External Wall insulation

[Flipjango]

We're just about to start renovating a 1910 detached brick house. Three walls (sides and back) are all rendered with cement render that has failed and needs to be removed, and I'm looking into options for insulating the house whilst we've got it all in pieces - whilst trying to keep costs down. There is a lot of penetrating damp in the walls which I'm keen to keep breathing, so we're looking for a more traditional/natural solution. Either we insulate the internal walls with something like Warmshell (which could cause problems as it would mean taking off all the plaster which has picture rails, skirting boards etc, and the window edges are not very deep), or insulate externally whilst we render. External insulation seems like a better idea in theory as its less disruptive, but if we do, we have two problems. Firstly, the front of the house is brick and we don't want to cover this up so I'm concerned about whether this will create thermal bridging problems if we don't insulate this section. Secondly we also have the issue of how a thicker render to the side walls looks where it meets the brick walls to the front - will it stick out really far and look strange?

So I'm looking for two pieces of advice please. Firstly, can anyone recommend which external insulation system is good (I've looked at warmshell and ecoCork so far. I like the idea of ecoCork as its thinner but I can see that the insulating properties aren't as good).

Secondly, does anyone know about the thermal bridging issue on the front wall? Would it not really be worth bothering if we don't do anything with this wall? Its north facing and not particularly exposed.

 

[Zebra]

I don't know which system to recommend if you are looking to get it as thin as possible. I used 100mm woodfibre EWI, and altered the eaves and windows. However, I don't think it's necessarily true that it's not worth doing if you can't do it all. My experience is very limited but I've got some walls which have less insulation, some where it's internal rather than external and some - the fireplace and chimney for example - which have none, and haven't experienced cold bridging or condensation other than on small isolated areas, such as the back door sill.
As for the junction between side and front, a render bead would usually be used for a vertical edge, and this might not look too pretty or traditional, especially if the render is thick. You could stop the render a little back from the front, or do the corner and then stop on the front of the house, but you can't really get away from having an edge. I suppose you could make your own timber edges if this is any prettier.

 

[MikeG]

This is always going to look odd. Really odd. On the front elevation you'll see brick, then a thin stripe of render down the edge (the width of whatever insulation you choose), with a big overhang at the plinth, and a rendered side. There is nothing you can do to make this look anything but odd.

You might have somewhat misunderstood the notion of thermal bridging (usually called cold bridging). This occurs where a design element means the insulated envelope is penetrated locally, allowing cold to bypass the insulation. Having a whole wall uninsulated isn't cold bridging. It's just having an uninsulated wall. It will behave as it does now.

 

[Flipjango]

Thanks guys. We've decided to use something called Bauwer light, which is a breathable insulated render product. We'd only need 50mm to bring up to required standards, which we're hoping to do by adding 30mm on the outside (hardly any thicker than the blown cement render we've just had removed) and 20mm on the inside, with 50mm on the inside only on the front elevation which is bare brick on the outside and won't be rendered. Hopefully this'll work!