Temp

Where do the pipes from the boiler fork to supply the heating and DHW? Presumably that's in the external boiler or the leak would affect both.

We have a mix of stone, engineered wood and carpet over UFH. It's nice having cool floors in summer and warm in winter. Particularly in bathrooms. I suppose there are days in spring when the heating is off that the floor feels a bit cold in bare feet. But socks are enough to prevent that. We certainly don't heat the floor. Mostly we walk around in bare feet all year round. I'm sitting with my bare feet on the stone floor as I write this.

Yup. If you fully fill between the rafters the membrane ends up flat. You need the counter battens to raise the tile battens off the flat membrane and allow any water to run down.

The duct should run to within a few inches of the pole. Typically you end up with a cable and a draw rope coming out of the end of the duct. What I did was wrap about 12" of the cable with electrical tape and pulled it back into the end of the duct. Then i squirted some expanding foam into the end of the duct creating a plug which I hope is only 6-8" into the duct. It wouldnt be too hard to remove it if I wanted to pull another cable through. I left the hole open until BT did the connection. They ran the cable up the pole and covered it with a galvanised cover strip from just below ground to several meters up the pole. I coiled up the excess draw rope and buried it in the hole.

If you use a vapour permeable membrane I don't think you need a 50mm ventilated void. I believe you only need a 25mm void to allow the membrane to drape. The drape is to ensure water can't become trapped above tile battens causing them to rot. The drape forms a gap under the batten so dirt and water can run down to the gutter.

With all plastic pipe systems they have to be assembled correctly. My builder wouldn't use anything but Osma Gold. The two errors to worry about with all systems are forgetting the insert and not fully inserting the pipe into the fitting. Our plumber always used a sharpie to mark the pipe to be sure it was fully inserted but he did forgot one insert that caused a leak. Lucky it was easy to fix.

Only if its a ridge board not a structural ridge beam. Big difference.

Simpson Ridge Rafter Connectors are under £3 but see above first.. https://technologyspareparts.co.uk/shop/simpson-strong-tie-rr47-ridge-rafter-connector-47x100x1-2mm-pre-galv/

Do the rafters "hang" from a structural ridge beam or is it just a normal ridge board? How is the roof triangulated?

You can get oak veneered plywood and add a bull nose. Might work out cheaper. Some of our window cills are left over engineered oak flooring. When I built an oak clad out building my neighbours had some of the left overs for their window cills. Only last week another left over board got used you make a coat rack for the village hall. Can never have enough oak.

We installed cable from our house to the bottom of the pole and left a coil behind the pole long enough to reach the top. We had loads of problems getting them to schedule an engineer but when he came he was happy to use our cable.

It's virtually impossible to get utilities to coordinate projects. You may find the electricity Co will come along and remove their cables but won't remove the poles as they still have BT lines on them. BT will want you to pay for them to remove the cables starting wth the surveyor to come and do a quote. If the BT line you want to move underground only serves your house then you can try disconnecting it and telling the electric co it's an old one not in use but they might not take your word for it. As for reconnecting.. you can just lay duct with two draw ropes to the bottom of the nearest BT pole that's staying. One draw rope to be used to pull copper, the other fibre when that happens. If the BT cables you want to move serve other houses then you will have to either get Openreach to quote to move them or wait until they do the fibre project and remove the copper, although I suspect they won't remove them. You might want to adopt Aporoved Document R for the duct and entry into your house?.. https://www.gov.uk/government/publications/high-speed-electronic-communications-networks-approved-document-r

Deleted.

I also used VP400. It survived being left uncovered for months.

Only issue I can think of is that side windows may now have to be frosted glass to be permitted development (or is that only first floor side windows?).

Take a look at this page.. https://www.ledspace.co.uk/pages/led-strip-kit-builders Their "kit builder" works out what you need to make complete mains powered light(s) including the power supply. It works out which power supply you need based on the length of the light fitting and/or number of fittings. I don't think the power supply fits in the channel if that matters. I'm sure someone must make a similar ready assembled unit if you don't want to build one.

There are also things like this.. https://www.ledspace.co.uk/products/flat-corner-led-profile?currency=GBP&utm_medium=cpc&utm_source=google&utm_campaign=Google Shopping&campaignid=14654411474&adgroupid=128524150738&keyword=&device=t&gclid=CjwKCAjwsJ6TBhAIEiwAfl4TWPewxg9PtEarXrFsksh6yetRWdh3Sep9GRwV_yek5PZFSSbY3XdcMxoCRaIQAvD_BwE

They look perfect if the heads fit the brackets. I would buy a few spares and drill holes in some scrap wood of same type to work out what pilot hole to use on the real thing. Don't want them to be so tight you shear off a head when in the wall.

This describes the ground beam approach.. https://www.diyfixit.co.uk/building/bridging-a-drain-run/

That's exactly what I meant in my post above. You may only need one home made beam in the middle wall and that will be shorter. You wouldn't use a curve at the front. Probably a 45 degree section into another inspection chamber on the original route.

We have beam and block with insulation and screed/UFH on both ground and first floors. Wish we had fitted more insulation on top but we don't notice any hollowness to the ground floor.

Get someone to sew up some fabric tubes?

I wouldn't do that. The pressure treatment is typically only a thin layer on the outside. I'm in the process of losing a fence because I used a strimmer around the posts. It damaged the pressure treatment layer and allowed the posts to rot. Other posts not strimmed are fine.

Oops @prodave posted while I was editing mine above.

or. Someone probably makes big stainless steel wood screws. These have hex head.. M8 X 120mm https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.ebay.co.uk/itm/190819704599&ved=2ahUKEwjf9q6Xs7H3AhXloFwKHRuHA10QFnoECBUQAQ&usg=AOvVaw3grdgHzL6PqOykR-vAEoDP