Attic Bedroom

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The semi-detached house we recently bought had a loft bedroom conversion done around 1987 by a company called Econoloft. They have hung the floor joists from two RSJ's spanning the room on either side, and made the floor on 18mm chipboard, then built the stud walls on top.
at the gable end, the chimney runs up one corner of the wall and is stepped about .5 metre above the floor - going from approx 400mm to approx 200mm protrusion from the wall; the stud wall at this end stands about another 200mm clear of the widest part of the chimney.

I am going to have a window installed in the gable end to give some more light into the room, and as it's going to be a music room, i would prefer to have the shelving for speakers/hifi on the solid wall instead of the suspended floor - to keep the wife happy :)

My plan is to take the stud wall down, and batten the wall and screw new plasterboard to this. I've spoken to the local building control office, and while i need to apply for notice for the window as it will require an opening in the gable end, as it will only be a small window, non opening and obfuscated (and approx 5m from the boundary), they don't require anything else. They also said as the stud wall does not affect the staircase/stairwell of the room, and is non load bearing, they aren't interested in me moving the stud.

The question i have is thus; the existing stud uses foil backed 9.5mm plasterboard with rockwool insulation between the studs, and strips of plasterboard on the back to hold the rockwool in place (NOT complete boards, just wide "batons" of board); the ceiling is the same. if the wall is now going to be directly against the external cavity wall, can i just use the rockwool between the studs fixed to the wall and board back over, or do i need to use something else instead? Also, the chimney stack has been (very) roughly covered with some sort of render up to approx 3/4 way up; I was thinking of either tidying the rendering up and leaving the chimney as a direct mortar rendered wall, or either D&D some board on it, or build a stud round it to board on. is there any issue with doing this round the chimney?

Also, the floor joists are 7"x2" and the last one is approx. 350mm from the wall; my thinking is to add a 7x2 and fix to the cavity wall with expanding studs to hold the extra piece of board it will now need at the end; that area is going to be behind wall mounted shelving so unlikely to have any weight; is this acceptable? I would hang from the RSJ, but the wooden joists bolted to the RSJ that the floor joist hangers are one end too soon!

My final question is about the floor joists. i've looked at the orginal plans, and the joists are shown as direct cross room joists, hung from the joist affixed to said RSJs; however the immersion heater cupboard is roughly one third into the room in the middle - so pipework ran from the far corner of the loft into the middle and dropped down. instead of rerouting the pipes (most of which are now gone), they have created a weird "lattice" of three of the joists, running diagonally along with the pipes; they are then hung onto a long cross joist which caps off 3 and is secured at either end to normal joists, which the diagonal beams being hung at an angle against other beams. the floor does bounce, but no more than i would expect in approx 4m wide room. Is this a safe way to have it, or should i look at replacing these diagonal joists with straight across beams instead?

Many thanks in advance - and sorry for all the questions! I'm used to tackling work myself, but not until i know exactly what i need to do and be aware of!
 
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Anyone offer any assistance?

I read your post and tried to pick out the questions.

I failed.

perhaps the clever people are on holiday.

Can you write a single question, much shorter, please?
 
I read your post and tried to pick out the questions.

I failed.

perhaps the clever people are on holiday.

Can you write a single question, much shorter, please?

Sorry - always told i write a story instead of an email :D


Ok - Questions:

1. The mishmash joists going round the pipework - now pipework isn't an issue, should i replace with correct joists or leave as is?
2. What insulation should I use behind the new boarding on the cavity wall - rockwool as everywhere else, or something else?
3. Should I batten or dot and dab and should I use foil backed board or polystyrene backed board instead (and not rockwool)
4. Tidying up chimney stack - any issue with batten and board or dot and dab round the stack, or should i attempt to tidy the rendering on it instead?
5. extra support on end wall - will a 7x2 joist bolted on with expanding bolt stud anchors be sufficient for so i need to think of something else?
 
2. What insulation should I use behind the new boarding on the cavity wall - rockwool as everywhere else, or something else?

If the cavity wall is already insulated, rockwool will be fine, because you are not desperate for every last bit of insulation. It is cheap and easy to fit with no precision cutting needed, and muffles noise a bit.

Additionally, mineral wool does not burn or emit poisonous fumes. Since Grenfell, I am very wary of foamed insulation slabs inside a house.
 
3. Should I batten or dot and dab and should I use foil backed board or polystyrene backed board instead (and not rockwool)

If you are an amateur I think you will find battens easier.

Foil backed board gives a moisture vapour barrier which may possibly be useful.
 
Thank you for the replies John - appreciated! I've done D&D plasterboarding before as well as battened boards on ceilings etc; the only reason i hate it do much is because while they are straight vertically, they always end up being out from left to right :D I'm a bit torn tbh - battens would make life very simple and i could have the wall done in a day, but the other side of it is that i plan to hang a large shelf for my Hifi Separates on the wall, some speaker brackets, and possibly another shelf to hold the turntables/mixer etc - so a fair bit of weight!

The other problem I have is if i go down the route of D&D I can't use foil backed PB as it needs mechanical fixing - so what options would i have with regards to insulation there?
 
if you are going to want heavy shelves or cabinets, use studs and noggins of adequate strength, and mark the ceiling and floor so you can find them again. You can fit them closer together if you want, for additional shelf-hanging options.

In drywalled kitchens, some people like to fit ply or OSB on the studwork, and plasterboard on top, so they can hang cabinets anywhere.

Run your cables for power, aerials, LAN and speakers before boarding over. If you use conduit you can pull or push wires through afterwards (but not so easily as before).

it will surely be easier to build, and easier to fix your shelves, than D&D.
 
Thanks John, that might be the option to go for then as there will need to be a fair few sockets, RJ45 ports etc in there! i was looking at 25x50mm battens, to give a wide enough area for the board joints; and either OSB3 or hardwood ply 12mm - i suspect the ply would be a better option for holding strength - or would i get away with standard softwood ply? also - if i'm putting a first layer of ply in, do i need a membrane between the board and battens and then use normal plasterboard on top, or is there a better way?
 

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