Strengthening joists by adding additional timber, glueing and screwing. Will
the new 3 inch timber be ....significantly.... weakened if first, a three
eighths diameter hole is drilled three quarters down, the screw driven
through into the lower piece, and then the hole filled by a tight fitting
three eighths wooden plug glued in place?

Just wondering..

ZD

"Zipadee Doodar" wrote in message
k...
Strengthening joists by adding additional timber, glueing and screwing. Will
the new 3 inch timber be ....significantly.... weakened if first, a three
eighths diameter hole is drilled three quarters down, the screw driven
through into the lower piece, and then the hole filled by a tight fitting
three eighths wooden plug glued in place?

Just wondering..

ZD


What?

"Zipadee Doodar" wrote in message
k...
Strengthening joists by adding additional timber, glueing and screwing.
Will
the new 3 inch timber be ....significantly.... weakened if first, a three
eighths diameter hole is drilled three quarters down, the screw driven
through into the lower piece, and then the hole filled by a tight fitting
three eighths wooden plug glued in place?


Is this on top or to the side of the existing timbers ?

If to the side then your BCO will (should) insist on proper coachbolts and
so on.
The use of glue is quite 'innovative' though. Any experts out there on
whether it will actually work or not ?

"Mike" wrote in message
...

"Zipadee Doodar" wrote in message
k...
Strengthening joists by adding additional timber, glueing and screwing.
Will
the new 3 inch timber be ....significantly.... weakened if first, a
three
eighths diameter hole is drilled three quarters down, the screw driven
through into the lower piece, and then the hole filled by a tight
fitting
three eighths wooden plug glued in place?


Is this on top or to the side of the existing timbers ?

If to the side then your BCO will (should) insist on proper coachbolts and
so on.
The use of glue is quite 'innovative' though. Any experts out there on
whether it will actually work or not ?


==============
It would appear that the OP is trying to attach strengthening timbers to the
top of existing joists with screws set in 2" (approx)deep countersinks in
the new 3" timbers. I think that this will probably not leave enough 'meat'
for the screws to give adequate strengthening to the new combined joist even
if it is glued as well. I think the side fixing with coach bolts etc.
suggested will be easier and more reliable.

Cic.

"Cicero" wrote in message
k...

"Mike" wrote in message
...

"Zipadee Doodar" wrote in message
k...
Strengthening joists by adding additional timber, glueing and screwing.
snipped
==============
It would appear that the OP is trying to attach strengthening timbers to the
top of existing joists with screws set in 2" (approx)deep countersinks in
the new 3" timbers. I think that this will probably not leave enough 'meat'
for the screws to give adequate strengthening to the new combined joist even
if it is glued as well. I think the side fixing with coach bolts etc.
suggested will be easier and more reliable.

Cic.



Try to make main joists taller by adding to the top? Why? That doesn't add any
strength to them unless the new section is banded around with metal strapping
every few inches. Or by the method you say of making the joists literally
doubled up side by side.

If you make the spacing between the joists smaller it also adds strength to the
floor by spreading the loads over more joists of the same strength. Like snow
shoes do on the top of soft snow.

Adding bits to the top won't do anything but make the joists taller, unless you
can ensure that joint between the two is properly solid fixed. Cutting bits out
of the additional timber will only make the joint between less strong.

"BigWallop" wrote in message
k...

"Cicero" wrote in message
k...

"Mike" wrote in message
...

"Zipadee Doodar" wrote in message
k...
Strengthening joists by adding additional timber, glueing and
screwing.
snipped
==============
It would appear that the OP is trying to attach strengthening timbers to
the
top of existing joists with screws set in 2" (approx)deep countersinks
in
the new 3" timbers. I think that this will probably not leave enough
'meat'
for the screws to give adequate strengthening to the new combined joist
even
if it is glued as well. I think the side fixing with coach bolts etc.
suggested will be easier and more reliable.

Cic.



Try to make main joists taller by adding to the top? Why? That doesn't
add any
strength to them unless the new section is banded around with metal
strapping
every few inches. Or by the method you say of making the joists literally
doubled up side by side.

If you make the spacing between the joists smaller it also adds strength
to the
floor by spreading the loads over more joists of the same strength. Like
snow
shoes do on the top of soft snow.

Adding bits to the top won't do anything but make the joists taller,
unless you
can ensure that joint between the two is properly solid fixed. Cutting
bits out
of the additional timber will only make the joint between less strong.


=============
I think that the OP has no screws long enough to go through the new 3"
timber into the existing timber - hence the 2" countersinks and plugs. It
doesn't really matter because, as you say, his method appears to be
seriously flawed.

Cic.

"BigWallop" wrote in message
k...
Adding bits to the top won't do anything but make the joists taller,
unless you
can ensure that joint between the two is properly solid fixed.

That's why I wondered if the OP was relying on the glue to make this joint.
My guess is that ResinW isn't quite up to this.

"Mike" wrote in message
...

"BigWallop" wrote in message
k...
Adding bits to the top won't do anything but make the joists taller,
unless you
can ensure that joint between the two is properly solid fixed.

That's why I wondered if the OP was relying on the glue to make this joint.
My guess is that ResinW isn't quite up to this.



:-) LOL !!! But Uni-Bond says it's "stronger than the actual wood". LOL !!!
:-)

BigWallop wrote:

Try to make main joists taller by adding to the top? Why? That doesn't add any
strength to them unless the new section is banded around with metal strapping
every few inches. Or by the method you say of making the joists literally
doubled up side by side.

Don't think that is true is it? Adding another beam on top of an
exisiting one will result in a stronger composite beam even if the two
are not fixed together. Admitedly not as stong as if the two were fixed
such that they were behaving as one.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

The message
from "BigWallop" contains these words:

Adding bits to the top won't do anything but make the joists taller,
unless you
can ensure that joint between the two is properly solid fixed.
Cutting bits out
of the additional timber will only make the joint between less strong.

The method seems to be a bit odd but the basic idea should work. All
that is needed is for the clamping force to be sufficient to overcome
the shear force along the plane and for the fixings to be close enough
together to prevent any buckling.

We don't know what it is the OP is adding to or even how wide but if he
is adding 3 x 2 on top of 3 x 2 he has at least the potential to get
close to quadrupling the strength of each beam. Laying another side by
side would only double it.

Personally I think 5" screws (without any counterbore) at say 15"
centres would probably be overkill but that is little more than a guess.

--
Roger

"John Rumm" wrote in message
...
BigWallop wrote:

Try to make main joists taller by adding to the top? Why? That doesn't
add any
strength to them unless the new section is banded around with metal
strapping
every few inches. Or by the method you say of making the joists
literally
doubled up side by side.

Don't think that is true is it? Adding another beam on top of an
exisiting one will result in a stronger composite beam even if the two
are not fixed together. Admitedly not as stong as if the two were fixed
such that they were behaving as one.

Hmm. I put a re-inforced concrete lintel under an existing wooden lintel
and the BCO insisted I prove the concrete lintel could take the load itself.

Mike wrote:

Hmm. I put a re-inforced concrete lintel under an existing wooden lintel
and the BCO insisted I prove the concrete lintel could take the load itself.

Its a bit different with dissimilar materials like that. The timber beam
would deflect far more for a given load than the concrete one. So having
concrete under a timber one, does to an extent remove the timber one
from the equation, since it will not be able to deflect far enough to
assert its stiffness and take much of the load. It will help spread
point loads on the concrete though.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Try to make main joists taller by adding to the top? Why? That doesn't
add any
strength to them unless the new section is banded around with metal
strapping
every few inches.
=============

.. It
doesn't really matter because, as you say, his method appears to be
seriously flawed.

Cic.

Hmmm. Obviously the opinions on this group vary from month to month,
considering that in previous longish threads, doubling up seemed to be the
consensus way to go.

Actually, the doubling up advice was given by a Local authority planning
officer, presumably speaking from experience and qualification, (although
the counter sinking was my own query), .....assuming the loft will only be
used for storage. The one bit of reliable advice ever given on this forum is
to consult your local planners.

"Zipadee Doodar" wrote in message
k...


Try to make main joists taller by adding to the top? Why? That
doesn't
add any
strength to them unless the new section is banded around with metal
strapping
every few inches.
=============

. It
doesn't really matter because, as you say, his method appears to be
seriously flawed.

Cic.

Hmmm. Obviously the opinions on this group vary from month to month,
considering that in previous longish threads, doubling up seemed to be the
consensus way to go.

Actually, the doubling up advice was given by a Local authority planning
officer, presumably speaking from experience and qualification, (although
the counter sinking was my own query), .....assuming the loft will only be
used for storage. The one bit of reliable advice ever given on this forum
is
to consult your local planners.


=============
Your query was about a particular method of attaching the strengthening
timbers. Your proposed method of screws in deep countersinks and glue would
probably be weak because there would be poor glue contact between the joists
and because there might not be enough strength with screws. Joists are
usually 'sawn' timber which is probably too rough for good gluing.

If it was possible to attach the new timber to the top of the existing joist
by coach bolts going through both new and old timber or (as suggested by
another poster) 'banding' with steel bands then that would be strong .
Either of these methods might not be practicable - possibly because of
access to the underside of the existing joist. In this situation the
alternative suggestion of adding timbers to the side of the existing joist
with coach bolts is a safe and reliable method of strengthening.

Since your 'Local authority planning officer' recommended 'doubling up'
presumably he also suggested some method of attachment. Can you say what
method of attachment he suggested, if any? Perhaps you found his suggestion
unworkable and as a consequence asked here for better advice. I assume that
you haven't asked him about *your* proposed method, but I think that he
would probably say very much the same as people have said here.


Cic.

"Zipadee Doodar" wrote in message
k...


Try to make main joists taller by adding to the top? Why? That doesn't
add any
strength to them unless the new section is banded around with metal
strapping
every few inches.
=============

. It
doesn't really matter because, as you say, his method appears to be
seriously flawed.

Cic.

Hmmm. Obviously the opinions on this group vary from month to month,
considering that in previous longish threads, doubling up seemed to be the
consensus way to go.

Actually, the doubling up advice was given by a Local authority planning
officer, presumably speaking from experience and qualification, (although
the counter sinking was my own query), .....assuming the loft will only be
used for storage. The one bit of reliable advice ever given on this forum is
to consult your local planners.



Do you think he meant doubling them up as in adding height to the joist as you
propose, or doubling up as in laying new joists alongside the original ones and
doubling the amount?

Laying joists of the same size as the originals will actually double the
strength of the floor by decreasing the spaces in between the joists. As long
as they are the same size and shape as the original joists that is.

Since your 'Local authority planning officer' recommended 'doubling up'
presumably he also suggested some method of attachment. Can you say what
method of attachment he suggested, if any?

Using PVA glue to BS 4051 with screws driven through at 6 inch distance -
for storage purposes only remember. We are not talking a full scale loft
conversion here.

Perhaps you found his suggestion
unworkable

Not at all - strikes me as reasonable, because although I am not qualified -
he is. And reasonable for a competent diyer.

and as a consequence asked here for better advice.

"Better?" Alternative maybe.

I assume that
you haven't asked him about *your* proposed method,

I asked here about the countersinking -a query, not a proposed method - the
main method is his, and one which, incidentally has been employed by at
least 2 other people on this group without problems.

but I think that he
would probably say very much the same as people have said here.

Obviously not.

Do you think he meant doubling them up as in adding height to the joist as
you
propose, or doubling up as in laying new joists alongside the original
ones and
doubling the amount?

Laying joists of the same size as the originals will actually double the
strength of the floor by decreasing the spaces in between the joists. As
long
as they are the same size and shape as the original joists that is.

No misunderstanding - he even drew diagrams for me! I agree that laying
additional joists would spread the load, but as other threads here have
pointed out, I feel that could be to the detriment of the ceiling. I am
happy with the general idea of increasing the height. Just the final details
to settle. This is not a full scale loft conversion - just to support
chipboard floor and boxes of household junk that SWMBO can't bare to part
with.

Thanks for taking time to reply

Zipadee Doodar wrote:

Hmmm. Obviously the opinions on this group vary from month to month,

Given that the "group" is a collection of individuals, is that so
surprising? ;-)

considering that in previous longish threads, doubling up seemed to be the
consensus way to go.

I think the consensus still is. Adding height to a joist will add
strength to it (more than adding the same quantity of timber in width).
The way you fix the timber on top however will alter how much strength
you add. You get least benefit if the timber is just resting on top, and
most if they are bonded together along their length.

Actually, the doubling up advice was given by a Local authority planning
officer, presumably speaking from experience and qualification, (although
the counter sinking was my own query), .....assuming the loft will only be

I think it was the counter sinking bit that was causing the main
problem. Why exactly do you want to countersink like this?

used for storage. The one bit of reliable advice ever given on this forum is
to consult your local planners.

The advice you get here is, as always, worth what you paid for it,
perhaps even more.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/