Exterior, pumped and interior insulation

[rkinsella]

Hi folks,

We are doing a substantial renovation of our house (gutting).

The wall cavity is pumped with something of an uncertain thermal value, some kind of foam that was done long before we bought the house.

The architect has specified has specified 100-120mm of exterior insulation. When I asked him, why we wouldn't remove the existing foam and start again. He said that even if we re-pumped the walls that the 50mm gap in the walls wasn't enough to reach our target energy rating.

As it happen my parents are also having insulation work done at the moment, they are having interior insulation fitted. Talking to their installer, he reckoned that interior insulation was going to do a better job at the expense of making rooms smaller.

So I am getting tired of all this third hand conflicting information - is there any decent source of this kind of data (that is consumable by mere mortals).?

Thanks,

Ray K

 

[tomfe]

If you're rendering anyway i would go for external wall insulation, helps with airtightness, don't have to worry about thermal bridging etc.
Internal is cheaper lower skill set.

 

[John D v2.0]

Personally I'd always prefer external, as above thermal bridging, condensation risk, loss of space, hard to hang things on the walls otherwise.

 

[Adam182]

Currently undergoing a full house renovation myself, having removed all the old plaster and dot and dabbed 38mm insulated PIR board the difference it has made already is obvious.

 

[oldbutnotdead]

If the external layout works, EWI well done will give you better results- additional protection from the elements, the house structure is on the warm side so will tend to be dry, the house structure becomes a thermal reservoir, you don't reduce room size.
There are downsides with EWI- if the roof overhang is small or nonexistent that'll need attending to, if you have a gable end with not much overhang that too. Any service pipes (drains, gas, water) will need moving or working round as well.

 

[rkinsella]

Thanks for that - the roof overhang is 230mm - so we should be ok.

 

[Bonni]

A mixture of things here. Personally, I don't and won't have render so I wouldn't go down the external route. Render to me is something that cracks in time and needs painted.

If it was my house, the cavity insulation would be removed, bridging the cavity is a no no. I would then dot and dab insulated boards on the inside, 55mm. Yes, you lose some room space, but then I would have nice clean flat plastered walls. If the house is gutted and the walls are going to be plastered anyhow, then internal insulation would be my way forward. It just means losing 2 inch room space on the inside face of the external walls.

External insulation and render are open to the elements, especially water. I know what the 'experts' claim about their products but rather than just having brickwork to maintain once in a blue moon, I can see external insulation with render and water penetration a problem 10, 15, 20 years down the line.