Cavity insulation

[gaz1]

Summarises the attitude of this forum

All tradesmen are cowboys and will rip you off

What a load of nonsense

Im surprised you haven't linked a video yet

aw come off it the simple answer would be to build a third wall

but builders dont want to do it neither do customers same as on here many dont want to lose the space they have

options for builders to use

knauf insulation board
composite insulation board clipped up by plastic clips

the third approach is build a third wall with insulation inbetween but that loses them size of the buildings digging into there profits

r30 in uk not unless you want 2ft walls

erm we have though 24" thick even burdekin has 20" thick walls

your standared house dosnt

4" blocks with either stone or brick faced 3-4" with a 2 " space if it has knauf or composite internal add another 2" spacing

total size 10"

everything is profit based

dont even get me started on how thin cavity walls are between houses used to be 4 bricks thick now its down to 2 blocks thick or even single 6" block thick

can hear everything including the dog bark

 

[Gareth J]

external insulation has its issues and can cause brick or stone damage

Care to elaborate? As far as I can work out, EWI is a win, win. Improved thermal mass (unlike IWI) increased wall temperatures so less risk of interstatial condensation (again, unlike IWI), chance to renew external coating with one that will be appropriate to the weather conditions.

What's the downside? Fire risk? Bad installation? To be fair, I can't imagine it doing very much good in a cavity wall situation, with wind blowing through it, unless the cavity is filled too.

PS, I'm genuinely interested as it's on my wish list here for whenever I either, can justify the significant cost, the government will help pay to do it or I have sufficient time/enthusiasm to do it myself.

 

[Morris]

Our house had cavity insulation done about 18 years ago. No issues at all and the house is warmer for it.
One of the areas with a lot of problem houses is South Wales where driving rain is common. Proper observance of the guidelines would have flagged them up as unsuitable.

 

[rtcosic]

Our house had cavity insulation done about 18 years ago. No issues at all and the house is warmer for it.
One of the areas with a lot of problem houses is South Wales where driving rain is common. Proper observance of the guidelines would have flagged them up as unsuitable.

Oddly although my 'problem' wall was the largest wall it was downwind of the prevailing winds. The wall that was exposed to the prevailing wind didn't display any symptoms. I agree that coastal Pembrokeshire is the land of horizontal rain though.

The bricks were also an exceptionally hard variety if that makes any difference to their permeability.

Youngest has EWI installed. He specified 300mm on the basis that once you have accounted for all the fixed costs of installation doubling the thickness adds little to the cost.

He now rarely has the central heating kick in at all, but has a challenge keeping the house below 30C in summer! It is a terrace with one face due south and the other due north. The south face has the most glazing! In Cambridgeshire so gets that fenland wind direct from the Arctic Circle

The only slight downside is that the surface finish is rather fragile compared to brick or stone and needs to be treated with some care. Otherwise, I would explore EWI options first.

Edit: can those cavity drains at DPC level and above lintels be retrofitted? Would that make cavity insulation viable?

 

[GRW]

I'm in West Wales, and in a reasonably exposed location.
Houses either side of me had cavity wall insulation.
I figured the air gap was there for a reason - and turned down all the approaches to get it done. I insulated the loft well, but figured I'd rather spend a bit more every year on Oil than get a damp house.
One of the two neighbours had to have the cavity insulation removed after a few years due to damp - while the other was a real shocker. The whole pine end of the house got so wet that the plaster fell off the internal walls from top to bottom, and the internal wall soaking wet. The only way to recover it was to remove the crud out of the walls, AND externally insulate and finish the whole pine end outer wall (with the stuff they use on older houses with no cavity to get the insulation values up).

Meanwhile, I had no issues. (These houses the internal skin is 6" Thermalite block, so a) not something you want to get wet, and b) gives a pretty decent insulation anyway.

 

[Mikes]

Johnser has hit the nail firmly on the head. Regardless of where you add insulation, you need to be careful of interstitial condensation. If you are seeking a quote from a firm to add insulation to a cavity then ask them to provide a condensation risk analysis. This is based on simple calculations (most frequently done within a computer programme but based on simple formula ) and this should show if and where in the structure condensation would occur. If they don't want to carry-out the calc and present it to you prior to you signing on the dotted line then they are not suitable for proceeding with.
The problem with retrofitted cavity insulation is that you can't install a vapour barrier so can end up with moisture being formed which migrates through the wall causing damp. Condensation risk analysis is equally important with both external and internal wall insulation but at least with these there is the option to add vapour barriers which might or might not produce a satisfactory result.
If you do proceed and want a calculation checked then I could easily do this.

 

[Gareth J]

Oh, I also forgot to mention, we do have cavity wall fluff in our very exposed to driven rain south gable end. That's the only bit of cavity wall on the house.

No issues, except a small patch inside which I suspect was down to deteriorating plaster outside. There is fluff throughout, can see it in the loft. Can see a small patch of, presumably missing fluff on thermal imaging camera.

That south end needs attention soon, EWI and wall hung slates would be great but, y'know.

 

[gaz1]

Care to elaborate? As far as I can work out, EWI is a win, win. Improved thermal mass (unlike IWI) increased wall temperatures so less risk of interstatial condensation (again, unlike IWI), chance to renew external coating with one that will be appropriate to the weather conditions.

What's the downside? Fire risk? Bad installation? To be fair, I can't imagine it doing very much good in a cavity wall situation, with wind blowing through it, unless the cavity is filled too.

PS, I'm genuinely interested as it's on my wish list here for whenever I either, can justify the significant cost, the government will help pay to do it or I have sufficient time/enthusiasm to do it myself.

air bricks is the answer

most houses use an air brick for air flow between the cavity

the flow generaly goes up inbetween your wall cavity over the attic space and back down the other side of the house

fiting loft insulation generally only bridges the internal walls therefore creating a cold roof

so fitting external insulation really does nothing due to the air brick and flow of air inbetween

the other issue is your roof side of it

if it fails water can go down the back of the insulation layer on the outside

this is how roof timbers rot at end of the roof to the gutter

Heritage House | BRE report into unintended Consequences of solid wall insulation

bre report into unintended consequences of solid wall insulation - its a disaster

www.heritage-house.org

 

[Morris]

That article is about solid walls using older methods of construction.
Edit. I've read the report cited and it's not condemning insulation in older buildings but points out the potential problems and suggests revisions to testing, materials, surveying etc so that it can be done without problems.
What it does not do is condemn insulation outright.

 

[Edward Teach]

Cement fallen down the cavity during the initial build, filling above DPC, there is the start of a problem !

 

[Gareth J]

That article is about solid walls using older methods of construction.
Edit. I've read the report cited and it's not condemning insulation in older buildings but points out the potential problems and suggests revisions to testing, materials, surveying etc so that it can be done without problems.
What it does not do is condemn insulation outright.

Think that's my fault, I sidetracked into talking about EWI on solid walls

air bricks is the answer

most houses use an air brick for air flow between the cavity

the flow generaly goes up inbetween your wall cavity over the attic space and back down the other side of the house

fiting loft insulation generally only bridges the internal walls therefore creating a cold roof

so fitting external insulation really does nothing due to the air brick and flow of air inbetween

the other issue is your roof side of it

if it fails water can go down the back of the insulation layer on the outside

this is how roof timbers rot at end of the roof to the gutter

Heritage House | BRE report into unintended Consequences of solid wall insulation

bre report into unintended consequences of solid wall insulation - its a disaster

www.heritage-house.org

Yea I can see that EWI on a cavity wall with no in fill insulation is going to be much less effective.

Interesting report, seems to me though that (for my area of interest, EWI on solid wall) it's not saying don't do it, rather, keep in mind potential pitfalls, use products appropriate to building in question and do it right.

Plenty of appropriately breathable options available to maintain vapour permeability and plenty of external render/cladding options to suit different situations.

 

[bricol]

I had an internal cavity wall insulated a few years ago - air blowing up inside it was acting like a really good heat exchanger. I provided the heat - the cavity directed it upwards and kept a few inches wide strip of roof nicely frost free in winter.

Had it insulated and now living room and bedroom actually get warm.

Previous owners had the external walls done over 30 yrs ago - every hole, including for extra windows, has revealed nice dry insulation. Guess I'm a lucky one.

 

[gaz1]

internal insulation is this

gg grant


half grant half not the framing and damp coarse is not

 

[nickk]

Thanks for all the observations and opinions.