8x2" new wooden joists - how much roughly?

[Tim S]

Hi,

I was down at the bungalow finalising plans, and had a rummage under the upstairs (dormer converted) floor.

Turns out that whilst the main floor under the dormers was augmented from the original 4x2" ceiling joists with strapping bits of 8x2" joists running between the external walls and the centre load bearing wall that...

they'd been a bit "cheap" in the alcoves (part of the main room, but restricted ceiling height due to the hipped roof). There, the 4x2 ceiling joists had been made up with a second bit of 4x2 well-fixed on top to bring the floor up. The packer is only present under the floor, not for the whole length of the joist.

Now, whilst this has not been a problem in practise (not a hint of a ceiling crack since the mid 70's when it was done), I'm a bit concerned about putting heavy things in these areas.

The span of all of the joists is about 3.4 meters. The joists overlap (not continuous) over the centre wall).

As I'm stripping the upstairs back to the frame, installing a few extra 8x2" (or presumably 200x50 in modern units), appears to be very nearly a trivial operation if I replicate what's been done already.

Before I decide to forget I even saw any of this, anyone know how much I might expect to pay per meter for suitable wood?

Cheers and TIA

Tim

[dom]

LOL - that's a long-winded way of saying "How much for 200*50 joists?"!

About =A32.50/metre for regularised, treated, C16 (the standard product), a little more for small quantities & delivery.

[Tim S]

[e-mail] coughed up some electrons that declared:

I'm good at that ;->

That's a lot cheaper than I expected! I can fix one entire section for less than 100 quid and a few bolts.

Excellent - thanks.

Tim

[The Natural Philosopher]

in building, materials are about 30% of the cost. The rest is labour.

[dom]

with their rubbish.

I suspect part of the reason for this is that loose timber at the yard tends to *be* rubbish.

When I'm buying "still in the strapping" bundles of 50 or 100 timbers, I might get up to 4 poorer ones on the pack corners, but usually no more.

From the timber merchant's POV, they're probably shifting several bundles a day - but only splitting the odd one open for sale bit by bit. That's the stuff that hangs about to be knocked about. The bulk packs are crane-handled, and so will get dinged on the pack corners only.

I've got the cheek (and because I'm a fairly regular customer) to say "I'll have that one, that one and that one", when I buy loose timber. Lots of other people probably do too. And then you end up with the poorest timbers from each successive pack hanging about in the stack for the unwary.

At least it's better than the diy shed, where it's all banana wood.

[meow2222]

You can stop worrying. Wood is springy and will sag a long way over

3.4m before anything breaks. The reason ther's no sign of sagging is that its strong enough to not sag - so its a very very long way from any risk of breakage.

New build standards are way beyond what is required for a reliable safe structure, thats precisely why the place started out with 2x4.

NT

[Tim S]

[e-mail] coughed up some electrons that declared:

The 4x2's were intended a ceiling joists only, but I take your point.

Not may houses these days are built with anything that substantial.

The reason I looked was that I aim to open out the alcoves even more to add low level storage space into the eaves, so I need to raise an extra bit of floor to the same level as the existing floor.

It looks likely that it's almost as easy to sling a few (about 8 3.5m lengths) new 8x2 joists in alongside the ceiling joists as it does to add packing to the existing joists, and for a ton it will be satisfying to know that another 5ft of floor is nice and stiff. Replicating what's been done already, it will be a case of slide joist up ladder and in through the window, bevel one end, slide into position across the wall plates, nails and noggins as necessary and job done.

But you're right. If it did turn out to be much more than non trival I won't bother.

Cheers

Tim

[dom]

Try standing on a single joist on edge, whilst set on blocks, a 3.4m span floor with 50*100mm joists would be a trampoline.

[meow2222]

I've got a 9ft 2x4, and its rock solid with someone on it, no noticeable bounce. 2x6 would usually have been used for that length rather than 2x4, and of course a floor structure is supported by lots of them.

NT NT

[Tim S]

[e-mail] coughed up some electrons that declared:

Well, yes - can't argue with that.

It's a little more complicated here: Obviously a man on the floor is distributing weight over typically at least two of the joists. The extra

4x2 packing seems well fixed (possibly glued) so it's stiffening the joists to some degree. In addition, the purlin supports are tied onto a beam which ties onto the joists, so there's a bit of a frame structure too. Quite likely the frame may be working the wrong way some of the time, ie it may be holding some of the floor load. Theer's so much wood it's hard to get a mental model of what's doing what.

The bottom line it, AFAICS: as it is, it's a bit dubious, but not seriously and it provably works. I'm changing the equation slightly by adding potentially more load to a larger area of this bit of the floor. So I'm taking the view that if it's easy and inexpensive to bolster it up properly, then no harm in doing so, especially while I've got the place in bits.

I normally shy away from structural things, but clearly it's impossible for me to make it worse by augmenting the existing joists and as I have a working installation method to copy (the bit that's been done properly) I can really make a pigs ear of it.

I can't wait to see the timber yard's faces when I try to haggle them down to somewhere around the figure mentioned (allowing for being in the SE) ;->

Thanks for all the comments.

cheers

Tim

[<me9]

And with herringbone strutting the load is shared with adjacent joists, reducing the deflection.

[Tim S]

Hi,

I'd be really grateful for some opinion on my roof, because I'm clueless when it comes to structures made of random bits of wood nailed together...

a diagram and supporting photos...

It's been like this for 30 years ish, except for the stairwell which was altered maybe 8 years ago. However, the overriding question is:

Is anything there dodgey (I think possibly)? If so, now is the time to fix it, not in 2 years when I've redecorated and fitted the place out(!) ;->

Ultimately, if it should be fixed, I'd rather fix it. If I'm worrying unnecessarily, then I'll leave it.

The specific things I'm concerned about:

a) Dodgey bearing plates?

In the photos 2,4 and 5 we see the correct approach to strengthening the floor (blue joists on diagram). Clearly, there's a wooden plate on top of a single brick centre wall. This looks OK to me. Other ends of joists sit on plate on perimeter wall (inner leaf of cavity wall).

But, in pictures 6 and 7, we see that the joists seems to be sitting on the plasterboard that makes up the ceiling below. I've poked it with a screwdriver and it's plasterboard alright, and there is definately something solid and hard under it (brick in all expectation).

Why anyone would do this is beyond me. I would have though it would be harder to work a full sized sheet of PB in there whilst jugging joists on top, compared to just putting in a wooden plate, fixing joists, then fixing PB.

It doesn't look like it's compressing, but should it get wet I suspect the floor upstairs might go down 10mm in a hurry.

In order to fix, I'd have to take a section of PB out from below, dig and clear the top of the wall and slide a bit of wood in. Not a stupidly difficult job, but it's more work and I'll mess up an otherwise OK ceiling.

I believe the affected areas are where the centre wall is marked yellow in the diagram, though I haven't verified all of it.

Panel's option - should I fix it?

b) Roof tie

In the last two pictures, is the beam marked by red text a "roof tie", designed to stop the roof spreading apart? At first glance I though so. But I'm not sure. Originally, as indicated by the purple lines on the diagram, there were two, at about 1/3 and 2/3 spacing. They've been cut where the dormer is, so I'm not sure how effective they are. Probably relying on being nailed (maybe!) to the dormer frame.

Not really very easy to fix, probably need to put tension bars in threaded steel through the middle of the 8x2 joists.

Should I worry?

c) The original question of inserting 8x2 joists in the alcove areas. Seems I can't easily do this without cutting the "tie beam" (or whatever it is) back further, which scares me a bit.

I ran up Superbeam earlier and assuming the 4x2 joists are C16, I reckon, over a 3.4m span, each one would take a load of about 40kg before deflecting 14mm. I'm not smart enough to make allowances for the extra 4x2 on top spreading the load. I'm >100kg (fat b*stard) and standing on a single joist doesn't seem to cause perceivable deflection. Maybe they are better than C16 and perhaps the frame of the dormer is tying them together.

I would envisage putting maybe 300-400kg of load in the alcove on the bottom left of the diagram in the form of books and tools plus me.

Should I worry?

==========

All of the above can take a tristate answer of yes, no, ask the BCO. I can ask the BCO to have a look first time he's there, but one is always mindful of the "let sleeping dogs lie" addage :) However the BCO is likely to get an eyeful when I get to the re-insulate-the-roof phase in 18 months, so that would be a very bad time for him to notice lots of stuff he wants fixed...

Many thanks indeed for your thoughts.

Cheers

Tim

[Tim S]

Bump - anyone?

Tim S coughed up some electrons that declared: