EXTERNAL INSULATION TO EXISTING CAVITY WALL

Builderfromhell

Looking at adding 150mm EPS external insulation to an existing wall made up as follows; 100mm block wall, 50mm Polystyrene insulation board, 50mm cavity, 100mm outer brick wall.

I know the weak point is heat rising in the cavity and escaping at the top - Thermal looping. This can be stopped by filling cavity with pumped insulation.

I am trying to think of an alternative to pumping insulation into the cavity to prevent Thermal bridging. One idea I've had is to drill 10mm holes every 300mm approx along joists in attic and spraying expanding foam into cavity at roof joist level only, thereby stopping warm air escaping in gable end of house.
Cavity should be closed below wall plate but thinking of drilling holes and spraying aerosol cans of expanding foam insulation in here so it will expand down into cavity by about 300mm thereby stopping warm air leaching out here too.

I would appreciate any views or opinions. I can't find much on-line.

Thanks

BryanF

Your post is confusing.

Is this a 'cavity block wall'?

If so,
Externally insulate, down to foundations, overlap with the windows, and lift the tiles/slates to seal an Epdm and insulation over top of the wall to meet ceiling vapour barrier/insulation

Builderfromhell

Thanks Bryan, I have edited my initial post for clarity.

shugy

BryanF wrote: »

Your post is confusing.

Is this a 'cavity block wall'?

If so,
Externally insulate, down to foundations, overlap with the windows, and lift the tiles/slates to seal an Epdm and insulation over top of the wall to meet ceiling vapour barrier/insulation

Is that on a newbuild?

Builderfromhell

Hi Shugy,
It's an existing house made up of an inner leaf of blockeork, cavity of 100mm with 50mm Aerobord in cavity and 100mm brick outer leaf.
We are proposing to add 150mm external insulation and are looking at best and affordable ways to avoid Thermal looping. That is where the warm air rises in the cavity and is lost where it leaves the wall at the gable or around the wall plate.
I am considering buying cans of expanding foam insulation, drilling holes in wall along line of ceiling joists and below wall plate and spraying expanding foam into the cavity. The purpose of this is to stop warm air rising in the cavity.

It is my understanding, that unless I address the heat loss from rising warm air in cavity the External wall insulation will have little value

Calahonda52

Lets get the tech spec language sorted here first.
If I read your posts correctly :
The purpose of this is to stop warm air rising in the cavity.

You then mention Thermal bridging and Thermal looping, almost interchangeably.
From an article on Thermal looping
In basic terms Lecompte (1990) found that the correct application of insulation in a cavity is vital to avoid heat transfer by natural convection or air flows through the insulation layer. Simply put, bad workmanship that leaves air gaps in the insulation and/or cavity had a devastating effect on the actual U-value W/m2K of a partially filled wall. This movement of air is also called a Thermal Loop as the air moves around the cavity in a loop.
https://www.kore-system.com/blog/bid/74137/Cavity-Wall-Insulation-The-Devastating-Effects-of-Thermal-Looping

So decide what you are trying to do and keep us in the loop:D with an updated post, paying close attention to what BryanF penned.
Thanks

BryanF

shugy wrote: »

Is that on a newbuild?

No

BryanF

Builderfromhell wrote: »

Hi Shugy,
It's an existing house made up of an inner leaf of blockeork, cavity of 100mm with 50mm Aerobord in cavity and 100mm brick outer leaf.
We are proposing to add 150mm external insulation and are looking at best and affordable ways to avoid Thermal looping. That is where the warm air rises in the cavity and is lost where it leaves the wall at the gable or around the wall plate.
I am considering buying cans of expanding foam insulation, drilling holes in wall along line of ceiling joists and below wall plate and spraying expanding foam into the cavity. The purpose of this is to stop warm air rising in the cavity.

It is my understanding, that unless I address the heat loss from rising warm air in cavity the External wall insulation will have little value

Thermal looping?!?
Pump the cavity !

Job done

893bet

Given the expensive of the application of external insulation it seems penny wise pound foolish not to pump the very small cavity.

Builderfromhell

Thank you for comments.
I admit I am trying to save on the cost of the often recommended solution of pumping all the cavity with insulation. It would appear to be a fool proof solution.

Before going ahead and pumping insulation to fill the cavity, thereby stopping any warm air entering the cavity and rising and being lost, I had hoped to achieve the same result by partially sealing the cavity with pumped insulation as described earlier.

I started the post in the hope of finding alternatives to pumping the cavity with insulation,

Thanks for feedback