Hello all! My first post on here, so please be kind....and sorry for so many questions on my first post the house we have moved into (late 60's semi) had a loft conversion done by Econoloft in 87. they got building regs etc for it so must have been done properly - although i must admit some of the work is rather Heath Robinson...nothing is straight or level! anyway....my questions The loft conversion has 2 velux windows installed - one either side. One is through the Purlin which has been cut out supported by 3x3 posts onto the Steel RSJ that runs down each side of the room. These RSJs have a joist bolted to them, and then the floor joists are hung from these. the floor is 18mm T&G chipboard, and the walls are then built on top of the floor using 3x2 and 9.5mm foil backed plasterboard (which is also used on the ceiling), which rockwool in the rafter and stud voids - and wide bands of plasterboard used to retain the rockwool on the back. so.. 1. the joists are meant to run perpendicular to the beams, but 2 of them have been changed to a mishmash of diagonals due to the pipework for the old header tank running into the middle of the room and down through the floor to the immersion heater cupboard. the original plans i've seen show none of this and just straight joists across.while i have the floor up, should i change these to the correct joists or leave as is? there are no noggins between any of the joists either, which for circa 4m span i would have thought there would be (no middle support wall) I want to fit a window in the gable end wall, but the stud wall that end is about 400mm away from the cavity wall. There is a chimney stack running up to one side of this wall - my thought is to take that wall down and board the end wall instead; and extend the t&g floor the extra 350 needed, and bolt a 7x2" beam to the wall using stud anchors to support the end of the floor, then add the extra board to the ceiling gap and side walls. this will then allow a window to be cut in and also means my hifi and speaker can be fixed to a solid wall and not sit on a bouncy attic floor! I've spoken to BC and as long as the wall isn't a supporting one and doesn't affect the fire escape or stairways/staircase, they aren't interested. (with the window they said as it's only going to be less than 1.5m sq they just want a building notice application, and get a catnic lintel installed and they will inspect - the window fitment will be covered either by the inspection of it all or by the the firm if i choose one instead of doing myself!) so... 2. The chimney has been very roughly rendered behind the wall - should I tidy that up and render, or board it using battens/D&D? are there any issues with regards to a chimney stack? 3. Th existing insulation is rockwool between rafters and between the studs (and joists as well). what should i use for the board on the gable end wall - stud and rockwool or should i D&D (which mechanical fixings as well) with some poly backed board instead? 4. With regards to the end wall support - this area isn't going to be stood on as a shelf will be installed on the wall once finished; will the bolted beam be sufficient? 5. Is rockwool a good idea for for insulation between the rafters? i though tit would cause condensation in there? My final question is about ventilation - the room is BOILING when the sun has been out, even when the window vents are left permanently open. are there any suggestions around changing the roof insulation or anything else that would help? there's no mould anywhere and i don't see condensation when i'm up there (except in the failed Velux window sealed units!) Any advice is greatly appreciated - and sorry for so many questions on my first post!