Cold Floors & Walls in an Old House ~ What Can Nick Do? 

Good advice on insulating the floor, that will make big difference. Roger should have pointed out that in the photo there appeared to be an air vent/ brick. Its important that isn’t blocked up as that suspended timber floor needs to breath underneath it. If using wool insulation just tack some vapour barrier at an angle to stop the insulation blocking the vents. Other option on the wall is to stud it out and insulate between.

I've just ripped out dot and dab plasterboard - the interstitial condensation meant there was massive mould growth and the board was very damp and crumbly

It depends if he wants it to be breathable. I've just done a similar job, we used corkboard, which we stuck to the walls with a lime based adhesive. Then lime plastered over the top of the cork. It is a more expensive method, as all the lime products take longer to cure and the process is slower, so more labour cost. I work in Cornwall and Devon where we have a lot of natural stone buildings held together with lime mortar. Breathability is very important for older property's, often sealing them up with modern materials causes more problems than it solves.

Reading the comments, and my being due to upgrade a Victorian end terrace.....it is surprising the lack of consensus as to how to proceed! Such a common structure across the country too!!

I’d add that whilst the floor is up, they might have a chance to run some Ethernet wiring that their old house wouldn’t have had before.

Ty Mawr Lime sell a lime plaster system that includes a cork board for insulation that you can plaster straight on to. Can be used internally and externally. Worth giving them a ring, they're technical support is really helpful.

If possible I would always try and install a couple of access traps for access for either crawling underneath if deep enough or even just being able to thread future pipes or cables. Conduits can sometimes negate the need, but it is all about thinking long term and future proofing.

I live in an old double brick house with no air gap circa 1930s. I've done everything I can to the point of external boarding now :) Works well, but never be as good as doing it properly from the ground up.

Personally, I try to avoid nailing or gluing floorboards down, preferring to screw them as you never know when you might need to lift them at a future date.

Ive started doting and dabbing all my walls with insulated plasterboard i have a few external walls then plastered and the difference is incredible ive not connected my radiator yet its december so its getting colder and the warmth of the room is brilliant. GET YOUR HOMES INSULATED its worth it !!!

i just want to say thnx for the video's..they help me a lot in what to do and choose in a lot of ways..in my old house..guys..thnx !! from the netherlands

It would be good if Skills builder could do a video on spray cork insulation for solid/ old walls. I believe it can be as thin as 8mm and can be plastered directly. This is something I am looking at as there are areas that wouldn't fit PIR or other boards.

We have an old house and we used the woodfibre system. Then it’s all breathable, very warm and we just used the lime solo finish coat over the top, looks amazing no painting required. But if you do paint; then make sure it’s breathable. These old houses with no cavity wall or very tight cavity’s, are designed to breath. Respect that and you won’t get any damp

Spot on advice about the walls , I dot and dabbed the insulation board on with Soudal low expansion adhesive foam as it really sticks to the board and the wall and about the same amount as normal dot and dab but with extra at the top and bottom on the board ( PVA wall first ) but buy it in boxes of 12 as it works out £7 a can not £18

Roger, if you put a vapour barrier on top of the joists, you then can’t glue the chipboard flooring on to the joists. Personally I’d recommend gluing the boards and not bothering with a vapour barrier.

Also, it looks like you have some support underneath the floor joists, please make sure you provide enough support for the insulation board such as kingsman. Otherwise there is a risk that even if the board is cut to a tight fit as the joists expand and contract that eventually the insulation board drop out. Good luck with the refurbishment.

Roger, mention the battens pinned to the joists to support the insulation. I’ve seen examples of dot and dab causing a thermal bridge which has generated cold spots on walls with subsequent mould patches. Your point about insulated board is well made.

I wonder if you might consider doing a video talking about this comment section and speaking to various experts / visiting older homes that have done various different methods. Clearly is something people are passionate about; would get millions of views! It doesn't need to be a how-to video, could just be a look at what everyone is doing alongside your own opinion on how difficult each method could be for us DIYers. Also the implications of how it makes jobs more or less difficult for plumbing, electrics, hanging TVs etc after all is done

If you screw the boards down they wont squeak, its the board moving up and down on the nail shaft that makes the sound.

I've put Rockwool between the floor joists to replace the mostly missing thin planks of styrofoam the builder who owned the house before us tacked in. The Rockwool is just friction fitted between joists so doesn't need precisely cutting to size & it's not going to fall out because it's so firm.

Bought my first house two years ago and have been renovating it on a low budget, I didn't want to buy the big thermal boards as the costs quickly add up for every room. Instead I bought standard plasterboard, used the plasterboard foam spray adhesive, sprayed a pattern onto the back of the board for adhesion, then I used standard insulation foam to fill any empty space on the back of the board and stuck them onto the wall. End result was cheap insulated 'foam' boards on the wall. Obviously not as good as proper insulation as it's not as thick, but still really pleased with the results.

Brilliant advice there. Solved my challenge with a cold internal wall.

Would use mineral wool insulation in the floor - agree on the vapour barrier…. the other consideration is if the brickwork wall which the floor joists are supported on has no DPC… using mineral wool allows any moisture from the wall which travels into the timbers to evaporate down and be taken out via the air bricks…alt. as you have access to the joists, I would wrap them in a DPC before slotting them back into the wall and then do the PIR…

I would think the last thing you would want to do is insulate/seal the breathing ability of the brick from the inside, leaving it exposed to freeze thaw outside. Isn't this why most brick historic buildings are falling apart on the outside?

Insulated plasterboard seems the best idea but maybe not too thick otherwise risk of interstitial condensation?

Subsites contain a lot of moisture and with rising water tables could have a few inches of water in now and again. I wouldn’t insulate the floor joists as I have replaced many a floor with dry rot outbreaks. I would put more plastic air bricks in and keep the underside nice and fresh, cold air does not rise. They could always put a thin layer of insulation on top of boards and combined with underlay and carpet would be ok. I would 25mm roofing batten the walls isolating the brick work with a plastic dpc to prevent any low level damp affecting the plasterboard. Then use 25 kingspan inbetween the battens and plasterboard on top. Or might be better to use an open cell insulation so any moisture can permeate.

Wood fibre insulation is an excellent product for insulating floors. You cut it oversize and it squishes gently in to make an air tight seal. You can run a breather membrane over the joists and under the insulation. For the walls, build out a stud wall to allow an air gap, or use a breathable product like spacetherm wallboard.

You could render the brick wall with a Lime render, which can be gauged to ensure no cracking or at the minimum mitigate against the possibility, the great characteristic of Lime is that it breaths and you will not get condensate on the surface, unlike a cement based render. £3k is heavy I would say, but depends on the area to be rendered.

There are lime plasters with added insulation. Great for heritage buildings. Now far U values less than PIR but still might be considered. There are also such thing as breathable insulation boards like Redstone calsitherm climate board

I'd fill the floor with concrete, 100mm insulation,underfloor heating and 100mm screed, walls insulated plasterboard using foam to stick it on, maybe blue grit walls 1st.

I am steadily wall insulating the whole of my ground floor Victorian flat by CLS battening out the whole wall with lengths & noggins (taking wallplugs/securing screws into brickwork below sound original plaster, then insetting with Kingspan/Celotex/Iko ultratherm or any of those insulating boards (min depth 25mm), then plaster-boarding over the whole lot. It takes forever doing it this way, but I never want to have to do it again! It keeps my rooms warm and provides some sound insulation.

I had my suspended wood floor insulated like this last week in a 1949 Dublin semi-d - the difference is unbelievable. The room would cool down in about 10 minutes when the heating went off but now there is a very constant ambient temperature without the heating. I personally would advise against internally insulating as the heating would never be absorbed by the masonry/walls. Insulated externally.

I do quite a bit of work on old buildings. Had flats that were damp, in various places. Some was a result of external ingress of rainwater and others were a result of condensation. I tried to resolve both issues: 1. I removed all of the old lime plaster on the walls 2. Did a 50/50 SBR mix X2 coats on the bare brickwork (stops salts from fireplaces and external water ingress) 3. Dabbed 50mm celotex to the walls (taped joints. Vapour barrier) 4. Fixed plasterboard onto celotex with Soudal adhesive (insulted plasterboard is very expensive) Worked perfectly so far.

If you dot n dab plasterboard to a party wall each dot will act as a sound transmitter. Seperate from the wall with a stud/metal frame. Only dot n dab internal walls.

Also make sure air flow is all good before putting the floor down.

Whatever way you decide to insulate this floor it is critical that you check the floor vents, ensure they are clear, then do a calculation for the ventilation requirement for a modern suspended floor. My calcs usually indicate that more vents will be needed. Also, older houses may have new paths or patio slabs increasing the level of the paths above the level of the subfloor, this will allow water to migrate to the subfloor with potentially disastrous consequences. Keep an eye on the subfloor with a hygrometer if you can, check every few months for around 2 years, just to see if it's trapping moisture. Good luck with your renovation.

Was hoping you might touch on Aerogel insulation under drywall. It's an amazing thermal insulator and very thin, I just don't know what the implications are in terms of breathability.

Can you explain what you would do on the window wall and how you would join up to the window and get a nice finish? Great vid, btw, very educational.

With floors up and bare walls it is a perfect opportunity to run in networking and power cables. More sockets and network outlets are never wasted but do plan them carefully. Oh, and take pictures of the cables on bare walls and in floor / ceiling voids before you cover them for future reference. Similar for pipework in kitchens, bathrooms and en suites of course.

Thanks Roger for posting this, the problem with making a decision on insulation on solid walls is there is so much information out there on how to do it and not to do it, a lot of it is conflicting. To improve the EPC they want a minimum of 50mm insulation, my concerns of using PIR is the release of toxins and possible shrinkage. My original idea was to cross batten with breathable superfoil and then plasterboard, which would allow moisture to travel both ways through the wall, unfortunately I can’t find any feedback out there of it being used to give me confidence in it. There is so many issues with insulating homes incorrectly which can be costly to correct in the future, thanks, Nick

Check the SPAB best practice on insulating old buildings. You aren't letting the building breath with modern materials which are better suited to modern construction.

our house is 300 years old 16 inch solid walls we had our room 14 ft square lime plastered for a few hundred quid using nhl2 and a lime top coat nhl2 is about twice the price as std cement

With period properties making up a huge % of 🇬🇧 housing stock this advice will certainly help a lot of people! 👍🏼

You often find that the cavity has filled up with debris over the years leading to a bit of damp at the base of the wall where the dpc or cavity has been breached and the brickwork is often very wet. With good old dense timber and ventilation the joists on that front bay wall may not rot easily in their current state BUT if insulated and injected with foam to seal the gaps as Roger mentioned you could have some issues in years to come.

Has anyone mentioned wood fibre board insulation with lime plaster? Completely breathable. Surprised dot dab with pir plasterboard was advised on a solid external wall.

Expanding glue is a must like your said roger, stops any noise and bounce, very messy glue but does a great job

I'd dot and dab polystyrene insulation onto the wall, then dot and dab plasterboard over the top. Or perhaps build a studwork frame if the wall is likely to move, in which to fit insulation, but that has its own issues. *Never* use plastic sheet in any building - tar paper (the thin variant like a roll of black card, not the thick roofing material) is better as it inhibits rot, doesn't create a cold area to attract condensation where it touches wood and if it gets soaked will give way such that one sees a problem (and water is released) before wood rots. It's also far easier and more pleasant to work with. For the floor, if there is space, i'd hang a layer of PU (Kingspan etc.) insulation under the beams before filling between them, to super insulate the room. I'd probably go so far as to insulate the ceiling of rooms, too, as we may face a time when we go back to being able to heat only one room much of the time - the cost/benefit ratio and return period combined with effectiveness considerations based on other factors in the house is of course a question for each household, but I say super-insulate every time - i've done it repeatedly in different countries and the feeling of quick warmth and lasting comfort into the night, or even 24 hours, is wonderful. I'd probably fit an inter-room adjustable vent in each room too, and probably one to the outside, to manage and optimise airflow around the house - dead cheap and simple to fit and nothing to go wrong. And i'd always fit a wood burning stove which draws cold combustion air from under the floor so that airflow under floors is enhanced.

If it's traditional solid wall construction, you do NOT want to use plasterboard, the moisture through the wall will eventually ruin it. They do a insulating lime render product which is meant to be really good, then skim with a lime putty.

Old houses need some modern mechanical ventilation system if you upgrade the insulation everywhere.. otherwise humidity will be a problem..

A Decent Miltifoil for the floor... Insulation & vapour control barrier, all in one, for the floor. Maybe the wall also, or insulated plasterboard with vapor control, sealed tgrn a decent graphite infused wallpaper, then a decent wallpaper liner, then a acrylic thermal paint, in a colour of your choice haha..

Fraught with potential problems. Many housing associations are now ripping out insulated plasterboard and PIR floors as they contribute to poor indoor air quality. My advice (as someone who works professionally within this field and therefore understands the science) is use lime and fibreboard, or other breathable products.

That looks like a solid wall, so it's very bad advice to put PU and plasterboard on it. It'll work ok for a few years, but slowly mould will grow behind and the joist ends get damp and rot off. There are so many people bodging up old houses now with inappropriate insulation that in decades to come builders will be cashing in putting it all right. Modern lime plaster mixes do not crack, we do it better now than they often did back in the day. Back then materials were expensive and labour cheap so corners were cut. There is no shortage of breathable insulation systems on the market now so aside from cost there is no excuse not to use the correct materials and systems. All you're doing is creating problems for future owners or yourself if you live there long enough, but then that's nothing new....

Is breathable insulation better here?

I have just had to re-new all the joists in my kitchen after substantial dry rot, the numerous contributing issues (various concealed leaks) have been rectified and it has completely dried out. I am having insulation between the floor boards like this, with no thermal barrier. The Installer has left a couple of gaps citing he wants to make sure it still breathes well after the dry rot. In my eyes he is concerned about it breathing the wrong way and it will surely negate the benefits of the insulation if there are a couple of potentially drafty, uninsulated sections. The underfloor can breathe well, there are numerous functioning air bricks all round the house. Should I insist he insulates as much floor area as possible and not leave such gaps?

What about adding a stud wall with rockwool?

What a great ding dong of comments !!!!!! Well done everyone ! Im certain Rog will revise and update Re IWI theres a gov publication & bristolian publication that basically says vapour open ( breathable) and swipiwi map that shows areas in uk for both open and closed !!! Im looking into it at the moment but certain its adding years on me and I aint got many left ...

Solid insualtion sheet is expensive today, rockwool batts would be less expensive and just as effective. Mind you s/h Celotex sheets would be an alternative.

Worth noting that any attempt to improve the thermal insulation of a property in an England does strictly speaking come under building regs. A big renovation like Nick is doing would require upgrade of thermal elements and needs to fit Part L of approved documents

Batten, insulation then plasterboard.

Why not put the polythene moisture barrier on the ground to stop the damp rising.

could he batton the walls insulate and plasterboard if the rooms are big enough to lose a bit of space ??

Surprised you didn’t mention to use gapotape in the floor to make it airtight. It’s The Plumber

I would stick with lime on a house that had it originally. There are lightweight insulating renders available with fibres using NHL2

I would use insulated lime render and maintain the breathability of the building like it was built to do. Cement and gypsum don't work in old houses

Do you have to remove the internal plaster on solid bricks walls first or not? I hear if you Dot n Dab, it bridges cold spots and damp through to the plasterboard..? Can you use fiberglass behind the boards? Thanks.

Good advice

He’s a menace to traditional built properties… I wonder how many out there took his advise ended up with wet walls, rotting timbers etc… 🤦‍♂🤦‍♂🤦‍♂

We layed a permeable windproof hammock over the joists, filled it with rockwool and layed a non-permeable vapour layer over the top.

What would you do on cavity wall insulation; we have a similar situation, lime mortar, soft red bricks on a slate dampcourse with 2" cavity.

hemplime would be a great job on the walls

Any advice for insulating a concrete floor? We’re in the process of buying a bungalow with concrete floors, obviously adding an insulated floating floor would be an issue with height. Is the foil bubble wrap stuff worth putting under a carpet?

Don’t use celotex or kingsman. Use breathable insulation and lime plaster for old houses

Hi Roger what video is the clip of Robin fitting the insulation under the floor boards from, I`d like to see how he fixes it in place and any other tips in more detail. Thanks

Foam rod round the floor edges - better than expanding foam

I've heard of some people putting up studwork and insulating between the studs but leaving a gap of 25mm or so between the brick and back of studwork/insulation to allow the wall to breathe. Is this necessary? Cheers

This is the advice I'd expect from a plumber that reckons he knows about building, carpentry, and plastering

What about dealing with where the moist warm air goes in such a well insulated / sealed room? Won't you get condensation?

I'm in a similar situation with a 100 year old, very cold property so this video is very interesting. My property has a 55mm cavity with a porous, silicate masonry block outer leaf with lime mortar and internal plaster. An energy assessor is trying to convince me to have the cavity filled with beads but I'm not convinced it's the correct thing to do. I have been considering insulated plasterboard, would this be a better option? I'm concerned this would then cause condensation in the cavity, I'm totally confused now.

Also put double the amount of sockets that you think you need!

Some installers recommend putting a breather membrane (e.g. roofing felt) under the insulation (i.e. on the cold side) to cut down drafts. But might this risk slowing down the penetration of any moisture through the insulation so it condenses on the felt?

I am currently insulating a 200 year Georgian place with SuperQuilt under the floorboards which gives the vapour barrier and insulation in one

Hi Skill Builder, have you ever used a lime, cork and clay based insulating plaster instead of plasterboard or visited a house that has?

Great video very similar situation just bought a 1920’s build. Working on upstairs. We’re not back to brick like this video so is there an advantage to hacking off the old plaster/bonding coat back to brick? Looking at kingspan k118 board and using the dot and dab as you were saying but open to suggestions if you think there’s a better board to choose from?

Excellent thank you, I need to do exactly this after christmas. It would be great to add some more details about how you would deal with the interface of the insulation board with the windows? Do you need to worry about condensation occurring on the uninsulated internal wall where it acts as a cold bridge to the external wall and if so how you'd deal with it? I have a feeling I might be overthinking this....

What’s the better solution for the wall? PIR in between treated batten’s (with DPC) and then plasterboard, or go straight to insulated plasterboard with dot & dab?

Insulating under the floor boards is way too big of a job I’d consider using some insulation on top and under laminate instead

Hi mate - you said cover in poly and then said glue to the joists. Doesn't that mean you are just glueing to the poly? I silver taped my PIR and overboarded - then glued joints of boards. I didn't bother glueing to joists as it'd just glue to silver tape...

Great advice as always. Is it an issue dot and dabbing PIR board directly to walls? I was told to batten the wall first then fix to the battens (I had already dot and dabbed to walls before being told this). Not sure the reason, possibly air flow.

Hi there Roger, so the insulated plasterboard from Wickes they don’t have a vapour barrier 50% of traders are telling me if is on a solid wall you don’t need it and 50% are telling me that you need a vapour barrier to the insulated plasterboard as the moisture will go in the foam and start stinking and gets mould . So which one is as it’s very cold and I wish to do this internal insulation asap. And on internet most people don’t tell you exactly what to do with or without?

those premade thermalboards are a rip off at £100 each! get some normal 50mm pir boards and normal tapered plasterboards and stick the 2 parts together with bondit Mega Stik from selco. stack them high. mine took me a 3 hours and saved me £1200

If there is a need to insulate an external wall what would be better out of external insulation or internal insulated plasterboard? The external wall will be getting rendered anyway Thanks

Where the joists meet the brickwork - that's a cold bridge. As you insulate everything else, those cold bridges get colder (compared to what it would have before the insulation). It's a shame that even builders that are aware of cold bridging only know of a few examples.

Tekwarm Thermal Basic Insulated Plasteboard -- is this the product you refer, with regards to the wall ?

Any good ways to suspend the insulation invetween the joists? I have just ordered some fibreglass insulation but its in a roll, not solid to be just push fitted tightly inbetween like others are doing here.

What thickness of insulated plasterboard should I put on a gable wall?

Do you need to insulate all the walls or just the external walls?

im thinking about digging up my cold concrete kitchen floor to replace with insulated block and beam.Would i need to ventilate this?Its one room only.....

Roger, this is timely for me. I have a Victorian End of Terrace house. No cavity on front elevation (gable end is) and I have been considering adding insulation board to the front either side of the Bay window and below. My question is would it be better to remove existing internal render 1st or just board over it? External is rough cast. Thanks so much.

How do you stick roof felt down?

Don't dot and dab. You creat a thermal bridge. Always wooden or metal frame.