I am currently looking to renovate, extend and add first floor to my bungalow in Bournemouth.
Whilst doing this I would like to increase the property’s green credentials as much as my budget will allow. I have cavity walls but would like to bring them to a renovation u value.
I have been looking for suppliers of external wall insulation but drawing a blank in this area, my architectural technician is suggesting internal insulation and cavity wall insulation but don’t really want to lose the space and my understanding is external wall insulation is better due to potential issues with condensation with internal insulation and cavity wall insulation.
Current build is brick cavity walls with timber suspended floors, 4 inch joists around 350 centres
Also trying to decided between insulating between the joists and using spreader plates for underfloor heating or taking out the joists, using hardcore to fill void (around 500mm) insulation and screed system.
I would like to use bamboo flooring throughout the house.

Can anyone help please?

Main questions
Any external wall insulation suppliers in Dorset?
Is worth paying the extra for external wall insulation I will need to render with a 0.7 m band of brick slips (planning permission). I have got one price from Welsh company of around £15,000. They will install from ground level to soffits, have asked for Kingspan kooltherm to keep insulation to 50mm to reduce amount soffits would have to be extended.
Any advantages/disadvantages to the different ufh system for ground floor.
If I go with screed can I use eps for insulation in the floor rather than celotex to reduce the required amount of hardcore ( my understanding is this would require me to double the thickness of insulation to 200mm but not sure if it would take the weight)

Yes, EPS sheets for EWI and you must also fill the cavity with say graphite EPS beads to eliminate thermal bypass.

EWI should go down into the ground as far as possible,

If I were you I would forget hardcore and fill the void with eps sheets, possible concrete and screed on top or a floating floor.

Bamboo sounds nice, if you go floating floor I would recommend a system to clip pipes into and t&g ply rather than chipboard under the bamboo with osb as a cheaper alternative.

Thanks for your response everyone.
Quick question re the eps. I currently have bare earth in my void, would I need to put in a concrete base to seal and level out before adding the eps insulation. Any idea what grade I need or would any work?

Tony any reason for going with eps rather than Kingspan cooltherm for the ewi?

Delprado would love to see your project, my little boy is 18 month so can definitely feel your pain with a new born. I managed to get my current flat finished a couple of days after coming out of hospital. He was early! Not sure how to exchange contact details on here is there a private message feature?

Posted By: SarahLWQuick question re the eps. I currently have bare earth in my void, would I need to put in a concrete base to seal and level out before adding the eps insulation. Any idea what grade I need or would any work?

You need a smooth surface, so the usual base underneath EPS is a sand blinding layer. If the load above is just a room, then any grade is fine; if there are any loadbearing walls or other specific heavy loads then you would need to calculate the correct grade.