Plating/trapping stacked joists with ply
Tim W
If you look at the joist on the far right of:
http://photos.dionic.net/v/public/bungalow/2009-04-06-img_0016.jpg.html
you'll see that it is a 4x2" stacked on top of the original 4x2" ceiling
joist before the roof was converted to a dormer.
I have a few like this, mostly in placed where the builder thought it was
too hard to put in 8x2s for some reason...
I'm proposing to plate these both sides with plywood to stiffen the assembly
for good measure. Plating also allows me to bridge out the horrendous gaps
in the top left by previous plumbers which will be essential prior to
reflooring with boards.
I will go to B&Q or wherever and get them to cut a 8x4' sheet into 6 strips
of 8'x7.5" wide.
Question:
What thickness and type of ply?
I think 18mm structural soft ply (eg spruce) would be more than adequate,
but it's fairly expensive compared to 12mm ply, which might be enough.
My plan it to screw the ply to the sides of the joist with a *lot* of small
turbogold or similar type screws (1.5" or so long). Possibly in 4 rows of
screws, each row being towards the top and bottom of each 4x2" joist at a
horizontal spacing of 4-6". This is easy enough with an electric driver. I
don't think glue would help as the joists are rough as buggery.
Any thoughts?
I'd like to do it before running wires down these joists, so I've brought
this job forward.
Cheers
Tim
--
Tim Watts
This space intentionally left blank...
The Medway Handyman
They make structural joists out of what looks to be 11mm OSB, so that would
prolly do the job.
I'd go for glue & screw myself, using a gap filling polyurethane.
--
Dave - The Medway Handyman
www.medwayhandyman.co.uk
Tim W
wibbled on Saturday 02 January 2010 12:13
> They make structural joists out of what looks to be 11mm OSB, so that
> would prolly do the job.
And cheaper by ba factor of 2... I've just read up on OSB - looks like it
would do nicely.
What's the difference between OSB2 and OSB3 - anything I should care about?
> I'd go for glue & screw myself, using a gap filling polyurethane.
Something like:
http://tooltray.com/abrasives,-fixings-&-hardware/adhesives-&-tapes/grab-&-
nail-free-adhesives/evo-grip-solvented-gap-filling-adhesive-
c20.htm?utm_source=Tooltray&utm_medium=Froogle&utm_campaign=Shopping
?
Haven't used such things, but that looks like a very good idea. With that,
the entire assembly should be stronger than plain 8x2 given the ply itself
will contribute to stiffness as well as prevent the original 2 timbers
sliding.
Thanks Dave!
Roof
"Tim W" <t...@dionic.net> wrote in message
news:hhnb0q$3v1$1...@news.eternal-september.org...
Simply on the basis of comparison of section properties, you need 4 @ 4" x
2" for flexural strength and 8 @ 4" x 2" for stiffness / deflection to be
equal to a single 8" x 2".
To get the re-assurances you need, that what you are proposing to do is
structurally competent, you should employ a structural engineer.
Bruce
Does the Institution of Structural Engineers approve of your touting
for business in this brazen manner? Aren't there better and more
effective ways for an under-employed or out-of-work structural
engineer to find paid employment?
PeterC
>> They make structural joists out of what looks to be 11mm OSB, so that
>> would prolly do the job.
>
> And cheaper by ba factor of 2... I've just read up on OSB - looks like it
> would do nicely.
>
> What's the difference between OSB2 and OSB3 - anything I should care about?
OSB/1
General purpose applications in dry conditions. Furniture and interior
fitments
ċç OSB/2
Load-bearing applications in dry conditions
ċç OSB/3
Load-bearing applications in humid conditions
ċç OSB/4
Heavy-duty load-bearing applications in dry or humid conditions
From:
http://www.osb-info.org/rightgrade.html
--
Peter.
2x4 - thick plank; 4x4 - two of 'em.
Dave Osborne
> The Medway Handyman <davi...@nospamblueyonder.co.uk>
> wibbled on Saturday 02 January 2010 12:13
>
>
>> They make structural joists out of what looks to be 11mm OSB, so that
>> would prolly do the job.
>
> And cheaper by ba factor of 2... I've just read up on OSB - looks like it
> would do nicely.
>
> What's the difference between OSB2 and OSB3 - anything I should care about?
>
It's all here:
http://www.wpif.org.uk/PanelGuide.asp
Section 2.3 and Annexe 2B
There are different types and different service classes.
Quote from a previous thread:
It seems [...] that the average Builder/Builder's Merchant has
cottoned on to the fact that you need Service Class 2 product and OSB3
product should be marked as such (i.e. service class 2), so you don't
need to explicitly know it's OSB3.
also http://www.osb-info.org/index.php?lang=uk has good stuff
and the thread I referred to above:
Roof
"Bruce" <docne...@gmail.com> wrote in message
news:q7guj5t16us920uku...@4ax.com...
You've lost me.
You don't work in a recruitment agency, do you?
Bruce
You know, I really hoped that we already had.
>You don't work in a recruitment agency, do you?
Not everyone has the same motivation in life as you.
You are giving structural engineers a bad name, so fuck off.
The Medway Handyman
> The Medway Handyman <davi...@nospamblueyonder.co.uk>
> wibbled on Saturday 02 January 2010 12:13
>
>
>> They make structural joists out of what looks to be 11mm OSB, so that
>> would prolly do the job.
>
> And cheaper by ba factor of 2... I've just read up on OSB - looks
> like it would do nicely.
>
> What's the difference between OSB2 and OSB3 - anything I should care
> about?
>
>> I'd go for glue & screw myself, using a gap filling polyurethane.
>
> Something like:
I was thinking of
http://www.axminster.co.uk/product-Titebond-Polyurethane-Glue-22585.htm
Roof
Yet another quality post. Look forward to further informed contributions
from you.
John Rumm
> To get the re-assurances you need, that what you are proposing to do is
> structurally competent, you should employ a structural engineer.
Or alternatively take that pragmatic approach that its been there like
that for 30 years without any structural problems, so you could use the
money you would otherwise spend on fees to further consolidate the
obviously adequate structure. ;-)
(IIRC, the spans in question are actually relatively short, so 8x2 was
probably quite over specced in the first place).
Plating the layered joists would add stiffness and reduce the floor
bounce if there is any. Adding some herringbone bracing would also
increase stiffness, and that's also an easy retrofit.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
Bruce
<redredred...@gmail.com> wrote:
>Yet another quality post. Look forward to further informed contributions
>from you.
You have *never* posted anything remotely helpful here. You post only
out of selfish self-interest.
The Natural Philosopher
> Roof wrote:
>
>> To get the re-assurances you need, that what you are proposing to do
>> is structurally competent, you should employ a structural engineer.
>
> Or alternatively take that pragmatic approach that its been there like
> that for 30 years without any structural problems, so you could use the
> money you would otherwise spend on fees to further consolidate the
> obviously adequate structure. ;-)
>
> (IIRC, the spans in question are actually relatively short, so 8x2 was
> probably quite over specced in the first place).
>
> Plating the layered joists would add stiffness and reduce the floor
> bounce if there is any. Adding some herringbone bracing would also
> increase stiffness, and that's also an easy retrofit.
>
glued, plating wont make any difference.
Tim W
wibbled on Saturday 02 January 2010 14:30
> Roof wrote:
>
>> To get the re-assurances you need, that what you are proposing to do is
>> structurally competent, you should employ a structural engineer.
>
> Or alternatively take that pragmatic approach that its been there like
> that for 30 years without any structural problems, so you could use the
> money you would otherwise spend on fees to further consolidate the
> obviously adequate structure. ;-)
Aye that's true - and you've seen it personally.
It started with "how do I bung up all these holes (4-6" wide 1-2" deep
hacks) made by random plumbers". It seemed a short plate either side
supporting an infill lump of wood[1] was the easiest solution. Then I said,
well, plating's easy and cheap so why not, just for completeness...
[1] I'm not going to fit infill blocks the traditional way as the holes are
ragged with non flat bottoms - each one would involve major surgery to clean
up the hole as well as a custom planed blocks).
The floor has been of that construction for 30+ years, but as the house has
previously been owned by elderly folk (AFAIK from neighbours) it's possible
that I might be dynamically loading the floor a lot more and more of the
time by using it as our TV room (think 6 mates come round and everyone's
bouncing around up there.)
It followed my usual line of reasoning that it's so easy to do, why not...
Just be better to do it before clipping cables and pipes there :)
> (IIRC, the spans in question are actually relatively short, so 8x2 was
> probably quite over specced in the first place).
That's true. Mind you, the stacked 4x2's are several in a row right by the
door (constant dynamic load) and the way they aren't fixed to much at one
end, they are doing little more than add thickness to the 4x2's.
It's this fact that bothers me more. The correct way would have been to use
joist hangers off the chimney breast (I think - I know chimney stacks have
issues with damp). But the builder didn't - he shoved a bit of 3x3 along the
chimney wall across the ceiling joists, then cut 3" out of the extra 4x2 and
hung the 1" ear over the 3x3, with a big nail through the side for good
measure.
> Plating the layered joists would add stiffness and reduce the floor
> bounce if there is any. Adding some herringbone bracing would also
> increase stiffness, and that's also an easy retrofit.
>
I did read the excellent WIKI article on bracing. I have a use for a few of
those too - but plating seemed easier to me (less measuring and cutting -
just a load of standard strips of OSB).
Tim W
wibbled on Saturday 02 January 2010 17:14
That's alas not the case. I'm lucky to find a nail every 4 foot. They can
certainly slide...
But yes, that is how I would have done it.
Tim W
wibbled on Saturday 02 January 2010 13:12
> It's all here:
>
> http://www.wpif.org.uk/PanelGuide.asp
>
> Section 2.3 and Annexe 2B
>
> There are different types and different service classes.
>
> Quote from a previous thread:
>
> It seems [...] that the average Builder/Builder's Merchant has
> cottoned on to the fact that you need Service Class 2 product and OSB3
> product should be marked as such (i.e. service class 2), so you don't
> need to explicitly know it's OSB3.
>
>
> also http://www.osb-info.org/index.php?lang=uk has good stuff
>
> and the thread I referred to above:
>
> http://preview.tinyurl.com/yagn3x5
Dave and PeterC,
That's cleared it up nicely - thanks to you both.
Tim W
wibbled on Saturday 02 January 2010 12:52
>>Simply on the basis of comparison of section properties, you need 4 @ 4" x
>>2" for flexural strength and 8 @ 4" x 2" for stiffness / deflection to be
>>equal to a single 8" x 2".
>>
>>To get the re-assurances you need, that what you are proposing to do is
>>structurally competent, you should employ a structural engineer.
>
>
> Does the Institution of Structural Engineers approve of your touting
> for business in this brazen manner? Aren't there better and more
> effective ways for an under-employed or out-of-work structural
> engineer to find paid employment?
As John Rumm said, it's obviously basically serviceable. I'm just making it
a bit better and certainly no worse, so I'm not at all bothered about
certifications. I have the floor up, the crap is cleared and there's no
pipes/wires in the way, so my motto is: if it's easy, why not... It will
never be this trivial to do again once the services go in. Simples ;-)
John Rumm
It will have less effect certainly, however the plating itself (when
restrained from Euler buckling) has significant significant stiffness
all by itself - much as a plate does in a flitch beam.
Tim W
wibbled on Saturday 02 January 2010 14:15
> Tim W wrote:
>>> I'd go for glue & screw myself, using a gap filling polyurethane.
>>
>> Something like:
>
> I was thinking of
> http://www.axminster.co.uk/product-Titebond-Polyurethane-Glue-22585.htm
>
>
Thanks Dave - if that's what you've used, then that's what I'll get.
John Rumm
> Aye that's true - and you've seen it personally.
Indeed, and I did not break it so it must be fairly decent ;-)
> It started with "how do I bung up all these holes (4-6" wide 1-2" deep
> hacks) made by random plumbers". It seemed a short plate either side
> supporting an infill lump of wood[1] was the easiest solution. Then I said,
> well, plating's easy and cheap so why not, just for completeness...
>
> [1] I'm not going to fit infill blocks the traditional way as the holes are
> ragged with non flat bottoms - each one would involve major surgery to clean
> up the hole as well as a custom planed blocks).
A quick and easy fix for notches that restores the compressive strength
is a pair of folding wedges. Glue up, hammer into place and add a pin or
two if you need:
http://wiki.diyfaq.org.uk/index.php?title=Wedges
> The floor has been of that construction for 30+ years, but as the house has
> previously been owned by elderly folk (AFAIK from neighbours) it's possible
> that I might be dynamically loading the floor a lot more and more of the
> time by using it as our TV room (think 6 mates come round and everyone's
> bouncing around up there.)
Oooerr, your TV sounds better than mine! ;-)
Plating the sides of any dodgy looking ones will add piece of mind for
little cost. Adding some herringbone will often take lots of bounce out
of a floor as well.
> It followed my usual line of reasoning that it's so easy to do, why not...
>
> Just be better to do it before clipping cables and pipes there :)
Pipes don't respond to being nailed to. DAMHIK ;-)
>> (IIRC, the spans in question are actually relatively short, so 8x2 was
>> probably quite over specced in the first place).
>
> That's true. Mind you, the stacked 4x2's are several in a row right by the
> door (constant dynamic load) and the way they aren't fixed to much at one
> end, they are doing little more than add thickness to the 4x2's.
If you plate them it will add greatly to the stiffness. Bracing between
them also improves the load sharing. Try and avoid too many plasterboard
joints on the ceiling under where you expect most flex.
> It's this fact that bothers me more. The correct way would have been to use
> joist hangers off the chimney breast (I think - I know chimney stacks have
> issues with damp). But the builder didn't - he shoved a bit of 3x3 along the
> chimney wall across the ceiling joists, then cut 3" out of the extra 4x2 and
> hung the 1" ear over the 3x3, with a big nail through the side for good
> measure.
Depending on joist orientation, they often use a stringer between a
couple of joists either side of the chimney, and then hand the
intermediate joists off the stringer.
Have you got a drawing of the joist layout and where the support points are?
>> Plating the layered joists would add stiffness and reduce the floor
>> bounce if there is any. Adding some herringbone bracing would also
>> increase stiffness, and that's also an easy retrofit.
>>
>
> I did read the excellent WIKI article on bracing. I have a use for a few of
> those too - but plating seemed easier to me (less measuring and cutting -
> just a load of standard strips of OSB).
>
> Cheers
>
> Tim
>
--
Simon Stroud
> The Medway Handyman <davi...@nospamblueyonder.co.uk>
> wibbled on Saturday 02 January 2010 14:15
>
>> Tim W wrote:
>
>>>> I'd go for glue & screw myself, using a gap filling polyurethane.
>>>
>>> Something like:
>>
>> I was thinking of
>> http://www.axminster.co.uk/product-Titebond-Polyurethane-Glue-22585.htm
>>
>>
>
> Thanks Dave - if that's what you've used, then that's what I'll get.
>
> Cheers
>
> Tim
>
few bottles of recently, it's very advisable to wear gloves. If you get any
of it on your hands and it dries, it can't be washed off or removed with any
skin-friendly solvents so you just have to leave it for about 4 days to wear
off. Not handy if, like I was, you are going through an "attending
interviews at possibly short notice" phase. Meeting and greeting strangers
with hands that look extremely brown and dirty takes some explaining.
Regards,
Simon.
Tim W
wibbled on Saturday 02 January 2010 12:42
> Simply on the basis of comparison of section properties, you need 4 @ 4" x
> 2" for flexural strength and 8 @ 4" x 2" for stiffness / deflection to be
> equal to a single 8" x 2".
>
> To get the re-assurances you need, that what you are proposing to do is
> structurally competent, you should employ a structural engineer.
I'd forgotten I killfiled you until Bruce quoted this.
If I needed an engineer for anything, I could really do with one to help me
design adequate ventilation paths through a complicated timber structure of
2 roofs and a dormer wall, where the stock "as new" solutions are wholly
inapplicable. But as I don't know any (or have any clue how to find one or
evaluate them) I expect I'll muddle through.
As for the floor - its works, I will make it work a little better (possibly
a lot better) and guaranteed it will not be any the worse, so no, I don't
need an engineer for this. Your advice might be on track if I were doing the
loft conversion and had to make the compromise the original builders made
and get it past the BCO, but this is irrelevant here.
Just after a few practical tips to perhaps save me from overdoing it with
relatively expensive 18mm ply.
Practical tips received with thanks - they just halved the materials cost
(OSB 11mm is about 10 quid a sheet rather than 18mm ply which is 25 quid.)
The Medway Handyman
> The Medway Handyman <davi...@nospamblueyonder.co.uk>
> wibbled on Saturday 02 January 2010 14:15
>
>> Tim W wrote:
>
>>>> I'd go for glue & screw myself, using a gap filling polyurethane.
>>>
>>> Something like:
>>
>> I was thinking of
>> http://www.axminster.co.uk/product-Titebond-Polyurethane-Glue-22585.htm
>>
>>
>
> Thanks Dave - if that's what you've used, then that's what I'll get.
I've not used it in your application. Half lapping 4 x 4 newell posts onto
6 x 2 deck frames. Used with a few coach bolts its 'kin strong.
The Medway Handyman
> "Tim W" <t...@dionic.net> wrote in message
> news:hho7j6$14e$2...@news.eternal-september.org...
>> The Medway Handyman <davi...@nospamblueyonder.co.uk>
>> wibbled on Saturday 02 January 2010 14:15
>>
>>> Tim W wrote:
>>
>>>>> I'd go for glue & screw myself, using a gap filling polyurethane.
>>>>
>>>> Something like:
>>>
>>> I was thinking of
>>> http://www.axminster.co.uk/product-Titebond-Polyurethane-Glue-22585.htm
>>>
>>>
>>
>> Thanks Dave - if that's what you've used, then that's what I'll get.
>>
>> Cheers
>>
>> Tim
>>
> If it's anything like the polyurethane "Gorilla Glue" which I have
> used a few bottles of recently, it's very advisable to wear gloves.
> If you get any of it on your hands and it dries, it can't be washed
> off or removed with any skin-friendly solvents so you just have to
> leave it for about 4 days to wear off.
Good point, exactly my experience.
The Natural Philosopher
> The Natural Philosopher wrote:
>> John Rumm wrote:
>>> Roof wrote:
>>>
>>>> To get the re-assurances you need, that what you are proposing to do
>>>> is structurally competent, you should employ a structural engineer.
>>>
>>> Or alternatively take that pragmatic approach that its been there
>>> like that for 30 years without any structural problems, so you could
>>> use the money you would otherwise spend on fees to further
>>> consolidate the obviously adequate structure. ;-)
>>>
>>> (IIRC, the spans in question are actually relatively short, so 8x2
>>> was probably quite over specced in the first place).
>>>
>>> Plating the layered joists would add stiffness and reduce the floor
>>> bounce if there is any. Adding some herringbone bracing would also
>>> increase stiffness, and that's also an easy retrofit.
>>>
>> If the layer cannot slide over each other, by dint of being screwed or
>> glued, plating wont make any difference.
>
> It will have less effect certainly, however the plating itself (when
> restrained from Euler buckling) has significant significant stiffness
> all by itself - much as a plate does in a flitch beam.
>
Why not simply fibreglass over the lot?
Or put coachbolts every foot?
John Rumm
> John Rumm wrote:
>>> If the layer cannot slide over each other, by dint of being screwed
>>> or glued, plating wont make any difference.
>>
>> It will have less effect certainly, however the plating itself (when
>> restrained from Euler buckling) has significant significant stiffness
>> all by itself - much as a plate does in a flitch beam.
>>
> some yes.
>
> Why not simply fibreglass over the lot?
Can't see that being any easier than screwing a plank to the side, and
certainly less desirable for fixing to or drilling through later.
> Or put coachbolts every foot?
You would have to countersink them flush to let the floorboard sit over.
Neil
<De-lurk>
Schools back this week so Ruth wont be back until Feb.
<Re-lurk>
Rick
> Hi,
>
> If you look at the joist on the far right of:
>
> http://photos.dionic.net/v/public/bungalow/2009-04-06-img_0016.jpg.html
>
> I think 18mm structural soft ply (eg spruce) would be more than adequate,
> but it's fairly expensive compared to 12mm ply, which might be enough.
>
> My plan it to screw the ply to the sides of the joist with a *lot* of
> small
> turbogold or similar type screws (1.5" or so long). Possibly in 4 rows of
> screws, each row being towards the top and bottom of each 4x2" joist at a
> horizontal spacing of 4-6". This is easy enough with an electric driver. I
> don't think glue would help as the joists are rough as buggery.
I would not bother with glue, use OSB as discussed ... but I would not use
csk head screws .... by the time they pull tight in the OSB there is not
much surface area to spread load of fixing.
If it were me I'd probably use a flange head screw of around 40 - 45 mm
length 5 x 40 ( 13/4" 10's) at 150 centres
pan head or even round head if you can't get flange ( I buy stainless steel
pan head self tappers for such work ... immense holding power in wood)
Tim W
wibbled on Tuesday 05 January 2010 22:38
> I would not bother with glue, use OSB as discussed ... but I would not use
> csk head screws .... by the time they pull tight in the OSB there is not
> much surface area to spread load of fixing.
>
> If it were me I'd probably use a flange head screw of around 40 - 45 mm
> length 5 x 40 ( 13/4" 10's) at 150 centres
>
> pan head or even round head if you can't get flange ( I buy stainless
> steel pan head self tappers for such work ... immense holding power in
> wood)
Rick - this is a very good point I hadn't thought about. Thanks!
Tim
geraldthehamster
> "Tim W" <t...@dionic.net> wrote in message
>
> news:hho7j6$14e$2...@news.eternal-september.org...
>
>
>
> > Â wibbled on Saturday 02 January 2010 14:15
>
> >> Tim W wrote:
>
> >>>> I'd go for glue & screw myself, using a gap filling polyurethane.
>
> >>> Something like:
>
> >> I was thinking of
> >>http://www.axminster.co.uk/product-Titebond-Polyurethane-Glue-22585.htm
>
> > Thanks Dave - if that's what you've used, then that's what I'll get.
>
> > Cheers
>
> > Tim
>
> If it's anything like the polyurethane "Gorilla Glue" which I have used a
> few bottles of recently, it's very advisable to wear gloves. If you get any
> of it on your hands and it dries, it can't be washed off or removed with any
> skin-friendly solvents so you just have to leave it for about 4 days to wear
> off. Not handy if, like I was, you are going through an "attending
> interviews at possibly short notice" phase. Meeting and greeting strangers
> with hands that look extremely brown and dirty takes some explaining.
>
> Regards,
>
> - Show quoted text -
It's worth having some of the solvent used to clean PU foam guns to
hand. Then if you do get any PU glue (or foam) on your hands, you can
clean it off before it cures. Obviously the worst thing you can do is
try to wash it off with water ;-)
Otherwise it attracts the dirt and cures with the moisture in your
hands.
Cheers
Richard