Renovation/modernisation of former miner's cottages + 1970s extensions

[lookseehear]

Hello all, introduced to the forum by my dad and looking forwards to learning a lot from the wealth of knowledge shared here.

 

My wife and I have just submitted pre-app for fairly significant works, but we still have a lot of details to work through. We're working with a local architect who has been great thus far. Our house consists of two old (c1800s) miners cottages with 400mm thick solid stone walls and solid floors. At some point in the 1970s a two storey extension was added to the rear and a single storey extension to one end, both concrete block faced with stone which leaves us with roughly 200m2. The windows are all aluminium double glazing but in pretty poor state of repair, with lots of blown units and missing catches. They also have no trickle vents and have faux georgian bars which we don't like the look of. There are various places where lime pointing has been replaced with cement mortar, and we assume a lot of the plaster and paints internally are not breathable. We don't have significant mould problems anywhere other than in the utility room which is on the south-east end of the house, but is unheated, uninsulated, poorly ventilated and next to the kitchen which produces a lot of steam from cooking and has no extractor so is to be expected. We get the odd bit of mould on the north-west end in a few spots and around some window frames where condensation forms, but we manage this by keeping most of the windows open a crack. In addition to all the above, the kitchen is in desparate need of replacement and the bathrooms could do with some work, so you can see we have a lot to do!

 

We knew most of this when we bought the house, so we always expected to do some work but we're now able to take on a more substantial project and have £250-300k to spend to make this house a place we want to live in for the next 15 years. We bought the house for £570k three years ago, and looking at rightmove for houses selling for £870k+ doesn't yield anything that would attract us over renovating our current house, so we've thought through the 'shouldn't we just move?' question.

 

The plans from the architect involve (as-is and proposed plans attached):

• Moving our living space upstairs to make it significantly easier to remove internal walls to create an open plan living/dining/kitchen space
• building a single storey extension which will become a new master bedroom, while having a flat roof which will become a first floor deck with access out to the garden from the open plan living space
• Second storey extension on top of existing single storey part of 1970s extension
• Significant work to the roof to allow vaulted ceilings in upstairs living space and putting in roof-level insulation and updating the roof line to allow for...
• ...full EWI with likely a diathonite breathable product, finished either with lime render, timber cladding or a mix of both (likely render for ground floor and timber clad 1st floor would be our preference)
• Enlargening some of the windows as most are quite low/small
• Moving and replacing staircase
• putting in skylights
• Probably loads more things that I can't think of currently

 

There are lots of questions in our minds at the moment. The biggest one is budget - we aren't expecting this to be fully finished to grand designs standard with all fitted furniture etc. We're not expecting a luxury kitchen, and are happy to manage subcontractors ourselves and to do work ourselves where we can and where necessary. I would also love to dig out the floor downstairs and put in wet underfloor heating, but again this is a question of budget. We're on oil central heating currently and would continue with this if it made sense and we could reduce energy requirements to something reasonable, with a view to putting in ASHP in the future. We spent £7k putting in a new external boiler and pressurised cylinder at quite short notice when the old boiler went 2 years ago.

 

We expect to replace all windows and doors to improve airtightness, and would consider MVHR if we can work out where to put it and fit it within budget. We also want to address any areas where incorrect materials have been used in an old building to set us on the right course, which will involve a lot of replastering/repainting.

 

I'd love to hear any initial thoughts on our plans, or to hear from anyone who has gone through a similar process and has experience to share.

 

 

[ETC]

Nope. Personally I think you are mad to swop over the bedrooms and living spaces.

[MikeSharp01]

Looks like a great project can we ask a couple more questions:

 

1. Does moving the living space upstairs bring anything else to the party - EG better views, neater connection with the garden, and what are the downsides - is this your forever home or just a stepping stone on the path to it, have you worked out the long term implications of life one floor up - should you include a lift?

2. Do you have any planning / structural implications for all this work EG - change of external material, building footprint (extending too much), foundations able to take the additional load of second story.  

[lookseehear]

3 hours ago, ETC said:

Nope. Personally I think you are mad to swop over the bedrooms and living spaces.

I saw your DM and will respond a little later - thanks!

[lookseehear]

6 hours ago, MikeSharp01 said:

Looks like a great project can we ask a couple more questions:

 

1. Does moving the living space upstairs bring anything else to the party - EG better views, neater connection with the garden, and what are the downsides - is this your forever home or just a stepping stone on the path to it, have you worked out the long term implications of life one floor up - should you include a lift?

2. Do you have any planning / structural implications for all this work EG - change of external material, building footprint (extending too much), foundations able to take the additional load of second story.  

 

Thanks for the questions - I'll try and add as much context as I can.

1. Lots of things. I'll elaborate below, but in summary it's higher ceilings, more natural light, better views

• Better views - (I've attached a comparison of the view from downstairs kitchen vs the bedroom above). There's a nice vista which we don't currently take advantage of but the new kitchen would have a view out across that aspect. It would also allow good views across the garden which wraps around the house.
• Higher ceilings - we need to address the roof anyway because there's currently no insulation on the 1970s portion and old fibreglass wool between the roof joists for the older portion, and insulating at roof level would mean we can remove the old felt and vault the ceilings. They're low pitch so there's little to no storage space up there and vaulting the ceilings means we can also add skylights to get in more natural light. Creating an open plan space downstairs where the ceilings are mostly 2.2m and below would (in my opinion) look like a long & low space without much natural light.
• Connection with the garden - because we're on a hill, we have steps to go up to access most of the garden when coming from the kitchen/patio. We'd be trading this for steps down from the first floor deck which would have a lovely west/south-westerly aspect and be a nice sun trap in the summer, as well as allowing some solar gain through bifolds/glass doors in the colder months. I've included a photo looking out onto the patio which would be the site of the single storey extension so you can see the steps up to the garden and the state of the patio and surrounding wall which really needs looking at in the next couple of years.
• The downstairs lends itself well to breaking up into bedrooms and would benefit from the 'cosy' lower ceilings and means we can get a new master bedroom from a single storey extension.

This is as close to a forever home as we can get. I'd say minimum 15 years but could easily be 25+. We're late 30s with two children under 10, so we shouldn't need a lift any time soon, and there's no step-free access to the house from the driveway anyway due to that being on the lower side, so being step free isn't really a concern.

 

2. Not clear at this point. We'd hope and assume that planning would be receptive to us using EWI and changing the exterior appearance, and we aren't listed or in a conservation area. We aren't adding a lot of footprint, and our architect is relaxed about how much we've included on pre-app. Not yet clear on foundations, but where we want to add the second storey I would expect this to be OK given there's already a small second storey bathroom on top of that construction.

[MikeSharp01]

OK so that all makes perfect sense now looks like a good location with good outlooks. I will give it all some more thought now I get your objectives.

 

 

[Roger440]

Ill limt my replies to the breathable aspect of the insulation and render.

 

Tread carefully. Just because products say they are breathable, doesnt mean they are in this context. Check the actual numbers.

 

This is quite a difficult thing to do succesfully without longer term issues. 

[lookseehear]

13 minutes ago, Roger440 said:

Ill limt my replies to the breathable aspect of the insulation and render.

 

Tread carefully. Just because products say they are breathable, doesnt mean they are in this context. Check the actual numbers.

 

This is quite a difficult thing to do succesfully without longer term issues. 

Thanks Roger. I've heard good things about diathonite - it seems to be the 'standard' breathable internal or external insulating render and has been used in a lot of properties. I intend to do my due diligence though.

[Redbeard]

You've probably looked all this up, but the Green Building Co (Greenbuildingstore.co.uk) has used Diathonite a bit, but internally if memory serves me correctly. Apparently v good for air-tightness. Can also be used for EWI, as you say. https://luneretrofit.com/ had it spray-applied externally a few years back.

[MikeSharp01]

Just been looking through this again. I like the basic plan. I worry about the external insulation, in fact the insulation in general. Doing it on the outside means extending the roofing out to cover the top. On the inside you loose room volume and combination of inner and outer is challenging on the cold bridge front.

 

How is your thinking on this front @lookseehear?

 

 

 

[Gus Potter]

On 25/12/2023 at 00:22, lookseehear said:

My wife and I have just submitted pre-app for fairly significant works, but we still have a lot of details to work through. We're working with a local architect who has been great thus far. Our house consists of two old (c1800s) miners cottages with 400mm thick solid stone walls and solid floors. At some point in the 1970s a two storey extension was added to the rear and a single storey extension to one end, both concrete block faced with stone which leaves us with roughly 200m2.

What a find!

 

On 25/12/2023 at 20:28, Roger440 said:

Ill limt my replies to the breathable aspect of the insulation and render.

Nice approach as plenty others chipping in on the Architectural side. I'll limit mine to some SE stuff and some of the history of many of these types of Miner's cottages. I've done a few of these in the past.. here are some of the things I have learnt along the way.

 

Mine owners built these houses at the lowest cost possible using the cheapest materials and labour cost.. just enough to keep their workers working. It's fascinating subject to research.

 

I'll assume these are coal miner's cottages. Often a byproduct of coal mines is clay.. (they often had to dig through this to get to the coal) used to make bricks. the good bricks got sold, the "seconds" were used on the cottages. The good coal went to the big houses and for ships boilers, iron works etc, the low grade, full of sulpher coal was supplied to miners to keep the houses above freezing. High sulpher coal creates not least sulphiric acid which rots the mortar in the chimney's something awful.

 

You have some cross walls but the mine owners didn't send their best masons to build the cottages, as they we often employed building the "manor", wool and jute mills ect. This means that the bonding of the cross walls is likely very poor. Also the external walls tend not to be that well bonded, the good stone went else where as did the best lime for mortar.

 

My inclination is to look  /ask.. on a fag packet what happens if we strip out all the internal walls on the original part and replace with thinner walls on a modern concrete slab with UFH. How much extra square feet are we going to generate? If that fag packet sum looks any way favourable then now we have a blank canvas to work with Architecturally.. a big open space. The new walls get tied back into retained external walls to provide any horizontal stability we need. How much easier / cheeper is it going to be to just cast a new insulated slab in a one go cf navigating round any internal walls? What savings can be realised by having a blank canvas in terms of abour / servicing and so on?

 

It would be interesting to know how the existing walls really are constructed and what they are resting on. Until you know this you can't really make informed design decisions. Everything you do will hinge on this;  the approach to insulating the external walls, you want to vault the ceilings?.. this will often introduce point loads.. you could end up wasting a load of cash if you don't get a handle on the existing construction in detail.

 

Can you tell us more about what you know about the existing ~1800c construction and the later 1970's one, is it a cavity wall, how wide is the cavity and what are the walls made of. The good news is that hopefully the two storey bit will be heavy so that can be inspected for movement.. if it is sound then you have the makings of a benchmark.. you can say.. well that bit has been sitting there at two storeys for 50 years.. good indication of what the ground can carry sitting on this type of foundation.

 

 

 

 

 

 

 

 

 

 

 

[saveasteading]

Exciting.

My outspoken initial thoughts.

EWI. As above, It needs the roof to be extended and all openings. The stone is encapsulated . It won't look remotely the same. Heritage?

Windows. These are like mine. The planners insisted on crittall until I found modern windows that look like that. What looks right?  There are very different qualities though.

Stone walls  400mm. These have been found to provide a lot more insulation than design programs allow. Of course it still needs more.

I'd build an internal stud, and insulate that. Read elsewhere on BH about the benefits of a service void.

 

I'd have to check  but I don't think any element has to be to current regs. So insulate the attic and floor more if you need to improve the numbers.

I

 

 

[Gus Potter]

6 minutes ago, saveasteading said:

These have been found to provide a lot more insulation than design programs allow.

This is a key concept  I like to write some of my own spread sheets for this kind of stuff and really delve into the formulae that back up the industry software. By doing so it lets me manipulate to achieve the best design particularly, at concept design stage on old structures.

 

 @saveasteading has referenced in the past recognised research by say Historic Scotland and other accepted data that demonstrates that old stone walls are better insulators than we often assume at the outset.

 

These old stone walls are not really solid, they have lots of air gaps / voids and have a significant insulating effect. Modern masonry walls have repeating joints and tend to be "thin" in comparison with old stone walls where the mortar joints are offset.

 

OK I mention Scotland.. but what about the some of the early buildings in Bath e.g. that were all constructed in stone.. facing stone on the outside, rubble fill with random stone on the inside.

28 minutes ago, saveasteading said:

Read elsewhere on BH about the benefits of a service void.

This is good design. @ProDave has highlighted issues where if you don't seal the service void it can set up nasty convection currents / drafts that bypass the insulating effect.

 

This is not that hard to do (seal the service void) in my mind if you are self building and want to do a bit of hands on stuff. If you do you'll end up with a great house for often less effort than you imagine. All you need to do is know when you have to say to the kit erector / etc.. hey this is the bit I want to do over the weekend before you sheet the inside of the walls.

34 minutes ago, saveasteading said:

I'd have to check  but I don't think any element has to be to current regs

This is a critical point. BC will look at the job and may say.. this part is new work so it needs to comply with the latest regs. But the other parts of the work are an "upgrade" Depending on each authority you'll get a different answer. Your Architect needs to be right on top of this and should be able to explain how the the BC game is played and at the same time understanding and explaining to you how each design decision will impact on you if it is your forever home.

On 25/12/2023 at 00:22, lookseehear said:

We're working with a local architect who has been great thus far.

 

Now if you are only paying your Architect a few quid.. then you'll get an off the shelf design. Pay them the right amount and a bit extra to phone friend (an SE who knows about this stuff) and you should at the end of the day save money in the round.

 

Expect your Architect's fee to double for them to get right into this. Now this might sound a bit scary but if you double your payment then in return they should be able to cover that in practical savings in construction cost (if an experienced Architect / Designer) and more as you have given them time to really do all they are trained for.. you can set them free and at the same time give them responsibility for the overall design, detailing / detailed drawings (very important) and budget constraints. 

 

@ETC is that fair comment?

 

 

 

 

[SteamyTea]

8 hours ago, Gus Potter said:

Mine owners built these houses at the lowest cost possible using the cheapest materials and labour cost.. just enough to keep their workers working. It's fascinating subject to research.

Something I would like to spend some time on.

It is amazing the number of 'miner's cottages' down here.  Most have been built after the major mines closed 150 years ago.  I think most are old agricultural worker's homes.  But no point in letting the truth get in the way of a good romantic story.  Mining is big business down here, and we don't have to take anything out the ground anymore.  Much cleaner.

My Mother lived in a Derbyshire mining community and the architecture is identical, only real difference is the materials used. Almost as if there was one design and it was just stamped out across the land.

[MikeSharp01]

1 hour ago, SteamyTea said:

Almost as if there was one design and it was just stamped out across the land.

One guesses that this is what the word vernacular was invented for - but it also tells you that much of the learning is transferable IE the Scottish insulation research mentioned above.

[lookseehear]

On 27/12/2023 at 21:37, MikeSharp01 said:

Just been looking through this again. I like the basic plan. I worry about the external insulation, in fact the insulation in general. Doing it on the outside means extending the roofing out to cover the top. On the inside you loose room volume and combination of inner and outer is challenging on the cold bridge front.

 

How is your thinking on this front @lookseehear?

 

 

 

 

We've previously been favouring external, given the scope of works we'll be doing, I would expect the detail around the windows etc to be straighforwards (as straightforwards as these things get!) I also really like the idea of insulating the thermal mass of the walls to buffer temperature changes. In the hot days in summer our downstairs stays pretty cool but the lack of any insulation in the loft means upstairs bakes pretty quickly! The 'box in a box' idea has me questioning some of this logic though (more below)

 

On 27/12/2023 at 21:54, Gus Potter said:

What a find!

 

Nice approach as plenty others chipping in on the Architectural side. I'll limit mine to some SE stuff and some of the history of many of these types of Miner's cottages. I've done a few of these in the past.. here are some of the things I have learnt along the way.

 

Mine owners built these houses at the lowest cost possible using the cheapest materials and labour cost.. just enough to keep their workers working. It's fascinating subject to research.

 

I'll assume these are coal miner's cottages. Often a byproduct of coal mines is clay.. (they often had to dig through this to get to the coal) used to make bricks. the good bricks got sold, the "seconds" were used on the cottages. The good coal went to the big houses and for ships boilers, iron works etc, the low grade, full of sulpher coal was supplied to miners to keep the houses above freezing. High sulpher coal creates not least sulphiric acid which rots the mortar in the chimney's something awful.

 

You have some cross walls but the mine owners didn't send their best masons to build the cottages, as they we often employed building the "manor", wool and jute mills ect. This means that the bonding of the cross walls is likely very poor. Also the external walls tend not to be that well bonded, the good stone went else where as did the best lime for mortar.

 

My inclination is to look  /ask.. on a fag packet what happens if we strip out all the internal walls on the original part and replace with thinner walls on a modern concrete slab with UFH. How much extra square feet are we going to generate? If that fag packet sum looks any way favourable then now we have a blank canvas to work with Architecturally.. a big open space. The new walls get tied back into retained external walls to provide any horizontal stability we need. How much easier / cheeper is it going to be to just cast a new insulated slab in a one go cf navigating round any internal walls? What savings can be realised by having a blank canvas in terms of abour / servicing and so on?

 

It would be interesting to know how the existing walls really are constructed and what they are resting on. Until you know this you can't really make informed design decisions. Everything you do will hinge on this;  the approach to insulating the external walls, you want to vault the ceilings?.. this will often introduce point loads.. you could end up wasting a load of cash if you don't get a handle on the existing construction in detail.

 

Can you tell us more about what you know about the existing ~1800c construction and the later 1970's one, is it a cavity wall, how wide is the cavity and what are the walls made of. The good news is that hopefully the two storey bit will be heavy so that can be inspected for movement.. if it is sound then you have the makings of a benchmark.. you can say.. well that bit has been sitting there at two storeys for 50 years.. good indication of what the ground can carry sitting on this type of foundation.

 

Thanks for the detailed reply. For some context I've added a few photos/videos to a google photos album here: https://photos.app.goo.gl/4UAU488iwKtiktg69. I'm not currently at home so these are just photos that I've grabbed from previously taken.

 

We don't know a lot about the history of the cottages, but it would have been linked to coal mining. The stone looks the same as used in lots of other local cottages. No brick in the original part - all stone. There's staining on the outside wall on one end where the main fireplace would have been from the sulphurous coal. We have no structural issues in that end that we're aware of, but do need to remove some cementitous pointing so we'll have a better look at the stone at that point. We have a log burner and the chimney has been lined for some time now so hopefully no more damage being done there.

 

When you say the walls aren't well bonded, do you mean external walls to cross walls, or do you mean the stone making up the walls isn't well bonded to the mortar? Given it has stood the test of time so far we didn't have any major concerns about the old stone walls, although there are some cracks which don't appear to be worsening. I think we probably need to get a SE involved from a very early stage.

 

In terms of a 'box in a box' design I assume you mean to keep the existing internal solid wall which divides the two old cottages. If so, we wouldn't get so much of a blank slate because those spaces wouldn't be that large, and there are thick solid walls on both sides of the entrance hall. Would casting a concrete slab with UFH have implications for moisture being pushed up through the walls where it would ordinarily be addressed via a breathable floor (foamed glass aggregate, limecrete slab & screed)? All I read about old buildings tells me we should avoid putting a concrete slab in the middle of it, but maybe that's mitigated by restoring the walls to ensure they can breathe.

 

I assume we just need to find a good SE with experience of this type of building to form an opinion on the state of the walls and foundations and suitability for point loads introduced with changes to the roof structure. We don't know a huge amount about the old walls other than they're stone, with likely some kind of rubble filled void. The photos may help here. The 1970s section is concrete block faced with stone. We talked with neighbours who have similar construction and who looked at doing cavity insulation. They got a camera in behind and there's very little in terms of a void/cavity between block and stone. No concerns from the two storey extension in terms of movement (to my untrained eye).

 

On 27/12/2023 at 23:24, saveasteading said:

Exciting.

My outspoken initial thoughts.

EWI. As above, It needs the roof to be extended and all openings. The stone is encapsulated . It won't look remotely the same. Heritage?

Windows. These are like mine. The planners insisted on crittall until I found modern windows that look like that. What looks right?  There are very different qualities though.

Stone walls  400mm. These have been found to provide a lot more insulation than design programs allow. Of course it still needs more.

I'd build an internal stud, and insulate that. Read elsewhere on BH about the benefits of a service void.

 

I'd have to check  but I don't think any element has to be to current regs. So insulate the attic and floor more if you need to improve the numbers.

I

 

 

 

We aren't concerned about the look of the stone from the outside and have made our peace with the stone being covered by a render if that ended up being the final finish. We've talked about the idea of finishing the first floor with timber cladding and the ground floor with render.

 

I would hope that we aren't pushed to keep this style of window, but we'll see what feedback we get from the pre-app hopefully in the next week or two. The new windows just need to be higher performing.

 

With the internal stud wall, would you suggest to do a box within each room or remove the upstairs floors and create a stud wall from ground level to the roof line? I have to say that I notice a significant difference in how difficult it is to keep the house warm when the walls are wet vs when they're dry. If we do the 'box in a box' design I assume we'd need MVHR, because the box would be sealed. Are there challenges tying the box into existing door and window openings? Would we lose window size because we'd effectively be lining the window openings? I assume we lose ceiling height if we don't vault the roof upstairs and take a 'room by room' approach rather than stripping all internal structures out and building the house as one big box within the stone structure.

 

23 hours ago, Gus Potter said:

This is a key concept  I like to write some of my own spread sheets for this kind of stuff and really delve into the formulae that back up the industry software. By doing so it lets me manipulate to achieve the best design particularly, at concept design stage on old structures.

 

 @saveasteading has referenced in the past recognised research by say Historic Scotland and other accepted data that demonstrates that old stone walls are better insulators than we often assume at the outset.

 

These old stone walls are not really solid, they have lots of air gaps / voids and have a significant insulating effect. Modern masonry walls have repeating joints and tend to be "thin" in comparison with old stone walls where the mortar joints are offset.

 

OK I mention Scotland.. but what about the some of the early buildings in Bath e.g. that were all constructed in stone.. facing stone on the outside, rubble fill with random stone on the inside.

This is good design. @ProDave has highlighted issues where if you don't seal the service void it can set up nasty convection currents / drafts that bypass the insulating effect.

 

This is not that hard to do (seal the service void) in my mind if you are self building and want to do a bit of hands on stuff. If you do you'll end up with a great house for often less effort than you imagine. All you need to do is know when you have to say to the kit erector / etc.. hey this is the bit I want to do over the weekend before you sheet the inside of the walls.

This is a critical point. BC will look at the job and may say.. this part is new work so it needs to comply with the latest regs. But the other parts of the work are an "upgrade" Depending on each authority you'll get a different answer. Your Architect needs to be right on top of this and should be able to explain how the the BC game is played and at the same time understanding and explaining to you how each design decision will impact on you if it is your forever home.

 

Now if you are only paying your Architect a few quid.. then you'll get an off the shelf design. Pay them the right amount and a bit extra to phone friend (an SE who knows about this stuff) and you should at the end of the day save money in the round.

 

Expect your Architect's fee to double for them to get right into this. Now this might sound a bit scary but if you double your payment then in return they should be able to cover that in practical savings in construction cost (if an experienced Architect / Designer) and more as you have given them time to really do all they are trained for.. you can set them free and at the same time give them responsibility for the overall design, detailing / detailed drawings (very important) and budget constraints. 

 

@ETC is that fair comment?

 

I've read a bit about the research being done about performance of traditional buildings and understand they don't work well in a lot of heat modelling tools because they don't really reflect the real structure of the walls.

 

We're very comfortable with the above in terms of investing in our architect and the planning stage to avoid problems later on. Measure twice, cut once and all that! We were expecting to subcontract any major aspects that are impractical to do ourselves due to the amount of time it would take. We'll likely be having to move out, so reducing rental and storage costs will be important.

 

If we go down the route of having a 'box in a box' construction, I assume we chip off all the mortar internally that's either loose or cementitious and leave the bare stone behind the service void and also repoint the external walls in lime. I imagine that this approach makes retaining any existing internal features challenging (eg the fireplace).

 

Thank you everyone for your input here. Lots of food for thought!

[saveasteading]

2 hours ago, lookseehear said:

I assume you mean to keep the existing internal solid wall which divides the two old cottages.

That is likely to be a critical element in the structure.  We can't possibly say without seeing i, and it won't even be calculable. 

But I'd keep it if remotely possible.

Any design to allow its removal will likely be hideously expensive.

 

2 hours ago, lookseehear said:

I assume we chip off all the mortar internally that's either loose or cementitious and leave the bare stone behind

Yes, or it will fall off over the years and fill the gap. You'll find that it is fairly clear if its loose or not.

 

2 hours ago, lookseehear said:

retaining any existing internal features challenging

 

Depends on the BCO.

 

Working with the Scottish Regs we had the advantage of 'as far as reasonably practicable'.  So when we proposed leaving an area of stone exposed, the bco was pleased to agree. He had the comfort of the rules, to allow it, while personally welcoming the retention of Heritage.

In the English regs there is no such relaxation. But ask, and find a way of compensating (in the loft?) if necessary.

 

2 hours ago, lookseehear said:

Are there challenges tying the box into existing door and window openings? Would we lose window size because we'd effectively be lining the window openings?

Yes. But also for any other method.

 

2 hours ago, lookseehear said:

We aren't concerned about the look of the stone from the outside

Isn't it interesting and appropriate ?

[SteamyTea]

6 hours ago, lookseehear said:

I also really like the idea of insulating the thermal mass of the walls to buffer temperature changes

Be careful here. You are really talking about volumetric thermal inertia.

'Thermal Mass' is a hand wavey term used by 'experts' who have no idea what they are talking about.

[joe90]

Yes thermal mass is a term used by many, and we all know what it means but it has no values attributed to it so it cannot be mathematically calculated like insulation (U or R values) I prefer to call a house heavy (if it has external insulation) or lightweight (like a caravan or house with internal insulation).

[SteamyTea]

15 minutes ago, joe90 said:

no values attributed to it so it cannot be mathematically calculated like insulation (U or R values)

k-value is a third of the way to e.

 

e = (kpc)^0.5

 

Easy peasy

[Roger440]

10 hours ago, lookseehear said:

 

In terms of a 'box in a box' design I assume you mean to keep the existing internal solid wall which divides the two old cottages. If so, we wouldn't get so much of a blank slate because those spaces wouldn't be that large, and there are thick solid walls on both sides of the entrance hall. Would casting a concrete slab with UFH have implications for moisture being pushed up through the walls where it would ordinarily be addressed via a breathable floor (foamed glass aggregate, limecrete slab & screed)? All I read about old buildings tells me we should avoid putting a concrete slab in the middle of it, but maybe that's mitigated by restoring the walls to ensure they can breathe.

 

 

It is possible/probable that a slab over conventional insulation may drive the moisture to the walls.

 

But, frankly, its difficult to know until its done. Every situation is different.

 

Our old house in bucks had had this done. It was a disaster.

 

Our house in Wales, exactly the same. Not really a problem at all. Who knows why? Just isnt. Both solid wall, no DPC.

 

What does it have now? Do you really need to tyake it up?

 

[saveasteading]

1 hour ago, Roger440 said:

moisture being pushed up through the walls

I'd say this is a minimal issue. The walls will be made of big lumps of stone, and yours don't look porous. so any damp would have to rise by capillary action through the mortar.

That is actual suction taking the water upwards. It fizzles out over about 300mm.

The central core will have gaps in it sufficient for draughts, horizontally and vertically. this might affect the air-tightness of your home, but will reduce damp: its a compromise.

 

[ETC]

@lookseehear

 

My latest option.

 

Not convinced about the front elevation - I would like to retain as much as the exiting original fabric as possible.

[ETC]

[renovator123]

I'm wondering about your EWI options- do you have a price per sq m for Diathonite, and have you had difficulty finding an installer?

 

We are also looking at breathable EWI and options seem limited- although Diathonite looks excellent it's very expensive. I wondered your thoughts on CorkSol / SprayCork, or wood eg Gutex / Steico for EWI instead? I am not sure about durability of wood or about the ability to keep it dry when render over it will crack/decay sooner or later.

 

We had calculations done for EWI using Diathonite, giving approx 57-60mm thickness (evolution, agrathem, etc) over 500mm stone but have recently found some solid walls are not uniformly that thickness, which affects ability to reach EnerPHit U values.

 

Diathonite is similar in U value to rockwool and supasoft/thermafleece options which leaves me wondering about value.