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Author Topic: Cavity Wall Insulation advice please  (Read 3013 times)
todthedog
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« Reply #15 on: August 28, 2017, 07:43:01 AM »

Will do Patrick. Quite a lot on YouTube. The insulation looks straight forward not so sure about the coating. Could be problematic as all the other houses are brick clad. It is job that I want to do once! surrender

Certainly less faffing with electics and radiators
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pdf27
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« Reply #16 on: August 28, 2017, 08:04:56 AM »

Will do Patrick. Quite a lot on YouTube. The insulation looks straight forward not so sure about the coating. Could be problematic as all the other houses are brick clad. It is job that I want to do once! surrender
Would it be possible to get someone to come in to do the rendering bit? That's a different trade to the insulation, and if it's all at ground level might actually be quite reasonable.
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Countrypaul
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« Reply #17 on: August 28, 2017, 08:16:24 AM »

As well as a through colour render on EWI it is also possible to get a brick finish so if the local area requires that it is a brick finish that does not stop EWI. No idea on cost though.
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dimengineer
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« Reply #18 on: August 28, 2017, 10:19:05 AM »

I can confirm the issues with added CWI. I've a 1920 detached house in suburban West London, with early cavities - must have been one of the first. Externally rendered. Adding CWI has definitely improved the thermal performance, but also definitely added damp. Its not dreadful, but its definitely there. One of the realities is that closing the cavity massivily reduces the ventilation, so any damp issues that were there (and on a 90 yr old house, they are there) were self-sorting - ventilated away. Now they are not.
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biff
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« Reply #19 on: August 28, 2017, 10:49:24 AM »

 Loads of cavity wall built houses in Tonbridge,
                                 Dating from before 1900, Galvanised fishtailed wall ties and zinc/bitumen dpc. Spiral flues and purpose built kitcheds. Large well laid out room with 8ft ceilings. All done in Brickwork but to look at it, you would think that the walls were solid because of the courses of headers done in mock  "English Garden Wall Bond" = 3 courses of stretchers and one of headers repeated. The headers were snap headers or Bats, meant to make you think that it was solid.
The technology was already there but somehow got lost in the wars.
                                                                        Biff
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todthedog
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« Reply #20 on: August 28, 2017, 02:20:58 PM »

The problems that I see with external insulation are
1 the render can I do it or will it require a contractor.
2 how breathable is the render, could I end up trapping moisture with nowhere to go but in.

I know internal insulation works and is doable.

If CWI gives problems in dryish west London I think in wet Wales would make it a problem looking for somewhere to happen!



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« Reply #21 on: August 28, 2017, 02:44:30 PM »

I quite wanted to do internal insulation on our current house which we're looking to do up over the next year or so, to keep the front brickwork which looks quite nice. Unfortunately the architects are quite strongly against it, and they seem to be right - if you put more than a certain amount of insulation on the inside, you risk moisture being trapped between the walls and the insulation, which will be cold enough that it then condenses. At least with external wall insulation the structure will be on the warm side of the insulation, so this seems to be less of a problem.
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Countrypaul
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« Reply #22 on: August 28, 2017, 03:08:52 PM »

We have had part of our house externally insulated and rendered. The insulation was 50mm of EPS, 4' x 2' board fixed with large plastic washers and screws. As tothe rendering, how good are you at plastering?

The render was put on by a plasterer, first was a coat of (what I beleieved to be) cement based backing then some mesh, covering the corners of windows, doors etc with 2 layers, then another coat of the cement based render (before the first was set) all smoothed off not quite to a plaster like smoothness but much smoother than sand and cement. That was allowed a few days to dry in our case. A primer was put onto the render and that was followed by a thickish coat of through colour silicone render (3-4mm I guess) which was allowed to largely go off before being "polished" off with a plastic float giving a very even textured finish. He made it look very easy, just like a plasterer makes plastering look very easy!  It is supposed to be breathable.

Some EWI systems put battens on over the insulation iirc, then a cement type board and render onto that.
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splyn
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« Reply #23 on: August 28, 2017, 05:44:25 PM »

I quite wanted to do internal insulation on our current house which we're looking to do up over the next year or so, to keep the front brickwork which looks quite nice. Unfortunately the architects are quite strongly against it, and they seem to be right - if you put more than a certain amount of insulation on the inside, you risk moisture being trapped between the walls and the insulation, which will be cold enough that it then condenses. At least with external wall insulation the structure will be on the warm side of the insulation, so this seems to be less of a problem.

Exactly this - interstitial condensation could be quite nasty. Apart from the potential for the growth of mould, fungi and other rot organisms behind the insulation, how are you going to stop condensation rotting wallplates and the ends of joists? At the least you would use plaster board/thermal boards with a vapour barrier and/or apply (several coats of) sealant and be diligent about sealing skirtings, ceiling joints, sockets etc. But it would be very difficult to prevent warm, humid internal air from cooking etc. getting to the ends of the joists. Even if you could, they are still vulnerable to damp moist outside air or rain penetrating the cavity.

Cavity insulation would help a lot and it may be prudent to lift some floorboards and spray the ends of the joists with preservative and better still drill holes into the top of the joists close to the end and inject preservative with a pressure sprayer or some gravity arrangement for a few hours/overnight.

How big a problem this is in reality is another matter and may only come to light a decade or more after insulating - but I'm sure there are some here who are well clued up on this issue.

You also have the problem of thermal bridges such as a brick internal wall. Where it joins the exterior wall it bypasses the insulation and being much colder than the insulated walls is vulnerable to mould growth - perhaps no worse than prior to insulating but in conjunction with other improvements to reduce heat losses to ventilation such as double glazing etc. it may be a problem. At the very least discolouration due to dust depositing on the colder surfaces may be a nuisance.
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todthedog
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« Reply #24 on: August 29, 2017, 08:13:16 PM »

Spoke to celotex and they could see no problems with using their plasterboard insulation bonded products provided the wall was sound and dry to start with.  fingers crossed!
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martin W
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« Reply #25 on: September 03, 2017, 11:54:23 AM »

Had polybead cavity wall insulation fitted around 10 years ago to a 1952 semi, we've had no problems.. Our cavity was a little over 100mm wide so decent amount of insulation...

Are you sure you only have a 50mm cavity?

We are in wales but around 5 miles form cost and not really exposed. Although the road funnels north wind directly onto the house.

House is painted rough cast concrete (a person to paint)...

We did have a tiny bit of damn in corner of hall way BEFORE the cavity wall insulation was fitted. after CWI fitted, small render repair and painting no damp now.

I know several people who have had nightmare with blow fibre insulation... I took the view of painting the outside of house to help stop the water ingrees and using poly beads to stop wicking... seems to be fine for my house...

I'd think if no obvious damp issues now and you poly bead and can paint external for now then it should be fine. I would still ALSO consider external wall insulation as well. super insulate the home especially on a bungalow it should save 400 on scaffolding cost alone....



 
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