3x2 Loft joist strengthening

[Gaffar]

Hopefully someone on here has the experience advice to help me (never been let down yet)

apologies for the slightly long post

Just finshed refurbishing the whole house (complete overskim and painting as well as an extension).

I have just started to board the loft for storage having cleared out the very old insulation and laid new stuff, have just realised that the old joists in the loft are only 3x2's

The question I have is I have bought 22mm 2400x600 flooring grade chipboard - green backed stuff- (without thinking) and am now not sure if these boards will be too heavy for the joists to handle The loft area is about 40sqm that I am boarding with the rest staying under old insulation for now.

The house is a semi from the 30's if it's any help and a bad ascii diagram below shows the setup of the joists The joists are laid 320mm apart and are joined together where they overlap. The 2 edge vertical lines are 6x2's above the joists (I thing the 3x2's are connected to these from underneath. The vertical line in the middle is a partition wall below

The celing underneath seems to be lath boards with cement/plaster which was artexted and has now been overboarded and reskimmed

A structural engineer spared me a couple of minutes on the phone and advised the joists should be ok to hold the weighth of the boards (although the celing below may crack but should not collapse), also advised agaist screwing boards into joists if possible as they may crack and distributing light storage weight into the sides.

Is this sound advice and is there anything you guys can think off that may help the situation or provide reassurances. WOuld writing off the cost of these boards be wise and just replace with ordinary loft bvoards that can be bought in B&Q and the likes.

Many thanks in advance for any advice

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[Rob Morley]

You need to use a fixed width font like Courier to make ASCII art work.

While the boards you have are heavier than the nasty little ones you get in the sheds, they will probably also spread the load a bit better when you are walking on them, and that's when the load will be highest. As he said the weakness will probably result in flexing rather than collapse, and if you're lucky this won't show through the new plasterboard. As you already have the boards why not lay them and see what happens when you walk on them - listen for creaking, feel for movement and have someone downstairs to shout if a crack starts to open up. If it survives that then store stuff at the edges or over the middle wall.

[Lobster]

I don't think the issue is the boards themselves; this is more to do with what you intend to store up there once the boards are down.

David

[Fred]

I think the OP posted this in plain text so the choice of font is yours.

In OE: View>Text size>fixed font

should make it all happen.

[Rob Morley]

I usually use a fixed width font - he didn't, so unless I can be bothered to try different proportional fonts to see which one makes it line up it isn't going to display properly.

Fortunately I don't use Outlook Express.

[John Rumm]

You omit the one bit of info we really need: what is the span of the existing joists?

So you have in effect the weight of two ceilings below....

Seems ok, not sure about the non screwing bit though.

Ordinary loft boards not not much lighter, so I would not bother. Stack stuff over the supporting wall or near the edges, or if you are feeling really adventurous you could stick in a "floor grade" set of joists etc to bring it up to loft conversion standards.

[John Rumm]

It looks fine here... (in Courier)

[dennis]

Screws tend to cut through the wood fibres so may weaken the wood.

A sharp nail will displace the fibres so the wood remains strong.

Nails pull out easier than screws but this shouldn't be a problem with flooring.

I doubt if the actual strength of the wood is very different after the screws have been inserted.

[Rob Morley]

The joists on the right are pushing bits of wall too far to the right (Courier New)

[Rob Morley]

Replying to myself:

It's a tab spacing thing - apparently this version of Gravity thinks a standard tab should be 7 spaces, and there's no way to change it. Of course the standard advice when creating ASCII art is "use a fixed width font and don't use tabs" :-)

[Fred]

Not sure if I'd like to hammer nails into the joists of a ceiling. It's certainly one way of opening up joints between the sheets of plasterboard! I think I'd stick to screws.

[Dave Fawthrop]

Non on my screwed boards show any sign of weakening. | | A sharp nail will displace the fibres so the wood remains strong. | | Nails pull out easier than screws but this shouldn't be a problem with | flooring.

IME this is totally untrue, every time I have taken up a floor board for the last 40 years, I have screwed it back. They all get taken up again, for some reason, and screws IME are much easier to take out than nails.

[meow2222]

you forgot to tell us how long those 2x3s are. If theyre say 10', theyll be adequate for light to medium storage, but once you get into 'medium' you may get cracks appears on the ceiling.

If theyre 20 ft, I'd be wary of walking on them any more than really essential. Note theres usually a frame wall halfway along that supports them, so the span is usually half the loft gable dimesnion.

The boards are a non issue. I would have picked 1/2" for a light structure like that, as it weighs less and is adequate, but its no big. I dont know why you got 22mm.

If theyre 10' long, Your best option is to glue and screw 2x3s onto the top of the existing 2x3s, thus creating a 2x6 structure. Then you've got a full duty floor fit for a living space. No, not to regs for habitable, but perfectly fit for it, and you can put just about whatever you want up there.

Or if theyre 20' long, maybe add 2x4.

Boarding a loft is one thing, but if you add stair access, you'll be into BR territory, which is more complex.

Oh, dont nail anything, that would be dim.

NT

[dennis]

What is untrue? Nothing in your post disagrees with what I said.

[Gaffar]

Joist spans are about 6.5 feet each with 0.5 foot overlap between the 2 approx 12 feet in total

With regards storage nothing extraordinary, 5-6 boxes of spare tiles, old books, baby pushchair bath, etc

From all the replies, it seems to me it should be ok, especially as I've been up there for the best part of a week. with an industrial hoover up there (cleaning old insulation) and 3 bags full of dust(weighing at least 20-25kg each all at the same time, also unknowingly stacked 8 boards on top of each other when taking them up and thankfully no visible cracks in the ceiling yet. The only sags i can see seem to be a red herring as it is under an area of the loft that I have not been in (probably the result of not overboarding securely enough)

Thanks for all the replies and reassurances

Regards Gaffar

[meow2222]

no worry then - im assuming its supported at the 6.5 ft place. If you mean 12ft between supports, I wouldnt put much up there at all, but a few boxes are no biggie.

NT

[John Rumm]

In which case, much less to worry about. I just did some calcs in Superbeam. Assuming a floor made from joists of this size configured as a load sharing system (i.e. flooring over the joists). When subjected to a nominal uniform floor load of 0.8kN/m you are only getting deflections of about 12mm in the centre of the span. Whilst this would not meet building regs for a genuine floor, for a storage space with less loading you are unlikly to get ceiling damaging deflection.

Put the heavy stuff toward the edges or over the walls and you should be fine.

You will get a certain amount of sag just due to "creep" (i.e. the tendancy for the joists to deform a little over time under load).