Spinny

Do you have any photos of the joists after the remediation work you did was done i.e. before you put the new flooring down etc ? From your photos it is tricky to see exactly how the damp was getting into the joist. The newer sister joist shows damp in the bottom 75% extending from the end through to where the bifolds are. I presume the newer joist originally reached all the way to rest on the wall but the end had completely rotted away ? Clearly the older joist was very rotten in that corner. So (a) it may (most likely) be that damp was reaching the joists at their ends through their bearing onto the wall. That is the bottom of the wall in the corner there and the ledge the joists sit on was getting damp. Then in the absence of any DPM between the joists and the masonry the damp was sucked into the joist ends and then down the joist length. or (b) it may (perhaps) be that the older joist is in contact with the masonry under the bifolds ? Or in contact with something on the possibly damp earth underneath (rags, or rubble, or timber shavings) ? Thus the older joist was getting damp and passing the damp into the newer joist by contact. I presume when you did your remediation work and replaced the rotten joists that a new DPM was put along the bearer wall the joists sit on, and really ideally up the very end of the new joists too? I presume all the damp rotten wood was removed and ideally the new joists treated with preservative/wood worm treatment ? I presume the only point of contact for the new joists would be at the ends on top of new DPM and there was no direct contact anywhere else such as under the bifold ? In your photo with the torch it looks as though there may be an aperture under the floor there through the dividing wall with your neighbour ? If so there may be passage of air via such a hole. It is even possible that damp is getting into that corner area from your neighbour's side - take a look over at what is on his side - a leaky downpipe, gutter, a gully drain ? When you lift your astroturf is there any/more evidence of damp near that corner ?

They are also labelled as 3000Kelvin colour temperature which is on the warm/organgey end - not ideal for task lighting, you would be better off with 4000K+

HATO appear to make agricultural lighting. Do yours look like this...https://www.hatolightingsolutions.com/hwdk-c-led/ ? And if so... So quite probably you are seeing the full brightness (unless perhaps they are second hand and someone might have changed the default setting.) Looks like they are 60V constant current LED strips rather than the more normal constant voltage type. Good for chicken sheds apparently.

And...

So...

Yes those joist pics are too compressed down now to see the detail. Looks a bit like ours, is it a 1930's house ? We had some damp in ends of joists adjacent to our porch (see photos) but not as severe as yours. Cut the ends off worst ones, some sistering, and modified joist layout with a hanger off the other wall. Ours was due to water getting through under the porch because the ground slopes downhill towards the house at the front. We have yet to get a new outside ACO type drain in ourselves. The original DPM directly under the joist ends was disintegrating (old bitumen felt type stuff). New DPM put in under and over the ends of the retained/sistered joists and everything treated with a boron woodworm/preservative. Nearest u/floor air vent was blocked with newspaper, which they apparently used to do in 'olden days' to try and keep warm. So cleaned that out and other bits of rubbish to improve air flow.

What is the makeup outside then ? Do you have a timber deck under the astro ? Then concrete or earth or something under that ? Is the astro fixed down somehow or can you peel it back ? Maybe you have some photos of before the deck and astro were put in ? Any photos of what the rotten joists looked like ? Did you have problems before they were put in ? Any air bricks down there ? Where is the DPC because ends of timber joists should be on top of DPC/DPM ? Any mold on the bottom of the wall inside or staining outside ? Presumably the joists run front to back in the room behind the bifolds ? I just think you need to be as certain as humanly possible about the cause in order to specify the best fix.

Our builder had to get someone with the right cutting equipment to cut timber lengths into the right taper for the furrings. Best to cut two lengths from each rectalinear timber. What is needed depends on your structural 'joist' layout and desired slopes. If all furrings/slopes are orthogonal to the joists then different furring thicknesses only are needed without the tapers. It is possible to get PIR slabs cut into multiway tapers to provide slopes, so you lay them on a flat surface and they create whatever contour you want on top. Of course you have no use for their insulation value outside. Will you have a roofer doing the single ply ? You could consult with them. Some single ply manufacturers have specific makeups/specs to be followed to provide a guarantee.

Yes, am also interested in this. Our flooring guy said yes any such coverings can chemically react with the LVT and cause discolouration. He cited a care home he had been to where the LVT had discoloured where there had been a high frequency of movement of old people's slippers shuffling over the same piece of floor and it had discoloured.

So is that some green artificial grass matting outside the bifolds ? Internal FFL looks as though it is lower than the outside ground level under the artificial grass. And which way does the ground slope, does it have a proper fall away from the bifolds ? I might guess rain goes through the artificial grass and pools underneath unable to runaway because of lack of slope, and the presence of the artificial grass stopping it from running away or indeed evaporating. Maybe consider lowering the outside ground level which looks like it could well be above DPC. If you are going to have to shell out then make sure it is a proper permanent fix you are going for. (Have you got an internal step up somewhere ?)

is there any case for extending the underground drain over to the carport ? Might you be washing the car under the carport ? Would you have use for a ground level drain gully to take ground water running away on any adjacent hardscaping ? (just wondering about taking the water away from the main building rather than towards it) PS Just looked at your 3d image - seems you do have a hard surface between carport and main building - this would normally run off away from the house - potentially to a ground drain ? Do you plan to have a tap (and electric light & power) to the car port ? Lighting under the walkway ? You could bury the services or take them across inside the walkway structure ? Garden/external lighting planned ?

What is the roofing material and how will the underside be finished ?

Looking good. Do you cover the cavities to keep the rain out ?

An Architect designs buildings, a builder builds them. A Landscape Architect or Garden designer designs gardens and landscapes, a landscaper builds them. They are different skill sets and IMO it is rare for a builder to be much good at design, or a landscaper much good at design. Rare to see a designer actually building things themselves too. It is easy for those with unlimited funds. One deisgner I spoke to was asking £8k for a 300sqm design. One landscaper £250+sqm. It adds up to a lot pretty quickly. Stealing ideas and a bit of direct labour becomes attractive. Lots of ways to go with steps...

Our place faces west as well. We are fortunate to get some evening sun flooding down the north side of the house into the back garden. perhaps you get a similar effect with some evening sun coming down into the back where you have your 2.7m wide area to the north of the house ? If so you might want to consider a seating area where the planters are ? When the sun sets the shadow of the house creeps over the back garden and a patio near the house becomes shaded. And then it becomes nice to (a) stll look out onto areas that remain sunlit as long as possible and (b) have a second sitting area to catch some evening sun elsewhere in the garden. Our back garden is longer but thinner and so we plan to have a patio near the house, and a second one at the bottom of our garden. Photo is 7pm on 7th July.