As a new forum member its been very educational scanning all the old posts , but its probably time ask for some views on my own project.

Background: 1950's bungalow , 50mm cavity walls, timber floor over airbrack vented void. currently 130m2

Plan: Maintain floor plan but add a complete new roof to add about 80 m2 of room in loft.
Luckily the neigbouring properties have had similar modifications including raising roof lines , so fingers crossed the planning will not be a show stopper.

Objective: Rebuilld the house to a good energy efficiency standard. I'm not on a crusade, but I would like to feel that I had done the renovation resposibly for the future. As such the actuall payback is not the deciding factor, but this is more about living in a house that I know is more energy efficient than most and being able to tell the kids down teh line that we at least tried to do the right thing.

Current thoughts / questions.

Plan to leave current extior walls (but thats about all that will remain) . Am assuming only option is to loose cavity fill.
Roof is probably going to be cut timber with rafters >200mm so should be plent of room for insulation between rafters + another 50 mm on the back of all of them.
Floor is one of teh aireas i'm unsure. Would like underfloor heating and I realise I need to insulate in some way as the draft coming up at the moment is criminal !. So options appear to be insulate between joists and lay UFH in the top of the insulation , or lay a new concrete slab with insulation built in and then lay UFH in screed on top.
Glazing will be triple on N facing wall and double E on S facing walls
Planning a heat recovery ventilation system, and realise that I will have to get the builder to do everything he can on the airtightness of the fabric of the house during the build.
Solar water heating appears to be a no-brainer as does rainwater catchment as both will be easy to do during such a major rebuild.

Am an engineer by trade, so can get my head around technical stuff , but this is a first time house renovation so any advice is very welcome.

Thanks

Appreciate the input

Have thought about the walls , but I need to keep the outside brick for the planners. Initial discusion with them suggested they want not want me to change to render. So i'm thinking that rules out external insulation. I do have a large floorplan so I could lose I little internal space potentialy.

Am also very unsure as to what is best with the floor. I know I absoutely have to do something or i'm wasting my time with the other stuff. The big question is would insulating betwen joists be a reasonable solution or should I go for a full insulated concrete slab.


Cheers

Thanks Tony

what do you mean by proposed occupancy ?

Got it

House will be empty for 6 hours, 4 days a week. Other than that house will be generally occupied.

Builder has suggested total demoloition might be an option, just leaving just the foundations as i'm happy with the current footprint.

How much has to be knocked down for zero VAT to apply and something to be clasified as new build ? I can imagine this is a grey area and it would be a disaster if I failed to get the VAT relief.

Hi,
I would echo the above comment. I’ve met that truculent youth in the post above, had him clumping round my house muttering expletives. Getting anyone even in these times to do work is hard enough. Let alone expecting then to work to standards that you believe in (or even seem obvious). To get workmanship to the level and accuracy you actually require is very very difficult. Not all are as bad as this, of course, but how do you know when you’re getting quotes or even later dealing with them.
This may sound negative, but in my experience the biggest emotional drain in what is un-questionably a difficult process is trying to be sure folk understand what you want and what you need. Not what they want, or always do, or (my favourite moaning mantra) “its good enough for everyone else” – Just reply “if everyone else lives in poorly constructed, poorly ventilated thermally inefficient houses that’s up to them I don’t”. This is where you will have to be strongest.
I hope that this is not too negative – stick to your guns, it’s your house, your money, your dream don’t lose that because others couldn’t be bothered.
Cheers
Mike up North (should be happier than this its Friday)