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While it's unconventional in the UK, an airtight layer on the outside can be made to work. But I would say it needs to be done with a proven wall and roof build up. If not then at the very least a full condensation risk analysis should be completed. I assume the makers of Wraptite-SA can suggest some appropriate wall build ups? Touchwood have the Airtight layer on the outside for their Passivhaus build-up and have gone to some lengths to mitigate any potential risks. http://www.touchwoodhomes.co.uk/index.php/en/renewable/how-does-your-wall-build-up-provide-a-vcl-vapor-control-layer The benefit of doing this is a simpler airtight layer, with fewer penetrations and avoiding the need for a service gap on the inside of external walls.

In the design you inherited, the insulation was probably not designed to be load bearing, since it was only under the screed. Since you are moving this to under the slab, it is now load bearing. What type of insulation are you going with? Just to be sure...is what you are calling the slab load bearing? ie. is there a thicker ring beam and internal beams where the load bearing walls are?

Before I decided on an insulated raft, I was looking at a similar, more traditional, buildup. For a polished finish, then its a "simple" case of concrete screed that is then polished. I didn't go this route in the end, but really liked some Lazenby floors that I looked at, with jots of different shading options. If I remember correctly it was about £90 - £100 sqr m. for pouring the concrete screed through to polished finish. It does require expansion gaps though. I think around 30 sqr m, or 6 linear m is about the max they like to do without a split. Alternate would be a micro-top / micro-screed / skim-coat finish over a standard screed. But I found this was almost as much as a concrete screed, so more money overall.

@Mikey_1980 Very nice floor! Looks very consistent, Is it as good as it looks all over?

Having said a Design SAP is not required for a Conversion, I did actually do one, but for the purposes of RHI. I paid £175 for the Design SAP which included several iterations and will pay an extra £30 for the update to as-built and the filing of the EPC. I used Pebble Energy

My thoughts are that the Title and Plan that are held with at the Land Registry show "general" boundaries, rather than specific boundaries so can't be relied upon to legally define the boundary position. They also only ask for a red line on an OS, so not sure that any additional lines that you put on (a new fence line for instance) would be accepted as anything more than indicative. To define a more specific boundary and declare who is responsible for maintaining a particular fence (Using T Marks as above) I believe would require a Title Deed to be generated that can be included with the TR1 form and hopefully be filed by the Land Registry along with the Title and Plan. With regards restrictive covenants, they are likely to reduce the value. You're inlaws may, not unreasonably, want to be compensated for this. No need to include anything regarding attaching to "your" fence, as long as it is clear that you own it and it is fully within your plot. Your are already protected in law. ie. a neighbour could not do anything to your fence without permission. To do so would technically be criminal damage.

My experience has been that, for a Conversion, a Design SAP is not required, and although an as built SAP is also not required to be submitted to BC, it is required to generate the EPC.

Download the desktop Google Drive app so that your PC keeps a synced copy of what Google is holding on their Servers for you.

It can be another Celotex board product, It would sit vertically off the Celotex on the floor and against the wall. In your case it would be 100mm high so it comes up to the top of the concrete pour and stops the concrete contacting the wall. The thickness is limited by your wall build up, and what is "overhanging" the poured floor, ie. plasterboard plus skirting board, so the upstand is then not visible.

A structural slab is load bearing and would therefore include reinforcing of some kind (steel mesh or fibres etc), and the load bearing external and internal walls are supported by it. The Insulation underneath it therefore needs a similarly load bearing capability, Your Celotex is not loadbearing, so it and the concrete on top will not go under the load bearing walls, it will go between the walls. This means it is likely that that there will be cold-bridging from walls to sub-floor as they won't be isolated from the sub-floor by the insulation. Your UFH will have to work a little harder to replace the heat lost through the walls to the sub-floor. You're likely to be mitigating this with an upstand of insulation between edge of newly poured concrete and the walls, but you are generally limited in how thick this can be. An insulated structural raft fully isolates the UFH from the cold sub-floor, so can generally be left on 24/7 at a very low temperature, maintaining a constant house temperature. Depending on your overall insulation levels and airtightness so may need a higher temperature on the UFH due to losses. That higher temperature and the use pattern of the house may mean it is not economic to leave the UFH on 24/7. Depending on those temperature swings will decide on whether 100mm thick of concrete around your UFH slows the perception of its response time down. It will likely still be OK. But it's no longer the certainty of my original comment.

Agreed, they are offering floating and "grinding" then sealing, so the costs look more reasonable. Will they do this on a structural slab? - a good find if they will. If you are having EPS under your floor, it may pay to hoover the EPS before the concrete pour. The power-floating can/will bring the little white balls of EPS up to the surface, which may not be noticeable when floated, but can become visible once ground.

For a low-energy property, it would be fine. Sounds like what is being offered is a power-trowel finish, rather than a true polished concrete where some form of surface grinding is normally done to expose the aggregate. No issue with that, but you have little control over the final appearance, so any surface cracking in the slab will be visible. Not that that's an issue, as long as that is what you are after. You can't expect the same level of finish as per a concrete screed poured specifically for polishing, or a microscreed designed to simulate that effect. If that pricing is "just" power-troweling and sealing, (not concrete and pump charges) it seems a little steep.

If you're not already aware, as soon as you reverse an ASHP for cooling, the installation is not applicable for RHI. Your predicted RHI payment may be so small that this is not relevant anyway. My experience of talking to installers for an ASHP install capable of cooling as well as heating makes JSHariss appear to have "discovered" the holy grail with his home-brew install. That's not entirely true, as I found some installers with commercial experience capable of designing a suitable solution. There's only a few manufacturers that state their UK pumps are capable of cooling, or sell a kit that can convert them. By no means the cheapest of these is Nibe who sell a cooling module to add to their ASHP's. I haven't bottomed out the control side yet, I'm being lead towards a rather expensive OJ Control system solution, but I'm working on the Home Automation system doing this directly, or understanding why the standard Nibe control is not capable.

While 7w/m2 is very low, on 425m2 that's a 3kW requirement to maintain 21 degrees. A higher input would be required if the house had been allowed to drop in temperature. A wet duct heater may be able to supply 3-5kW through the MVHR, but it will likely need +60 degree water temperature (at least that's what I found). Where do you plan to get the hot water from for the wet duct heater? ie. direct from the ASHP? or a buffer? May be only 2.5kW from the wet duct heater is realistic (again, that's what I have found) However it's not very often that this peak heat will be required. A higher cost lower capital solution may therefore be appropriate so perhaps an electric pre-heat on the MVHR rather than UFH. Personally I need the cooling so I've installed UFH. Even if I didn't I think I would still go with UFH. Note: I'm only at install stage, so my opinion is only theory...

What does PHPP say is your peak heat load? Can you easily supply that through Duct Heating. How about cooling? Is there any risk of overheating, if so what strategies do you have for dumping heat. It's much cheaper to instal UFH in the slab than retrofit...

If that's the one that has a 3mm ish rubber layer under the poured resin then I think it's aimed at a nursery play area type of environment. It's a bit too soft for normal flooring. I was surprised how their standard floor felt (without the rubber mat), I expected it to be hard, but it does compress a little and feels warm under foot even without UFH.

I considered polishing our passive slab (incl. UFH). It was only the lack of control you have over how it will look that stopped us doing it. Ie. If you're polishing a screed: more prep can be done, dyes added and controlled cure to ensure a consistent finish but on a passive slab, with strong concrete, the finish is a lot less controlable. We've now decided on a poured resin. It's very clinical and not a look that suits everyone. But it gives a seamless finish, even over expansion gaps; it's also softer, warmer and better acoustics. By coincidence a neighbour has just put it down in a new build. It will mark and care needs to be taken with things like kitchen fit, there's no dragging cabinets accross it. But hard enough for dog claws not to mark. Maintenance will be similar to a polished concrete or stone, requiring a new top coat (seal) in 5 to 15 years depending on traffic. But can be refinished or colour change at any point in the future. Costs around £75 - £100/m2 which is a rip off compared to prices on the continent. I was quite impressed with Senso Floors UK, but they have just bought themselves out from their Dutch partners and are now branded as Sphere8, should be the same quality, but I haven't been back to them yet.

You may not require SE calcs at all for a strip foundation. Are there any unusual features within your build that are producing abnormal loadings, or do you have "difficult" ground conditions? If not, your Main Contractor should be able to agree depths with Building Control during the excavation, there are some pretty standard rules applied. However, what's stopped you going the insulated raft route. Is there a technical reason for your specific site conditions? If not, a passive raft may well be cheaper, with a lot more benefits beside.

I'm going with a Tata Colourcoat Urban. I'm not personally doing it myself, but they do put a short course on to teach you how, and others at ebuild did just that. Ball-park cost came in at £40ish /m2

I can only imagine that was an all consuming experience. Enjoy the break!

Sounds like anarchy to me

I found this a really useful, and surprisingly accurate, tool at the conceptual design stage. With it I identified the "sweet spot" for wall and roof thickness as well as U Values for windows and doors. The "sweet spot" being the level at which further improvements did not garner cost-effect improvements. Just in case, I ensured +/- 50mm on roof and wall thickness, over the identified target values, would still work with room sizes and window/door positions, but I needn't have worried, using PHPP at the detail design stage just confirmed the same values. To put it into numbers, the "Fabric and Ventilation Heat Loss Calculator" identified of a little over 8kW worst case heat loss for my build. PHPP with all its extra layers of detail analysed the heating requirement as 5.0kW. The difference being the solar gain. Kicking off the PHPP phase in the right ball-park for all the main U values allowed us to concentrate on strategies for mitigating the solar gain for our build.

Congrats Mike!

Decision has to be within 56 days, so there can't be a "long drag". Just make sure you understand all the caveats to the PD and ensure you present your barn correctly. I've seen a barn get refused just because it had been used to store logs for the house log burner and was therefore not solely used for Agriculture.

Welcome, and good luck with the barn. Have you got PD approved yet? My conversion is just underway of a steel portal framed cow-shed to dwellinghouse. Planning via Class Q PD.