Does anyone know how to calculate suitable board thickness for joists
at 1000mm centres? I have some stones with a roof in France I want to
board out, and the joists are approx 220mm x 150mm at 1000mm centres.
Currently the rotten boards look like waney edge oak boards, around
30mm thick, but too soft now to know if that was ever a good idea.

I'm assuming ply would be the best material, assuming eventually I'll
want to lay some smarter looking regular floor boards on these.

Thanks.

sheepish wrote:
Does anyone know how to calculate suitable board thickness for joists
at 1000mm centres? I have some stones with a roof in France I want to
board out, and the joists are approx 220mm x 150mm at 1000mm centres.
Currently the rotten boards look like waney edge oak boards, around
30mm thick, but too soft now to know if that was ever a good idea.

I'm assuming ply would be the best material, assuming eventually I'll
want to lay some smarter looking regular floor boards on these.

Thanks.


Calculate? that's a bit 'advanced' innit?

Trouble is, what are your criteria? how much give do you think is
acceptable.

In all likelihood the joist themselves are out of spec anyway. Consider
just using normal flooring but adding more joists and herringbone bracing.

sheepish wrote:
Does anyone know how to calculate suitable board thickness for joists
at 1000mm centres? I have some stones with a roof in France I want to
board out, and the joists are approx 220mm x 150mm at 1000mm centres.
Currently the rotten boards look like waney edge oak boards, around
30mm thick, but too soft now to know if that was ever a good idea.

I'm assuming ply would be the best material, assuming eventually I'll
want to lay some smarter looking regular floor boards on these.

You could try http://www.woodbin.com/calcs/sagulator.htm which might help
calculate any deflection.



--
Dave
The Medway Handyman
www.medwayhandyman.co.uk
01634 717930
07850 597257

You don't say what the span is on the joists.

If we assume joists of 220x150mm at 1m centres are equivalent to
joists of 220x50mm at 330mm centres in loadbearing ability - that
would be a typical "design from tables" figures for a 4m span (at
600mm centres). It needs proper calculation to be certain - not my
estimate.

But if your span is 4m, your joists are probably adequate.

(Assuming all in good condition and haven't suffered the same fate as
the floorboards and are equivalent to at least a C16 strength class -
remember you're putting a lot of reliance in a very few joists, a
single failure could result in a floor collapse)

It would have to be a very thick ply for 1m centres - the Building
Regulations (and you have to work to the French regulations, not ours)
specify 19mm or better tongue and groove for 600mm centres - however
oak flooring is reasonably priced in France - the original builders
using 30mm solid oak boards probably knew what they were doing.

If you want to run the calculations for yourself, I recommend
Structural Timber Design, Abdy Kermani - Blackwell Science ISBN
0632050918

http://www.amazon.co.uk/Structural-T...566208&sr=11-1

In all likelihood the joist themselves are out of spec anyway. Consider
just using normal flooring but adding more joists and herringbone bracing.

That may be the simplest solution - add 50x220mm joists in between
every pair of original joists, taking the centres to 500mm, then board
out in 19mm t&g.

On 25 Apr, 12:38, The Natural Philosopher wrote:
sheepish wrote:

Does anyone know how to calculate suitable board thickness for joists
at 1000mm centres? I have some stones with a roof in France I want to
board out, and the joists are approx 220mm x 150mm at 1000mm centres.
Currently the rotten boards look like waney edge oak boards, around
30mm thick, but too soft now to know if that was ever a good idea.

I'm assuming ply would be the best material, assuming eventually I'll
want to lay some smarter looking regular floor boards on these.

Thanks.

Calculate? that's a bit 'advanced' innit?

Trouble is, what are your criteria? how much give do you think is
acceptable.

In all likelihood the joist themselves are out of spec anyway. Consider
just using normal flooring but adding more joists and herringbone bracing.

Once youve calculated you can get 1 piece and check it does as
expected. Ply is indeed the toughest option for 2 reasons:
- not only is it the toughest of the wood products
- but also its sheet format means all loads are spread over a wide
area of wood, unlike traditional boards.

9x6 is very large joists, so unless its a huge building those will be
more than strong enough.

I wouldnt want to use chip. Nor 1" boards.

Ply is not cheap, there are 2 optoins to reduce costs if needed.
1. Use OSB, whish is somewhat like ply but cheaper
2. Run some extra smaller joists at 90 deg to the existing ones,
positioning them so each ply sheet is supported on all 4 sides. Then
you could use half inch ply. I'd only do that if present joists arent
worth looking at and will be covered.


NT

On 2007-04-24, 21:21 Z,
in oups.com,
sheepish wrote:
Does anyone know how to calculate suitable [plywood sheathing]
board thickness for joists at 1000 mm centres? I'm assuming ply
would be the best material, assuming eventually I'll want to lay
some smarter looking regular floor boards on these.

sheepish: The design requirement is stiffness driven. In your
specific scenario, we can multiply the required design concentrated
live load, P, by 1.206 to account for the required design dead load.
The typical deflection requirement for floors is delta = L/360.
Typical plywood modulus of elasticity is E = 8000 MPa. Assuming no
piece of your plywood has a width less than b = 900 mm, then the
required plywood thickness would be t = [108.5*P*(L^2)/(E*b)]^0.333
= {108.5(1335 N)[(1000 mm)^2]/[(8000 MPa)(900 mm)]}^0.333 = 27.1 mm.

On 26 Apr, 15:44, "David H. Neumann" wrote:
On 2007-04-24, 21:21 Z,
egroups.com,
sheepish wrote:

Does anyone know how to calculate suitable [plywood sheathing]
board thickness for joists at 1000 mm centres? I'm assuming ply
would be the best material, assuming eventually I'll want to lay
some smarter looking regular floor boards on these.

sheepish: The design requirement is stiffness driven. In your
specific scenario, we can multiply the required design concentrated
live load, P, by 1.206 to account for the required design dead load.
The typical deflection requirement for floors is delta = L/360.
Typical plywood modulus of elasticity is E = 8000 MPa. Assuming no
piece of your plywood has a width less than b = 900 mm, then the
required plywood thickness would be t = [108.5*P*(L^2)/(E*b)]^0.333
= {108.5(1335 N)[(1000 mm)^2]/[(8000 MPa)(900 mm)]}^0.333 = 27.1 mm.

That would be right for a conversion in UK. L/360 is an excessively
tight requirement, and French regs may be very different.


NT

On Apr 26, 3:44 pm, "David H. Neumann" wrote:
On 2007-04-24, 21:21 Z,
groups.com,

sheepish wrote:
Does anyone know how to calculate suitable [plywood sheathing]
board thickness for joists at 1000 mm centres? I'm assuming ply
would be the best material, assuming eventually I'll want to lay
some smarter looking regular floor boards on these.

sheepish: The design requirement is stiffness driven. In your
specific scenario, we can multiply the required design concentrated
live load,P, by 1.206 to account for the required design dead load.
The typical deflection requirement for floors is delta =L/360.
Typical plywood modulus of elasticity isE= 8000 MPa. Assuming no
piece of your plywood has a width less thanb= 900 mm, then the
required plywood thickness would bet= [108.5*P*(L^2)/(E*b)]^0.333
= {108.5(1335 N)[(1000 mm)^2]/[(8000 MPa)(900 mm)]}^0.333= 27.1 mm.

Can you run through the notation in this calc please. Esp what I do
with L in the calc (or L/360) and what "^" signifies. My maths is v
rusty!!

Thanks

Mike

In message . com,
writes
On Apr 26, 3:44 pm, "David H. Neumann" wrote:
On 2007-04-24, 21:21 Z,
groups.com,

sheepish wrote:
Does anyone know how to calculate suitable [plywood sheathing]
board thickness for joists at 1000 mm centres? I'm assuming ply
would be the best material, assuming eventually I'll want to lay
some smarter looking regular floor boards on these.

sheepish: The design requirement is stiffness driven. In your
specific scenario, we can multiply the required design concentrated
live load,P, by 1.206 to account for the required design dead load.
The typical deflection requirement for floors is delta =L/360.
Typical plywood modulus of elasticity isE= 8000 MPa. Assuming no
piece of your plywood has a width less thanb= 900 mm, then the
required plywood thickness would bet= [108.5*P*(L^2)/(E*b)]^0.333
= {108.5(1335 N)[(1000 mm)^2]/[(8000 MPa)(900 mm)]}^0.333= 27.1 mm.

Can you run through the notation in this calc please. Esp what I do
with L in the calc (or L/360) and what "^" signifies. My maths is v
rusty!!

Well this is the first post I've seen in this thread

without even engaging brain I would say that L = angle and ^ = to the
power of

I'm sure that if you had thought before posting rather than the other
way around, you might have worked this out


--
geoff

On May 25, 7:57 am, raden wrote:
without even engaging brain I would say that L = angle and ^ = to the
power of

I'm sure that if you had thought before posting rather than the other
way around, you might have worked this out

L = length

--
Nige Danton

wrote:
On Apr 26, 3:44 pm, "David H. Neumann" wrote:
On 2007-04-24, 21:21 Z,
groups.com,

sheepish wrote:
Does anyone know how to calculate suitable [plywood sheathing]
board thickness for joists at 1000 mm centres? I'm assuming ply
would be the best material, assuming eventually I'll want to lay
some smarter looking regular floor boards on these.
sheepish: The design requirement is stiffness driven. In your
specific scenario, we can multiply the required design concentrated
live load,P, by 1.206 to account for the required design dead load.
The typical deflection requirement for floors is delta =L/360.
Typical plywood modulus of elasticity isE= 8000 MPa. Assuming no
piece of your plywood has a width less thanb= 900 mm, then the
required plywood thickness would bet= [108.5*P*(L^2)/(E*b)]^0.333
= {108.5(1335 N)[(1000 mm)^2]/[(8000 MPa)(900 mm)]}^0.333= 27.1 mm.

Can you run through the notation in this calc please. Esp what I do
with L in the calc (or L/360) and what "^" signifies. My maths is v
rusty!!

L=length..in this case the unsupported span between joists.

the ^ is the exponent..so l^2 is understood to be length, squared.

I think this calc is a wee bit conservative, as it does not take into
account the fact that the ply is not freely supported over the
joists..it is in fact nailed across several.

Also, I am not sure that ply is stiffer than chipboard. Its stronger,
but is it stiffer?

with the requirements to add boards over, I might be tempted to compare
cots of the recommended 1" ply with say two layers of flooring grade
chip laid over one another and glued..or even - if the boards are of any
real thickness (not laminate) just one layer of 19mm chip.

Thanks

Mike

On 25 May, 04:41, The Natural Philosopher wrote:

Also, I am not sure that ply is stiffer than chipboard. Its stronger,
but is it stiffer?

very much. And OSB is a fairly similar product at lower cost.
http://wiki.diyfaq.org.uk/index.php?...heet_Materials


NT

On 25 May, 00:57, raden wrote:
In message . com,
writes



On Apr 26, 3:44 pm, "David H. Neumann" wrote:
On 2007-04-24, 21:21 Z,
groups.com,

sheepish wrote:
Does anyone know how to calculate suitable [plywood sheathing]
board thickness for joists at 1000 mm centres? I'm assuming ply
would be the best material, assuming eventually I'll want to lay
some smarter looking regular floor boards on these.

sheepish: The design requirement is stiffness driven. In your
specific scenario, we can multiply the required design concentrated
live load,P, by 1.206 to account for the required design dead load.
The typical deflection requirement for floors isdelta=L/360.
Typical plywood modulus of elasticity isE= 8000 MPa. Assuming no
piece of your plywood has a width less thanb= 900 mm, then the
required plywood thickness would bet= [108.5*P*(L^2)/(E*b)]^0.333
= {108.5(1335 N)[(1000 mm)^2]/[(8000 MPa)(900 mm)]}^0.333= 27.1 mm.

Can you run through the notation in this calc please. Esp what I do
with L in the calc (orL/360) and what "^" signifies. My maths is v
rusty!!

Well this is the first post I've seen in this thread

without even engaging brain I would say that L = angle and ^ = to the
power of

I'm sure that if you had thought before posting rather than the other
way around, you might have worked this out

--
geoff- Hide quoted text -

- Show quoted text -

Ahh... touching... Thanks. BTW, L appears to be length *not* angle.

On 25 May, 04:41, The Natural Philosopher wrote:

Also, I am not sure that ply is stiffer than chipboard. Its stronger,
but is it stiffer?

very much. And OSB is a fairly similar product at lower cost.
http://wiki.diyfaq.org.uk/index.php?...heet_Materials


NT

wrote:
On 25 May, 04:41, The Natural Philosopher wrote:

Also, I am not sure that ply is stiffer than chipboard. Its stronger,
but is it stiffer?

very much. And OSB is a fairly similar product at lower cost.
http://wiki.diyfaq.org.uk/index.php?...heet_Materials


NT

Well I didn't see any stiffness figures quite there at all.