6M wide, single story with built in attic. During renovation the internal plaster was removed and I was horrified to see / feel the amount of air movement coming through the wall. Once the restoration was complete part of the property was rented.

The tenants used the lounge a couple of weekday evenings and at weekends. Once the cold weather arrived they turned down the rad in the lounge and used the wood burner when the lounge was in use - so for most of the time the heating was low and the room colder than the rest of the flat. After a few weeks they complained that there was black mould on the NE facing wall of the lounge which they had to clean weekly. When they washed the wall with bleach then it lasted 10 or so days before the mould returned.

I put 10cm of EPS EWI on the affected lounge wall, oversailing the lounge area by a meter or so. Problem solved!! The next spring I put EWI on the whole NE side of the property and a couple of years later I did the rest of the property (all with 10cm EPS) That was 10 years ago and there have been no problems since and no mould has returned. The property is much better thermally both summer and winter. That is a more stable temperature.

When putting on the EWI the builders wanted to render the wall first to get a uniform flat surface which was going to put up the cost tremendously. Instead of that I told them to put a thick bead of adhesive around the edge of each slab of EPS with 3 or 4 doughnuts in the centre and press the slab on to the wall. This they did (reluctantly) There were no mechanical fixings used as drilling the basalt stone proved impossible without causing significant damage to the EPS due to the drill skating around the stone before biting in.

10 years on there have been no problems with either the EWI or the wall with no damp apparent on the walls. The internal render was sand lime cement mix and the building has concrete floors.

Posted By: lookseehearPeter's suggestion to just glue the outer edges seems a radical one, as does not using mechanical fixings, but it does appear to yield good results.

It is not 'just glue around the edges,

Posted By: Peter_in_Hungaryput a thick bead of adhesive around the edge of each slab of EPS with 3 or 4 doughnuts in the centre and press the slab on to the wall.

The thickness of the bead and the doughnuts has to vary to take account of the lumps and unevenness of the wall. I have found that this method uses more adhesive than the usual method of a toothed float as used on a flat surface but still way cheaper than rendering the wall flat first.
The lack of mechanical fixings is because it was impossible to put them into the basalt rock from which the walls are built. Over here mechanical fixings are not recommended on all types of walls used in new build. e.g. Ytong type blocks don't use fixings and others only recommend mechanical fixings in exposed locations.

With regards to breathability my walls being basalt rock the only breathable bit would be the earth between the rocks, that said I have a bit of a problem with a statement from the link

Quote
Because heritage properties are typically made of porous materials such as sandstone and limestone, they rely on the breathability of these materials to allow moisture to escape from their structures.
End quote.

If EWI is put on properly this provides a weather screen on the outside which will prevent any precipitation going into the wall, and if during renovation proper ventilation is addressed which will control moisture (condensation) from the inside then what moisture is left that needs to escape through the walls to the outside?

I do not subscribe to the notion that modern materials should not be used on old buildings. Typically 'traditional' materials were used because that was all that was available. Building materials were what was available locally within transport distance by horse and cart, which is why my building are basalt stone, 30km away the buildings are red sand stone in one direction and adobe 30 km in the other direction. Material choice should be based on performance and characteristics and not because that was what was used back in the day.

Posted By: lookseehearMy understanding is that to be 'breathable' a material must be
* Vapour permeable
* Capillary open
* Hygroscopic

I don't think so. I think breathability generally just refers to the vapour permeability. There are roof membranes that claim to be both breathable and waterproof for example. Hygroscopicity is often a useful property found usually in organic materials, but is sometimes a nuisance. So:
* breathable = vapour permeable
* capillary open = transports liquids, usually water
* hygroscopic = capable of storing liquids by absorbtion

As you say there are a lot of potential sources of information. Some are biased by commercial interests; others by well-meaning misunderstandings, and yet more by pure prejudice. Some places are better than others. It's very confusing sadly.

Posted By: Peter_in_HungaryIf EWI is put on properly this provides a weather screen on the outside which will prevent any precipitation going into the wall, and if during renovation proper ventilation is addressed which will control moisture (condensation) from the inside then what moisture is left that needs to escape through the walls to the outside?

It's best to think of waterproofing as an external layer outside EWI. Weather screening is provided by the render or cladding and drainage plane membrane rather than by the EWI itself.

Proper ventilation doesn't mean there's no moisture in a house. There's as much moisture in internal air brought in from outside as there is in external air (measured by absolute humidity) plus there's moisture emitted by human activity inside (transpiration of plants, animal and humans; cokking; washing etc). The RH may be lower because it's warmer inside but that doesn't make molecules disappear. Most excess moisture is carried outside by the ventilation system along with the 'used' air and indeed preventing a moisture build up is one of the main reasons for ventilation rates. But there can still be vapour pressure driving moisture into the walls from inside. (or from outside if the inside is artificially cooled).

Posted By: fostertom

Posted By: Peter_in_HungaryIf EWI is put on properly this provides a weather screen on the outside which will prevent any precipitation going into the wall, and if during renovation proper ventilation is addressed which will control moisture (condensation) from the inside then what moisture is left that needs to escape through the walls to the outside?

AFAIK there's constant traffic of moisture alternating in both directions, tho mostly from inside to out, depending mainly on changing weather/time of year, only slightly on internal moisture generation. It seems best to allow this, not to intentionally or accidentally obstruct it - provided that the configuration of the 'sandwich' checks out well in WUFI or equivalent - or is known from experience and custom to be OK.

Agreed. And if there is no DPC, then moisture from the ground may also be a consideration; more so if the original floor has been replaced with concrete + DPM.

Posted By: fostertomHence no obvious call for internal vapour barrier, in new BS5250.

Logical and, as you probably know, UK Government advice for IWI (Retrofit Internal Wall Insulation Guide to Best Practice) is already to drop the vapour barrier, while stressing the need for an air barrier.

Posted By: fostertomspecify internal vapour barrier, but the expensive self-regulating kind, which 'disappears' (as far as vapour resistance) when it senses high RH. Which seems an expensive way of leaving the vapour barrier out!

At least according to Pro Clima's explanation, it's the difference between internal and external temperature (rather than RH) that changes the vapour resistance; hotter outside than in and the resistance drops. But yes, I'm not convinced that they make a big difference, though I'd like to read more on the topic.

Posted By: djhHygroscopicity is often a useful property found usually in organic materials, but is sometimes a nuisance

The ability to absorb and desorb moisture is a very useful property for IWI & cold-roof insulation. A considerable quantity of moisture can be safely buffered within the cell walls of the material, rather than condensing out. One of the reasons that I'm using hemp-based insulation on my current refurb.

And on that topic, if anyone knows of study into hemp insulation in an unventilated cold roof in the presence of MVHR, I'd be very interested!

Are you talking a combined MVHR/ExhaustASHP (I am not sure if 'assisted by' means 'integrated with')? I have not looked at such systems for nearly 10 years but, IIRC, they would only have been much use with almost Passive-House levels of insulation and air-tightness. Maybe bigger systems exist but I'd have thought that the inherent slow speed air-shifting of an MVHR would militate against this. If you think of the almost silent running of an MVHR and the fairly loud 'rush' of an air-con external unit on 'full chat' it may give you an idea of the different volumes. (But I am definitely not an expert on this - I usually concentrate on insulation and air-tightness and getting the heat-load down really low, then whatever heating system you end up with is probably the smallest it can be. Others with more knowledge of ASHP and particularly EAHP/MVHR may be along soon.

I am more worried about the heat-loss (and 'comfort-loss') from the walls, though if you try to calculate pure payback I daresay it would 'tell you' not to do EWI. I doubt my EWI will pay back till after I am dead, but I am wholly satisfied that it's the right thing to do.

Unless the roof void to which you refer is entirely un-ventilated (not the norm) I would question whether the multifoil is doing anything. Therefore I feel your 'radical' roof works are likely to be a good idea.

It sounds like you have come a long way since your earlier posts, and I hope the next stages go well.

You say ''I'd written this as a new post but I can't seem to create one as my membership expired and it wouldn't let me renew for some reason.''.

It may be worth trying again. Have a look at Keith's post (dated 2009 or 2007, I think) at the top of the 'menu'. Strictly the forum is closed to new members but there are at least a couple recently (welcome, all!) who have succeeded in posting.

I just took a look at the Genvex Premium Preheat 250 details. I'd be concerned about noise levels - some of the number look quite high. As Nick said, an MVHR is limited in how much heat it can supply by the low speed air used. I have a 1.8 kW post heater attached to my MVHR, but at the normal level of ventilation it limits itself to about 1.2 kW because there isn't enough air flow for it to use full power. Our internal volume is 414 m³.

So if I were to think about buying one of these units, I'd want to see some pretty convincing evidence of it in use somewhere else first and be able to ask about noise levels, power output and such like.