25mm engagement into timber should be adequate. Think of how much is held by a hinge screw on a blanket box or cupboard door and you'll quickly understand why.

If it's plasterboard, then I'd only use the screws to hold it in place while adhesive behind it cured. The plasterboard that I've seen is not strong enough and would break through. When building walls with plasterboard, the nails/screws are only to stabilise the board while adhesive sets.

For the bonus point, you get what you pay for. I've got two of those tools. One is gathering dust in the back of the shed (Unreliable cheap imiatation) while the other has been used extensively with true appreciation. The good ones will assist people like us (Who don't do that sort of thing daily) to not overdrive the screws and fracture the board. They do take a little bit to set up to get the correct depth, but once set work really well.

Cheers, I'm not sure about the value of trying to glue the expanded polyeurathane insulation to an artexed ceiling which is only held up with nails anyway.
The board/foam is pretty rigid, and I will use plenty of screws into the joists.
The whole job is a bit of a make do effort. Ages ago I re-roofed that part of the extension with EPDM, it needed doing quickly and cash was tight. I wish I'd added the insulation and another layer of ply before the EPDM. I did it that way on the next bit I did on a second extension to the side of the house and it made a huge difference to the warmth of that room.
Easy to be wise after the event, s'pose it's called experience.
I'm dreading the light fittings, I don't think there's much spare cable length and the damn solid core wire with pvc insulation always seems to go hard (I think the old multi strand with rubber insulation was better.
I may add a junction box and short extra length to the new ceiling rose.
Can't tell with these jobs until you get stuck in.
Del
(I'll get a decent quality... thingy tool)

I have seen advertised extension fittings for electrical boxes - you may have them in your country also.

Stiff T&E:

The copper is usually OK until it's been bent a few times; unfortunately hardened copper can't be annealed without destroying the PVC.

PVC insulation gradually loses plasticiser and goes hard. If that's the problem you can probably improve matters by warming the wire - a hair-dryer is quite useful, probably set on low heat; but check on a spare piece of wire that it can't do any harm before doing anything significant.

25mm into the joists sounds good.

Re. the driver bits - d'you mean the torque limiter type? If so, does the screw head/plasterboard contact give enough resistance compared with the torque needed to get the screws into the wood?

No I mean the sort with a sort of cup/disc around the bit so it bottoms out on the plasterboard and stops it running in too deep.

Like this

Del
_{(I said bottoms)}

Oh right - haven't seen them. The blokes I've watched have generally used nails and an "electronics screwdriver" (AKA hammer), and skimmed it afterwards to hide the dents and joints. Hammering upwards is no fun, tho'.

Yeah, it's tapered edge board and if I'm careful I can get waay with just glass mesh tape over the joints and skim the jlints not the whole boards. Spot fill over the screw heads. I've got away with it like that before... skimming a ceiling is a real tradesmans job, well beyond me and they charge a small fortune these days.
The old ceiling is just held up with nails, hence my reluctance to use glue adhesive
Del

"The old ceiling is just held up with nails"

Therefore, the length of the screw should normally be = thickness of old ceiling + thickness of new board + 25 mm.

You mean 10 + 40 + 25 = 75mm?

Let me hear, what Del has to say. I may have miss-understood the OP.

Cheers, yup 25mm in the wood gives me 75mm.
I had originally thinking of 65 and then thought I was going a bit short.
It's new board+insulation = 40, old ceiling = ~10 and 25 into timber, totals 75.
Del

I have used them with moderate success. Though I find just being careful with a variable speed driver (low speed) works just as well.

With the gyproc (plasterboard?) we have in Canada, if you over tighten the screw and it breaks through the paper cover rather than just dimpling, all the strength is lost.

In our neck of the woods, we don't glue the plaster board to the framing. Better construction uses special screws (marketed as drywall screws) for the board. If it is in a damp location, such as a shower room, they even recommend stainless. If you go cheap you can nail, but they are much more prone to "popping" over the next couple years.

Del, if your wood ceiling joists are dry, solid and without wet/dry rot your screws should have enough bite to support the drywall (we call it gypsum board here). Just make sure you install the screws about 8-inches on-center and at the corners to help support the self-weight.

I don't think you need to go the route of using a construction adhesive, unless of course your screws break through the paper facing of the gypsum board. It is gypsum board, correct?

Your screw driver should be okay to use if it isn't a cheap one. Conduct a trial test on a small scrap piece of gyp board with a scrap piece of lumber to make sure it dimples correctly + doesn't drive the screw head into the core of the gypsum board. I've used several different ones over the years. There are very good ones (like DeWalt, etc.) and cheap imitations (China etc) that don't work good at all or break when your trying to balance the gyp board on your head and shoulders.

Also, I suggest that you fabricate a pair of DEADMEN from scrap lumber to hold the gyp board tight to the ceiling joists. Make sure you can adjust them in some manner along the vertical piece if your either floor or ceiling joist aren't level, otherwise it be a real bear to get them to hold the gyp board tight to the ceiling joist. You can also use a pair of large wood wedges under the bottom of the vertical piece of each deadman to adjust them. Either the deadman, or find a friend that has a drywall lift! You can also rent them, but if the ceiling area is small it is cost prohibitive.

Good luck with your project!

Deadmen alread constructed.
I made dead squirrels first off, but they weren't tall enough.
I use my mains powered electric drill, I don't have a cordless, as I don't use one enough to keep the batteries charged, and then they die.
Maybe I could borrow one from work tho' as the mains one can be a bit vicious.
Del

First of all, DO NOT buy any of that drywall/plasterboard from Lyn/Dell Industries. It comes from an Asian country that I will not mention. The current drill drivers have an adjustable clutch that is good for controling torque to the screws. It would save your arms while working overhead to use a lightweight cordless. Today's 9 to 12 volt lithium drivers should do exactly what you need. Good luck on the project. Being short by that length on the wires is rough.

Dont suppose you have this stuff over there?......http://www.kingspaninsulation.com.au/Products/Kingspan-AIR-CELL.aspx

Its good stuff.

If you want something to spread the load more.....google cap screw washers.

Cheers.

Yeah, that's just the sort of insulation, but without the Ali' foil and it's already stuck to the plasterboard. I used that stuff on the other roof which I did to a better standard.
Del

Del, The driver that you offer in the picture is the sort that I've left to gather dust. As the screw gets closer to full depth, the driver has progressively less engagement and eventually chews the end of the bit to pieces.

The one that I use drives positive until it reaches an adjustable stop and the the bit is spring extracted from the screw, so you get full driver engagement until it releases.

I'd also suggest you try a dry run with some screws into the existing joists. The dry timber might shear the screws, or at least that's what i've seen happen with plaster screws into Ausie hardwood that's seasoned.

Sounds like you're doing the stitch in time before your next cold season. Enjoy.

Ah! cheers, that's exactly the question I was asking as the concept did seem slightly flawed!
I shall try and find a decent spring loaded one
Del

Damn, the only place I can find a fancy dimpler with a built in clutch is on Amazon in the US everywhere else just seems to have the cheapo ones, or a slightly more upmarket spring loaded cheapo one.
I'll do a trial run on some off cuts.

BTW, Drywall gyproc plasterboard are all the same thing.
Oh, does that stuff actually harden with age? It always seems much harder when ripping out old stuff, I wondered if it absorbed moisture over the years and actually hardenend?
Any thoughts?
Del

Answer to supplementary question:

• The kitchen ceiling has just been done here at the bothy. Experiments proved that a Bosch hand-held battery drill with the torque setting at "2" onto 38mm drywall screws into softwood roof joists was the right combo for the job. None of those fancy bottom-bits () in sight. The plasterer's skills hid many items of woe where the screws either went in a bit too deep or steered off at an angle. Renewing a plasterboard ceiling is a soul-destroying and horrible job, best not done solo.

Cheers, I'll prob borrow a cordless from work.
Del
My list of in house potential assistants is limited to Mrs Cat who is of limited stature, my son in his wheelchair and a cat.

Ah ha! Just found a Bosch dimpler bit with built in clutch. £23 but if it saves me having to get the ceiling skimmed...
Del

"but if it saves me having to get the ceiling skimmed..."
This partly depends on how many coats of paint you are prepared to apply - but more on how fussy you are.
I've never seen anyone get perfect alignment at the edges of plasterboard sheets, and it's probably even more difficult when the sheets are backed with polystyrene.

1010T

I would recommend a good construction adhesive. Get your self a good screw gun with torsion settings to control the depth of the screw. The foam may compact around the screws a little more. Causing you to do more mud work or you will have depression around all the screws when finished. With the adhesive and screw gun you won't have to worry about that. You can adjust it so it don't compress the foam backing to much and have an even job thru out.

I have tried some of those screw depth setting tools. Haven't found one that works that well. Usually marred surface around the screw or damaged the screw head.

Dell

Firstly you can just fill and smooth the joints then wallpaper with a thick lining paper the results are good compared to plastering. secondly you can remove artex with a steam stripper, its not as permanent as people think. I have just had to patch my ceiling in my extension due to a leaky roof. I removed the old board, removed a strip of lining paper around the patched area, re boarded and cut in the new lining paper. Looks quite good for a patch but doing the full ceiling is a better option. You will need some help those boards are heavy and awkward, less cursing that way.

Arrrghh no! I'm allergic to wall paper.
I've stripped off artex before and it's no fun. Luckilly I have V high ceilings in the extension (8'1") so the insulation backed board is a win win as it covers the artex and insulates. I've just reviewed my kitchen ceiling and it's pretty good having been done with joint tape skimmed over and the screw heads filled, there are a couple of heads you can just detect if you look hard, but you can't see the joins.
I think I did that one with my power drill, but maybe I did the final screw tightening by hand... it's all lost in the mists of time.
Ta for all the suggestions.
Del

Caution! Old Artex contains the dreaded [a-word], so do take appropriate precautions in the respiratory department if disturbing it.

If you extend the light cable Del you will now need a MF (maintenance free) junction box to BS5733 so as to conform with BS7671 (2008).

They aren't very easy to track down at the moment.

i think it's a judgement call. i'ld have at the least 1-1/2" of screw lengh into the rafters. when your doing anything that you expect to out-live you, overkill is the best way to go.

the tool that del posted does an excellent job of setting the screws slightly below the face.

if you have problems driving the scews, put a lubricant on the theads. i use dish soap or just spit on them.

I wasn't familiar with ARTEX (Canadian ehh?) - Be sure what you are dealing with - it may contain asbestos. -Wikipedia -

Until the mid-1980s, the Artex coating was made with white asbestos to strengthen it. This means that only old Artex manufactured by Artex Ltd. will contain asbestos and most probably any Artex applied after 1990 will not contain any harmful material whatsoever. It is also worth noting that the texture is only harmful when in a powder form, i.e., being sanded, and poses no risk whatsoever while it is undisturbed on ceilings or walls and covered with emulsion paint.^[2]

Removing even more modern non-asbestos coatings can expose the operator to hazardous dust particles. Older coatings, containing asbestos, pose a particularly serious hazard. Inhaling microscopic asbestos fibers can cause asbestosis, a fibrosing lung disease; pleural mesothelioma; a cancer of the lining (pleura) of the lung; and peritoneal mesothelioma, a cancer of the lining (peritoneum) of the abdomen. Those removing the coating or working with a surface covered with it should wear effective dust-proof protective clothing and masks -- and the area being worked on should be sealed off. Professional advice is advisable. Removal of Artex is covered by the UK's Asbestos (Licensing) Regulations 2006, which make it unlawful (if it contains asbestos) for a contractor not licensed by the country's Health and Safety Commission to undertake most work on asbestos coatings.^[3] However, this has been recently reviewed. In the UK, once removed, Artex and any other substance containing asbestos must be disposed of as hazardous waste. If the coating is left alone and coated with paint and undamaged, it may be safe to leave the coating in place and managed in situ by annual inspection.^[4] Plastering over the coating may ensure it is safely encapsulated^[5]

Indeed, the extension was built in the 60s so I figure, I'm better off boarding over and leaving it well alone.
Del

Ideally I would say yes 25mm is ample length to hold the sheeting in place but be careful you may have to settle for less as at 75mm long the screws will twist a lot if the wood is a hard & dry. You may find that you cannot get 25mm penetration into the wood. I would get a screw & try driving it into the ceiling to see if you can get it in far enough before the head twists off. I have had this happen & the mess you are left with is a real pain to patch. The screw has to go in first hit, if not, 95% of the time the head snaps off on the second attempt to get it all the way home.

As for the drive attachment I have never found any of them to be effective unless you are willing to spend a lot of money on the better quality ones.

Del,

the last ceiling that I covered the way that you are talking abour was simple and straightforward.

The only point of note was this was when I made my first discovery that Plasterboard screws are PHILIPS not POZIDIVE - you must have the right screwdriver!! I found out the hard way.

I wondered why the screws did not drive in easily.

I am sure that the whole thread knows this but as I only learned this a few years back I thought that I would pass this on!

Good Luck with the job.

Sleepy

I had spotted that, but ta anyhow!
Del

Getting the correct amount of "dimple", is not automatic. Even with torque adjustable screw guns or driver/drills, the amount of dimple will depend on the density of the wood. You may find the correct torque setting in one place, but go to a beam that is less or more dense, and the dimple will be either too deep or proud. I just use a cordless drill and forget about torque setting, by "jogging" the trigger until I get the correct dimple. A few screws may over drive, so just put in another screw an inch or two away.

You will not get away from skimming with mud. The tapered joints and screw heads will have to be skimmed over. An expert plasterer can go with one skim coat, ready to paint with NO sanding.

75 mm sounds like the right length. The next larger size may be too long. Don't forget; get the screws with the coarse thread.

"Even with torque adjustable screw guns or driver/drills, the amount of dimple will depend on the density of the wood."

I guess that this is why Dell is looking to use the specialist tool - and why it needs to be the one with a surface activated clutch. And if it was my job going through yukArtex I would use self-taps - even if it turned out I needed to use twice as many screws.

1010T

You know of course, the ceiling goes up first then the walls. Do you have anything to drive the screws into at the top of the wall? Sorry for the late reply; you probably have the job all finished.

ronseto

very insightful, the last couple that I did both needed extra support at one or more wall edges and with access to the space above I was able to fix that. Believe that it made a more secure job.

Also listened to GW - that was the sort of spacing that I used,

I don't beleive that they will fall down.

Dell with the bag of screws that you have bang in some more! You don't want to be doing it again in a few years!

Sleepy

I've just read this thread and i didn't see any mention of bugs like cockroaches and crickets that like to live in the small gaps between two layers of anything. And also silverfish. I don't know if you get the Indian Cricket ( common name, so it may be called something else over there ) but i know that the racket will drive you crazy and you won't be able to bait or spray.

We don't get too much of that sort of thing in the UK.
The odd wasp nest, but this won't be open to the outside.
Although when I did the roof from the topside (about 7 years ago) I did find some evidence of mice in the insulation. I ripped off the whole deck, only because the cheapskate b£$"%^d who did the original ran out of decent plywood and used chipboard for the last sheet which degraded, and once I'd started ripping that out I had to do the lot... then the rain came and I had to finish it quick to a tight budget, hence the need to beef up the insulation now
Del

I am sure i know the type you have, sort of a grasshopper. We have those too but in the last few decades we had an introduced menace that very quickly proliferated. It likes to live in cracks. It is small and flat with a three pronged tail and stripes on its body. A stack of bricks will harbour hundreds of the little %&%#$*s.

One other point to add to all the helpfull advice so far, you must not break the paper when putting in the screw. Obviously you need to pierce the paper but don't put the screw in so far as to tear, shred, punch through or "break" the paper.

One of these is the ducks nuts;

Thanks for the advice guys.
I've got the first board up, borrowed a cordless drill from work set to a suitable torque to avoid overdriving. Used one of the cheapo dimplers in the end, but went on the side of caution and I've done the last turn by hand on about 25% of 'em.
My first mistake was cutting the board too close, the walls aren't rue and it jammed on the way up... I was stuck there for a while, I also had to modify my helping hands with a block of wood to stop 'em slipping too close to the wall and up between board and wall.
Now I've done one, I know what I'm at...
next one has that B light fitting.
Del
(I've got 15 screws in that board... maybe I should put in a few more as I've 500 of the damn things)

8" apart on the edges, 12" apart on the joists, 4'x8' sheet - I get around 40 screws per sheet if you have 16" OC Joists. (depends if long edge is on a joist or the short edge)

Each board is cut to 7' and 3 joists running along it. 5 screws along each at ~14" centres. No screw on edges as there is nothing there to screw to!
I lucked out with the first wiring, just enough to pull through
I'm half way there, done 3 out of the 6 sheets, first was the worst, my daught was round in the afternoon so her, me & Mrs Cat chucked the last one up in a few minutes.
Del

I would double the screws on the abutting edges. Otherwise the drywall slowly sags in between them over the years - especially if the humidity is high.

If that was a wall I think you would be fine.