Transition Culture

Have you considered removing a brick yourself to try sucking out the old cavity insulation?
Others things I’d be asking…Are there any signs of mould in the main house or kitchen, and what kind of insulation did they suggest to blow in?

The amount of time, finance and effort that needs to go into retrofitting existing housing stock should not be underestimated… a longer term solution might be to pull all the poorly built houses down and start again!

Insulating everything to a high standard is important, but doing it in a way that doesn’t lead to other problems, such as damp from lack of ventilation / or lack of breathability in walls, needs serious consideration.

Hi Rob,
Until the kitchen is Insulated, it must be regarded as a LEAK to the OUTSIDE. A Well Insulated “Door” with draft excluder/s and possibly heavy curtains to draw across – would at least help the rest of the house maintain what warmth you have inside. – until somebody contacts you with -“the correct’ way to solve the problem..

I dont suppose in the first signs of summer, you might PRESSURE CLEAN (water blast) the old insulation out, then take a weeks holiday while the walls dry out again??? I guess that depends on what the walls are made of..?

Tony – Perth

Tony… thanks for that. I have to say the slooshing it out with water solution sounds terrifying, as well as wondering what to do with tons of sodden insulation! These days of course, the summer can be wetter than the winter!

Hi Rob – 2 suggestions:

1: Before worrying about insulation, how are you for draughts? No point insulating until you are completely draught proof. This means everywhere! Maybe even get a pressure test done to spot the worst places.

2: External insulation has come a long way. The Green Building Forum is excellent. I’d solicit some ideas there – the lack of rood overhang may not be as problematic as you think.

http://www.greenbuildingforum.co.uk/forum114/

In the meantime get those teenagers chopping firewood!

To try and identify how bad the current insulation is and where the holes are could you blow hot air into the cavity (assuming the cavity is sealed at the top of the wall) and then put an infra-red camera over it?

I think this is the catch 22 all over the place and what we need to understand to make the correct decisions in my view is to do energy payback periods on upgrades, not financial. How may years to pay back the energy to dry line your walls? How many years to knock the garage and start again? If the payback period is good but the cost is too high, this is where the government could effectively loan the money to the house – not the householder – and the loan gets paid back, any residual amount staying with the house if it is sold. A bit complex to setup but this applies not just to insulating houses, but house that are being repeatedly flooded. At some point these house are going to be abandoned, would it not be cheaper to do it sooner rather than later?

But getting back to your house, if most of the insulation has sunk to the bottom, would it be such a big job, in these days of underutilised tradesman, to take out the odd brick, pull out the rockwool out and put the brick back?

Hi Rob,
Sounds like you’re a bit chilly at the moment…I think there is a solution, but I’m not sure of the cost of the process; you can get an interior insulation cladding. The only down side to this would be that your rooms would decrease in size. Other than that all I can think of is to purchase a very warm jacket and some thermals!

Hope you manage to find a solution

Jennie

[…] This post was mentioned on Twitter by GreenFeed and Rob Hopkins, Health and Beauty. Health and Beauty said: My House Retrofit Comes Up Against a (Poorly Insulated) Brick Wall …: I remember going to Chepstow last year .. http://bit.ly/5aPV2F […]

Govenment grant schemes only work well when the solution is simple. One example is when home owners board over their loft for storage space and then want to increase the insulation in the loft with a grant. To get the grant you have to insulate over the boards (no storage space without lifing and raising the boards) and no grant covers insulation to the underside of a pitched roof! In your case, you could consider Sempatap insulation to the internal walls from http://www.mgcltd.co.uk , which is 10mm thick on a roll and applied rather like wall paper . However, this is not cheap (12.5m roll 1m wide retails at about £182 – ask about local discounted schemes) and requires ‘some’ skill to DIY apply. I agree with the draught proofing comment and TTLewes is running a trial draught busting day project at one local home in Lewes. Perhaps your TTEnergy Group could organise a similar event?

have you come across Sempatap? recommended for solid walls, but might be beneficial: http://www.mgcltd.co.uk/Products/Thermal_and_Acoustic_Insulation/SEMPATAP/

I know that the Centre for Sustainable Energy in Bristol recommends a product called Sempatap for houses like mine (Victorian, therefore solid 9 inch walls with no cavity) I know nothing about it myself but apparently it is a thick padded stuff that is applied to the inside walls like wallpaper, and then can be painted. This site even suggests that it can be applied to external walls.
http://www.enviro-materials.co.uk/products.asp?c=305
Perhaps ditch the cavity wall option altogether and try this?

Might be worth getting some more advice, and quotes.

http://www.glowarminsulations.co.uk/products.htm
“…include reblowing of properties that have already been cavity wall insulated…”
Not sure how that works? Maybe give them a call for some technical advice – 07598 319830

Just to second the recommendation of the Green Building Forum – post the question on there (although you may end up with more info than you can handle!)

I do remember that when we had our cavity filled in our last house there was some hoo-hah about whether there was some exising insulation of a different type in the space between the two semis. We were supposed to have something called a ‘brush’ to separate it from the new stuff, but when the insulation guys turned up they said not to worry as it wasn’t such an issue after all. Perhaps get a 2nd opinion…

We were also told that the yellow type of glass wool is recycled and often you get a choice.

We are having our own (expensive) nightmares with our 1902 house, I feel your pain!
Anybody with advice for solid walls out there?

Hi Rosemary… I’ve insulated our single skin garage wall with Celotex. The wall construction is like this…

– single skin external brick
– 45mm Celotex on internal wall (edges and joins sealed to form a vapour barrier)
– 25mm x 50mm batten (holds the insulation against the wall)
– 12.5mm plasterboard

The Celotex is not cheap but has excellent performance. The pdf’s on the website are quite handy for looking at different solutions: http://www.celotex.co.uk

Rob

According to some-one at a recent community advice session, when they did a heat-scan, they discovered the following in a house with a kitchen extension.

The cavity wall between the kitchen and main house was acting as a chimney between the two areas, drawing heat from both and venting it into the loft above the house. Obviously the top of this wall was not covered by insulation so the rising heat was keeping the loft toasty.

Might be worth checking whether you top-up the cavity or not.

Hi Rob

I would concur with Tom’s advice re draft proofing / air tightness as there is little point in efficient insulation without it. And the green building forum is an excellent resource, growing every day in content and useful advice.

In the mean time isolating the Kitchen area makes sense to at least minimise the amount of heat being sucked into it.

Just be thankful you’re not living in an Irish Stone House without the funds to externally insulate and not enough space to insulate internally!

I know little to nothing about this, but in Germany we often just put polystyrene blocks outside of the wall with a cover of wood or some prefabricated covering. This makes the walls very thick, but warm.

I note that you have the original certificate for the work and would suggest in the first instance going back to Rentokil and seeking their advice. They should be able to advise on how best to extract the original insulation. Or better still, to supplement it where necessary with compatible insulation – especially if they can give you a new certificate for the upgraded work.

BTW, chalet bungalows are notorious for allowing cold air to pass through the first floor structure between eaves levels, taking a lot of heat with it. Hopefully you have got this aspect sorted.

regards

I suppose you could “sacrifice” the brick wall on the kitchen. Add a new outer wall outside it, insulate the new cavity, replace windows with deep-casing framed, double or triple paned windows.

Or learn brick laying and insulation.

What are the modern cavity fills like? …I’ve read a few scary things on damp bridging and it’s quite off putting http://www.askjeff.co.uk/cavity.html

A straw bale expert told me that a good way of retrofit insulating is to use flax or hemp board on the house exterior walls and either render / or batten and plank. Also said it’s really important to make sure the cavity is filled.

Is it just me or has the whole world gone insulation mad – consider your health – your home needs to breathe so you can!

A thermal camera would show the cold spots where insulation was missing and you could fill the gaps yourself (if the company won’t do it) with DIY kits. Maybe one of the nearby Transition Groups has access to a camera; I have heard of one group which bought a camera with a CCF grant. Extrordinary! Another maybe cheaper possibility is with an infrared spot thermometer which does the same job as a camera but doesn’t give a pretty picture. You could go round with chalk and mark cold areas. To do either of these well you’d need at least a 10 degree C difference between inside and outside temperatures. This is the season!

I doubt the company’s suggestion that mixing insulation would cause damp or condensation, unless the house is already very air tight, or already prone to condensation, in which case you should first ventilate the problem rooms better. A recent report in Green Building (admittedly sponsored by Kingspan)found that 90% of moisture transfer takes place through air leakage rather than through the building fabric, suggesting that the breathability of the walls is insignificant factor in moisture movement, unless a house is particularly air tight.

I agree with other suggestions that an air tightness test could be useful, but you can generally find the main leaks by sealing cracks along floor/skirting joins, plumbing and electrical penetrations in cupboards and other suspect areas. Unless you are a meticulous duster of every nook and cranny spiders webs are a good indication of tiny draughts!

Many older houses can have the equivalent of a 1-2 square ft hole in the wall if you added up all the small gaps and cracks. Most can be easily filled with decorators caulk at around £1-£2 a tube.

Sorry I can’t be much more specific but it can be tricky dealing with houses holistically as one thing affects another, people have widely differing habits etc etc…no silver bullets I’m afraid.

Good luck.

Just a couple of points. Don’t get confused by a wall ‘feeling’ cold, it may be warmer than you think. Something ‘feeling’ cold is just a measure of how quickly that material can conduct the heat out of your hand. It gives a comparative measure of its thermal conductivity not its temperature. A simple demonstration would be to place your hand on a variety of objects from the kitchen. Compare a wooden bread board, a plastic bowl, a china plate and a metal saucepan. Each will feel progressively colder but they are all the same temperature since they came from the same room. Anything that is colder than your hand will feel cold. Unless you have the room up to body temperature, everything in it will be colder than your hand.

Secondly we had our walls filled with blown glass fibre. (Apparently this is where most bottles from the recycle bin end up). The installers drilled holes every couple of feet all over the walls and started filling from the bottom, only stopping when the infill started coming out the holes above. Then they moved up to the next row of holes, eventually till it came out in the loft. For weeks some would be wind blown into the porch. This is a bungalow as well but the cavity should never be closed at the top or any where else.

The installers removed every air brick that allowed air under the floors and fitted a sleeve to prevent the insulation blocking these vents. You should also have these air bricks around the house so removing one would let you remove the sleeve and check where the filling is. If you want to check further up, taking a long but small diameter masonry drill and sacrifice a bit of wall by drilling through wall in a few places from the outside. The drill should drag some insulation out with it as you remove it. Only drill from outside to avoid any electricity cables. These should, never run through a cavity wall but take care.

Finally but I should have mentioned this first. A local builder checking some work on an extension we’re having built commented on the trend for filling cavity walls. “Do you know they’re now saying that the air gap on its own is as good as it gets and there’s no need to add any more insulation except in the loft!” This was only a couple of months ago and after the tax payer subsidised all our wall insulation. Don’t know where he got the information from or who ‘they’ are but its something to do with the increasing problems of bridging the cavity and causing damp problems through lack of ventilation in the wall.

I would do all the recommendations received about research but probably only insulate the kitchen, using the grant. Then you can compare the two and hopefully find that the rest of the house isn’t that bad. Draughts are the first thing to check. I’ve just tamped sheep’s wool into the gap below the skirting boards where I could feel a slight draught.

I don’t know if that builder is right Adrian, but I always thought that air was a poor conductor of heat and that is why string vests were good for keeping you warm.
Pete

Hi Rob,

Can I recommend lots more information from you please, before you make up your mind? Building which have been altered over the years & extended incrementally, or parts which have been converted from bits meant to house animals (or vehicles) are notoriously difficult to analyse, let alone decide on the miriad of potential solutions. Internal insulation might give you a solution which allows for a quick warm-up whilst leaving the outer skin(s) to deteriorate. An external skin of insulation might give you a waterproof jacket yet allow interstitial damp to rot some of those residual materials hidden in the cavity, but could also improve the thermal mass of the building (absorb some of your daytime heating for re-release overnight for a more comfortable thermal environment). You might want to discount certain ideas as you have kitchen fittings or services you don’t want to shift. You might want to consider a different roof covering if it’s reaching the end of its life. Feel free to send me lots more photos & info if you need a more detailed analysis, I am very happy to help.

The key to any retrofit is the delicate but important balance between insulation, ventilation (especially in the moisture-laden air in a kitchen or bathroom) & heating.

Another thought on the chilly kitchen! If like this bungalow and in fact many houses your garage was built on the side the house it will be the only room in the house with three outside walls. This bungalow is built on a slope so the previous owner built over the garage so we have a living room with three outside walls that is only used at Xmas time when the whole family is round here and its worth lighting the extra fire. Otherwise we live in the kitchen with only one outside wall and the original living room with only two outside walls. Even if three outside walls are well insulated its still going to be the coldest room in the house. Lining the walls with kitchen units must be some help but often leaves no space for a radiator. You might consider building a lean to shed against an outside wall or if it gets any sun, a greenhouse would become a solar collector so as well as useful for growing plants, could heat the house if you painted the wall black. Just a thought.

Hi Rob,
Thanks for writing this article which is receiving some great responses!
I have a couple of totally different suggestions to make:

1.Why don’t you trade your time for the labour to help you clear the existing insultation and solve the problem? I know you must be very much in demand to speak and appear at TT events–how about asking for some labour in return to help you out?

2. How about trading on your name recognition and contacting The Guardian or Green Building Magazine or similar to suggest they help you through this dilemma in return for being allowed to write about it (you may not want this level of intrusion into your private life, but maybe a series about ‘TT’s Rob Hopkins Retrofits His Home’ would pull up the socks of circulation figures? The companies involved with the materials would get free and very useful media coverage.)

3. How about approaching the different insulation companies directly with a joint publicity/Corporate Social Responsibility proposal: they solve the problem for you/with you either using their products for free or at a subsidised rate. In return they demonstrate their product, and their CSR credibility because anything they do with you they automatically know will become viral in the bloggosphere and media–‘TT’s Rob Hopkins shows the not-yet-Transition-folk how to retrofit their home using Acme Insulation Products…’.

Forgive me if all this sounds dreadfully corporate and cynical–but I think with your customary modesty you might be able to do it without supping with the devil, and also help publicise TT and retrofitting in one go. (Eg you’re already engaging with retrofitting in online forums, but how many mainstream building and insulation companies and their publics are aware of TT? It works both ways.)

4.How about TTs starting a kind of WWOOFing scheme, but doing retrofitting, sustainable building, strawbale construction, etc? People come and stay, offer their labour in return for room & board for a limited period. You get the labour, they learn the skills and permaculture design thinking…

Best wishes with your project!

This probably belongs in the quick-fix string vest section: we’ve double-glazed our windows with bubble-wrap. Cut sheets of bubble-wrap to fit each window pane; spray each sheet with water; attach. It’s quick, cheap, and works like a dream.

There are a couple of options still left to you. I work at Kingspan Insulation, so we obviously have a vested interest in this, but the link here may help. http://www.insulation.kingspan.com/uk/pdf/refurb_booklet_2009.pdf

An option is to use insulated plasterboard,(K17 on a cavity wall or K18 on a solid wall). Although this will take up some room space, the Kooltherm insulation has a lambda value of 0.020. Other methods, not manufactured by us, include Aerogel (a type of nano gel technology) or putting more traditional insulation between battens fixed to the wall. The latter option clearly takes up more.

Hope this help.

Has anyone out there got any experience of using Thermilite insulating paint additive? Website claims that you just add it to paint and it reduces the absorption of heat by the wall. This is a very seductive claim to a very chilly, busy, cackhanded and impoverished homeowner. Too good to be true?

Also take a look at Nansulate (as well as Thermilate). Sorry, I don’t have experience of them.

We have experience of soya-based ‘thermilcoat’. We used it in our kitchen (repainted last summer). It is meant to insulate and reduce condensation. We have found that we had no condensation whatsoever until this very cold snap. So we are planning to use it in our bathroom and other outer walls.

Whether soya based ‘thermilcoat’ works or not, its hardly environmentally friendly to ship it from Argentina or wherever to coat your walls. I won’t touch anything with soyas in it for that reason. As s food its indigestable unless fermented so just acts as a cheap filler whether supended in water as milk or in Roses chocolates where every wrapping warns that it contain soya. The damage to the environment is summed up in this extract from a report from the Guardian back in 2004. “Seven years after GM soya was introduced to Argentina as an economic miracle for poor farmers, researchers claim it is causing an environmental crisis, damaging soil bacteria and allowing herbicide-resistant weeds to grow out of control.” Its now impossible to tell if soya is GM or not. Finally there’s the added CO2 that has NOT been absorbed by the rainforest cut down to grow soya.

While at college I remember a visit to the Building centre where there was an exhibit showing the relative thermal characteristice of common materials. I was amazed to fgind the plain old wall paper was equivalent to several inches of some insulation materials. I would never try and use anything that just treats the effects of condensation. If you find the source of the moisture, a double layer of wallpaper is pretty good insulation. If it starts to come off the damp problem still exists.

Some useful links;

Developing a refurbishment strategy – http://www.greenspec.co.uk/html/refurb/strategy.html
Embodied energy – http://www.recovery-insulation.co.uk/insulation_comparison.html
Insulation comparisons & Life Cycle Assessment – http://www.greenspec.co.uk/html/materials/insulation.html
Kingspan on embodied energy – http://www.kingspanpanels.com/Resource_Centre/Technical-Information/Sustainable-Construction/Sustainable-Insulation.aspx
BBA certificates search – http://www.bbacerts.co.uk/certificate_search_results.aspx?SearchType=Product&KeywordSearch=insulation

Please be extremely careful when making decisions based on the claims made by these ‘coatings’ companies. Although nanotechnologies have their place there are already many proven, simple, renewable and low-embodied-energy materials available for domestic insulation and most of these coatings are very expensive. A little delving revealed the following;

Thermilate – I have requested technical details from Thermilate as they are not readily available on the website. However looking at the testimonials is revealing as it shows the low number of referrals, duplicate names and non-scientific comments to ‘prove’ their efficacy (eg. “The investigator was amazed that the paint was reflecting the warm heat immediately away from the roof, once it had dried on the surface. This was easily noticeable by simply touching the surface.” or “To our excitement, the temperature in the room is now 4 degrees higher”). DEFRA’s report ‘Environmentally Beneficial Nanotechnologies’ says ‘This product does not make use of nanotechnology, but of micro technology, and independent verification of its claims has not been obtained.’
Thermilcoat – The technical test downloadable from was a simple basement room heated ‘before & after’ with no windows, undertaken by the University for Architecture, Construction and Geodesy in Sofia. Despite claims that the material was developed by NASA there is no real technical explanation of how it works or what its make-up is.
Nansulate – has a cure time of 30-60 days. It incorporates a nanocomposite called Hydro-NM-Oxide, a product of nanotechnology. From the H&S report “Nansulate Coating is a water based product consisting of less than 10% dipropylene glycol monobutyl ether, a proprietary styrene-acrylic copolymer, several commercial surfactants and amorphous silica.” and “Avoid eye contact and prolonged or repeated skin contact with the product. Provide good general ventilation is use areas by opening windows and doors. Avoid breathing dust that may be generated during dry sanding, etc. of surfaces treated with the coating.”

Defra also says ‘…. such applications are relatively niche and these products do not appear to be replacements for mass insulation. The cost of such applications will remain prohibitive until the environmental implications are assessed. There is also a range of water based coatings; the Nansulate range of products from Nanotech Ltd which are designed to be applied to residential buildings on walls, metallic and wood surfaces and exterior walls and claim to significantly reduce heat transfer. Such a range of products may begin to address the market gap of insulation appropriate for solid wall buildings, but there is little independent verification of the efficiency of these products so far…….. A technical challenge remains in the aesthetic insulation of solid walls, but claims of the potential of nanotechnologies in this area are tenuous….. There is much work remaining before solutions at the nano‐level represent a way forward for insulation.

Architects generally would suggest you use materials recommended by the British Board of Agrément. An Agrément Certificate is awarded to a product only after it has successfully passed a comprehensive assessment involving laboratory testing, on-site evaluations and inspections of production. These tests are done in identical test situations so that products can be readily compared and you can search for all approved products on their site.

There can be no substitute for a site visit, careful consideration of the existing building & its needs, assessing the available budget & the practicalities associated with any potential option. I would suggest you find a reputable architect or building surveyor & think about a ‘whole-house’ retrofit plan. I will attach some relevant links in an additional post, I find that posts appear out of sync as your moderation hangs on to some of them!

This looks like a magnificent example of one of the more daunting features of ‘transition’ – masses of information/disinformation/old views/wives’ tales/new materials all crammed into a ‘marketplace’, where once we used to have a familiar problem with a tied and tested solution!

New developments in building technology are happening all around us,and some will be superceded/discarded before fully trialled, as better ones come along.
Tempting to suggest ‘sticking plaster’ approach till the upheaval settles and a consensus amongst professionals emerges about best practice. But will it settle?
We’ve just renovated our house (and gained experience of triso super 10, mineral wool,celotex/kingspan, sempatap, hempbatts).All have limitations: I suspect a multifoil, high performance, breathable insulation is about to make most of them redundant.
Hidden moisture can cost more, financially and in terms of carbon emissions, than draughts and cold-bridges.
So, my advice would be, get a professional and get a guarantee that means some thing, or do it yourself in a way that can be taken apart again easily, and cheaply (Old woollen blankets/carpets/tapestries on the walls for the winter)

Hi Cliff,

You are right in that new technologies are happening all around us but sometimes the better product fails because there was more money behind the successful market leader. It sold only because they had superior advertising and marketing, not necessarily a better product. Personal recommendation and unbiased advice (if you can find it) are the best sales tools.

Your last paragraph is the best for the DIYer. I always try to make/do only things that can be reversed so I don’t get put of improving on my last mistake because of all the energy put into it. Screws may cost a bit more than nails and take longer to use but are much easier to disassemble if necessary.

Finally your last recommendation about blankets/carpets/tapestries is excellent. Some of those old castles weren’t always cold and draughty when they would line the walls with tapestries. They weren’t just decoration, they were insulation!

On a slightly different subject, isn’t the Transition movement all about surviving after peak oil and reducing our dependence on it. If we are true to that ethos, surely we should not be endorsing insulation products that are oil based?

Not sure if it really answers your question, but this is an interesting link for others in the same boat …

http://theyellowhouse.org.uk/

Personally I’d tend to avoid miracle products ‘developed by NASA’, especially magic paint.

I’d also avoid Sempatap. With a thermal conductivity no better than mineral wool, and at 10mm thick, it’s effect will be pretty minimal.

Internal insulation has potential problems. With a cavity wall it might be easier to prevent, but with solid walls there’s a real risk you could seriously damage the fabric of a building. With careful detailing it might be OK, but that’s easier said than done.

Hi Seanie,

I agree with you regarding miracle products but I don’t understand how internal insulation could damage the fabric of the building. I would have thought that it was less likely to harm a building than insulating from the outside and accidentally preventing it from breathing.

It is true that insulating the outside has the advantage that the mass of brick or concrete forming the structure within this envelope would act as a thermal store. This prevents you loosing all the heat from a room every time you open the door if the air is the only store of heat. However ideal this might be I think it would be impractical on a retro fit and is best for new build properties. The cost of tiling and cladding the outside would be prohibitive. Many older buildings are wood panelled from floor to ceiling and those pannelled up to waist height were usually an accepted way to keep the rising damp (prior to damp proof courses) from the bottom of the walls, from cooling the room. Four Poster beds and the box beds found in vernacular buildings were one way of creating a small space within a cold building that could be kept warm with hot water bottles etc.

Building a shed within a large room would be an extreme form of internal insulation with a huge air gap.

Internal insulation, particularly to a solid wall, is potentially damaging. By insulating you’re making that wall colder which increases the risk of interstitial condensation. The conventional ‘solution’ to that is to incorporate a vapour check to reduce the transfer of moisture, and that’s what’s recommended by insulation manufacturers. But an effective, continuous vapour check can be all but impossible to achieve. For one thing you’re likely to have joists sitting into your wall; if you get condensation there, your joists ends could rot away.

People have tried a variety of ways to try and address this, but most haven’t been tested over time. There isn’t really a strategy for internal insulation that you could confidently say will work, short of gutting the property and rebuilding a shell within a retained facade. That’s not to say it can’t work, just that it’s a very tricky area and should be approached with some caution.

Seanie, As I remember my physics, condensation happens when warm air that can hold moisture invisibly, is cooled so it can no longer hold that moisture. The moisture then falls as rain, hangs in the air as fog or condenses on any object that is colder than the air. Morning dew on grass, the mist from a boiling kettle that most people erroneously call steam, or a cold mirror in the bathroom. If you insulate a wall on the inside you cannot be cooling it. You are simply preventing the warmth from the room from warming it up so it remains the same temperature as the outside air. For condensation to form on the wall there must surely be an air gap for warm moist air to get into. If you are leaving an air gap then this should be vented to the outside, not the room. Assuming the moisture is within the building from say, the kitchen or a bathroom, then this room must be better ventilated. I understand what you mean about joists into a wall but the underfloor space should be ventilated and insulation put either above the joists or fitted between them. Surely the only insulation to use in these circumstance is a breathable insulation like sheep’s wool or glass fibre etc. Using anything with solid foam or vapour barriers will prevent it breathing and is more likely to be the cause of moisture build up and condensation which, as you suggest, would then condense on the cooler wall and feed mould spores. I think those ‘manufacturers’ want you to buy a vapour barrier to sell you something more. I don’t think you should need one.

Adrian,

I agree entirely with Seanie’s comments (13 January). The issue of interstitial condensation has been well established over a number of years and calculations are recommended to calculate the location of the dew point (the point at which condensation is likely to occur in the construction). This is set out in BS 5250: 2002 – Code of practice for control of condensation in buildings. It is not simply something that the manufacturers have created to sell more product. Manufacturers do however give details of how their own products can be best used to meet the recommendations of the Standard, which should not be ignored. And no, I don’t work for a manufacturer in case you wondered !

When people talk about ‘breathability’ of buildings they can mean different things, but it usually refers to the movement of moisture. Most materials are permeable to vapour to a greater of lesser degree and, most of the time, the pressure differential in a house is from inside to out. The internal air is at a higher pressure, with more moisture, and that moisture will migrate through the fabric of the building to the outside.

With a traditional solid wall that’s not a huge problem. There will be times of the year that you may get interstitial condensation in the fabric of the building but as long as that’s minimal it’s not necessarily damaging. Moisture can still migrate to the outside, partially helped by the heating from the inside. Also, over the course of the season, saturation from the outside will dry out, again partly helped by that internal heating. Some moisture may also evaporate back inot the house, but this isn’t so significant.

If you come along and insulate that wall, you will inevitably make it colder thatn it would otherwise be, and if you use a ‘breathable’ construction, allowing moisture to penetrate through to the now colder wall unhindered, you run a considerble rick of severe, potentially catastrophic, interstitial condensation.

Also bear in mind that other interventions, as well as modern lifestyles, are also likely to have increased vapour pressures internally compared to what the building was designed to deal with; you’ve draughtproofed your windows and doors, you’re blocked up the chimney or replaced it with a stove, you may well be accustomed to significantly higher internal temperatures, you’ve a washing machine, dishwasher, shower etc.

Your generating a lot of moisture just being there, let alone with what you’re doing, and whilst traditional walls may be ‘breathable’ that’s a relative term. They don’t transfer moisture all that rapidly, and your walsl are certainly less permeable than the breathable insulation you may’ve gone and lined them with.

So with no vapour control moisture will pass happily through that insulation and come to a ‘relatively impermeable’ surface that’s also rather cold.

That’s a recipe for disaster.