Has anyone considered/priced d-i-y lattice joists?

I need to replace the timber roof joists on one of my flat roofed barns.
Span about 18'0 so not trivial in timber. The existing rolled steel
sheet could go again and be fixed to 100x47 purlins at 4'0" intervals
with 1/2" shuttering ply under and 75mm PIR foam between. Or stretching
the budget, new twin wall insulated sheet.

I suspect finding the correct grade of timber, buying the steel webs and
assembling will not bring a huge saving over putting the job out.

any thoughts?


--
Tim Lamb

On Tuesday, May 13, 2014 9:07:30 PM UTC+1, Tim Lamb wrote:
Has anyone considered/priced d-i-y lattice joists?
I need to replace the timber roof joists on one of my flat roofed barns.
Span about 18'0 so not trivial in timber. The existing rolled steel
sheet could go again and be fixed to 100x47 purlins at 4'0" intervals
with 1/2" shuttering ply under and 75mm PIR foam between. Or stretching
the budget, new twin wall insulated sheet.
I suspect finding the correct grade of timber, buying the steel webs and
assembling will not bring a huge saving over putting the job out.
any thoughts?

Its unclear exactly what youre looking at making


NT

In message ,
writes
On Tuesday, May 13, 2014 9:07:30 PM UTC+1, Tim Lamb wrote:
Has anyone considered/priced d-i-y lattice joists?
I need to replace the timber roof joists on one of my flat roofed barns.
Span about 18'0 so not trivial in timber. The existing rolled steel
sheet could go again and be fixed to 100x47 purlins at 4'0" intervals
with 1/2" shuttering ply under and 75mm PIR foam between. Or stretching
the budget, new twin wall insulated sheet.
I suspect finding the correct grade of timber, buying the steel webs and
assembling will not bring a huge saving over putting the job out.
any thoughts?

Its unclear exactly what youre looking at making

These things..


http://www.crendon.co.uk/userfiles/gallery/e_46.jpg


--
Tim Lamb

Tim Lamb writes:

In message
,
writes
On Tuesday, May 13, 2014 9:07:30 PM UTC+1, Tim Lamb wrote:
Has anyone considered/priced d-i-y lattice joists?
I need to replace the timber roof joists on one of my flat roofed barns.
Span about 18'0 so not trivial in timber. The existing rolled steel
sheet could go again and be fixed to 100x47 purlins at 4'0" intervals
with 1/2" shuttering ply under and 75mm PIR foam between. Or stretching
the budget, new twin wall insulated sheet.
I suspect finding the correct grade of timber, buying the steel webs and
assembling will not bring a huge saving over putting the job out.
any thoughts?

Its unclear exactly what youre looking at making

These things..


http://www.crendon.co.uk/userfiles/gallery/e_46.jpg

Would JJI joists do? I tried to get some when boarding out my
loft, but they wanted a much bigger order, so probably not for
you either. On the other hand, making something of that style
would probably be cheaper and easier than lattice joists.

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2014-04-05)

In message , Jon Fairbairn
writes
Tim Lamb writes:

In message
,
writes
On Tuesday, May 13, 2014 9:07:30 PM UTC+1, Tim Lamb wrote:
Has anyone considered/priced d-i-y lattice joists?
I need to replace the timber roof joists on one of my flat roofed barns.
Span about 18'0 so not trivial in timber. The existing rolled steel
sheet could go again and be fixed to 100x47 purlins at 4'0" intervals
with 1/2" shuttering ply under and 75mm PIR foam between. Or stretching
the budget, new twin wall insulated sheet.
I suspect finding the correct grade of timber, buying the steel webs and
assembling will not bring a huge saving over putting the job out.
any thoughts?

Its unclear exactly what youre looking at making

These things..


http://www.crendon.co.uk/userfiles/gallery/e_46.jpg

Would JJI joists do? I tried to get some when boarding out my
loft, but they wanted a much bigger order, so probably not for
you either. On the other hand, making something of that style
would probably be cheaper and easier than lattice joists.

I could make those as well:-)

Finding C24 timber in 5.5m lengths might be tricky. Sadly their load
chart does not offer roof figures.

Somebody on E-bay was selling the metal webs for £1.00 ea. so unlikely
to be a cheap solution. I like the idea of the open web for service
access although you can also drill largish holes in the JJI Sterling
board.


--
Tim Lamb

On Wednesday, May 14, 2014 8:28:41 AM UTC+1, Tim Lamb wrote:
In message ,
writes
On Tuesday, May 13, 2014 9:07:30 PM UTC+1, Tim Lamb wrote:

Has anyone considered/priced d-i-y lattice joists?
I need to replace the timber roof joists on one of my flat roofed barns.

Span about 18'0 so not trivial in timber. The existing rolled steel
sheet could go again and be fixed to 100x47 purlins at 4'0" intervals
with 1/2" shuttering ply under and 75mm PIR foam between. Or stretching
the budget, new twin wall insulated sheet.
I suspect finding the correct grade of timber, buying the steel webs and
assembling will not bring a huge saving over putting the job out.
any thoughts?

Its unclear exactly what youre looking at making

These things..
http://www.crendon.co.uk/userfiles/gallery/e_46.jpg

OK, I'll keep it general. Timber webs are easier to make and far cheaper than steel. Set up a mitre saw with an angled end stop and you can cut them up pretty fast. They can be made from some firewood, green roundwood, bananawood etc. Web end fixings are the weakpoint, with splitting being the main risk, so they need to be thicker than would appear to be required for strength alone.

Any such structure has to be tested before use to ensure adequate load rating. If you want to know what broke and why, you need a high frame rate camera, as failures typically consist of a fast chain reaction of failures, making it impossible to determine just by inspection afterward.

Where timber has to be joined, you can wrap the epoxied finger joint with extra timber around 3 or 4 sides, all glued & screwed every 6".


NT

In message ,
writes
Its unclear exactly what youre looking at making

These things..
http://www.crendon.co.uk/userfiles/gallery/e_46.jpg

OK, I'll keep it general. Timber webs are easier to make and far
cheaper than steel. Set up a mitre saw with an angled end stop and you
can cut them up pretty fast. They can be made from some firewood, green
roundwood, bananawood etc. Web end fixings are the weakpoint, with
splitting being the main risk, so they need to be thicker than would
appear to be required for strength alone.

Any such structure has to be tested before use to ensure adequate load
rating. If you want to know what broke and why, you need a high frame
rate camera, as failures typically consist of a fast chain reaction of
failures, making it impossible to determine just by inspection afterward.

Where timber has to be joined, you can wrap the epoxied finger joint
with extra timber around 3 or 4 sides, all glued & screwed every 6".

er? I take your point about timber being cheaper than metal but a web of
Sterling board sounds easier still.

Before anything else, I am going to check the nettle patch for long
steel beams:-)
--
Tim Lamb

On 14/05/2014 20:20, Tim Lamb wrote:
In message ,
writes
Its unclear exactly what youre looking at making

These things..
http://www.crendon.co.uk/userfiles/gallery/e_46.jpg

OK, I'll keep it general. Timber webs are easier to make and far
cheaper than steel. Set up a mitre saw with an angled end stop and you
can cut them up pretty fast. They can be made from some firewood,
green roundwood, bananawood etc. Web end fixings are the weakpoint,
with splitting being the main risk, so they need to be thicker than
would appear to be required for strength alone.

Any such structure has to be tested before use to ensure adequate load
rating. If you want to know what broke and why, you need a high frame
rate camera, as failures typically consist of a fast chain reaction of
failures, making it impossible to determine just by inspection afterward.

Where timber has to be joined, you can wrap the epoxied finger joint
with extra timber around 3 or 4 sides, all glued & screwed every 6".

er? I take your point about timber being cheaper than metal but a web of
Sterling board sounds easier still.

Before anything else, I am going to check the nettle patch for long
steel beams:-)

Not a metal web but everything you didn't want to know various timber
composite beams:

http://researchrepository.napier.ac.uk/2/1/ABJphd.pdf

I was thinking of doing something like this for my new loft joists,
assembling on the top floor from overlapping 8' lengths because of
access problems. Currently engaged in improving access in the hope I
can get some real timbers up there, instead...

On Wednesday, May 14, 2014 8:49:02 PM UTC+1, GMM wrote:

Not a metal web but everything you didn't want to know various timber
composite beams:
http://researchrepository.napier.ac.uk/2/1/ABJphd.pdf
I was thinking of doing something like this for my new loft joists,
assembling on the top floor from overlapping 8' lengths because of
access problems. Currently engaged in improving access in the hope I
can get some real timbers up there, instead...

That's the doc I was looking for, but failed to find. Bear in mind the injected foam has a bit of stabilising effect on the sheet.


NT