DIY Bedroom Internal BISF Insulation Project by Member ED

DIY Bedroom Internal BISF Insulation Project by Member ED 1

Internal Insulation Project of BISF Bedroom by Ed
BISF House has a number of valuable members who take the time to share project ideas, thoughts and designs for the benefit of other members and readers of the site.

In this latest update we follow one such member as he undertakes a project to insulate the rear bedroom walls of his newly acquired BISF House .

Ed knew that his new home required a lot of internal renovation and from the very start he has been determined to keep the buildings original features. He knew that an external insulation system would strip the property of its unique character so internal insulation would be his only option.

Ed obtained as much advice as possible and drew up detailed plans outlining his chosen construction method. He also opened an inspection hole into the existing hardboard wall to expose the timber stud-work and calculate the thickness of insulation required The wall cavity was already well ventilated so solid insulation panels were chosen as they provided excellent insulation properties and continued air circulation.

Ed has recorded his ongoing project in the Your Home section of the website but we feel that his work and dedication requires its own dedicated page so that other members can follow the project. The original posts made by Ed will stay on the Your Home post.

We Shall pick up at the point where Ed starts to check the structure of the bedroom walls.

All of the text below has been written by Ed himself and re-posted here with only minor edits to aid continuity.

I’ve cut out and removed a piece of hardboard from the back bedroom exterior wall in the corner next to the party-wall to investigate the construction and shed more light on how I’m going to insulate it. I took it out from just above skirting board height and about 50cm high by 100cm long.

DIY Bedroom Internal BISF Insulation Project by Member ED 2

It’s not quite what I was expecting but it gives me a much better idea of what I’m going to do. I took some photos but they don’t really show it very well so I’ve drawn a cross-section sketch. The timbers are smaller than I imagined, but closer together. Each one is roughly 45x25mm and they are about 50cm apart horizontally and 30cm apart vertically arranged to form a grid. At the steel uprights there are two against the steel vertically. At the base there is a floor plate. The cavity between the hardboard and the inner surface of the steel cladding is 175mm (ie where it is nearest in the corrugation).

My plan is to place Celotex/Kingspan PIR board in the cavity, up to 75mm of PIR would still leave a 55mm cavity for ventilation but the exact thickness will depend on availability/cost. Then 50mm of expanded polystyrene board in the gaps between the studs, then 12mm plasterboard.

I used this u-value calculator: ..and with the materials described I should get a value of 0.18 W/m2K.

In reality it will not be quite as good as there will be a little cold bridging, but for comparison a new build house has to be no worse than 0.27. I think (the lower the value the better) and inputting the values for the original upper storey BISF construction gives 0.55 assuming the glass fibre insulation is 50mm thick (it’s hard to tell how thick is is, as it seems to have collapsed a bit).

Here’s my plan (steel and timber original“ rest to be added):-

DIY Bedroom Internal BISF Insulation Project by Member ED 4

I may not bother with the polystyrene, as it was a bit of an afterthought., just to fill the gaps between the studwork/noggins.

I’m thinking if the plasterboard is laid horizontally as was specified in the plans, the timber will probably be in the right place for fixing.

DIY Bedroom Internal BISF Insulation Project by Member ED 6

I’ve also made a diagram of the original construction, but I haven’t included the glass fibre insulation.

Ed March 12, 2012 at 11:41 am

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

DIY Bedroom Internal BISF Insulation Project by Member ED 8
DIY Bedroom Internal BISF Insulation Project by Member ED 10

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.

DIY Bedroom Internal BISF Insulation Project by Member ED 12

The picture rails removed showing edges of hardboard wall covering.

Then the hardboard could be stripped off the walls. It could mostly be removed with bare hands (or gloved to protect from the glass fibre behind).

The original insulation is glass fibre 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

DIY Bedroom Internal BISF Insulation Project by Member ED 14


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 installed in one piece.

DIY Bedroom Internal BISF Insulation Project by Member ED 16
The original insulation is glass fibre 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.

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 glass fibre insulation. Underneath the steel is in very good condition it seems.

More to come later as I’m still rebuilding the studwork and putting in insulation, so you can see that too.



  1. good job ED , just inherited mother in laws bisf in inverness and looking for all / any info.
    do you intend to replace heating system ,ours is mains gas with original ruby cylinder totally goosed .

  2. This has been really useful – we’ve just started on the same room.
    I WISH we had your walls, Ed. The wall that backs on to the master bedroom was a state. The framework above the cupboards was so shonky. Totally not in line so the board coming down from the ceiling actually sat over the top of the cupboard walls. There was a big lip sticking out.
    We had to undo and try to relevel the framework with the rest of the wall. What a nightmare!

  3. Hi all, I’m in the process of purchasing a BISF house and scouring the web for insulation ideas. EWI seems massively expensive and the way Ed did this project DIY is, I imagine, a much cheaper way to go, especially as there is no more Green Deal to benefit from. Once we get in I will find out exactly what is behind the walls already then probably start a new thread when I’m under way with the job. In the meantime, hints and tips on best price suppliers for plasterboard/insulation/foam all appreciated!

  4. Hi Ed, Thank you for this amazing write up, it is great to see and read the real make up of these walls, and I intend to use this as a guide for my own renovations.
    I have a couple of questions if I may.
    Did you need to seek any kind of planning/building control approval for this work?
    As you have moved on to doing other rooms about the house have you been able to asses how well this is working, has it avoided interstitial condensation on the steel?
    Anything you would do differently in hindsight?
    Thanks in advance. +im

    1. Hi Tim, I’m glad you liked it! I didn’t seek any building control approval as I never got to the bottom of whether it was necessary or not. Building control speaks of needing to seek approval to insulate a cavity wall, but no-one seemed to know whether a BISF wall counted as a cavity wall. It has a cavity, but is not usually called a cavity wall.

      I haven’t got to the point of insulating downstairs below a room I have done already, so I haven’t found any signs of condensation or not yet.

      The things I’d do differently now I think would be paying a bit more attention to air-tightness with taping the joins in the insulation board and gaps around the edges with expanding foam (especially around the window – I did this afterwards in the living room by drilling holes in the wooden reveal, but it would be easier before).

      Also, before putting carpet down I’d probably put board down on top of the floorboards and seal the edges round the skirting to prevent air leakage there and also make it feel more even.

      Putting some sort of monitoring device for temperature/humidity like an iButton could be interesting.


      1. Thanks for the reply. That puts me at ease. I’m actually part way through doing my first room and I got myself into a bit of a panic Smile
        I’ve been repeatedly going through posts on here to gain as much insight as possible about the various tasks ahead while we were waiting for the sale to go through. In some ways I was feeling very prepared. The waiting seemed to go on for ages, but since we have moved time appears to have shifted up a few gears. I’ve had this week booked off for a while and we decided it would be a great time to make a start, but it came around all too soon and all of a sudden I felt totally un prepared, and part way through, totally out of my depth.

        We have started with the small room above the stairs. All the diagonal bracing of the steel at the corners has made putting the insulation in a challenge. Lots of cuts have been needed to get into awkward spaces. We have been wedging in slithers of insulation where we have ended up with unintended gaps and taping over all joins, that expanding foam did occur to me part way through, i’ll get some for the next room. We are at the point of putting the thinner insulation in the stud work right now, much more enjoyable, how i’d foolishly expected it all to go.
        Well, back to it I guess, I’ll make a write up when i’m done and we can compare notes.

  5. Hi Doug, thanks for your reply! I guess it’s obvious now, but I originally assumed there was no intermediate support for the steel beams. I was thinking that they would be the size of the RSJs used in masonry houses, but repairing the floorboards I saw they were quite a bit thinner and so would obviously require support in the middle.

    Have you noticed that the wall that this beam is in is thicker at the top than at the bottom? I noticed it while papering, maybe it’ll make skimming difficult. It’s thicker above the picture rail than below, presumably to accommodate this beam.

  6. Hi All
    Think I might have solved the Kitchen/hall doorway half-height glazing issue. There is substantial steel I beam which runs the width of the house supported by vertical beams at regular intervals. This is set lower than the ceiling then the ceiling beams sit on top of it the kitchen /lounge wall is secured to the underside. As it passes over the top of kitchen door it reduces the height available for the glazing.

  7. Hi Ed your kitchen door glazing is different to any i have
    seen and having removed my kitchen door and glazing and in filled found no
    pipework above door, but that’s not to say there isn’t. I also had a pipe
    sticking out from the wall in the same place although mine was copper and yours
    is steel, it’s probably is a gas supply pipe feeding a cooker point running
    under the bathroom floor into the soil and vent box with the cooker located
    into the corner by the back door. As a guess the second branch is also a gas supply
    feed to the back boiler this might be the pipe running in the wall along with
    the hot water pipe above the door thus a reduced height of the glazing, as my
    old back boiler had a surface gas pipe mounted above the kitchen door in the
    hallway through the wall into the lounge dropping down into the fire surround.
    It would make sense to run pipework in the walls from first build as most of
    the heating and gas pipe in my house was run on the surface due to a council refurbishment
    in the early 80s and looks/looked awful. Doug

    1. It sounds as though you have the same problem as me with pipes and cables surface mounted, which is a real eyesore I think. This is the other side of the kitchen door with the gas pipe going round the top of the door from the meter cupboard to the boiler in the living room and the cable to an electric shower in the bathroom run in a conduit. 

      In fact most of the sockets downstairs are wired in using surface mounted conduits to take the cable down from upstairs (there is only one ring main) and central heating pipes are either surface mounted or poke out from odd places. Where I have reconstructed the walls in the back bedroom I have removed the surface-mounted sockets and lightswitch and visable cable and put dry-wall box mounted sockets and switches in and put the cable in the wall – it really does make a big difference I think, it’s much neater.

      I hadn’t thought about those steel pipes being gas pipes, but you’re probably right, though I thought the back boiler was originally heated by a coal stove.

    2. Here’s an extract from the original architects plans that Alexandra uploaded and they clearly show the half-height glazing above the kitchen/hall door, unlike the full-height glazing above the bathroom door (and all the other internal doors in the house).


      There must be a reason for it, because it looks a bit odd and you wouldn’t mismatch the doors for no reason. Also, as there is no window in the hall downstairs, it can be quite dark and so needs some borrowed light, so it looks as though Gibberd squeezed in a half height glazed area as a compromise. My hallway is especially dark because the front door doesn’t have much glass, but I believe the original door was half-glazed (looking at neighbours, the top half was glazed and the bottom solid)

  8. *Hi All ref the hot water pipe, a 22mm pipe leaves the cylinder  and drops into the floor of the back bedroom and runs towards the window then bends about .5 metre from the outside wall passing through a hole in the I Beam and continues to the bathroom both hot and cold supplies then drop down the side of the soil and vent pipe to the kitchen hope this helps


    1. Hi Doug and thanks for your message. I have a radiator on the wall between the two bedrooms and had some of the floorboards up in front of it to repair/replace them where they had been damaged when the central heating was put in (in the 1970s at a guess). I never noticed a 22mm pipe under there though but perhaps it was too far to the left to notice.

      I’m still wondering what is above the kitchen door. Everything about a BISF house is logical but sometimes a bit surprising, so I think there must be something in there. There are pipes sticking out of the wall next to it which are quite an eyesore and can hopefully be removed. They are not hot water pipes in use because they do not warm up if you run hot water


      Kitchen/hall doorway (half-height glazing)


      Kitchen/hall doorway with pipes


      Kitchen/dining room doorway (full height glazing)


      Some more decoration

  9. I have taken the old radiator out as it was the old single type with no thermostatic valve. It’s on a microbore system and had a strange connector with the inlet and outlet at the same place. While at it we replaced the radiator in the main bedroom which was directly behind it, taking the opportunity to put some extra noggins in for it to be attached to while the hardboard was off the wall (the old radiator was just attached to the hardboard and was falling away from the wall).

    We are going to replumb them so that the pipework runs underneath the floorboards, as it does to the bathroom radiator, instead of coming out of the built-in cupboard in the back bedroom and out of the flue box in the main bedroom.

    While repairing a floorboard that had been cut to put in the central heating but left unsupported (I wondered what the hole under the old carpet was!) it was possible to see how the 8mm microbore central heating pipes and ring main cables just fit through the gap between the ceiling and the steel floor beams.

    But the mystery to me is how the 15mm hot water pipe gets from the hot water cylinder to the bathroom washbasin. Do the steel beams have special holes for the pipe?

    1. *Hi Ed, the beams don’t normally have any holes cut in them but I am all too familiar with microbore as it was fitted into one of my properties just as you described. Lying just onder the floorboards Smile

      If I recall correctly, I think the 15mm hot water pipe leaves the cylinder in the bedroom cupboard up through the loft space and returns into the bathroom inside the stench pipe casing. Don’t take my word on that though as it has been a while since I refitted one of the bathrooms.

      Does your feed come to the sink via the stench pipe casing?

      Also, I’ve spent the last few days trying to develop a way for you to access and edit your entire bedroom post. It’s been a bit of a nightmare lol but I’m still working on it. I’ve been sat here all day so far thanks to the rain and thunder here but I haven’t got very far as I have also been trying to develop a better comment system of forum integration.

      I really liked your last update right down to the picture rail detail.

      Amazing job!

      BTW is your central heating fed from a boiler or the immersion tank?


      1. Hi Marc, I’m glad you like it! I think the two-tone colour scheme works well. Putting the woodwork back up after reboarding the walls was quite an effort but it was worth it as I think it gives a nice combination of original BISF style with a contemporary update.

        Our hot water comes from a cylinder in the cupboard in the main bedroom next to the boxed-in flue, and it is heated from a back boiler behind the fireplace downstairs. It comes up from under the floor under the handbasin and definitely doesn’t go through the loft. Now I think it goes through the wall between the hall and kitchen downstairs (under the steel beams) and that is why there is only an odd-looking half-height glazing above the kitchen door unlike all the others which have glazing all the way to the ceiling. Perhaps the hotwater pipe goes above the glass. Originally I assumed that was a later bodge, but I notice the half-height glazing is in the architects plans so there must be a reason for it.

  10. Hi all, just a quick update with some photos. As you can see it’s almost done, just needs some touching up and the doors putting back, radiator and lamp replacing etc but I need a bit of a break from decorating now!

    Is it OK if at the end I rewrite things a bit because there are some things I did differently from how I planned and some things I discovered along the way?

  11. Hi Ed and Marc
    really great to see how you both have gone about your projects as i will be doing the same at some point bathroom first its been really useful. Interesting what you were saying about the joists and noggins as i have my lounge celling down

  12. Hi Ed,
    How is the project coming along?

    Did you overboard the ceiling or did you opt for a clean install? I ask because sadly I have the exact same job coming up very soon and I haven’t yet decided which way to go.
    I know over boarding will be less messy but those noggings can be pesky blighters to accurately screw into. Smile


    1. Hi Marc, sorry for the slow reply! Things are coming on a bit slowly as I’m having to fit it in between work and don’t want to start too early or carry on too late to avoid upsetting the neighbours, who have young children.

      In the end I removed the fibreboard from the ceiling completely and replaced it with plasterboard. It’s very soft and spongy and can be broken up by hand.

      I found a few things that complicates it a bit (well, I knew they were there, but hadn’t really thought of them before).

      Firstly, the noggins are just notched and fitted into the steel beams so they can be moved around. They are not attached at all. The old boards span the whole room, so there are no cross timbers to butt two plasterboards up against (they are bigger than modern plasterboard sheets). Also, as the noggins are loose, I thought the ceiling would probably crack if you ever stepped on the noggins in the loft.

      Secondly, the old ceiling boards were obviously put up before the walls as they are continuous from one room to another. It’s the same with the hardboard on the party wall, which continued behind the built-in cupboard.

      What I have done is put new timbers in at right angles to the old noggins to stop them from moving about and to provide something for the boards to meet on. It’s also quite fiddly to break off the old ceiling boards above the internal walls without leaving any sticking out.

      It might have been easier to put up the plasterboard on top of the fibreboard, but it doesn’t seem like such a good way of doing it.

      1. Hi Ed
        Great to see the room partly plastered, I bet you can really feel the difference in warmth already!

        I remember from a previous job that the noggins were all loose, as in free moving and slotted into the support beams which can be a bit of a pain when trying to line up the screws from below. I agree that overboarding just doesn’t seem the best way so I think I will relace the noggins on this job to match the metric plasterboard sizes.
        I was fortunate last time as I did most of the stripping down of the ceiling and left my friend to do most of the boarding. I remember his frustration with the shifting noggins lol and how comical it was with him downstairs with the screws and myself in the loft trying to guide the noggins in place.

        I think using right angle timbers is a great idea to keep the noggins stable. If I remember correctly the noggins wern’t very wide either.

        Looking good though my friend, You have done a huge amount of work in such a limited time but it’s well worth the effort. Smile


        1. Thanks Marc, as you can see i’ve used 900x1800mm boards for ease of putting up and placed them at right angles to the original noggins. It did involve putting up several rows of extra noggins between the original ones to hold them in place. The noggins are only narrow, 37x75mm I think, but some of them (where the old boards met) are doubled up so I placed the new joints there too.

          I used one of those electronic stud detectors to find the noggins when screwing the boards up, because they are not completely evenly spaced.

          Thinking about it again, it might have been easier to hold the noggins in place by screwing long pieces of timber in on top of them in the loft and then only putting the individual cross pieces in where the boards meet.

          I don’t think you’d want to get rid of the original noggins because then you’d have to notch new ones so you wouldn’t really gain anything and it would probably be difficult to notch them all the same to get the ceiling level (I imagine they were all delivered pre-notched from the factory). I can’t think of any way of attaching them to the steels apart from slotting them in like the originals.

          I did it all in a bit of a rush so unfortunately I didn’t take photos, but I’ll take some from above.

          1. Hi Doug, the ceiling noggins are just like that except they are thinner and of course once you take the ceiling boards off they’re loose, instead of being held in place by floorboards.

            With hindsight, it may have been better to fix them in place from above before removing the ceiling boards.

  13. Ed,

    Considering this is your first project I must admit that I am very impressed by your high standard of workmanship and attention to detail.

    This is probably the very first BISF house, internal insulation guide that has ever been published and your project certainly sets the standard. I sincerely hope that other BISF owners find your project as useful and as interesting as I have to date.

    I know how much research you have undertaken to get to this point and this is clearly evident in many ways. I think the Jablite on the back of the steel uprights is an excellent idea and this should eliminate all risk of thermal bridging. Your stud-work looks clean and precise and I have no doubt that despite your outlay on materials so far, you will easily recoup this cost in a relatively short time.

    Your steel cladding panels and support rails also appear to be in excellent order. It can often be beneficial to give the visible steels a quick coating with a rust prevemtion paint at this stage but to be honest your steels don't look like they need this. Whilst you have the structure exposed it's a good idea to pay particular attention to any nuts and bolts that may be visible as these were often not coated or galvanised but judging by your attention to detail so far you have probably already done this. Smile

    Keep up the good work my friend and I look forward to seeing more of your work!


    1. I agree with Marc completely – the quality of work and attention to detail is astounding. I bet the room feels warmer already! :D

      Finnegans (now Hammerite) No.1 could perhaps be a good paint to treat any visible rust spots, I’ve used it on cars in the past and it seems to perform well.

      Looking forward to your next update.


  14. Just a quick update on how I’m building the new studwork. Here it is almost finished. I have put in a second layer of 50mm Kingspan board between the timbers instead of the expanded polystyrene I originally planned. I found it easier to put the Kingspan in and then the noggin on top and so on rather than build the studwork first and then put the Kingspan in afterwards.

    You can see the Celotex behind where I haven’t quite reached the top yet. This bit was a bit trickier as the original woodwork at ceiling level was not attached to the steel joist above.

  15. Here’s the wall with the glassfibre insulation removed. You can see the trellis-like original timberwork better now and the red-painted back of the steel cladding. The splashes on it are mortar from when the party wall was built.

    I cut out all of the original timber except for the frame of each panel (ie the bit against the ceiling, floor and steel uprights), as it’s very thin. The wood is held to the steel uprights with special clips so it’s best to leave those pieces in and screw your new timbers into them, as attaching to the steel would be difficult.

    A little tip I got from an energy efficiency and insulation forum was to insulate the back of the steel uprights with 25mm expanded polystyrene (jablite). I cut 60mm wide strips and applied them with instant-grab adhesive and wedged them in place where necessary. I’m not sure how much difference this will make, but the jablite is very cheap though it is a fiddly job!

    Next I put in 70mm Celotex PIR insulation board. It comes in a number of other brands such as Kingspan and different thicknesses, but 70mm seems the ideal width to fit into the cavity and still leave a 55mm cavity in front of the steel cladding for ventilation. 70mm also fits into the steel C-section uprights if you notch the edge slightly.

    I forced the Celotex down below floor level until it sits on the steelwork just above the ceiling in the room below as I thought that would mean it’s accessible when I do the downstairs. Ideally I think you’d do downstairs first. I also put it so it was sticking up into the loft a little so it forms a little barrier to stop the loft insulation blocking the ventilation under the eaves (as the pitch is shallow, it’s hard to get under there to see if you’ve left enough of a gap when putting the loft insulation down).

    In front of the Celotex I’ve started building the new studwork to put the plasterboard on using 63x38mm CLS timber. I have formed a frame screwed to the original timber at the floor, ceiling and steel uprights and then put in uprights at 600mm centres with noggins roughly 600mm too (as I found, it seems better to make the noggins very slightly closer together to fit the height of the inner insulation rather than to have to use two pieces for each opening).

    As a slight change to my original plan the inner insulation is 50mm Kingspan PIR board which came cut to 1200x450mm pieces.

    1. Hi Ed, is it OK to post here?

      Once again a very nice set of pictures, there has been much talk about insulating the internal walls of BISF houses but this may well be the only step by step style project to date.

      I imagine this will be an extremely useful page for those wishing to carry out this work on their own BISF houses and I can't wait to see the finished article :).

      Do you have anything special planned for the party wall such as sound proofing etc?

      1. Hi Denton, of course it is!

        I was a bit surprised that i couldn't find anything about this on the internet and Marc was the only person I could find who had any experience of it. There must be over 30 000 BISF houses still in existence so I expected to find more information.

        I hope it will be useful to other BISF residents, as it should be within the means of many DIYers (bearing in mind I was shown how to build the studwork by my dad, but after that have been doing it myself).

        Also, replacing the hardboard with plasterboard is a good thing to do in itself for redecorating and adding the extra insulation doesn't make it that much more difficult or expensive.

        I haven't decided how to soundproof the party wall. Any suggestions? It's not in much need of extra soundproofing as there is a double layer of concrete blocks plus an air cavity and then board on each side, so I think it's better than an average party wall, but I thought while I'm reboarding I might as well improve it. I was thinking of maybe polystyrene-backed plasterboard.a

        1. Hi Ed,

          Indeed, all I could find during the (lengthy) purchase of my house seemed to be unanswered questions and opposing views on insulation/condensation problems.

          I would have been thrilled to have found this website when researching BISF houses for the first time & project pages like this would have been marvellous.

          Replacing and adding insulation to the internal walls is definitely a good idea, I'll get a few pictures when trying this myself as our houses seem to be different in many ways.

          I haven't yet had chance to look at sound insulation in depth but disconnection of an attached solid surface (such as plasterboard) using some sort of sandwiched dampening membrane seemed to be a route. It's something I need to look into for the neighbours' sake rather than mine as they seem pretty quiet.