Temp

Yes but I would still consider fitting one loop per room. By all means use one central stat so its all one zone but aving a loop per room makes it possible to separate it into multiple zones later if necessary by just adding stats. It also allows you to balance the system if one room is too hot/cold by tweaking the manifold flow rates. In our case we tend to heat the bathrooms for more of the season than the bedrooms so we have the master bathroom on its own zone. The stat is on the wall outside the bathroom with a remote sensor in the bathroom.

Ideally you want a bit more insulation in the floor if you have UFH. We have 80mm and would fit >120mm if building again. It works but in our first winter we had to turn up the flow temperatures - not an issue as we have an oil burner. What will the floor coverings be? With UFH Stone and tile works best, then Engineered wood and lastly carpet. The TOG value of carpet and underlay should be kept below 2 ideally. Special underlays with TOG of 0.6 are available. Carpet with TOG of 1.4 isn't exactly thick shag pile. Some companies make two versions of their carpet with foam rubber or Hessian backing. The Hessian backed versions have lower TOG but may feel a bit hard under foot. Go test some combinations of underlay and carpet. Beware the small print on order forms allowing them to supply either version at their discretion. Small rooms tend to have proportionately less exposed floor area. Proportionately more is hidden under beds, sofas, book cases, kitchen units etc than with large rooms. This can reduce heat output from the floor. You might want to think about reducing the UFH pipe spacing to fit more pipe in the floor.. Costs more pipe but its a lot easier to turn down the flow temperatures than fit more pipe later.

Attenuation (only) tanks are sized to cope with a storm surge. After the storm passes they empty slowly so in theory they are empty by the time the next storm arrives. This type doesn't store water for recycling use, it only slows down the rate of discharge to the drains but thats enough to minimise flooding. Combined tanks that do both Attenuation and rainwater recycling are available. After a storm they drain out slowly but only down to about the half full level. So they still have space for the next storm but also provide some storage.

We had a near identical situation. Clay soil and flooding 100m down the hill. Highways said "they wouldn't want us to make the flooding worse". We proposed an underground Rainwater Storage tank with overflow to the highway drain. The planners approved it discharging the condition without further consulting highways even though ours doesn't actually provide storm attenuation when full. We use it to wash the car, water the garden in summer. These days people are more aware of the need for genuine storm attenuation so you might need to propose a tank that just does attenuation or both storage and attenuation. For example a 3000L tank might store 1500L and provide 1500L of storm attenuation. They need a fairly deep hole with concrete at the bottom to prevent the tank floating out of the ground when empty. Also a nearby electric supply for a submerged pump.

It's just intended to prove you are a self builder not a professional builder trying to get around the CIL. Remember to follow the exemption process to the letter before starting any work on site.

Neighbours pressure OK? Perhaps check the water co website. In our area we get regular water main failures. They have to bridge the fault with hoses until they can fix it, meanwhile we get somewhat reduced pressure.

@Penny926 I have sent a PM.

I have a feeling I know the answer but I haven't actually seen a "grant" for this type of Planning Application. Lets say you submit an application under the Prior Approval/Neighbourhood Consultation Scheme for larger extensions... Are the planners obliged to check your plans actually meet Permitted Development Rules as part of the Prior Approval process? If not then it looks like most people should probably ALSO submit an Application for a Certificate of Lawfulness at the same time. Otherwise you could find yourself lulled into a false sense of security by the grand and end up building something that needed a Full Planning Application. In an ideal world you would hope the planners would check but I have a horrible feeling they don't. Anyone?

Does it have a light or laser and do they work? Otherwise search youtube for vids like..

My choice woukd be to build a cavity wall of block and brick and no paint/render. Would specify a low efflorescence brick. I wouldnt paint or render a solid retaining wall but rendering a cavity retaining wall with the correct drainage should be OK. Not all render is approved for damp conditions, most say not for use below DPC and the whole of a solid retaining wall is effectively below DPC.

Did the planners not say anything about the combined extensions being wider than half the width of the original house? Suppose the original house was 8m wide and the first extension "A" made it 3m wider and extended out the back 3m. If you then want to build a rear extension "B" onto the original house that connects to the previous side extension "A" its width is limited to just 1m. That's because the width of the combined side and rear extension cannot be more than 4m wide (4 being half of 8m). If on the other hand your rear extension "B "did not connect to the previous side extension "A" its width could wider. In practice it could be say 6m wide, just not the full 8m as that would connect it to the first side extension. This is from the Technical Guidance..

People with solar PV are to be charged when they export to the grid...

I wouldnt put wood into the ground unless it's oak. Pressure treated softwood is barely OK but never use a strimmer near it. It cuts the pressure treated layer. I found out the hard way. Our house has some external oak posts, typically holding up roof overhangs. We dug pad foundations filled to just below ground level, then brick piers (1.5 * 1.5 bricks, 4 courses high with the top course being 45 degree plinth bricks). The hole in the middle was filled with concrete with a Stainless Steel pin sticking out the top. Then a square of lead was put on top, dressed about 1" down the slope. Then the post drilled with a hole to take the pin. You could also buy or cast your own concrete block pier to get the wood out of the ground... https://www.ebay.co.uk/itm/275700203774?chn=ps&_ul=GB&var=577119817626&_trkparms=ispr%3D1&amdata=enc%3A1l_9kbZx_TFyjSM9PSQnmNw71&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&mkscid=101&itemid=577119817626_275700203774&targetid=1647205089000&device=c&mktype=pla&googleloc=1006886&poi=1006818&campaignid=21194089662&mkgroupid=162053931300&rlsatarget=pla-1647205089000&abcId=9406426&merchantid=6995734&gad_source=1&gclid=CjwKCAjwyJqzBhBaEiwAWDRJVIW55VLnv0qmo2qIlY1t4Av1Unz35lGaM2bEf3tGRdE1ezBMKB1ZZRoCV-EQAvD_BwE

This was a requirement when we built our house in 2006/7. That's 17 years ago. How can builders and Architects still not know about this?

I don't have any answers I'm afraid. According to Google we use 1.9bn bricks a year in the UK with about 0.5bn of those being imported. That's just under 1 in 4. Data from 2022. That's the impression I got. When we looked for bricks we found many companies selling the same physical bricks under different names, particularly the imported bricks. In many cases the photos were identical so a Google reverse image search might work.

I've used a lot of smaller clips and ties in electronics projects and usually go for makes that use 3M adhesive. They stick OK to metal and plastic but not sure how well they stick to (dusty?) OSB.

+1 We just brought 110mm up through the floor under the kitchen sink and used a rubber (?) adaptor down to 40 or 50mm. We have inspection chambers on all 110mm junctions outside. I think all other rooms such as the downstairs WC have 110mm stub stack with AAV.

One option might be to create a square platform outside the door with a step down straight ahead and a ramp off one side.

In cold weather/winter the air outside is frequently drier than indoors. So I'm thinking it might not be a low humidity problem. Could it be dust mites? We designed our house to have mostly tiled, stone and wood floors rather than carpets and that helped me quite a bit.

Probably too late but I would raid the skip and recover as many of your tiles as you can in case they come in handy for repairs.

PS Actually if they make one you probably want one that takes hot in the side, cold in the bottom and mixed on the other side so it's easier to insert in the existing pipe.

Yes but... Most shower mixers require the hot to be 10-12C hotter than the shower water. So if the hot to the shower is limited to 48C the shower will probably be limited to 36-38C ish. However google says the ideal shower temperature is 37-38C. You might see lower in practice due to losses down the pipes. You could fit a mixer valve that can blend up to 60C and turn it up a bit or remove it when the BCO is gone. I'm not sure if they need specific fail safe features or could be a regular mixer. Google found this one intended for UFH but again it's not one I've used. The one we have is no longer available. https://www.amazon.co.uk/Temperature-underfloor-Compression-Kudos-Trading-delivery/dp/B085GLWX73?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A2S4BLAJZOXGY6

There are whole estates or two storey houses closer together than your proposal. One option might be to mirror your design left to right and possibly reduce the resulting part of the L nearest the other house to one storey. Do this and rotate it to the same angle as the other house? You might also consider making a street scene ddrawing as proposed showing both houses as viewed from the road showing the heights and gap between them to scale. Perhaps run that drawing past a planning consultant before submitting it.

Is there a danger of it freezing if not deep enough? Old houses frequently have cast iron stacks on the outside of the building so it was probably allowed in the past. One issue Is that stack should have a large radius vertically mounted bend at the bottom. Not sure how you would do that. How wide are the footings and how many pipes do you need to cross's them? Could you core drill a hole through them?

So you have fully filled trench foundations and want to run your soil pipes over the top? Above ground?