tonyshouse

On tonyshouse website if you dig, yes windows behind reveals, no plywood boxes

I can get you one, and the doors, what colour?

Looks like it might need to underpinned, cheaper to start again with real foundations and new walls

Yes, but in the great scheme of things it pales into insignificance

I have installed thousands of Velux windows to loads if different roof and roof coverings, never had any leaking, never used additional kits but always careful with membranes and aim for fail safe

300mm cavity for me but I start with a target U-value of 0.1

What is behind the two layers of sheet material, masonry?

Helifix mortared or resin mortared in ?

It looks like a catch pit to me - I would want to keep it

One niggle, manhole/inspection point needed at each change of direction even fall is best

I hate cavity closers, they will give you more thermal bridging than what you have and worse draughts and they cause cracking where they join the blocks. if you are doing dit and dab then draughts will be a massive problem I did something similar to you and used thermal board to close my cavities, (normal plasterboard on my canted reveals) then wet plastered everything, no problems 11 years on

Looks never used

600 in my book and if no one looking 500 too

Ventilation strategy needs thinking through, trickle vents do too little when it is calm and too much when windy

Two lintels, 100mm of concrete seems a bit thin to me, 50mm sand has been discussed before but I have seen it percolate into the hardcore leaving a void so never use it , drain in or below the hardcore is best

Follow roof light fitting instructions for tiles they should touch up to high upstand possible problem to RHS should have bigger upstand on roof under window sill lead should be one piece at the top not two, verge, wrong verge cloak and wrongly fitted

Off the record and without liability I have been sealing up chimneys for years, never a problem on internal walls, no air vent, sometimes filled, often take a brick out in the loft. Insulate well, and up the chimney breast in the loft i think the need to ventilate them dates back to before central heating was the norm - how can a chimney structure inside a heated envelope be cold enough for condensation to form in it? caping the top needs to still allow air to circulate, they can stream with condensation if not and that can run down inside the flues

If it is only 50mm thick then long screw into the masonry. QED

I think Leicester reds or seven valley reds ‘orange I would carefully drill out a few bricks from behind/under leadwork or in loft/garage totally more crucial is going to be getting the mortar colour perfect also consider adding a movement joint

Half brick out from each side of the stone window shifts it across enough to give him a brick skin his side and does you no harm. Easier just the LHS half brick out

Try in the loft or garage!

Is the draught coming in from outside or from inside pipe boxing? Do the pipes run to outside or into an internal soil pipe in a box? Is it a cavity wall house or is it dot and dabbed?

The Rolls Royce of windows are Internorm ali clad wood hotly pursued by Velfac and Nordan, go 3g it is now standard in Northern Europe

Easy now then ?

When I left Uni I worked as a volunteer on a building project for 6 months and three months later became a builder - only qualification was the price! retired at 51 owning several houses and later built my own house I did get a demolition certificate was corgi registered under grandfather rights, never did any formal building qualifications, nothing is difficult my advice - just start doing it!