my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]

DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


You don't put bits of wood anywhere, you cut out the joists (birds mouth) so
that they sit flush, like this:

https://activerain-store.s3.amazonaw...9422947349.png

On Sunday, June 5, 2016 at 2:28:54 PM UTC+1, Phil L wrote:
DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


You don't put bits of wood anywhere, you cut out the joists (birds mouth) so
that they sit flush, like this:

https://activerain-store.s3.amazonaw...9422947349.png

i could cut the joists on the right
(but wouldn't that weaken them?)
however on the left of the picture
they've got to be a few inches higher
so rain drains
therefore i will need some kind of wood inbetween...

On 05/06/2016 12:54, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]

Won't open. Says I have to join Facefart. ******** to that. Use a proper
file sharer.

Bill

On Sun, 05 Jun 2016 04:54:01 -0700, DICEGEORGE wrote:

my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?
fbid=10154177270524882&set=a.10150328836674882.395 536.666809881&type=3&theater

[george]

I know exactly what you mean. Been there; done that. But unless you can
cut those angles to *precisely* match those of the rafters (presumably
90') and perfectly in line with them laterally then it's not going to
make for any improvement. And that's not really a DIY job.

On Sunday, June 5, 2016 at 2:53:53 PM UTC+1, Bill Wright wrote:
On 05/06/2016 12:54, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]

Won't open. Says I have to join Facefart. ******** to that. Use a proper
file sharer.

Bill

sorry i thought settings of facebook were open to everybody,
and its easy to upload there from my phone...
photo copied to he
http://stonehengecampaign.org.uk/psimg/joists.jpg

On Sunday, June 5, 2016 at 3:32:11 PM UTC+1, Cursitor Doom wrote:
On Sun, 05 Jun 2016 04:54:01 -0700, DICEGEORGE wrote:

my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?
fbid=10154177270524882&set=a.10150328836674882.395 536.666809881&type=3&theater

[george]

I know exactly what you mean. Been there; done that. But unless you can
cut those angles to *precisely* match those of the rafters (presumably
90') and perfectly in line with them laterally then it's not going to
make for any improvement. And that's not really a DIY job.

Or cut some wood off the top of the old oak purlin in line with new joists?

Or make 2 triangular wedge shape bits of wood for each side?
(this wouldnt work on the left where I need the joists a bit higher)

Car body filler would crumble wouldnt it as the roof flexes over time?

[george]

DICEGEORGE wrote:
On Sunday, June 5, 2016 at 2:28:54 PM UTC+1, Phil L wrote:
DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the
load, how to do this so that they'll last a hundred years and not
split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


You don't put bits of wood anywhere, you cut out the joists (birds
mouth) so that they sit flush, like this:

https://activerain-store.s3.amazonaw...9422947349.png

i could cut the joists on the right
(but wouldn't that weaken them?)
however on the left of the picture
they've got to be a few inches higher
so rain drains
therefore i will need some kind of wood inbetween...


do you mean to say that the water will be flowing this way:

http://i66.tinypic.com/ljgxx.jpg

If so, the joists should be running the way of the blue arrow in this pic

Phil L wrote:
DICEGEORGE wrote:
On Sunday, June 5, 2016 at 2:28:54 PM UTC+1, Phil L wrote:
DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the
load, how to do this so that they'll last a hundred years and not
split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


You don't put bits of wood anywhere, you cut out the joists (birds
mouth) so that they sit flush, like this:

https://activerain-store.s3.amazonaw...9422947349.png

i could cut the joists on the right
(but wouldn't that weaken them?)
however on the left of the picture
they've got to be a few inches higher
so rain drains
therefore i will need some kind of wood inbetween...


do you mean to say that the water will be flowing this way:

http://postimg.org/image/avpqoqk1n/


If so, the joists should be running the way of the blue arrow in this
pic

tinypic seems weird today so I've upped it here instead

On Sunday, 5 June 2016 12:54:03 UTC+1, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]

Bolt them to the common rafters using timber connectors.

https://search.yahoo.com/yhs/search?...display~chrome

DICEGEORGE wrote:
On Sunday, June 5, 2016 at 2:28:54 PM UTC+1, Phil L wrote:
DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


You don't put bits of wood anywhere, you cut out the joists (birds mouth) so
that they sit flush, like this:

https://activerain-store.s3.amazonaw...9422947349.png

i could cut the joists on the right
(but wouldn't that weaken them?)
however on the left of the picture
they've got to be a few inches higher
so rain drains
therefore i will need some kind of wood inbetween...

I'd expect the joists to be horizontal in both planes and then firring
strips added on top to give the desired fall. This enables the ceiling
below to be flat. Now in your application there might not be a ceiling
on the underside of the joists but you could still do it the same way.

On Sunday, June 5, 2016 at 4:58:01 PM UTC+1, Phil L wrote:
Phil L wrote:
DICEGEORGE wrote:
On Sunday, June 5, 2016 at 2:28:54 PM UTC+1, Phil L wrote:
DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the
load, how to do this so that they'll last a hundred years and not
split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


You don't put bits of wood anywhere, you cut out the joists (birds
mouth) so that they sit flush, like this:

https://activerain-store.s3.amazonaw...9422947349.png

i could cut the joists on the right
(but wouldn't that weaken them?)
however on the left of the picture
they've got to be a few inches higher
so rain drains
therefore i will need some kind of wood inbetween...


do you mean to say that the water will be flowing this way:

http://postimg.org/image/avpqoqk1n/


If so, the joists should be running the way of the blue arrow in this
pic

tinypic seems weird today so I've upped it here instead

top corner is where the orange saw is, water will flow out diagonally opposite

DICEGEORGE wrote:
top corner is where the orange saw is, water will flow out diagonally
opposite

That's as clear as mud.
Is the water going the way of the blue arrow or from the saw handle to the
bottom of the saw?
If it's running from the saw, then you don't need blocks of wood under the
purlin as it's running down already and if it's running the way of the
arrow, the joists are in the wrong way, they need to run from left to right.

On Sunday, June 5, 2016 at 6:03:35 PM UTC+1, Phil L wrote:
DICEGEORGE wrote:
top corner is where the orange saw is, water will flow out diagonally
opposite

That's as clear as mud.
Is the water going the way of the blue arrow or from the saw handle to the
bottom of the saw?
If it's running from the saw, then you don't need blocks of wood under the
purlin as it's running down already and if it's running the way of the
arrow, the joists are in the wrong way, they need to run from left to right.

The purlin is not straight or level.
Highest point will be corner where saw is.
Lowest point the diagonally opposite corner.
Water will flow towards the middle of the bottom edge of the photo.
You can see a block under the second joist,
a scrap of OSB under the third,
and the fourth just sitting on the corner of the purlin,
I'm musing on how to improve this.

Wood with the grain parallel to the purlin would probably split over time.

But as Cursitor Doom noted cutting them to exactly fit will be difficult,
especially as the purlin is not straight or square!

Maybe do it as well as I can with cutting and chiseling and sanding
and then put car body filler in between to fill the gaps,
or glue,
or lead from old flashing,
or flexible frame filler,
or chisel off the top of the purlin so the joist will lay on it?

(The 5x2 joists are not big enough for the 3.4 meter span,
I'm having 7x2s delivered next week)
[george]

On Sun, 05 Jun 2016 08:27:00 -0700, DICEGEORGE wrote:

Or cut some wood off the top of the old oak purlin in line with new
joists?

Or make 2 triangular wedge shape bits of wood for each side?
(this wouldnt work on the left where I need the joists a bit higher)

Might be a good idea; certainly better than attempting cut-outs.


Car body filler would crumble wouldnt it as the roof flexes over time?

No filler! Bad idea!!

A new inside photo of joists temporarily resting on purlin is now at:
http://stonehengecampaign.org.uk/psi...-on-purlin.jpg

I will also add a new support for the flying end of the purlin,
which is at the moment nailed upwards.

When the joists are safely sitting on the purlin
I will probably nail them to the sloping rafters.

I believe nails are better than screws as they can be removed
if and when the roof is reslated in another hundred years.

[george]

"DICEGEORGE" wrote in message
...
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

I can't see that adding anything flat under the joists is doing any better
than what the bottom of the joist is already load spreading wise.

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]

On 6/5/2016 5:05 PM, harry wrote:
On Sunday, 5 June 2016 12:54:03 UTC+1, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]

Bolt them to the common rafters using timber connectors.

https://search.yahoo.com/yhs/search?...display~chrome


That's what I would do.

On Sunday, June 5, 2016 at 12:54:03 PM UTC+1, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

[george]
The joist are all laid flat and fixed to the perlin. to form a slpe to drain the rainwater off you put fering strips on top of the joists

On 05/06/16 18:44, DICEGEORGE wrote:
A new inside photo of joists temporarily resting on purlin is now at:
http://stonehengecampaign.org.uk/psi...-on-purlin.jpg

I will also add a new support for the flying end of the purlin,
which is at the moment nailed upwards.

When the joists are safely sitting on the purlin
I will probably nail them to the sloping rafters.

I believe nails are better than screws as they can be removed
if and when the roof is reslated in another hundred years.

[george]


I was going to say that - well, screw then to the rafters, with a couple
of corrosion resistant 6mm screws (self drill and/or pilot holes as
required).

I would not just sit them on the purlin - you are loading it the reverse
way to what it was designed to do - and your new rafters will try to
pull it off the old rafters.

In fact I would consider running a new beam on the top of the old
rafters to the load is going the *right* way.

Screw the new beam into every rafter.

On Sunday, June 5, 2016 at 9:34:00 PM UTC+1, Tim Watts wrote:
On 05/06/16 18:44, DICEGEORGE wrote:
A new inside photo of joists temporarily resting on purlin is now at:
http://stonehengecampaign.org.uk/psi...-on-purlin.jpg

I will also add a new support for the flying end of the purlin,
which is at the moment nailed upwards.

When the joists are safely sitting on the purlin
I will probably nail them to the sloping rafters.

I believe nails are better than screws as they can be removed
if and when the roof is reslated in another hundred years.

[george]


I was going to say that - well, screw then to the rafters, with a couple
of corrosion resistant 6mm screws (self drill and/or pilot holes as
required).

I would not just sit them on the purlin - you are loading it the reverse
way to what it was designed to do - and your new rafters will try to
pull it off the old rafters.

Sorry, I dont understand that
In fact I would consider running a new beam on the top of the old
rafters to the load is going the *right* way.

At the level of the purlin?
(Not below because the bottom of the rafters looks bodged,
its not sitting on a wall plate.)
Screw the new beam into every rafter.

isnt it better to nail them than screw them?

On 05/06/2016 12:54, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater

Since we are talking about a flat roof, its presumably not carrying much
load anyway?

I would simply fix them to the adjacent rafters (probably with a bolt
through, and a timber "dog" between the timbers).

If the purlin is not level. then use different heights on the rafters to
get your new joists level. You can use firrings of like slope, but
increasing thickness to get your compound slope.

--
Cheers,

John.

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

On 05/06/16 22:31, DICEGEORGE wrote:
On Sunday, June 5, 2016 at 9:34:00 PM UTC+1, Tim Watts wrote:
On 05/06/16 18:44, DICEGEORGE wrote:
A new inside photo of joists temporarily resting on purlin is now at:
http://stonehengecampaign.org.uk/psi...-on-purlin.jpg

I will also add a new support for the flying end of the purlin,
which is at the moment nailed upwards.

When the joists are safely sitting on the purlin
I will probably nail them to the sloping rafters.

I believe nails are better than screws as they can be removed
if and when the roof is reslated in another hundred years.

[george]


I was going to say that - well, screw then to the rafters, with a couple
of corrosion resistant 6mm screws (self drill and/or pilot holes as
required).

I would not just sit them on the purlin - you are loading it the reverse
way to what it was designed to do - and your new rafters will try to
pull it off the old rafters.

Sorry, I dont understand that

Purlin is under the old rafters.

Putting a downwards load on them is going to try to pull them off.

Normally, the purlin is in compression against the rafters (to support
their mid span) - you proposal reverses this and I think that's dubuious
- unless you add some plates or other means to tie the purlin to the old
rafters under tension.

In fact I would consider running a new beam on the top of the old
rafters to the load is going the *right* way.

At the level of the purlin?

Wherever height you want the support for the new rafters (which I assume
is the same height as you were going to use the purlin as support,
weren't you?

(Not below because the bottom of the rafters looks bodged,
its not sitting on a wall plate.)

Right...

So where's the downward load going to go, when you hang the end of your
new roof off the purlin?

If the wall plate and/or old rafter ends are knackered, is the purlin
well and independently supported to accept a vertical load (normally
purlins take load at 90 degrees to the rafters and usually have thrust
poles running back to the centre wall)?

I think we need some pictures from inside the roof of the old rafter
ends and wallplate and the purlin support poles.

Screw the new beam into every rafter.

isnt it better to nail them than screw them?

I prefer thin self drilling screws - minimum disruption to the wood
(like nails) but more subtle. Spax do a nice one, that I've been using
for a not totally dissimilar job:

http://www.spax.com/uk/craftsmen/scr...l-thread-wirox

Available from Amazon.de (seems to be no problem shipping to the UK and
took 2 days for me).

But it's not somethign to argue about - nails have served people for
centuries in this role. In my case, I did not want a lot of banging
disrupting the good bits of the roof.

On 06/06/16 00:14, John Rumm wrote:
On 05/06/2016 12:54, DICEGEORGE wrote:
my new flat roof joists are going to sit on the purlin,
but it seems wrong to have them sitting on the point at the top,
so should I make pieces of wood to sit in between and spread the load,
how to do this so that they'll last a hundred years and not split?

photo at:

https://www.facebook.com/photo.php?f...type=3&theater


Since we are talking about a flat roof, its presumably not carrying much
load anyway?

I wouldn't underestimate snow load - I did the calcs on mine and dry,
the roof weighs an estimated 1000kg (adding the per m2 mass of the
roofing components). Adding worst case snow load to SE England standards
that I found somewhere on the web took the total potential mass to 2400kg.


I would simply fix them to the adjacent rafters (probably with a bolt
through, and a timber "dog" between the timbers).

That's what I would have considered as an option, but the OP did say
something about the old rafter ends and/or wallplate being dodgey - I
think we need to know more


If the purlin is not level. then use different heights on the rafters to
get your new joists level. You can use firrings of like slope, but
increasing thickness to get your compound slope.

Tim Watts wrote:
{I wouldnt unerestimate snow load]

I asked an architect who said 5x2 rafters for the span of 2.4 meters,
but the span increased to 3.6m
so i'm now using 7x2 rafters.

I'll ask hereford bulding control for another visit when the woodwork's done, before sticking down EDPM

Photos of today's joist ends o0n my facebook at
https://www.facebook.com/photo.php?f...6809881&type=3

The spax screws someone recommended look great
https://www.youtube.com/watch?v=YynF0ZZXjpU#t=80
(I'm temporarily nailing as the project evolves)

[George]