Purchasing & Renovating a BISF House – Help Needed.
I am buying a BISF house, and would appreciate hearing about the experiences of people who live in BISF houses.
I suspect that whatever insulation there is in the external walls is poor by today’s standards, so I was thinking of improving it by taking off the plasterboard inside, putting in insulation and then replacing the plasterboard. This should be fairly straightforward and inexpensive compared with external insulation (which I also think makes a bit of a mess of the look of the house).
My concern is reports that this may cause condensation problems for the steel structure or cladding. Does anyone have experience of internal insulation?
Hello just bought a bisf house in hornchurch and eanted to know if there was any reason y I shouldn’t put wool insalation over original insalation thanx john
Strange- I found this thread through seeing your most recent comment Marc but cant actually find it on the featured list..?
I really look forward to the forum feature being reintroduced to be able to see this kind of project unwrap slightly easier
Hi Grangey, it looks like a glitch in the system as your post has only just popped in recent comments for me. I will have to investigate this as something isn’t working right.
Hi Ed, I’ve been busy moving some of the old posts from the previous system into new individual topic posts including this one of yours. It should help to keep the posts more compact rather than fragmented but there are still many posts to go through.
I’ve just been looking at your fantastic image of the completed living room and it instantly reminded me of this image that you posted a while ago. I have several archive photographs of similar views taken around this same period and I will post one here and some more in your other thread.
Seems I forgot to include the actual photo!
Looking at the Kitchen it’s hard to imagine how at the time these were classed as top of the range having modern appliances and the most up to date storage!
How times have changed
Just found these interesting and rare photos of BISF interiors shortly after they were built. It’s quite common to see old photos of new BISF houses from the outside but I’ve never seen one of the inside.
You may remember a while ago I was having problems with my porch subsiding slightly. As the house is built on a hillside the front door is about 30cm above ground level and the porch sits on small stone retaining walls. One of the walls had collapsed and the one side of the porch had sunk slightly.
My dad repaired it the other day and it has worked well. He lifted the concrete slab that the porch is founded in with a car jack and repaired the wall underneath. I was a bit worried that the slab would break as it’s only thin, but it was fine.
About the windows, I’ve noticed from the few houses around here that still have their original windows that the windows for the dining room and two main bedrooms appear to be a pair of units next to each other, rather than one big window. I think they are actually who window units the same as the smaller windows (ie in the kitchen etc) and the upright between them is just to provide something for the frames to be attached to.
No worries Marc, thanks for the comment! We didn’t actually get the walls skimmed as we thought it would be quicker and cheaper to do it ourselves using lining paper as we didn’t have much time off work or spare money. As it turns out lining paper is pretty time consuming to put up so probably wouldn’t do that again!
You can see the joins between the boards in places, but I can live with that for now. The living room we’ll get skimmed I think.
I have some mid-century furniture that I inherited from my gran or found at various places, like a wing-backed cocktail chair, coffee table, atomic style magazine rack and Metamec clock, but it’s going to have other things that go like the new Ikea sofa (real 50s sofas are very expensive, plus I’m not trying to make a historical reconstruction!)
Something slightly odd I found when papering is that the middle wall is thicker above the picture rail than below, perhaps to accommodate the steal beam in there. Also it seems to be thicker at ceiling height than at the rail with the plasterboads not put on vertical which might be a problem when skimming.
OK, so the dining room is now pretty much done. No reconstruction so far, just redecorating as we didn’t have time off work for a major project but it’s a big improvement I think!
Hi Ed, Sorry for the delay in replying but my other job has been taking a massive toll on my time lately not to mention exhaustion.
I think you colour scheme looks great and it goes really well with the floor. It looks like the walls have been plastered as you have a nice smooth finish. I’m really looking forward to seeing the furnished result of the overall project. Are you thinking of incorporating period style furniture or are you going for a mix of retro and new?
OK, I’ve taken up the carpet to reveal the parquet floor in the dining room. It’s mostly in quite good condition, but there is some water damage underneath the radiator where it has leaked some time in the past. Hopefully it can be sanded out, but it shouldn’t be too noticeable because of the position down in the corner.
Neither the estate agent nor the sellers ever mentioned parquet floors, surely a mistake on their part. I’m surprised more isn’t made of the attractive original features of BISF houses like the floors, panel doors, built-in wardrobes etc unlike slightly older houses.
Diningroom floor, next to kitchen door.
Some water damage under the radiator – note how they didn’t lift the carpet to paint the skirting board!
Hi Ed, what a fantastic floor! I see from your previous comment that other houses nearby have similar flooring in the dining rooms.
This is the first that I have heard of parquet flooring being fitted as standard to any BISF property.
Most properties had quarry tiles on the kitchen floors and floorboards presumed over concrete in the dining room.
Apart from the slight flood damage they look to be in excellent condition and perfect for your back to original project.
What a lucky find, you must be chuffed?
Do all BISF houses have parquet floors in the dining room and living room or is this unique to Bath?
I was quite surprised when I pulled back the carpet in the corner and found it, so exposing and restoring it should be the next job. I think it will look fantastic.
This is not mine (still all covered in carpet) but one in a house for sale nearby:
Hi Ed
My BISF had a major refit by the local council in 1989, consisting
of a complete rewire, plaster boarding throughout the upstairs and downstairs
taped on joint then papered with the dreaded industrial strength woodchip which
I’m sure would withstand a nuclear strike, along with new bathroom. It already
had a gas fire/boiler fitted in the late 70s but was replaced with a new
system. External cladding mounted over insulation and new plastic windows and
metal roof. Although the standard of workmanship in places could have been
better it’s a great family house along with a huge garden. Presently I have
added a 2 story extension Inc. a garage on the side and now gutting and
updating what I call my big shed. I wish
I had come across this site earlier as it was so difficult to find people that,
when you had a problem they could understand what you were talking about! I had
to overcome quite a few problems regarding attaching the new to the old with
the right size of access points including the removal of some of the existing
steel frame and adding new supports to allow doors and large opening from the
kitchen into the new dining room. Been at it about 4 years now and can see the
end in sight!!
I thought I had a good knowledge of the BISF house but have
learnt so much more about these houses through your site and when I come to
start the bedrooms I know what to expect thanks to the detailed posts. It’s also
good to see what other people have done, proving how versatile these houses are.
Great site
I will be removing the old flue tube and fire box end of June
so will keep you posted including pictures.
Great site
Doug
Hi all, got a bit more done on the house today. Just woodwork and decoration type stuff at the moment. Most of the little room is now papered in 2000 grade lining paper painted in magnolia & I've got some feature wall paper on order for the wall with the window (hopefully it will draw the eye from some of the defects on the walls).
I've never really worked with wood so this is a bit of a first for me. I managed to get the door test fitted to see how it works & apart from the bit of wood it's attached to being as straight as a dog's hind leg, it seems to work.
What do you guys think of the structure so far? Do you think there are any improvements I could make at this point?
I still need to add a few support pieces to the partitions either side of the door opening to support the fascia. Hopefully that will be done tomorrow so the decorating can be finished :D
Here's a picture of my loft area. Once again it's different to your BISF house Ed. Notice the welding rod poking up through the ceiling? I was trying to find something solid to screw through to but unfortunately it would seem the joists up there are thick but very far apart.
Hi Denton
I'm amazed at how quick your project is developing, it's looking really good. I'm just on my way out of the office for most of the day but I hope to have a good look through your images later. The straw in the cavity is a first for me, I did wonder if it was nesting mateial but you say it's very thick. I know straw has been used in the past for insulation because it has good insulation properties but I have never seen it used in a BISF house.
I think your project could also do with a page of its own so that it is easier to track your progress, that's if you don't mind.
I should be able to sort it out on my return tonight.
Hope you have another productive day!
Marc
I'm impressed with how quickly you're coming on too! Have you done anything like this before? I haven't, but my dad (who is a builder) showed me how to build the studwork, he did the bit to the right of the window and then I have done the rest now I know what to do.
What is the upstairs ceiling made from? If it's plasterboard perhaps it explains the larger noggins placed further apart? The LDF I have is pretty weak stuff so it would need fairly closely spaced supports (a bit like the hardboard on the walls) but is light so it only needs small timbers. Did you put down that loose insulation material?
Hi all, here are a few pictures of my house. The upload function on bisfhouse.com doesn't seem to be working for me at the moment – a single image seems to take an infinite amount of time to upload.
Here is the original unit above the staircase:
http://imageshack.us/photo/my-images/851/20120309 …
This is a picture of an exterior wall:
http://imageshack.us/photo/my-images/24/201203111 …
The little room at the front was going to be a spare bedroom, but the project has snowballed. Now I'm going to scrap the spare bed and turn the room into a 'dressing room'. It will make use of a wasted room, remove the 'comfort' from my friends' stop-overs and allow me to remove both wardrobes in the master bedroom (I planned to replace both wardrobes with a large and modern sliding unit, concealing a TV attached to the chimney breast). Attaching a television to anything attached to the party wall isn't ideal due to noise.
Here's what I want to do:
http://imageshack.us/photo/my-images/35/bisflittl …
Here is the other side of my staircase, I'll replace the supporting pieces I've removed –
http://imageshack.us/photo/my-images/593/20120311 …
Dropping through the above by accident would be painful to say the least.
Here is the corner, you can see an upright for the wardrobe in this pic:
http://imageshack.us/photo/my-images/190/20120311 …
JC
Hi Denton
They are a great set of images arn't they!
I'm surprised to hear you have fibreboard on the walls Denton, I Know it is often used on the ceilings of BISF house constructions but I've never heard of it on the walls.
Is it on the side wall of the staircase or on the party wall?
Thanks Denton! I didn't take photos of the board I removed as it was just ordinary hardboard, identical to the stuff you can buy today with a shiny front and rough patterned back (it said made in Canada actually).
I'll take photos of the ceiling board when I get some down as it's more unusual, it's low density fibreboard, so quite a bit thicker and softer and spongier than the hardboard.
Your drawers in the small bedroom are identical to mine right down to the handles, but I don't have a cupboard underneath, though it looks as though there is little room in there.
Hi Marc & BISF community,
yesterday we started rebuilding the back bedroom, and as promised I took plenty of photos. My aim is to refurbish completely to modern standards with extra electrical sockets, ethernet and wall insulation to make the walls at least as good as a newly-built house without destroying the BISF character that attracted me to the house to start with.
Here's the room before, decorated in badly-hung floral wallpaper that has been stuck over the picture rails etc. On the plus side there is a nice original 'shaker' style door and another on the built-in cupboard and a number of other original details:-
The first job was to roll up the carpet and carefully prize off the skirting boards, picture rails and other woodwork for re-use later. They came off very easily.
Then the hardboard could be stripped off the walls. It could mostly be removed with bare hands (or gloved to protect from the glassfibre behind).
The original insulation is glassfibre in a brown paper casing. It was actually in much better condition than I expected. It is nailed to the back of the timber studwork with a washer so the nail head doesn't go straight through. The damage in the far corner was where I first opened the wall up to investigate the structure.
As you can see the timber studwork/noggins are pretty small and flimsy. They do not match what is in the architects plans, so I guess this part was modified when hardboard was used instead of plasterboard. Interestingly, from the way they are nailed together from the outside, you can tell that each section was prefabricated off-site a bit like a garden trellis, and the whole panel put in in one piece.
The party wall is a bit different as the board was nailed to battens applied directly to the concrete blocks.
Next came the messy and itchy job of pulling out all the glassfibre insulation. Underneath the steel is in very good condition it seems.
More to come later as it will only let me upload 5 files per hour and I'm still rebuilding the stud-work and putting in insulation, so you can see that too in a bit.
Hi Ed, what a brilliant set of images, thank you for sharing your project with us as they really will prove invaluable to other users considering a similar project.
These are undoubtedly the best that I have seen to date showing the full internal studwork and insulation structure of a BISF house and full credit to you.
Apologies for the image upload restriction, I have removed this for you so you should be able to upload freely.
I think your whole project so far has been very well thought out and deserves a post of its own.I have migrated your project post into a post of its own as I really do think it deserves its own page. I hope you don’t mind.
You can view the post here
http://bisfhouse.com/internal-insulation-project-of-bisf-bedroom-by-ed/
Thanks Marc, that’s fine! I have made a few changes as I went along, so I might need to change a few things or just say in the post where I have changed from my original plan.
In case you’re wondering, I used an ultra-wide angle lens to fit everything in but it does make the room look enormous.
Great set of pictures Ed, your project definitely deserves a page of its own.
It's very interesting to see inside the walls, do you have a picture of the boards you removed?
I've also started to wreck my BISF house and it would seem my walls are completely different to yours. The upstairs walls to the outside of the building are not plasterboard as I originally thought, instead they are a thick compressed straw material that looks like a real fire hazard. Unfortunately that means it doesn't seem to have studwork like your house, which will mean more work & expense when re-boarding and insulating.
On a positive note, the previous owners had the upper level of the property covered in uPVC cladding which may well be insulated.
Will post a few pics on this page.
Thanks Ed
I did wonder how you got all the room in the frame, I struggle with my mine as it has a large telephoto lens and not at all good for room shots.
I will try out a small compact that I had for Christmas and see how it goes.
That's a really strange material Denton, I've never seen anything like it. It's not at all like the LDF on the upstairs ceiling of my house either. Can you tell what it is? Could it actually be straw or is it wood shavings?
It looks very much like straw although it appears to be compressed together making for a strong wall. Ill try to remember my camera tomorrow and get a clearer picture.
Hi Marc, I was wondering if you had any more information regarding the wall insulation. I’m hoping to start work refurbishing the back bedroom in the next few weeks as my OH is getting impatient to get it done up.
I’m fairly confident I can work something out, but until the board is off the walls it’s hard to know what to do as I don’t know how much space is in there and how the timber and steelwork obstructs things.
My intention is to replace the fibreboard on the walls and ceiling with plasterboard and get it skimmed, then put back/replace with something similar the timber beading at the wall/ceiling angle and the one near the top of the wall so it matches the rest of the house and retains a bit of the 1940s charm.
Hi Ed Sorry for the delay, I’ve been off my feet with a touch of Man Flu but feeling a little better today.
Boarding the walls in the bedroom is pretty easy. Once you have removed the old boards you will have a clear view of the studding underneath.
You may find that on the outer facing bedroom wall there may not be many vertical studs but you wont know this untill the existing board is removed. You may also find that where a vertical stud is present it probably wont be in the right place needed to screw the edges of your new plasterboard into.
Image (1) below shows a typical view from the outside looking in.(in this case the steel cladding has been removed).
You will find that when you offer the board to the wall you will have no timber to screw into at the edges.
Image (2) shows replacement studs but you can see them more clearly.
You have two choices here.
1) Fill in the studwork with new studs. Mark the centre point of the new timber with a long vertical line down the entire length. Rember that one side of this line will be used to screw the left board on the other half will be used to screw the edge of the next board and so on.
In other words remember to space the new vertical just under 1200mm apart. I find CLS timber the best for this as it is cheap at just over £3 for 50X75 (3X2) 2.4m length. So if using this timber you would want to place the vertical studs at 1125mm apart.
Theres a good link here Although it does cover the entire construction of a wall.
You could use loose noggins behind the plasterboard to mate the edges together but it doesn’t actually support the wall, it only keeps two plasterboard edges flat and in general it’s not good practice.
2) You could dab new boards on but that’s not good if you want to replace the insulation in the cavity.
Insulation.
It’s been a while since I opened up a wall Ed but I do know that cavity isn’t very deep. Around 2.5 – 3″ if I recall correctly.
I used Kingspan Insulation Boards on one of my projects as it is solid insulation, very easy to cut and available in 50mm and 100mm thickness. Wickes do a similar product called Celotex it comes in 2400 x 1200 mm sheets but costs around £24 to £28 per sheet.
I bought my Kingspan off ebay as there is a pro seller on there who sells slight seconds and I found it much cheaper.
Remember too that you only need to insulate the outside facing wall. You can do all the cavities in the room if you want better sound insulation though.
The solid insulation works well as it can be postioned in the middle of the cavity allowing for air space from the outer steel wall and the inner plasterboard which prevents thermal bridging and an increased chance of condensation.
The picture rails can be put back on anytime after the walls have been plastered of course.
Also when you take of the old plasterboard, make sure the existing wall and floor plates are deep enough to take a plasterboard screw otherwise you may find you have nothing to screw the top of bottom of the plasterboard into.
I hope this makes sense Ed.
You can always send me your contact phone number via the contact us form on the home page and I can give you a ring if you have any questions.
Marc
Here's a photo:-
I’ve just noticed a fairly small problem that the sellers seem to have cleverly concealed when I bought the house.
The small retaining wall near the front door that supports the right hand side of the porch has broken up and fallen down – I think they had propped it up to make it look OK.
It looks as though the concrete slab that the one side of the porch is in has subsided very slightly and perhaps the porch has too but if it has it’s very slight.
Anyway, I wondered if you had any advice for repairing it? I was thinking of wedging in some bricks or concrete blocks to support it before I put the stone facing back, as that looks more decorative than structural.
I don’t want the porch to get damaged as I like it.
Here are two photos of the problem:-
Someone on the MSE forum has suggested ramming the void full of very dry concrete mix and letting the soil water set it, which seems like a good idea.
You can also see the small retaining wall in front of the house is falling forward but as that isn’t structural, it’s not so urgent to repair.
Ed, I think you have two choices. If your not not too good with brick work call in a brick layer as to be honest the whole wall is leaning forward and looks as though it needs re-laying.
It’s also important to excavate directly under the porch pad and either build it back up underneath with concrete using some shuttering, then backfill. The wall needs re cementing and pointing too.
If it were me I would have a crack myself as even though I’m no Brickie I have repaired a few walls and it is pretty easy.
The porch slab would need supporting though whilst the underneath was excavated.
I personally wouldn’t use a dry mix, I would use wet concrete to build up under the porch slab and mortar to re-bed the wall.
The problem at the moment is not knowing what is supporting the porch slab. Also if it is a large void underneath you could always remove just the face bricks by the corner of the step and see if it’s deep enough to take a cut breeze block then fill any gaps with concrete before using mortar to set the face bricks back in place.
Hope that makes sense as I’m just thinking what I type here.
Marc
A few more photos of some presumably original BISF features.
First some nice four-panel doors from the hall into the larger bedrooms upstairs (not so nice floral wallpaper).
The built-in cupboards in the main bedroom. On the left is the chimney flue, then the airing cupboard, behind the blank panel is a cupboard for the back bedroom.
The staircase I think would look good with the paint stripped off and the wood varnished/polished if it is an OK quality underneath. Anyone have any experiences?
Hi lots of interesing chat going on here i have some good pics from my renovation of a BISF house 4 years ago will try to upload some in the following days totally removed everything upstairs ceilings floors and every innch of wall down stairs a few alterations hope the pics help they have certinatly helped my neighbours lol
Here's one of the back room and kitchen for now:
Hi Ed
Good to hear back from you.
The air vents that you mention are indeed for ventilation however the one on the wall adjoining the hall appears to serve little or no purpose and in every internal renovation I have seen it has been removed simply by over boarding. On inspection this vent does indeed only serve the cavity of that small section of wall and is not linked to the outside wall service directly as where the inner wall joins the outer wall studding is affixed.
I have not suffered any ill effects in blocking that vent neither has anyone else I know.
If you intend to do the same it may also be worth over boarding the glazed section directly above the entrance door to the lounge from the hall if it is still in it’s original glazed form. Some people remove the glass and the surrounding frame around it and simply re-stud above the door others remove some of the protrusions and overboard locking the glass behind new plasterboard but remember that it may involve re-boarding the whole wall as new plasterboard is thicker than the old hardboard that was often used on the walls but I digress a little.
The outer vent should remain in place and depending on what fire you have installed you may also need to include a second vent around 12″ down from the top of the ceiling from the inner to the outer wall to ensure correct air ventilation for your appliance. ( I shall include some images for you upon my return).
The original boilers to these houses were the old coal fired back boilers but many were replaced by local authorities / tenants with rear gas fired boilers such as the Baxi Bermuda. These were a vast improvement but by today’s standards they are not as efficient as wall mounted condenser boilers.
Just as you suggest many BISF owners have now opted to have the boiler fitted in the kitchen or garage where applicable.
The ceiling joists are indeed similar to RSJs but smaller if my memory serves me right. Cutting through the beam is not recommended as it could reduce the structural integrity. I have only ever seen a beam drilled once by a plumber to accommodate a 12mm pipe using a special tipped bit but not only was access a problem but the girder was also extremely tough and the plumber decided another method was in order.
Just as you describe the most common type of gas feed that I have seen is via a 12mm or in some cases a 22mm pipe from the main gas feed which then runs through the kitchen wall above the rear door to where most people position the cooker due to the presence of a cooker feed. This pipe sometimes branches off across and above the hall / kitchen door into the living room to feed the gas fire. Sadly this is very ugly.
I opted to re site my cooker and use electric. Close off the hall / Kitchen door completely and use the existing gas cooker feed to run my boiler.
Rather than seeing an ugly pipe running above the back door my pipe was encased in a protective sheath and the rear wall was re studded and boarded so that the pipe was hidden.
In my case I then removed the entire original stench pipe / Soil pipe that runs from the bathroom down into the kitchen and replaced it with a plastic pipe on the outside of the house giving me room to mount my boiler on the outer facing kitchen wall.
After that I removed the fireplace and flue and installed a flueless gas fire but that is a whole different story.
It’s a little hard to explain so I will add some images shortly to show you an example.
I hope the above makes a little sense?
Thanks very much for your reply, it makes perfect sense.
The front room does have a gas fire, but I doubt I’d use it and will probably want to remove it. I’m not really interested in having any type of fire there.
As for the glazing above the internal doors, I like it, it’s a pretty typical mid-20th century design and lets more light in so I wouldn’t want to remove it unless there is some real reason to. All of the doors, door frames etc seem to be original and pretty good quality compared with most new ones, so I think it will look best to leave them as they are and just repaint them.
The gas supply to the kitchen isn’t visible and as the cooker is in the corner where you have your boiler, I guess it must already be in the wall where you’ve marked in your picture above the back door. The bodged pipe is in the hall around the door to the kitchen (the one you’ve filled in.
I’ll take some photos to post here.
Hi, I have another two questions for you as your first answer was so good!
Firstly, in the sitting room there are two small air vents in the walls. One is under the window, in the external wall, and the other is high up in the internal wall that separates the room from the hall, but near the corner with the external wall. Any idea of the purpose of these vents? My thinking was that any ventilation of the wall cavity should be from the outside and you would not want warm, damp air from inside the house entering that cavity. You spoke of installing ventilators, and I assumed you meant on the outside of the house, is that correct?
There are no other ventilators like that anywhere else inside the house that I can see.
Secondly, I understand that the floor beams are steel and run from the front of the house to the back. In diagrams they look as though they are "I" section RSJ type beams. I'm interested in changing the position of the boiler from behind the fireplace to the kitchen or under the stairs, so that the two rooms downstairs can be opened up. Is it possible to get the water and gas pipes under or over those steel beams in the floor? Obviously they cannot go under the floorboards downstairs as they normally would as the downstairs floor is concrete.
At the moment the gas pipe from under the stairs to the boiler has been bodged by going all the way round the kitchen door exposed on the wall and they've boarded up half the fanlight to do it so it mismatches all the others.
I am buying a BISF house, and would appreciate hearing about the experiences of people who live in BISF houses. I suspect that whatever insulation there is in the external walls is poor by today's standards, so I was thinking of improving it by taking off the plasterboard inside, putting in insulation and then replacing the plasterboard. This should be fairly straightforward and inexpensive compared with external insulation (which I also think makes a bit of a mess of the look of the house). My concern is reports that this may cause condensation problems for the steel structure or cladding.
Does anyone have experience of internal insulation?
Welcome Ed
I can reply to some of your comments from personal experience.
Indeed the existing insulation inside a typical bisf property is very poor by todays standards. It consists of a thin layer of grey fibre insulation (similar to lost insulation) encapsulated in a brown paper covering. Due to the poor thickness of this insulation, over time it often sags and the paper covering degrades causing it to bunch up thus offering little thermal protection.
Many of the interior walls are actually simple sheets of hardboard fixed onto stud frames. The noggins used in the frames do help to prevent a total collapse of the insulation. Some properties have the walls covered in a fibrous type of board not dissimilar to plasterboard and you will often find this used on the ceilings. This type of wall board however is best removed and replaced with plaster board as it has a high combustibility factor.
In one of my properties I did indeed remove all the outer wall boards, lined the stud cavities with a good quality insulation and I inserted several small circular air vents along the base of each external wall in order to maintain airflow and reduce the risk of condensation. This was around 4 years ago and since doing this I have not suffered from any visible signs of condensation or degradation to the steel.
I did consider using insulated plasterboard but I didn't want to lose any floor space whatsoever. I also considered using Kingspan insulation sheets but I found that buying subsidised loft insulation was considerably cheaper.
The jury is divided regarding condensation issues and I am sure you are aware that external cladding is said to offer a lower condensation risk. I am aware of several councils who did indeed "upgrade" a large number of properties by using the exact same method discussed here to no ill effect.
My personal view is that a bisf property left with its original insulation only will indeed produce more condensation to the frame than an internally insulated house simply due to the warm internal air meeting the cold surface of the steel. Maintaining some degree of ventilation should in theory limit the chance of moisture collection and allow the property to breathe.
I hope that others may add their own views or experiences for you to peruse and I wish you the very best in your renovation.
It would be fantastic if you could share some photographs as you go along as one of my only regrets in renovating two of my properties is that I didn't take many pictures.
Marc
Thanks very much for your reply Marc, it is very encouraging! I will certainly take plenty of photos and post them here if I go ahead with this project as this type of construction interests me a lot.
Ed