Internal Insulation and Chimney Breast

[Routers]

Hi,

We are just about to start a refurb on our 1920's detached house. Although we have a small cavity (60mm) we aren't convinced it is sound and therefore are reluctant to get cavity wall insulation due to the increased risk of damp. We are instead leaning more towards internal wall insulation on the external walls. We aren't worried about the loss of internal space that comes with internal insulation.

We will be looking to take the old plaster off and will just be left with bare brick. We thought that the Knauf Thermoshell system looked good but I've just found out they have taken this off the market. http://www.knaufinsulation.co.uk/media/915296/kine1089gid_-_iwi_design_guide.pdf

I wondered if anybody can recommend something along the same lines? I've seen the Insulated Kingspan plaster board but not sure how effective it is.

We also have lots of chimney breasts throughout the house on external walls (every bedroom and in livingroom/ sitting room) and wondered what we do about insulating them? Most of the chimneys won't be used and are capped off but we want to retain them. Do we therefore insulate across the front of the chimney breast or do we leave it. Leaving it seems a bit odd as in my mind defeats the object of insulating the other external wall in the room of we don't bother with the chimney breast wall.

I've also read that you need to avoid thermal bridging by continuing the insulation below floor level and returning it 600mm on the adjoining internal wall. Is this supposed to be at the same thickness (guessing 100mm)? Surely by doing this you are left with a step on the internal wall. The only way to avoid this step would be to carry on the insulation all the way along the internal wall which would obviously mean further loss of internal space and increased phaff around door frames. Is there some magic insulation that you can use on the returning wall that won't result in a step but prevent the thermal bridging?

Thanks in advance.

 

[jeds]

Kingspan thermal laminate - or equivalent - is the best solution. Don't batten, just fix direct to brick with mech fixings. Not a lot you can do about returning along internal walls. One solution is to use a thinner laminate (25mm instead of 60mm) but it still needs to go the full length of the wall. The other solution is to just leave it. Yes you'll get a small thermal bridge but that won't necessarily cause a problem and the heat loss will be insignificant compared to your overall improvement. Similarly chimney breasts; heat loss through the breast won't be huge so it's not the end of the world if it doesn't get done. I'd say do it if it is relatively simple but leave it if it causes too much trouble. Also the floor; If it's doable, do it, but ninety nine times out of a hundred it'll be too disruptive. Don't lose sleep over the heat loss though. I've insulated hundreds of houses just like this and can't recall an issue with thermal bridging.

 

[jeds]

Double post.

 

[Routers]

Thanks Jeds that is helpful. We will actually be pulling the floor boards up as well and want to insulate under them, do you have any recommendations for the under floor insulation for the upstairs bedrooms? We are installing underfloor heating on concrete downstairs so will be using the relevant insulation for that but not sure what is best to use upstairs?

 

[Routers]

Sorry one more question, is this the stuff you mean?

http://www.kingspaninsulation.co.uk...herm-K17-Insulated-Plasterboard/Overview.aspx

Ta!

 

[jeds]

That's the stuff. K17 is for dot and dab, which is ok as long as your walls are in good condition and not subject to excessive dampness. Otherwise use K18 and fix mechanically. Insulation is normally used in first floor suspended floors as noise control - it has no thermal value. Filling with 50mm acoustic mineral is sufficient but it's also common to use 100mm standard mineral quilt which is a cheaper option. Whilst the floorboards are up insulate the external walls - between the joists - with 60mm PIR foam.