SWMBO and I are the initial back-of-an-envelope stage of planning a Big Shed
(approx. 16' x 16', not-quite-square to fit the corner of the garden behind
some trees, replacing a pair of 8x8 sheds, one on a concrete raft, one on
piers) which I hope may end up accomodating a Proper Lathe (in the ton to
ton-and-a-half weight range) so could use some advice regarding the floor -
I'm pretty sure I'll need more than the 4" of concrete on scalpings/sand
blinding/DPM, is a 6" pad with steel reinforcement at 2" and 4" going to be
inadequate, adequate or overkill? would it be wise to go for 8" with 4" of
concrete between the reinforcement to get a bit more stiffness?
The shed itself probably will be of wood construction with a cut roof
(possibly mansard to allow some more storage above) with a couple of brick
pillars (braced with brick buttresses) to support an RSJ for lifting, I
hope. Fortunately I can get away with a few feet of extra height by taking
my "highest point of the surrounding terrain" reference from the neighbour's
garden the other side of a dwarf wall (on my side of the boundary)... So
ridge height could be as much as 14' above the base! At this size am I
likely to need to add a trench foundation in addition to the raft I've
envisaged? The neighbour has a couple of tall (approx 30' cypressus (sp?)
close to the boundary, will they need their roots dealing with if they're
below the level of the scalpings etc.?

Thanks in Advance,

Dave H.

--
(The engineer formerly known as Homeless)

"Rules are for the obedience of fools, and the guidance of wise men" -
Douglas Bader

On 04/02/2010 14:29, Dave H. wrote:
SWMBO and I are the initial back-of-an-envelope stage of planning a Big Shed
(approx. 16' x 16', not-quite-square to fit the corner of the garden behind
some trees, replacing a pair of 8x8 sheds, one on a concrete raft, one on
piers) which I hope may end up accomodating a Proper Lathe (in the ton to
ton-and-a-half weight range) so could use some advice regarding the floor -
I'm pretty sure I'll need more than the 4" of concrete on scalpings/sand
blinding/DPM, is a 6" pad with steel reinforcement at 2" and 4" going to be
inadequate, adequate or overkill? would it be wise to go for 8" with 4" of
concrete between the reinforcement to get a bit more stiffness?
The shed itself probably will be of wood construction with a cut roof
(possibly mansard to allow some more storage above) with a couple of brick
pillars (braced with brick buttresses) to support an RSJ for lifting, I
hope. Fortunately I can get away with a few feet of extra height by taking
my "highest point of the surrounding terrain" reference from the neighbour's
garden the other side of a dwarf wall (on my side of the boundary)... So
ridge height could be as much as 14' above the base! At this size am I
likely to need to add a trench foundation in addition to the raft I've
envisaged? The neighbour has a couple of tall (approx 30' cypressus (sp?)
close to the boundary, will they need their roots dealing with if they're
below the level of the scalpings etc.?

Thanks in Advance,

Dave H.


Have a look he

http://www.pavingexpert.com/

particularly these pages:

http://www.pavingexpert.com/concrete.htm and

http://www.pavingexpert.com/reinfrc1.htm and

"Dave H." wrote in message
...
SWMBO and I are the initial back-of-an-envelope stage of planning a Big
Shed (approx. 16' x 16', not-quite-square to fit the corner of the garden
behind some trees, replacing a pair of 8x8 sheds
snip

This is somewhere around 5m * 5m or 25 square metres floor area.

You should therefore check
http://www.planningportal.gov.uk/eng...noutbuildings/
if you have not already done so to make sure you are far enough from your
boundaries.

[You probably have, as you talk about maximum heights]

Cheers

Dave R

"Dave H." wrote in message
...
SWMBO and I are the initial back-of-an-envelope stage of planning a Big
Shed (approx. 16' x 16', not-quite-square to fit the corner of the garden
behind some trees, replacing a pair of 8x8 sheds, one on a concrete raft,
one on piers) which I hope may end up accomodating a Proper Lathe (in the
ton to ton-and-a-half weight range) so could use some advice regarding the
floor - I'm pretty sure I'll need more than the 4" of concrete on
scalpings/sand blinding/DPM, is a 6" pad with steel reinforcement at 2"
and 4" going to be inadequate, adequate or overkill?

A 6"/150mm reinforced base is reported as adequate for a garage so as cars
can weigh 1.5 tons I would guess you should be all right with the smaller
lathe.
2.5 tons over a small area is above what you would expect with a car so I
presume that your deeper slab might be a good idea.


would it be wise to go for 8" with 4" of concrete between the reinforcement
to get a bit more stiffness?
The shed itself probably will be of wood construction with a cut roof
(possibly mansard to allow some more storage above) with a couple of brick
pillars (braced with brick buttresses) to support an RSJ for lifting, I
hope.

These are likely to need extra foundations, I would think.
What weight are you considering lifting?
Construction of these is likely to be a seperate design operation.


Fortunately I can get away with a few feet of extra height by taking my
"highest point of the surrounding terrain" reference from the neighbour's
garden the other side of a dwarf wall (on my side of the boundary)... So
ridge height could be as much as 14' above the base! At this size am I
likely to need to add a trench foundation in addition to the raft I've
envisaged?

I suppose it depends on the amount of wood you use :-)
I wouldn't have thought so - the 6" slab is reported to be fine for a
concrete sectional garage.
However, see above for the brick pillars.
Re-reading your post (always a good idea) I see you are possibly going to
install a 2.5 ton lathe so I would suggest that the floor loading for the
lathe is going to be considerably more than the loading for a wooden shed
wall.

The neighbour has a couple of tall (approx 30' cypressus (sp?) close to the
boundary, will they need their roots dealing with if they're below the
level of the scalpings etc.?

If you go for 6" concrete and at least 4" of MOT (scalpings?) underneath
then you are set up for 'poor ground' so I would expect that you would be
O.K.
They tend to be shallow rooted anyway so you are likely to go through any
roots over your side when you are digging out (assuming you are digging out,
of course, and not laying the slab directly on the surface).
Oh, and what kind of soil are you on?
Sand and loam are generally more forgiving than clay.

Hopefully the experienced people who have been helping me out with my shed
(only slightly larger than yours) can add their advice.
I am going with a 4" reinforced slab with 8" deep by 16" wide round the
edges to support the block walls.
However I don't plan to put a 1.5 ton to 2.5 ton lathe inside, or a hoist
:-)

Talk to building control - they are usually more than willing to give free
advice.

HTH

Dave R