Home insulation - cavity wall?

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 The Potato 09 Dec 2019

Anybody in the know on home insulation? Whats the latest thinking on cavity wall insulation, is it better or worse?
thanks

 Jack B 09 Dec 2019
In reply to The Potato:

Are we talking about putting it in at build or a retrofit?

OP The Potato 09 Dec 2019
In reply to The Potato:

sorry yes retrofit

 Jockspotter 09 Dec 2019
In reply to The Potato:

Is it better or worse than what? Its certainly better than no insulation if that is your question? ... but it depends on the structure and the U-value requirements if any. You can have insulation boards, spray fill or rolls. Spray fill is the less intrusive for refurbishment purposes.

2
OP The Potato 09 Dec 2019
In reply to The Potato:

well yes is cavity wall insulation better than cavity wall space

At some point people thought having a space was better insulation than having fill.

Ok so you say getting it spray filled will improve insulation rating, thanks.

Post edited at 11:02
1
 Neil Williams 09 Dec 2019
In reply to The Potato:

Did they?  I thought the view against it was a risk that it might affect other aspects of a cavity wall, e.g. assist damp in getting through.  (I don't however believe it does).

Post edited at 11:08
 JLS 09 Dec 2019
In reply to The Potato:

I have it in my house. It had been retro installed by a previous ower. The house is considerably warmer than the house I'd moved from which was built in 2000 with the same "themalite" block inner skin construction method.

I do however worry about whether long term the infill will compress and create a bridge for damp.

I'd probably not have risked installing it myself for that reason but obviously I did risk buying a house with it...

 dread-i 09 Dec 2019
In reply to The Potato:

I had mine done about 2 weeks ago. Its certainly cut down on drafts. (The house had a number of spurious air bricks. The installers were at a loss to explain why we'd need so many.) The house feels warmer, but that is mostly subjective. I've looked at the graphs on the Tado and it looses less heat over night, but only by a degree or so. It would be nice to export graphs from last year when the temp was similar, and overlay them, but I cant seem to export graphs.

They used polystyrene beads, coated in a heat reflective coating. It took about a day and was fairly painless. In theory it will pay for itself in 3-5 years or so. If you sell your house, you'll be marked down on an energy saving report. A bit of a no brainer really.

 Jockspotter 09 Dec 2019
In reply to The Potato:

Certainly not the consensus anymore and hasn't been for about 20 odd years I believe. It depends on the building, if its timber frame or traditional build? Spray fill is the better option as it required a small hole to be drilled into masonry/brickwork for the nozzle to fit but solid board-type insulation is better for external walls as you really need to have a gap between the insulation and the external leaf to avoid damp transfer issues. Damp insulation is as good as no insulation,.

Rigid Raider 09 Dec 2019
In reply to The Potato:

Quicker and easier to get a builder to dry-line the walls with a couple of inches of Kingspan or equivalent then plasterboard backed with polystyrene foam. You'll lose a couple of inches off the room size but it makes an astonishing difference to the warmth and sound-proofing. If you're doing it before moving into a new house you can also get rid of the previous owner's crap decor and move some sockets and pipes around. 

1
 jkarran 09 Dec 2019
In reply to The Potato:

Retrofit insulation in the cavity will likely cut down on draughts and certainly convective losses in the cavity. The risk if your house is weather beaten, pointing imperfect or bricks quite permeable is penetrating damp. Knowing water gets into my cavities in driving rain I decided against, opting for internal insulation instead which comes with its own risks. External insulation is likely to be the best technical solution if you can live with the look. Often looks ghastly on partially done terraces or half a semi.

Pretty much mandatory for new brick builds and hard to argue against since properly installed in slab form an air gap is maintained.

Your walls might not be the problem.

jk

 JLS 09 Dec 2019
In reply to Rigid Raider:

>"Quicker and easier to get a builder to dry-line the walls with a couple of inches of Kingspan"

That sounds like a nightmare job!

1
 Neil Williams 09 Dec 2019
In reply to Rigid Raider:

That may be superior in terms of the result, but I can't imagine any possible way of it being quicker or easier unless you are in the process of a full gutting back to brick and interior rebuild prior to moving in.

Post edited at 11:35
 summo 09 Dec 2019
In reply to The Potato:

The problem is the air gap is there for a reason. Bricks are permeable, moisture will condense on the inside of them, hence the need for vents and air gaps so you aren't bridging to the inner layer. I think in many instances insulating the wall often just turns it into a solid wall.

Internal insulation is great but lots of work and given the fact many house builders design rooms that you can just squeeze a bed into a room, you can't afford to lose much space. Plaster board and 40mm of insulation internal won't lose much space but will make a vast difference.  You'll  have to redo the trim and sills on windows though, but that's a chance to make sure they've been done properly too. 

Sadly double layer brick / block walls are old tech, functional, but on their own offer limited insulation. They should have been banned decades ago. 

Post edited at 11:45
 MeMeMe 09 Dec 2019
In reply to The Potato:

I don't think there's just one answer. How old is your house?

Cavity walls aren't necessarily all the same.

 Ridge 09 Dec 2019
In reply to The Potato:

Must admit the idea of damp bridging and the potential cost of having it removed has put me off cavity insulation.

The 50mm kingspan on the internal walls works well. I did it on our living room before we re-decorated and it,s made a tremendous difference to that room. It's nowhere near as big a job as you might think if you're going to redecorate. 2” battens, kingspan, plasterboard and coving is dead easy, new wall boxes for the sockets aren't too difficult (get a sparky if you're not happy doing it yourself) and maybe a plumber to move rads. Also a plasterer to skim the plasterboard is worthwhile.

 Billhook 09 Dec 2019
In reply to The Potato:

We had our 1948 house fitting with blown fibre wool (I can't remember the exact make up but it looked like shredded cotton wool).

It was blown into the cavity through smallish 15mm? holes drilled every 3 ft or so at brick junctions through the mortar.  It took only a few hours to do our detached house and if you now llooked at the house you just don't notice where the holes were drilled.  They also used thingamajigs to stop the fill blocking off the airvents below the suspended wooden floor.  

It made a noticeable difference to the overall house temperature, particularily extending the time rooms took to cool down when the heating went off.  We were lucky enough to get a grant for this and I think we only paid around £150 or so for it to be done.

 Munch 09 Dec 2019
In reply to The Potato:

As a builder, we generally don't recommend retrofitting cavity insulation. As said above, the cavity is there for a reason (to keep moisture out). Air bricks are also there for a reason. If you have a joisted floor, you will have a ventilated void underneath. If you block up the air bricks (which often happens with cavity insulation), you will have damp / rotting joists. If you have drafty floors, you need to insulate the floor. As said above, we often insulate the internal walls using as little as 25mm celotex /Kings pan etc with 2x1 batten and plasterboard / plaster. It is more work, as you'll have to renew the skirting / window boards etc, but a better job done. 

 Toerag 09 Dec 2019
In reply to Ridge:

>  new wall boxes for the sockets aren't too difficult (get a sparky if you're not happy doing it yourself)

...as long as the existing wiring has enough slack, otherwise you're looking at a re-wire.

With reference to retro cavity fill, don't do it if the outer leaf is bare brick with cement mortar. The contraction ratio of drying cement means that the cement in the vertical joints ('perps?') is guaranteed to come away from one brick as it dries, thus leaving a crack which rain can be driven through. If the outside is rendered then there's much less of an issue. Personally I'd look at external insulation.

Rigid Raider 09 Dec 2019
In reply to The Potato:

We insulated our son's freezing cold bedroom, which has 3 outside walls and is above an unheated garage, by dry-lining as descrbed above. We also topped up the ceiling insulation to three layers. The transformation was remarkable; the room is always warm and quiet and when he was at home and playing Grand Theft Auto hard on his computer the cooling fan knocking out a few hundred watts kept the room comfortably warm. 

 summo 09 Dec 2019
In reply to Rigid Raider:

> We also topped up the ceiling insulation to three layers. 

Indeed, putting a hat on your house! Lots of people make do with one layer of 100mm, multiple layers over lapping or criss crossing 300-400mm is way ahead. 

 Timmd 09 Dec 2019
In reply to The Potato:

Some people have had terrible problems with dampness after getting cavity wall insulation, going on what I've heard on Radio 4 at least.

paulcarey 09 Dec 2019
In reply to The Potato:

we had it done to our end of terrace 1906- built house which has 13 airbricks ( we need them it's kent and the house flooded in '53 and is still damp in places). It was the cotton wool type material rather than polystyrene balls.

on the plus side. the house is definitely warmer. It was unbearably cold the first winter in here. but isn't brilliant but its better.

Downside - we definitely have worse damp problems. Random patches of damp appearing halfway up the wall and all round the bay window probably showing where water is bridging across.  We are considering removing it from the front wall of the house.

 La benya 09 Dec 2019
In reply to paulcarey:

Still damp 60 years after the flood! You need to stop being cheap and turn the heating on 😅

paulcarey 09 Dec 2019
In reply to La benya:

Lol

all the houses are like it in area. Damp and salts from the seawater still coming out of the bricks. And there are loads of springs in the area to make it worse

 jasonC abroad 09 Dec 2019
In reply to The Potato:

Got it done for free in my last house, there was a government run scheme, it worth looking to see if it is still running, we were not on benefits etc but still got it.  Made a big difference and the cupboard under the stairs stopped getting mouldly.  Didn't have any trouble with it.

Rigid Raider 10 Dec 2019
In reply to The Potato:

We are building a timber-frame house in Scotland. The complexity of the build and the precautions against damp and air penetration are something else, the regulations nowadays really are extraordinarily tight and precise. The walls will be about 18" thick, most of it insulation and extra insulation.

 summo 10 Dec 2019
In reply to Rigid Raider:

Presuming you are having different layers or heights of battening and insulation, either side of timber framing? So there is no solid direct line from inside to out? Some form of membrane under the outer most layer? 

450mm ish sounds thick. 300-350mm is more normal even in the nordics. 450 must be carbon neutral, zero heat loss and then some for luck.  

Rigid Raider 10 Dec 2019
In reply to summo:

The word "about" is key to my estimate of the wall thickness. We are having the "medium" level or insulation, U Value to equal or better 0.17 W/m2K, which is in between Building Regs standard and passive haus. Here's a cut and paste of the bits of the spec. that cover the external walls:

50mm cavity with perpend cavity vents @ 1200mm approx centres at top and bottom of each wall area excluding mid-floor level (ventilated intumescent cavity barrier fitted horizontally to maintain ventilation within the cavity under normal circumstances).
FR 30 rated cavity barriers to be fitted around all openings (windows, doors etc.), and vertically down each corner of the dwelling.
FR 30 rated ventilated intumescent cavity barriers to be fitted horizontally at mid-floor level, maintaining ventilation within the cavity under normal circumstances.
External timber frame wall panels of 140mm thick pressure treated framing, clad with 9mm OSB boards, all as designed by the Structural Engineer/Timber Frame Manufacturer.
Holding down straps, truss clips and stainless steel wall ties to be fitted in accordance with the Structural Engineer’s detailed specifications and Timber Frame Manufacturer’s recommended centres.
Glidevale Protect TF200 Thermo, or equal, insulating/foil faced breather membrane fixed to exterior sheathing, with laps taped up in accordance with the Timber Frame Manufacturer’s printed instructions.
140mm thick Knauf Frametherm Roll 40 (0.040 W/mK) glasswool insulation quilt fitted tightly between framing.
Polythene Vapour Control Layer and air barrier fixed to the studs/internal face of wall panels, with all reveals/laps taped up in accordance with the manufacturer’s instructions.
25mm thick Kingspan Thermawall TW55 (0.022 W/mK), or equal and approved, rigid insulation boards fixed to wall panels (through the vapour/air barrier membrane).
35mm deep service void created using 35x45mm softwood vertical battens
12.5mm thick plasterboard screw fixed to panels with skimmed finish.

 

 summo 10 Dec 2019
In reply to Rigid Raider:

Sounds good. I think you will better that u value of 0.17. But I guess that's the highest value on the weakest point. 

Post edited at 10:19
Rigid Raider 10 Dec 2019
In reply to summo:

I'm sure they publish pessimistic figures to protect themselves. There is also a standard for the air-tightness of the building, which is actually a measure of how thorough the builder has been in sealing all the gaps. They test it by sticking a big fan in one open door and measuring the pressure drop inside the house - or increase, I'm not sure. The timber frame manufacturer pre-builds the house in their factory using the most amazingly detailed CAD linked to robotic equipment, which cuts everything precisely then nails it all together. Really impressive. 

 Tringa 10 Dec 2019
In reply to Rigid Raider:

> Quicker and easier to get a builder to dry-line the walls with a couple of inches of Kingspan or equivalent then plasterboard backed with polystyrene foam. You'll lose a couple of inches off the room size but it makes an astonishing difference to the warmth and sound-proofing. If you're doing it before moving into a new house you can also get rid of the previous owner's crap decor and move some sockets and pipes around. 


Agree. We have a small extension to the house which was always cold. I found out by poking in the plasterboard that it was a single skin of breeze blocks and the only insulation was the polystyrene stuff you get in a roll that was about 2 or 3mm thick.

We had a builder strip the outside walls back to the breeze blocks and insulate it with 50mm Kingspan, then put in new plasterboard. As said above the difference is astonishing.

Dave 

 gergorlan 12 Dec 2019
In reply to The Potato:

i'd get a firm that is an accredited installer of a Cavity Wall insulation system, and ensure that the manufacturer/supplier has  a back up warranty system. ensure that you have an interstitial condensation analasys carried out. A guarantee by a installer is worth nothing if the firm goes under.

consult with your mortgage company and building control.

 gergorlan 12 Dec 2019
In reply to Rigid Raider:

just a note regarding Passivhaus 'Standard' --regarding U values, 0.15 is the worst U value you are allowed for a Passivhaus-- but what you are actually allowed to have depends on the size, form factor, area of glazing etc. so in practise you will often have to have a wall with a U value of 0.13 or 0.1.

a Passivhaus triple glazed window loses 6 times more heat than the wall so if you have a lot of glazing then you will have to increase the wall U values to compensate

 Neil Williams 12 Dec 2019
In reply to dread-i:

> I had mine done about 2 weeks ago. Its certainly cut down on drafts. (The house had a number of spurious air bricks. The installers were at a loss to explain why we'd need so many.)

Sometimes badly placed airbricks can themselves cause issues.  I had one in my kitchen which was behind a unit with a hole at the bottom, and so all the hot air went out of it by the chimney effect (there was a permanent breeze).   I redid my kitchen without a unit over the top of it and fitted a grate, and now that doesn't happen.

Post edited at 15:09
 blurty 13 Dec 2019
In reply to The Potato:

Another builder here, cavity insulation is generally a bad idea, both in terms of damp/ water tracking across from the outside, and also condensation forming in the cavity insulation when moist warm air migrates from the inside of the house and reaches the 'dew point'. 

Consider either external insulation +render (Butt ugly, I wouldn't do it) or lining inside with high performance (expensive but thin) insulation & plasterboarding.

Cavity insulation settles over time and becomes a wet heap in the bottom of the cavity.

'Spurious' air bricks? - It all made sense in the days of coal fires and the area of air brick required was carefully regulated at the time.

 Siward 13 Dec 2019
In reply to blurty:

What are your views on insulation, clad in larch, probably with a membrane somewhere? I am thinking about - in the long term- cladding our mostly single skin brick house (which has been rendered in the past) with something along those lines. Internal insulation just wouldn't cut it without destroying all the internal features.

 blurty 13 Dec 2019
In reply to Siward: I’d never use timber cladding on the outside of a building  - too high maintenance. The vapour check membrane would need to be on the inside face of the inside wall, difficult!  
 

rockwool and render would be my advice  

OP The Potato 14 Dec 2019

This is exactly why I asked this question, theres still a lot of variation in advice regarding cavity fill

seems like condensation is a big issue, so ill probably leave it. Insulating inside is not an option at the moment and I cant afford an external+rerender.

No matter, thanks for the input everyone.

 Jamie Wakeham 14 Dec 2019
In reply to The Potato:

I wouldn't dismiss it out of hand - it's very dependant on your house's exact construction and its location.  If it's bare brick,or exposed to high wind and driving rain, than it's a pretty poor idea because it'll provide a moisture bridge.  OTOH if you're sheltered, and have painted render, then it's a pretty good idea because very little moisture should be getting into the cavity in the first place.

We're very much in the second category and it's made a huge difference - as a poster said above, it makes the house 'hang on' to heat for far longer.

Any decent firm will give you an industry-backed 25 year warranty.


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