Hi, after a decade of reading I am finally not in a position to renovate by house. So, i have decided to start with or without the funds as we are sick of living in a cold, mouldy property.

Built around 1970, brick, block and apppox 50mm filled cavity.

Initially my money is going on squaring the property off with dome some extensions.

Externally insulation applied to the property.

The BI has said i can build a cavity as we have currently and then external insulate to meet reg as i wish to do the whole house, or single skin block 190mm block and insulate — any thoughts on the preferred?

I was also looking at Marmox thermoblocks as a whole retrofit -crazy? Would these need to be added to the internal and external skin, it doesn't look like the do a block wide enough to bridge the cavity? This bring me onto the next question.

The other big/massive job I’m considering is smashing the solid concrete floor and installing insulation, which would tie into the Marmox.

If anyone has any initial guidance it would be appreciated.

O'course 190mm block doesn't exist - except in anticipated arrival of EU-standard sizes at the time of the Regs. So 215 block, to meet the deemed-to-satisfy Reg. But 140 or even 100 block will do fine in many situations, cheaper easier and space-saving - but needs a Structural Engineer's calc to say so.

Posted By: englishjohnsmashing the solid concrete floor and installing insulation

Or leave it untouched: instead carry your EWI in trench down to the bottom of the founds (incl out and over the toe of the strip found), put in a french drain, backfill with Leca aggregate for extra insulation at a price, or sharp clean aggregate as rainwater-permeable fill, wrapped in geotextile optional. As a coffer-dam of insulation, continuous unbroken with the wall EWI, the heat-conduction path distance down thro the subsoil under the house, outward under the bottom of the found, and back up to the garden surface (the main destination of floor heat loss) is greatly lengthened and provides a pretty good standard of floor insulation, without internal dispruption. And the subsoil block forms a massive heat store helping to stablise house internal temperature.

Wall EWI won't make the floor any warmer, as it doesn't interrupt the heat-loss path from the floor; extending the EWI down def does interrupt (lengthen) that heat-loss path.

Posted By: englishjohnBuilding inspector said the min was 190mm which he showed me from a gov document

That'll be the Building Regs; 190mm is the thickness which is 'deemed to satisfy' the Regs i.e. gets automatic approval without calcs to prove structural stability (i.e. to remain flat/straight etc between butressing corners/block partitions etc). Where such butresses are close-ish together, then thinner (140 or 100) blockwork may remain flat/straight but an Engineer needs to do calcs to prove the case.

Posted By: fostertomO'course 190mm block doesn't exist

I know nothing about the subject, but a quick search for 190 mm wall block shows lots of products?

50 mm slab would work IF the substrate was consolidated and smooth and the concrete was of the correct mix and the correct rebar was properly in place and it is laid with care. Too much to get right to avoid failure. Much easier to put in 100 mm with rebar mesh or 150 mm without rebar. (ferro-cement boats have hulls about 20 mm thick so thin gauge concrete works)

Retro fitting UFH is a really big job and I for one wouldn't contemplate it. But if you do want it then digging out the concrete floor to insulate in preparation is the way to go because you don't want to do the job twice i.e. do it now.

I have made big improvements to the thermal properties of solid floors by putting 20 mm of XPS covered by click fit flooring of what ever quality that suits your budget and SWMBO's demands but it adds 30mm or so to the floor height which may be a threshold issue but easier to alter the threshold than dig up the floor.

Wot Tom said about taking the EWI down to the base of the foundations +1

Re the walls - I would go for single block and EWI, as said above easier and cheaper and easy to get any U value you want by increasing the thickness of EWI. If you go down the cavity route you will need wider than normal cavity to get really good U value and if you are not doing the work your self you will need to watch the builders like a hawk to ensure the cavity insulation is installed properly because once the wall is up you can't see any bad workmanship. Over here it is all single skin block and EWI. Even walls of Ytong blocks (a type of Thermalite block) used here have added EWI to improve the U value.
The only caveat is that if the PP demand a brick finish, whilst you can get brick slips for EWI realisticly it would probably be a cavity wall-

Maybe the dream of having an ultra insulated house needs to be met with reality and enjoying a well insulated house.

Extension single skin + ewi. I shall wait to see what the se says about block size.
Existing house with pre-filled cavity + ewi
My existing floor - ceiling is 2340mm so maybe just overlay with 20-40mm and then enjoy life (for a while)

The more I think about it removing the concrete floor seems too much, i could still use overlay UFH.

Ultimately compared with what i have it will be a big difference, hopefully.

On another note, my wife has said my username is akin to someone who sits on the far right, lol. I had never thought of it like that I assume I cant change it?

In a previous house we did have a floor dug out and relaid with insulation, but wouldn't do it again, the cost and mess outweighed the gains. Also a lot of carbon is emitted to manufacture the cement/concrete/polystyrene, more than would be saved by the insulation*. Next time we will lay insulation over the existing floor, as you described.

Actually a lot of the benefits of the new floor came from stopping up draughts where the floor meets the walls, the bottom few inches behind the skirting were not plastered. And getting a warm-to-the-touch floor covering such as wood or thick carpet, instead of our previous thin carpet, which let the solid floor suck the heat out of bare feet! Could be quick wins there? UFH helps with the bare-feet problem but only in the hours of the year when the central heating is running.

*For the same reason, have you considered doing the extension as an insulated timber frame? Much less carbon emissions than conc blocks covered with plastic insulation.

I'm no longer in Aberdeen but haven't changed my user name!

Zero VAT on the retrofit EWI and floor insulation, if kept separate from the extension

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=17827

Thanks, i have just read through that thread.

Work has to be done by a contractor so I can not submit a claim from HMRC thereafter myself.

The builder (who is also a friend) is sole trader and i don't think is vat registered though that could me be misunderstanding the difference between how companies are set up ect. Historically he just charges the cost of materials by giving the invoice from his jewsons account or whoever and then chargers labour on top.

It would be so much nicer if all these materials were just zero rated at purchase, it appears to be a whole lot of extra bureaucracy and paperwork.

Moving onto windows and placement. I have read and looked at lots of ways you all do it like, plywood box pushed out into ewi, larger frame attached to external wall by ordering a larger window ect. As I’m creating new openings is the idea of creating these holes bigger, running the ewi back into the window reveals and sitting the new windows in place a terrible idea?