Dave Jones

could foam it after board is in.

motorhome bathrooms have the waterproof holders.

be mindfull on the top and sides that by bringing the membrane inside you are giving moisture a track to get it via gravity.

they are interlocking so would be water tight laid straight with the correct headlap, as would a single row on its own for example. But as others said would look 'different'.

you have a cold roof, this means it MUST have airflow under the tiles to remove moisture. You can insulate upto 50mm of the bottom of the underlay below the tiles as long as the eaves and ridge are open to airflow.

48m x £1500 for cheap = £72k more realistic using trades 48m x £2000 = £96k

hang it from ceiling joists?

if the soil stack is already in the attic can you not simply run it to a tile vent ?

so the rain would dribble down the front of the window. Better option would be to do it properly and fit a gutter and downpipe.

you could router in intumescent strips they do a good job of sealing against draughts.

interesting. Have you costed it yet ?

second vote for IR panel, can plaster them in or put in loft.

in the absence of any gutters where are you expecting the water to go ? Waterfall off front of window or dribbling down the render ? First job is to get water away from the structure as you don't want permanently soaked walls/render. Pointless worrying about any staining/damp until you have that sorted.

you cant choose randomly it will be specified on the the beam drawing so check it.

a cheaper version of mvhr is the vent axia multivent. Can pull from 3/4 rooms and dump via wall/ceiling vent. approved for building control and only a few hundred quid. https://www.vent-axia.com/range/lo-carbon-sentinel-multivent-plus

then pipe it into the sewer anyway.

you have two options. board the walls to bring it out far enough or cut back the insulation.

shouldnt be the profile sits tight to the floor over the top of it. This is where you find out how good the screeder was.

shadowline looks good, you need a trim or stopbead for the plaster to finish on. https://www.barbourproductsearch.info/renderplas-makes-shadow-gaps-simpler-with-new-news016813.html

150mm below dpc (2 bricks). Maybe easier to make a feature step for the doors ? a linear drain wont stop rain splashing above the DPC, you may be ok and it not get too much weather on it to worry about then again you may not.

dont submit the minor amendment, you are enacting your planning permission. If you change how you do that the council could enforce against you. Sounds like a job for your local councillor to sort out.

how far away is your nearest connection point to the storm system ? A pumped chamber (if no fall) fed by an attenuation tank (cheap crates) would be pretty cheap.

a vertical cavity tray effectively moves the level of DPC higher. Very handy if your on sloping ground for example and you want to bank up against the building.

the person with most to lose in this situation is the owner, even if the extension is built under the radar when it comes to sell up a search reveals the gas main he wont be able to sell it, or rather if the purchases requires a mortgage they wont get one. May get lucky with an indemnity policy but thats a roll of the dice.

doors are generally ok to flush upto as there is no cavity above dpc to let the wet in, as its a door! Although you do need to pay attention to the door/wall junction. Some use a gravel channel next to the house, as its splashing water your trying to avoid soaking the brickwork above DPC and therefore letting damp into the cavity. You can get some paint on waterproofer as well. We allways have a tray 600mm above dpc on our last two homes that way you can safely lay patio flush to finished floor level inside and have no worries about damp getting in.