Replace flat roof and deck

[greenasgrass]

I moved into a 1936 built bungalow a while ago, its got an old extension on the back (bathroom) and a new extension alongside it (dining room to patio). I do intend to extend again subject to planning permission in the future. When the new extension was built both extensions were felted as if its all one roof. The original bungalow pitched roof is asbestos tiles.
ok thats the full spec but heres the problems
I've just got round to fixing up the bathroom, first job being to remove the sagging wooden tongue in groove ceiling, you guessed it, above this was a sagging plasterboard ceiling. Above this was a load of old insulation and above this was chipboard in pieces, hanging off, falling off and disintegrating. That was the deck!
Yes it seems when the whole extension was felted the the old part had some very artistic wooden lattice work wedged in to support the felt in the absence of the vanishing chip board.
I've decided to tackle this myself, (I think), but as I intend to extend again I want a sound job but not to last forever.
My questions, I want to use a plywood deck not osb, the bitumen covered osb puts me off, I mean cutting that would be a nightmare, so is plywood ok to use and which grade.
Next, How do you get the old felt off, do I need any special tools, like sharp ones
I'm intending to refelt both extensions as I've just discovered the bathroom is leaking, as you can imagine I've no confidence in the previous roofers, ie lattice work. I'm thinking of using the self adhesive polyester felt, its on offer innit!
Next question. Do I put it over or under the liner on the pitched roof, what I read is it goes over but to me under must be better. Also, do I have to remove the asbestos tiles to do this?
Final question (for now) is it better to put the ceiling up before the deck and felt as it must be easier to drop in the insulation as opposed to putting it up with the plasterboard ceiling.
Thanks for your time, any form of help is appreciated

 

[lynnfot]

Are you sure that the 'decking' is load bearing? woudn't want to think of you plunging through. how big are the rafters holding up the roof and how far apart are they?

 

[cott99]

18 MILL PLY TO REDECK

To remove the old felt, if your going to replace the boards, you remove the felt aswell as the boards, ie same time, brush off any stone chippings, bag up and remove, get a sharp spade cut down the felt were the joins are, usally were the joists are

You need 2 people to prize the old boards up, lifting a bit at a time moving along, when its up remove, de-nail and lay a new board, not really a diy job!!

If the roof is bad, you can soon go through

 

[bendylow]

no need to use extenal or marine ply why not use plain osb it doesn't have to be bitumen coated.it's cheaper and just as good.to remove old stuff you need a sharp spade(not a shovel)your bound to know someone who's got an old one lying around,just sharpen the edge on a grinder.if you can strip and reboard in one day then do the ceiling first,but,be careful if it has been leaking badly and over a period of time you may need to change the firring strips(or diminishing strips whichever is the case)this can be time consuming if your doing the job yourself.think carefully before taking this job on,it sounds like it's quite a big roof,it takes time to do a flat roof properly,ask yourself these questions,do you know which felts to use,and in what order,do you know how to cut and fit flashings,do you know how to cut the edge detail around corners,do you know how to cut the edge so that they butt together straight and have no gaps.and most importantly can you use a blow torch safely, if you're flashing into a pitched roof there is a serious risk of fire in the roof space,the timber in there will be tinder dry.hope this helps.