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  #1   Report Post  
Gaffar
 
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Default 3x2 Loft joist strengthening

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

| | |
|-------------------------- | |
| --------|-----------------------|
| | |
|-------------------------- | |
| --------|-----------------------|
| | |
|-------------------------- | |
| --------|-----------------------|
  #3   Report Post  
Lobster
 
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Default

Gaffar wrote:

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.


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
  #6   Report Post  
John Rumm
 
Posts: n/a
Default

Gaffar wrote:

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.


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

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


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

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


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

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.


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.

--
Cheers,

John.

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

Rob Morley wrote:

I usually use a fixed width font - he didn't, so unless I can be


It looks fine here... (in Courier)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #8   Report Post  
dennis@home
 
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Default


"John Rumm" wrote in message
...

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


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.


  #11   Report Post  
Fred
 
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Default


"dennis@home" wrote in message
.uk...

"John Rumm" wrote in message
...

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


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.


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.



  #12   Report Post  
Dave Fawthrop
 
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Default

On Sat, 01 Oct 2005 13:04:05 GMT, "dennis@home"
wrote:

|
| "John Rumm" wrote in message
| ...
|
| Seems ok, not sure about the non screwing bit though.
|
| Screws tend to cut through the wood fibres so may weaken the wood.

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.

--
Dave Fawthrop dave hyphenologist co uk
The London suicide bombers killed innocent commuters.
Animal rights terrorists and activists kill innocent patients.
  #13   Report Post  
 
Posts: n/a
Default

Gaffar wrote:

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



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

  #14   Report Post  
dennis@home
 
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Default


"Dave Fawthrop" wrote in message
...
On Sat, 01 Oct 2005 13:04:05 GMT, "dennis@home"
wrote:

|
| "John Rumm" wrote in message
| ...
|
| Seems ok, not sure about the non screwing bit though.
|
| Screws tend to cut through the wood fibres so may weaken the wood.

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.


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


  #15   Report Post  
Gaffar
 
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Default

John Rumm wrote:

Gaffar wrote:

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.


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

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


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

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


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

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.


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.

--
Cheers,

John.

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


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


  #16   Report Post  
 
Posts: n/a
Default

Gaffar wrote:

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


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


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

  #17   Report Post  
John Rumm
 
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Default

Gaffar wrote:

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


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.

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


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

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)


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).

--
Cheers,

John.

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