Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).


I have always thought a gambrel roof would look pretty - but this has to
take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof with
tie beams.

On 22/05/17 09:50, Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.


Symmetrical loading won't impose partucularly large forces.

But the gussets can take it.

In essence consider whether the gusseted rafter would break at the
gusset or elsewhere under load.

Once the answer is 'elsewhere'. its strong enough :-)



I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).


I have always thought a gambrel roof would look pretty - but this has to
take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof with
tie beams.

You could tie the top section for extra strength.

And put in verticals in other places. The ply skin adds a huge amount of
strength in all other directions

However in this case I would pay a structural engineer to sign off any plans

Then you can sue if it falls down


--
€œBut what a weak barrier is truth when it stands in the way of an
hypothesis!€�

Mary Wollstonecraft

On 22/05/17 10:00, The Natural Philosopher wrote:

You could tie the top section for extra strength.

That is certainly possible.


And put in verticals in other places.

Not possible here as they would become columns to the floor.


The ply skin adds a huge amount of
strength in all other directions

Yes.


However in this case I would pay a structural engineer to sign off any
plans

Then you can sue if it falls down



Possibly metal gussets would be an option - very very strong...

Tim Watts wrote:

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.

I either have a bookmark (or an open tab hiding amongst the others) for
sketchup plugin that did calculations for various roof/truss types, I'll
see if I can find it ...

On Mon, 22 May 2017 10:39:51 +0100, Tim Watts
wrote:

On 22/05/17 10:00, The Natural Philosopher wrote:

You could tie the top section for extra strength.

That is certainly possible.

So your 'roof' would actually for part of the shape of the structure,
rather than being a roof over an existing/separate floor/roof, as per
the example in your link?

I ask because I assumed the 'tie' would have been provided by the
ceiling of the existing structure and with only 2.5m high to the top
ridge I'm assuming you would have to put ties across at maybe the
first joint (as TNP suggests) to be able to store stuff in the roof in
any case?

Basically I's imagine that unless the gussets were 100% strong enough
to stop the base of the roof splaying under *any* (worst case) load,
then you would probably need ties somewhere?



And put in verticals in other places.

Not possible here as they would become columns to the floor.

Interesting project idea / project though, I could do with more space
in my garage / workshop roofspace but with the walls already 8' high
there isn't much room for a gambrel roof (and stay under the permitted
development limits). ;-(

Cheers, T i m

On 22/05/17 11:01, Andy Burns wrote:
Tim Watts wrote:

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.

I either have a bookmark (or an open tab hiding amongst the others) for
sketchup plugin that did calculations for various roof/truss types, I'll
see if I can find it ...


Cool - that would be very interesting Andy

Andy Burns wrote:

I either have a bookmark (or an open tab hiding amongst the others) for
sketchup plugin that did calculations for various roof/truss types

Description say it does gambrel trusses, not tried it

http://design.medeek.com/resources/medeektrussplugin.html

On 22/05/2017 09:50, Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).

In the wikihow, the top of the roof was way above the top of the walls.
So, how will that work if you are going to be limited to 2.5m total
height? Will you have dwarf walls, with almost the whole structure being
roof? The height of the roof part is a function of the width of the
building and the angles used, but it looks about half to two-thirds of
the width being spanned.

So, if your workshop is 5x3m, your roof height is around 1.5-2m, leaving
you not much vertical wall at all, and much of the interior with reduced
headroom.


I have always thought a gambrel roof would look pretty

Won't it look a bit like a Nissen Hut?

On 5/22/2017 9:50 AM, Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).


I have always thought a gambrel roof would look pretty - but this has to
take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof with
tie beams.

Personally I would glue the gussets and fit them with 6 mm coach bolts.
Then they are going to be stronger than wood.

On 22/05/17 11:13, T i m wrote:
On Mon, 22 May 2017 10:39:51 +0100, Tim Watts
wrote:

On 22/05/17 10:00, The Natural Philosopher wrote:

You could tie the top section for extra strength.

That is certainly possible.

So your 'roof' would actually for part of the shape of the structure,
rather than being a roof over an existing/separate floor/roof, as per
the example in your link?

Yes - very typical 4x2" framed shed sort of thing


I ask because I assumed the 'tie' would have been provided by the
ceiling of the existing structure and with only 2.5m high to the top
ridge I'm assuming you would have to put ties across at maybe the
first joint (as TNP suggests) to be able to store stuff in the roof in
any case?

I think ties at the top level will work well - will be around 2m off the
floor.

It would be ties at the base of the roof that would be hard - although a
tension wire hooked up to the ridge and down the other side could be an
option (sure I've seen that in a real large roof somewhere once).


Basically I's imagine that unless the gussets were 100% strong enough
to stop the base of the roof splaying under *any* (worst case) load,
then you would probably need ties somewhere?

That's what I'm wondering. Or buttresses outside (that would look a bit
heath robinson!)




And put in verticals in other places.

Not possible here as they would become columns to the floor.

Interesting project idea / project though, I could do with more space
in my garage / workshop roofspace but with the walls already 8' high
there isn't much room for a gambrel roof (and stay under the permitted
development limits). ;-(

I'm building on a slope - the PD tech notes say measure from the highest
local ground to the highest point on the building.

So I might be able to buy a foot or so legitimately. It was my plane at
least to dig it into the ground a bit so the floor structure was lost
downwards and the entry was dead level with the lower part of the hill.

On 22/05/17 11:34, Andy Burns wrote:
Andy Burns wrote:

I either have a bookmark (or an open tab hiding amongst the others) for
sketchup plugin that did calculations for various roof/truss types

Description say it does gambrel trusses, not tried it

http://design.medeek.com/resources/medeektrussplugin.html

Super - thanks very much

On 22/05/17 11:35, GB wrote:
On 22/05/2017 09:50, Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term
project as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).

In the wikihow, the top of the roof was way above the top of the walls.
So, how will that work if you are going to be limited to 2.5m total
height? Will you have dwarf walls, with almost the whole structure being
roof? The height of the roof part is a function of the width of the
building and the angles used, but it looks about half to two-thirds of
the width being spanned.

Yes. Walls would be reduced to suit - and the roof would not be that
extreme. Depending on the rood covering options, the top slope might be
anywhere from 10 deg to 22.5 deg.

And the sides 45 deg to 80 deg.

Theer are some nice self bonding plastic "slates" thate are certified
down to 10 degrees pitch but only up to 45 degrees.

There are some more normal synthetic slates that I think are OK down to
22.5 right up to vertical.




So, if your workshop is 5x3m, your roof height is around 1.5-2m, leaving
you not much vertical wall at all, and much of the interior with reduced
headroom.


I have always thought a gambrel roof would look pretty

Won't it look a bit like a Nissen Hut?


I hope not

Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).


I have always thought a gambrel roof would look pretty - but this has to
take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof with
tie beams.
I reckon this is a non starter for 2.5m ridge height. Note that the wiki
article shows a flat deck on which the beams bear. this is critical to
the strength as it will be in tension to support the roof weight. Even
if you replaced this with horizontal joists they would end up around
chest height.
If you want to stay within PDR then there is little option but to have a
very very low pitch roof which rules out most tiling systems and you
possibly will have to go with EPDM rubber which is practical but not pretty.
Bob

On Monday, 22 May 2017 13:35:27 UTC+1, Bob Minchin wrote:
Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).


I have always thought a gambrel roof would look pretty - but this has to
take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof with
tie beams.
I reckon this is a non starter for 2.5m ridge height. Note that the wiki
article shows a flat deck on which the beams bear. this is critical to
the strength as it will be in tension to support the roof weight. Even
if you replaced this with horizontal joists they would end up around
chest height.
If you want to stay within PDR then there is little option but to have a
very very low pitch roof which rules out most tiling systems and you
possibly will have to go with EPDM rubber which is practical but not pretty.
Bob

You can use tiles at a very low pitch if you fit asbestos or similar first. Joints must overlap.


NT

On 22/05/2017 13:30, Tim Watts wrote:

Yes. Walls would be reduced to suit - and the roof would not be that
extreme. Depending on the rood covering options, the top slope might be
anywhere from 10 deg to 22.5 deg.

And the sides 45 deg to 80 deg.

Theer are some nice self bonding plastic "slates" thate are certified
down to 10 degrees pitch but only up to 45 degrees.

There are some more normal synthetic slates that I think are OK down to
22.5 right up to vertical.

I suggest spending a lot of time producing visualisations of the end
product, to make sure you are completely happy before you build it. With
the lower sections at 80 degrees and the top sections at 10 degrees, it
may just look like a flat roofed structure put together by someone
without a spirit level.

On 22/05/2017 09:50, Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.

Its probably stronger than a straight rafter design in some respects
since you are approximating a more "arch like" design.

I am wondering - as I am musing plans for my workshop, long term project
as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).

I have always thought a gambrel roof would look pretty - but this has to
take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof with
tie beams.

It will make the internal space a bit more usable. (try and avoid having
any horizontal timbers at eves level that are less than 8' from the
finished floor. Being able to get full sheets of ply through on end
really helps. (and having "high" areas where you can poke longer stuff
up is even better).


--
Cheers,

John.

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

On 22/05/17 13:34, Bob Minchin wrote:

I reckon this is a non starter for 2.5m ridge height. Note that the wiki
article shows a flat deck on which the beams bear. this is critical to
the strength as it will be in tension to support the roof weight. Even
if you replaced this with horizontal joists they would end up around
chest height.
If you want to stay within PDR then there is little option but to have a
very very low pitch roof

I'm starting to think you're right Bob.

which rules out most tiling systems and you
possibly will have to go with EPDM rubber which is practical but not
pretty.
Bob


http://www.ecosystemsdistribution.com/eco-slate/

10 degree pitch. I've had my eye on these for a while...



It's either that or sink the structure into the ground a bit to gain
some extra height - but there's a limit as anything other than a gentle
ramp down isn't a great idea for a workshop.

I've got an awkward corner plot with the house set back to boot - that
gives me two front elevations that I cannot build beyond (PDR) and
forces anything else to be near a boundary.

I am glad the old 5m from house rule was scrapped!

I also have a shared sewer I need to stay clear of (I'm going to sink
footings about 1.5m away and at the same depth or slightly lower and
have about 50cm of overhang on the base (cantilever).

On 22/05/2017 15:57, Tim Watts wrote:
On 22/05/17 13:34, Bob Minchin wrote:

I reckon this is a non starter for 2.5m ridge height. Note that the
wiki article shows a flat deck on which the beams bear. this is
critical to the strength as it will be in tension to support the roof
weight. Even if you replaced this with horizontal joists they would
end up around chest height.
If you want to stay within PDR then there is little option but to have
a very very low pitch roof

I'm starting to think you're right Bob.

The old church builders wanted to avoid beams halfway up the height of
the nave. Besides that, they were building in stone, which is not good
in tension. Their solution was buttresses, and a similar idea would work
with your shed. (Not seriously.)

Basically, Tim, what you are gradually working out from first principles
is why most sheds have a roof with a very low pitch, and covered in
roofing felt. It's simple, it maximises internal space, and it's easy to
build.



which rules out most tiling systems and you possibly will have to go
with EPDM rubber which is practical but not pretty.
Bob


http://www.ecosystemsdistribution.com/eco-slate/

10 degree pitch. I've had my eye on these for a while...



It's either that or sink the structure into the ground a bit to gain
some extra height - but there's a limit as anything other than a gentle
ramp down isn't a great idea for a workshop.

I've got an awkward corner plot with the house set back to boot - that
gives me two front elevations that I cannot build beyond (PDR) and
forces anything else to be near a boundary.

I am glad the old 5m from house rule was scrapped!

I also have a shared sewer I need to stay clear of (I'm going to sink
footings about 1.5m away and at the same depth or slightly lower and
have about 50cm of overhang on the base (cantilever).

On Mon, 22 May 2017 13:26:30 +0100, Tim Watts
wrote:

snip

I think ties at the top level will work well - will be around 2m off the
floor.

I helped put up an apex roof type wooden 10 x 6 shed the other day
that was modular (5 x 6 x 2) and the middle truss was, useless. If you
put it in place and put any weight on it you could feel it sagging /
collapsing. It wasn't even the same profile as the two ends of the
building and they stated in the instructions that the roof wouldn't
carry the weight of a person.

We rebuilt the truss (properly, with a tie either side and at a lower
level) and daughter sat on the roof putting in the felt tacks and it
didn't move at all. ;-)

It would be ties at the base of the roof that would be hard - although a
tension wire hooked up to the ridge and down the other side could be an
option (sure I've seen that in a real large roof somewhere once).

Yes, a pair X ties like that can work well. Isn't triangulation
clever. ;-)


Basically I's imagine that unless the gussets were 100% strong enough
to stop the base of the roof splaying under *any* (worst case) load,
then you would probably need ties somewhere?

That's what I'm wondering. Or buttresses outside (that would look a bit
heath robinson!)

Well, they could be made to look ok, many Churches have them as
features after all. ;-)




And put in verticals in other places.

Not possible here as they would become columns to the floor.

Interesting project idea / project though, I could do with more space
in my garage / workshop roofspace but with the walls already 8' high
there isn't much room for a gambrel roof (and stay under the permitted
development limits). ;-(

I'm building on a slope - the PD tech notes say measure from the highest
local ground to the highest point on the building.

So worst case for you then. ;-(

So I might be able to buy a foot or so legitimately. It was my plane at
least to dig it into the ground a bit so the floor structure was lost
downwards and the entry was dead level with the lower part of the hill.

Yes, I think keeping something as low as possible (subject to drainage
and holding back any cut-away land etc) all helps it to become less
visible. ;-)

Cheers, T i m

In message , John
Rumm writes
On 22/05/2017 09:50, Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.

Its probably stronger than a straight rafter design in some respects
since you are approximating a more "arch like" design.

The construction method is similar to my ply on oak framed boat, which
uses 2 gusset plates at each joint epoxy glued and copper riveted
through.

What surprises me is why the longitudinal ridge piece (I don't know
names of building components) is not one or more long pieces of wood
notched into the frames at the ridge. The graphics show short lengths
fitted between each frame with no indication of what holds them in
place.
--
Bill

On 22/05/17 16:29, GB wrote:
On 22/05/2017 15:57, Tim Watts wrote:
On 22/05/17 13:34, Bob Minchin wrote:

I reckon this is a non starter for 2.5m ridge height. Note that the
wiki article shows a flat deck on which the beams bear. this is
critical to the strength as it will be in tension to support the roof
weight. Even if you replaced this with horizontal joists they would
end up around chest height.
If you want to stay within PDR then there is little option but to have
a very very low pitch roof

I'm starting to think you're right Bob.

The old church builders wanted to avoid beams halfway up the height of
the nave. Besides that, they were building in stone, which is not good
in tension. Their solution was buttresses, and a similar idea would work
with your shed. (Not seriously.)

Basically, Tim, what you are gradually working out from first principles
is why most sheds have a roof with a very low pitch, and covered in
roofing felt. It's simple, it maximises internal space, and it's easy to
build.




But not the felt - I hate felt...

On 22/05/17 16:56, T i m wrote:
On Mon, 22 May 2017 13:26:30 +0100, Tim Watts
wrote:

snip

I think ties at the top level will work well - will be around 2m off the
floor.

I helped put up an apex roof type wooden 10 x 6 shed the other day
that was modular (5 x 6 x 2) and the middle truss was, useless. If you
put it in place and put any weight on it you could feel it sagging /
collapsing. It wasn't even the same profile as the two ends of the
building and they stated in the instructions that the roof wouldn't
carry the weight of a person.

We rebuilt the truss (properly, with a tie either side and at a lower
level) and daughter sat on the roof putting in the felt tacks and it
didn't move at all. ;-)

It would be ties at the base of the roof that would be hard - although a
tension wire hooked up to the ridge and down the other side could be an
option (sure I've seen that in a real large roof somewhere once).

Yes, a pair X ties like that can work well. Isn't triangulation
clever. ;-)


Basically I's imagine that unless the gussets were 100% strong enough
to stop the base of the roof splaying under *any* (worst case) load,
then you would probably need ties somewhere?

That's what I'm wondering. Or buttresses outside (that would look a bit
heath robinson!)

Well, they could be made to look ok, many Churches have them as
features after all. ;-)




And put in verticals in other places.

Not possible here as they would become columns to the floor.

Interesting project idea / project though, I could do with more space
in my garage / workshop roofspace but with the walls already 8' high
there isn't much room for a gambrel roof (and stay under the permitted
development limits). ;-(

I'm building on a slope - the PD tech notes say measure from the highest
local ground to the highest point on the building.

So worst case for you then. ;-(

No - best case. You only measure from the *highest* ground point. Any
part of the building that is lower is "for free".

Which is reasonable as digging into the ground does not make things
worse for the neighbours.


So I might be able to buy a foot or so legitimately. It was my plane at
least to dig it into the ground a bit so the floor structure was lost
downwards and the entry was dead level with the lower part of the hill.

Yes, I think keeping something as low as possible (subject to drainage
and holding back any cut-away land etc) all helps it to become less
visible. ;-)

Cheers, T i m

On Mon, 22 May 2017 17:44:16 +0100, Tim Watts
wrote:

snip

I'm building on a slope - the PD tech notes say measure from the highest
local ground to the highest point on the building.

So worst case for you then. ;-(

No - best case. You only measure from the *highest* ground point. Any
part of the building that is lower is "for free".

Right, so your ground drops 2m over the allowed range of PD so you can
build something 2.5 + 2m high as long as you build it at the deep end?
;-) shrug


Which is reasonable as digging into the ground does not make things
worse for the neighbours.

Ask someone who needed to get their house underpinned!

I can see how you could dig out the ground on the uphill side as long
as the building was no higher than 2.5m above the ground at the
highest point. You couldn't have say the back at 2.5m and build the
front up on a raised platform.

If you dug out 2.5m at the top of the slope you could have something
5m tall or if we do it at the deep end (if I understand you correctly)
it could be 7m tall. ;-)

Cheers, T i m

Tim Watts wrote:
On 22/05/17 13:34, Bob Minchin wrote:

I reckon this is a non starter for 2.5m ridge height. Note that the
wiki article shows a flat deck on which the beams bear. this is
critical to the strength as it will be in tension to support the roof
weight. Even if you replaced this with horizontal joists they would
end up around chest height.
If you want to stay within PDR then there is little option but to have
a very very low pitch roof

I'm starting to think you're right Bob.

which rules out most tiling systems and you possibly will have to go
with EPDM rubber which is practical but not pretty.
Bob


http://www.ecosystemsdistribution.com/eco-slate/

10 degree pitch. I've had my eye on these for a while...



It's either that or sink the structure into the ground a bit to gain
some extra height - but there's a limit as anything other than a gentle
ramp down isn't a great idea for a workshop.

I've got an awkward corner plot with the house set back to boot - that
gives me two front elevations that I cannot build beyond (PDR) and
forces anything else to be near a boundary.

I am glad the old 5m from house rule was scrapped!

I also have a shared sewer I need to stay clear of (I'm going to sink
footings about 1.5m away and at the same depth or slightly lower and
have about 50cm of overhang on the base (cantilever).


Having thought about it a bit more. You could add a substantial ridge
board and purlins each end of which is supported down through the end
walls. In that way you can get the Gambrel shape without excessive
forces trying to splay the walls as the roof weight is "hung" off the
ridge and purlins
If you can get the purlins just above head height, then it should allow
comfortable movement inside.

Bob

On 22/05/17 19:26, T i m wrote:
On Mon, 22 May 2017 17:44:16 +0100, Tim Watts
wrote:

snip

I'm building on a slope - the PD tech notes say measure from the highest
local ground to the highest point on the building.

So worst case for you then. ;-(

No - best case. You only measure from the *highest* ground point. Any
part of the building that is lower is "for free".

Right, so your ground drops 2m over the allowed range of PD so you can
build something 2.5 + 2m high as long as you build it at the deep end?
;-) shrug

Apparently - the technical nots on PlanningPortal seem very clear about
it and I found an analysis (called planning loopholes) that agreed.

In either case, you could sink it into even level ground a foot or two
subject to drainage.



Which is reasonable as digging into the ground does not make things
worse for the neighbours.

Ask someone who needed to get their house underpinned!

I'd be hardpressed to undermine my neighbours from the corner of the
garden


I can see how you could dig out the ground on the uphill side as long
as the building was no higher than 2.5m above the ground at the
highest point. You couldn't have say the back at 2.5m and build the
front up on a raised platform.

If you dug out 2.5m at the top of the slope you could have something
5m tall or if we do it at the deep end (if I understand you correctly)
it could be 7m tall. ;-)

On 22/05/17 19:30, Bob Minchin wrote:

Having thought about it a bit more. You could add a substantial ridge
board and purlins each end of which is supported down through the end
walls. In that way you can get the Gambrel shape without excessive
forces trying to splay the walls as the roof weight is "hung" off the
ridge and purlins
If you can get the purlins just above head height, then it should allow
comfortable movement inside.

I agree...

Tim Watts wrote:
Very hypothetical...

http://www.wikihow.com/Build-a-Gambrel-Roof

How strong is that? There must be some not insignificant spreading
forces going through those gusset plates.



I am wondering - as I am musing plans for my workshop, long term
project as the house is nearly done (yea!).

Going for 15m2 to use permitted development (near 2 boundary fences,
wooden, so limited to 15m2 and 2.5m roof height).


I have always thought a gambrel roof would look pretty - but this has
to take some load: snow load, tiles (synthetic, so not as bad as
concrete/clay) and hanging/storing stuff in it.

It's not as easy to visualise the strength as a simple pitched roof
with tie beams.

Get trusses made, they work out cheaper than trying to make them yourself
and are much stronger.

In message , Tim Watts
writes
On 22/05/17 16:29, GB wrote:
On 22/05/2017 15:57, Tim Watts wrote:
On 22/05/17 13:34, Bob Minchin wrote:

I reckon this is a non starter for 2.5m ridge height. Note that the
wiki article shows a flat deck on which the beams bear. this is
critical to the strength as it will be in tension to support the roof
weight. Even if you replaced this with horizontal joists they would
end up around chest height.
If you want to stay within PDR then there is little option but to have
a very very low pitch roof

I'm starting to think you're right Bob.
The old church builders wanted to avoid beams halfway up the height
of the nave. Besides that, they were building in stone, which is not
good in tension. Their solution was buttresses, and a similar idea
would work with your shed. (Not seriously.)
Basically, Tim, what you are gradually working out from first
principles is why most sheds have a roof with a very low pitch, and
covered in roofing felt. It's simple, it maximises internal space,
and it's easy to build.




But not the felt - I hate felt...

Insulated box section rolled steel roofing. 12.5 deg. pitch. Prolly need
the same trusses to meet snow load anyway. Can come in a tasteful slate
blue...:-)


--
Tim Lamb

On 5/22/2017 1:34 PM, Bob Minchin wrote:
Tim Watts wrote:
Very hypothetical...


It's not as easy to visualise the strength as a simple pitched roof with
tie beams.
I reckon this is a non starter for 2.5m ridge height. Note that the wiki
article shows a flat deck on which the beams bear. this is critical to
the strength as it will be in tension to support the roof weight. Even
if you replaced this with horizontal joists they would end up around
chest height.

I'm not an expert, but I am not sure this is true.

In a traditional pitched roof, the apex is assumed to be pin jointed. So
that the rafters produce an outward thrust where they rest on the walls,
because when a distributed vertical load is applied they want to "flatten".

But when you add a tie beam, you have a triangular structure which can
support a distributed vertical load, and convert it into two vertical
loads, one into each wall, without a spreading force. The tie beam does
not have to be at the bottom of the rafters.

In a gambrel roof, the fillets resist the bending moment which tends to
make the structure "flatten". How rigid it is depends on the size of the
fillets, and how well they are fastened to the main beams. Doesn't it
become equivalent to the "Tee" structure drawn below in T's. The walls
are drawn with W's

T
T
T
TTTTTTTTTTTTTTTT
W W
W W
W W
W W

In reality there will be a small spreading force in the gambrel case
because of flex in the joints.

Structural analysts please shoot me down in flames.

On 22/05/2017 17:44, Tim Watts wrote:
On 22/05/17 16:56, T i m wrote:

So worst case for you then. ;-(

No - best case. You only measure from the *highest* ground point. Any
part of the building that is lower is "for free".

Which is reasonable as digging into the ground does not make things
worse for the neighbours.

Hmmmm, workshop "super basement" here we come ;-)


--
Cheers,

John.

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

On Tuesday, 23 May 2017 14:41:28 UTC+1, John Rumm wrote:
On 22/05/2017 17:44, Tim Watts wrote:
On 22/05/17 16:56, T i m wrote:

So worst case for you then. ;-(

No - best case. You only measure from the *highest* ground point. Any
part of the building that is lower is "for free".

Which is reasonable as digging into the ground does not make things
worse for the neighbours.

Hmmmm, workshop "super basement" here we come ;-)

Wonder if I can buy a cliff! 'With PP for a 8'x16' shed 20 stories high'


NT

On Tue, 23 May 2017 14:41:30 +0100, John Rumm
wrote:

snip

Hmmmm, workshop "super basement" here we come ;-)

I (think) I've always been envious of those who have
house-footprint-sized basements, possibly more than I've been happy to
have a loft space that is useable (not a mesh of balsa wood trusses
all stapled together).

All good and dandy if your house isn't built on a flood plane.

(I saw some fairly local 'new build' houses going up near a river and
they were flooded just after they had installed the damp-proof-course
(ironically)). ;-)

Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?

Cheers, T i m

On Tuesday, 23 May 2017 19:02:41 UTC+1, T i m wrote:
On Tue, 23 May 2017 14:41:30 +0100, John Rumm
wrote:

snip

Hmmmm, workshop "super basement" here we come ;-)

I (think) I've always been envious of those who have
house-footprint-sized basements, possibly more than I've been happy to
have a loft space that is useable (not a mesh of balsa wood trusses
all stapled together).

All good and dandy if your house isn't built on a flood plane.

(I saw some fairly local 'new build' houses going up near a river and
they were flooded just after they had installed the damp-proof-course
(ironically)). ;-)

Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?

Cheers, T i m

basements cost more than ground floors, so are common in high land price areas.


NT

On 23/05/17 19:02, T i m wrote:
On Tue, 23 May 2017 14:41:30 +0100, John Rumm


All good and dandy if your house isn't built on a flood plane.

*giggle*



--
"What do you think about Gay Marriage?"
"I don't."
"Don't what?"
"Think about Gay Marriage."

On 5/23/2017 2:02 PM, T i m wrote:

Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?

_Every_ house I've lived in, in the US, had a basement. One of them
flooded badly a few times.
Of course, it's a big country, and there are some areas where basements
are not at all common.

On Tue, 23 May 2017 15:22:32 -0400, S Viemeister
wrote:

On 5/23/2017 2:02 PM, T i m wrote:

Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?

_Every_ house I've lived in, in the US, had a basement. One of them
flooded badly a few times.

So, did you still use it and if so what? Was there something that was
done to stop it flooding or was it just a matter of pumping it out
(automatic pump possibly)?

Of course, it's a big country, and there are some areas where basements
are not at all common.

Thanks for the feedback.

Cheers, T i m

On 5/23/2017 7:02 PM, T i m wrote:
On Tue, 23 May 2017 14:41:30 +0100, John Rumm
wrote:

snip

Hmmmm, workshop "super basement" here we come ;-)

I (think) I've always been envious of those who have
house-footprint-sized basements, possibly more than I've been happy to
have a loft space that is useable (not a mesh of balsa wood trusses
all stapled together).

All good and dandy if your house isn't built on a flood plane.

(I saw some fairly local 'new build' houses going up near a river and
they were flooded just after they had installed the damp-proof-course
(ironically)). ;-)

Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?

Cheers, T i m

I had a colleague who lived in Canada for many years, he said that the
norm for houses there was for everything to have a basement, except that
it was usually at ground level. So all the normal living space was first
floor or above. The "basement" was for the workshop, the laundry room
(with a drain in the floor), the car as well as storing garden tools,
bicycles, etc. Sounded very civilised.

On Tue, 23 May 2017 22:20:02 +0100, newshound
wrote:

snip

Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?


I had a colleague who lived in Canada for many years, he said that the
norm for houses there was for everything to have a basement, except that
it was usually at ground level.

I've seen those that are sort of sunken into the ground with the
basement having just a small window at ground level.

I've also seen those where the house is on a slope so one end is fully
submerged (ala typical basement) whilst at the other it's 'at' ground
level. ;-)

So all the normal living space was first
floor or above.

That's also something you are now seeing when houses are built next to
rivers.

The "basement" was for the workshop, the laundry room
(with a drain in the floor), the car as well as storing garden tools,
bicycles, etc. Sounded very civilised.

Doesn't it just ... and you can see why some pay *millions* to have
one fitted underneath an existing house! ;-(

Now, that could be an interesting boundary dispute!

Cheers, T i m

On 5/23/2017 4:58 PM, T i m wrote:
wrote:
On 5/23/2017 2:02 PM, T i m wrote:
Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?
_Every_ house I've lived in, in the US, had a basement. One of them
flooded badly a few times.

So, did you still use it and if so what? Was there something that was
done to stop it flooding or was it just a matter of pumping it out
(automatic pump possibly)?

We put everything important up on platforms. Lots of pumping, and a
dehumidifier. The washer, dryer, boiler, hot water cylinder and main
freezer live down there.
Our place in Scotland has no basement. I miss the extra space, but I
don't miss dealing with wet messes.

On Tue, 23 May 2017 19:57:58 -0400, S Viemeister
wrote:

On 5/23/2017 4:58 PM, T i m wrote:
wrote:
On 5/23/2017 2:02 PM, T i m wrote:
Are there any countries where basements are the norm? You seem to see
them quite a lot on American based films?
_Every_ house I've lived in, in the US, had a basement. One of them
flooded badly a few times.

So, did you still use it and if so what? Was there something that was
done to stop it flooding or was it just a matter of pumping it out
(automatic pump possibly)?

We put everything important up on platforms.

So when you say 'flooded' you don't typically mean 'to the ceiling'
then?

Lots of pumping, and a
dehumidifier.

Understood.

The washer, dryer, boiler, hot water cylinder and main
freezer live down there.

I've often seen reference to people (Americans) having the 'furnace'
in the basement so is / can that be the same as what we would
typically call 'a boiler' or are they specifically only when the
heating system uses blown air?

Our place in Scotland has no basement. I miss the extra space, but I
don't miss dealing with wet messes.

I was thinking on from that and I guess the value of a basement may
depend on if the country you happen to live in has a high water table
or not? Over here you hear of basements having to be 'tanked' and
potentially drains would be more likely to let water in than out?

Cheers, T i m