Comments on content please:
There has been enough debate on this forum and elsewhere to suggest that the ideal is to retain thermal mass and insulate externally. I want to look at the vast number of situations where this simply is not feasible unless it's part of a whole-block approach. Take a Victorian inner-terraced house, for example. The neighbours don't want to insulate externally, to do yours alone would look daft, possibly be a trespass if you're a straight-onto-the-street terrace, and may have probs with cold bridging anyway.
I hope we can discuss the various up- and down-sides, with practical solutions and, almost as importantly, note where a non-green compromise may be required (in places where space is at a premium, for example)
Check list.
1. Space reduction
2. Cold-bridging (between ceilings and floors, at reveals, ?at party walls?
3. Other detailing
4. The importance of achieving the same U-value throughout
5. Air-tightness and breathing walls
6. Types and suitable insulation for such retrofitting
7. Can Green materials achieve low U-values without excessive loss of space?
8. Vapour control issues and mould growth
9. Substrate issues
10. Building Regs
1. Space reduction
This may be an issue when considering internal insulation and needs to be considered before going to far into the technical aspects. To some it may be the overriding decision to others negligible. Certainly the amount of space goiven over to the insulation can vary depending on the type of insulation used and what U-values you may wish to achieve but at a minimum 75mm off each external wall will need to be considered.
2. Cold bridging
Cold bridging will be inevitable but need not be of such a great concern as to scupper the idea. It can be minimised on walls with small returns onto internal walls (fig.1). The most difficult cold bridge area my considered to be the ceiling but if the wall thickness is being extended into the living space the some of the ceiling could be carefully removed and insulation inserted (fig.2)
3. Other detailing
Detailing will be dependent on the type of insulation used and the type of wall to which the insulation is being attached.
4. The importance of achieving the same U-value throughout
In theory any surface with a higher u value than any other is at risk of condensation, and thus mould growth. While typical u values differ for floors, walls and so on, to me the ideal for any house is to have all walls with the same u value, all bits of roof, ditto, etc. Otherwise you could be chasing a condensation problem around the house.
5. Air-tightness and breathing walls
Adding internal insulation may be an opportunity to improve the airtightness of the building. Before proceeding, a good deal of thought should be given to the opportunities for this.
6. Types and suitable insulation for such retrofitting
Most regular insulations could be employed as internal wall insulation but each will have their own particular installation requirements (quirks) . For instance, rigid insulation such as polystyrene can be self supporting so could be used without any supporting framework but obviously it will need fixing in some way so mechanical fixings or some sort of adhesive will need to be employed. Sheep's wool on the other hand will need a supporting framework but may appeal to those who wish to keep to natural insulation or breathing wall principles (see above)
7. Can Green materials achieve low U-values without excessive loss of space?
Yes they can but the user needs to understand that most natural insulations rely upon trapping air for their insulation value. if you plan to use a natural insulation you will need to have convinced yourself that the required space may be taken form the room. 4 inches (100mm) may suffice but six inches (150mm) or more would be best.
8. Vapour control issues
Including, has your chosen board even got a vapour barrier included. Some do, some don't. How good is your vapour barrier?-joints, the life of the 'sticky' on stick tape, etc. Vinyl-type paints often let you get away with a bad underlying VB, but breathable natural paints may not.
9. Substrate issues
Basically, are you trapping stuff behind which will rot? Timber studs (but arguably only if the VB is compromised), wallpaper, lintels. Keith suggested Gypsum plaster, but I have never had a prob with that, provided of course that you are, at the outset, satisfied with the stability of the substrate, partic when relying on adhesive only.
10.
Building Regs
You need this now. If you do work to more than 25% of a thermal element you need to comply. No policing, though. No-one would stop you if you dry-lined your whole hse with a woefully inadequate board which gave a u val of, say, 1.0, instead of the 0.35 required by Part L1B of Bldg Regs
Then close with supporting refs and credits to those inputting.
Nick
Books 
Comments
This does not rule out external insulation indeed it could very well be the best thing to do. A typical row terraced houses will have a wide variety of finishes from brick, rendered, roughcast, painted, fake stone facings etc So why not external insulation. Yes there will be a little cold bridging at the edges but theirs will be worse than ours. Even listed buildings could be done by maintaining the same look.
The rear of the property does not present near so many problems and for sure should be insulated on the outside.
You seem to imply that the party walls need to be insulated -- they dont in my way of looking at it -- so long as next door is occupied then and even in not too.
Chimney breasts dont need insulation and it is also possible that they do not need to be ventilated to the rooms especially totally internal ones.
It is not necessary to have the same u value throughout though it is desirable not to leave any surface cold as it will pick up condensation.
Yes, but a typical row of terraces has facings that vary in thickness from 0 additional thickness (normal brick frontage) to approx 40mm max (stone cladding). A good BR-compliant ext cladding system could add (?) 75 to 150mm, depending on material.
''The rear of the property does not present near so many problems and for sure should be insulated on the outside.''
Accepted, but ext is not nearly so DIY-able, generally, as int.
''You seem to imply that the party walls need to be insulated -- they dont in my way of looking at it -- so long as next door is occupied then and even in not too.''
No, I don't think that they do, but 25+ years ago when we started internal ins the prophets of doom said that unless we returned the ins round the party wall (some said as far as the ch brst) we'd have pty walls covered in mould. We didn't, but I am interested to see if anyone still thinks this is an issue.
''Chimney breasts dont need insulation and it is also possible that they do not need to be ventilated to the rooms especially totally internal ones.''
We-e-ell, still means you will have an area of wall with a u val of abt 1.5 next to your newly-insulated bit with 0.35, or is that my fault for specifically stating terraces, where the ch brst will be be on a pty wall? If so, accepted, but on a semi, end terr or detached, ch brst arguably does need ins. (Tricky with wood-burner, though!
''It is not necessary to have the same u value throughout though it is desirable not to leave any surface cold as it will pick up condensation. ''
Ergo it is *desirable*, if not strictly essential, to have similar u vals, no?
Nick
- 'Importance of vapour control and prevention of mould growth'
- 'Do I need a building regulations application?' (technically yes but....)
J
Also there should be some discussion, perhaps a heading of its own of the substrate that is being overclad. Materials that could rot or deteriorate should be removed before work. This would include wallpaper, paint and even gypsum plaster perhaps.
Perhaps add 'Substrate Considerations' to the bullet list Nick?
N
Perhaps a major portion of this fundamental discussion needs to examine whether the space being closed off is a ventilated space or not. I guess that a completely breathing solution may be deemed suitable where gypsum is involved but maybe extra emphasis needs making about doing dew point calculations in such conditions.
"A solid external wall may be insulated on the inside or the outside. Where it is on the inside a cavity should be provided to give a break in the path for moisture"
Note this is not a ventilated cavity but a moisture barrier, so perhaps could be provided by a Tyvek / Knauf Breathline membrane against the wall...?, however have seen the 'insulation-hard-against-the-wall-between-studs-with-vapour-barrier-behind-the-plasterboard' detail inspected without query.
Also EST best practice guide:
( http://www.energysavingtrust.org.uk/uploads/documents/housingbuildings/ce17.pdf ), makes no mention of a moisture break gap, I suppose the idea being that in relation to existing houses the solid wall has proved its ability to resist moisture...?
Incidentally the EST doc is very informative and well worth a look at... not sure how it relates to the CE184 document...?
( http://www.energysavingtrust.org.uk/uploads/documents/housingbuildings/CE184%20-%20practical%20refurbishment%20of%20solid-walled%20houses.pdf )
RE ventilation lime and cement based things can survive damp and dew point calcs are imperative but I think that the mold growth is a much bigger issue than materials deterioration.
Anybody know of a free interstitial condensation calc software...?
J
J
I disagree with the idea of a cavity or void in an insulated wall behind the insulation it must be going to moulder.
Have argued with inspectors plenty of times about this one.
Personally, I have always been wary of internally insulating over walls which contain any kind of timbers, whether these are lintols or joist ends; or even redundant wooden plugs used for old fixtures such as picture rails. Others seem to have no problem with doing this and presumably in some cases there isn't a problem with rot? However, I don't like any risks, no matter how low.
I'm not sure if anyone has mentioned the level of exposure to bad weather? This should be a serious consideration in my book for anyone considering internal insulation.
An alternative scenario where I would use internal insulation is, for example, a cavity wall construction, where there is a high level of exposure to bad weather; and where the cavity should remain uninsulated for this reason - a contentious point!
Getting on to how it should be installed. Again many variables. I have dot and dabbed PUR laminated plasterboards the inner leaf of cavity construction., especially onto flat plastered surfaces. I would say this can be done without compromising air tightness, though this is yet another contentious point [which probably needs a blob and dob topic of its own]
Others advocate battens, which I would not use, as doing so may create a dank environment where all sorts of nasty mushrooms and pizzas may thrive. Ventilating such a space rather defeats the object in my book, best not to use battens at all.
That’s my twopeneth for now
PS I know it as plasterboard on dabs.
I have come across the howling wind behind scenario but on that occasion the problem was not due to unjointed blockwork, but to air infiltration from between the block wall and the sub floor void. This I think is a common failing on many new sites which are built on sloping ground. Because of the gradient, sub ventilated beam and block flooring seems to be a common method, and as the screed is normally laid last, the perimeter behind the dot and dab walls is not sealed by the screed resulting in air circulation behind the plasterboard.
How about this as a rough start Nick:
Most people who want to upgrade the insulation of their walls will likely be living in a home that has solid walls (i.e no cavity). Solid walls are usually made from brick or stone. if made of stone then the wall will probably be twin skin with the space between the skins being filled with rubble, small rocks, lime and subsoil etc (hence the name rubble walling). Solid walls can (but not always) suffer from or become damp through a number of routes: rising damp, penetrating damp and condensation from warm internal atmosphere coming into contact with the cold wall. It would be wise to determine which, if any of the above relates to a particular wall or building before continuing with the installation of internal insulation. Then the most suitable solution can be adopted. For instance, if condensation is proven to be the culprit then internal insulation of almost any type will likely remedy the problem by warming up the surface.
The above having been said, solid walls are also good contenders for external insulation if the roof overhang projects far enough.
It is also worth noting that external insulation should not be considered on walls that are of cavity construction as most of the heat is actually lost through draughts in the cavity space.
Perhaps a sub-section on "Hazards, perceived or real" might be good?
Example: even here,trying to be "green", there are many site references to various foam based products (eg polystyrene, polyurethane). All polymerised products contain small amounts of un-polymerised material (styrene, urethane from the above examples)these will leach out over time. Both are known health hazards and with the current pressure on making houses leak proof many of these plastics are hardly to be recommended in the living space..
I understand that some suppliers sell 'seconds' Is it possible that thes are the basis of the claims?
Regarding the seconds Mike. This market is usually made up of the foil-backed PUR foams where the foil is coming unstuck in corners or edges. For the manufacturer, it is more economical to sell off the rejects cheap than try and get the foil off and push back through the system. They call it recycling which I guess it is to some extent.
PS: I have edited my previous comment too.
There is readily available acute toxicity data for all these chemicals but where is the data on chronic toxicity (low dose/long term exposure)? Very little such data exists; the research is difficult, expensive and long term - not good for your career prospects as a researcher! Funding is also problematic. The government does not require the building industry to show that its products are safe over a lifetimes exposure at low levels. (A similar scenario exists for pesticide residues in food or timber preservative chemicals).
If you ask about synergistic effects (the effects of exposure to multiple chemicals) AND chronic toxicity then there really is no data.
Warm sealed houses might have significant levels of various chemicals in their air; the analysis is not difficult but is anyone doing it?
That lovely smell you get in a new car is just a few chemicals of the 70+ identified in car interiors. I recall Volvo was attempting to reduce this number - just another reason to get on your bike or drive an old car.
Of course if you smoke or sit around a smoky wood fire your exposure to PAHs( Poly Aromatic Hydrocarbons) means you could argue that you need hardly worry about a few more chemicals.....as Spike Milligan said: Life is a long illness cured only by death.
To answer your question 'why use them'? Mainly because of thier performance/thickness ratio and the fact that natural insulations are often not suited to such varied applications. Also natural insulation is unaffordable [for me]
Good point Tony.
However I do not recall ever seeing a study that compares the risks from nature against the risk from man-made materials. It would make interesting reading.
Lets all remember, especially newbies, that when we talk about airtight homes we don't mean it literally.
Don't get me wrong. Chemicals and man-made products should be watched carefully and use reduced wherever possible.
Out of interest, what is your background and interest Noyers? Are you a chemist?
I am also aware that we are wandering off subject a bit which will not make Nick's job any easier. Shall we start a thread on the subject of plastic insulations?
For me this means build very tight (less than 0.1) and ventilate with a MHRV (See glossary)
Then the air quality is amazing and the above problems and worries non existent unless you only breathe bottled air.
You stay warm and never have to open a window although you can if you want to or need to.
This is a complex argument and might be better dealt with in the GBB if we think that people might start to do it in volume?
I am minded to disagree with such a sweeping statement as there would be many factors at play here and you risk putting a lot of people off from improving the comfort of their home at a time when energy prices are set to skyrocket. What alternative are you suggesting.
I also thought that lower temperatures would mean lower humidity?