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How to prop up floor joists



 
 
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  #1  
Old May 20th 08, 03:11 PM posted to uk.d-i-y
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Posts: 1,105
Default How to prop up floor joists


I want to support my ground floor joists. This is partly to take the
weight of a piano and also because the joists do deflect rather a lot
anyway when weight is put on them (such as bookcases, cookers etc.
The joists in these houses (8"x2" at 18" centres) are, apparently, of
rather poor quality and have shrunk and bent in every house in eth
development. They were built in 1964 - part of the "Span House"
movement. When the floor deflects the walls that are built on it (of
block) move and crack which is not nice.

Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.

One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.

Does anyone have any other suggestions?

Robert

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  #2  
Old May 20th 08, 03:21 PM posted to uk.d-i-y
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Posts: 286
Default How to prop up floor joists


"RobertL" wrote in message
...

I want to support my ground floor joists. This is partly to take the
weight of a piano and also because the joists do deflect rather a lot
anyway when weight is put on them (such as bookcases, cookers etc.
The joists in these houses (8"x2" at 18" centres) are, apparently, of
rather poor quality and have shrunk and bent in every house in eth
development. They were built in 1964 - part of the "Span House"
movement. When the floor deflects the walls that are built on it (of
block) move and crack which is not nice.

Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.

One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.

Does anyone have any other suggestions?

Robert


House bricks and put a piece of insulation in between the joist and the top
brick ie plastic sheeting doubled over.


  #3  
Old May 20th 08, 03:48 PM posted to uk.d-i-y
Rod
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Posts: 2,893
Default How to prop up floor joists

RobertL wrote:
I want to support my ground floor joists. This is partly to take the
weight of a piano and also because the joists do deflect rather a lot
anyway when weight is put on them (such as bookcases, cookers etc.
The joists in these houses (8"x2" at 18" centres) are, apparently, of
rather poor quality and have shrunk and bent in every house in eth
development. They were built in 1964 - part of the "Span House"
movement. When the floor deflects the walls that are built on it (of
block) move and crack which is not nice.

Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.

One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.

Does anyone have any other suggestions?

Robert


Robert,

It is not clear to me whether you are talking about temporary or
permanent support. I can imagine jacks as a temporary measure (e.g.
while you address the other problems) but not never as permanent. But
the 4"x2" props sounds more permament as do your worries about damp
conducting.

My thoughts shout "piles of concrete blocks" and inserting a DPM as they
are built up. But I have no idea of what should be done to the earth
beneath them - or whether this is something that requires Building
Control involvement.

There may well be ways of reinforcing the joists (e.g. slap an extra
piece of timber either side and bolt through) that are much better ideas.

Clearly you should also be considering a) insulation under the floor; b)
airflow; c) anything else you might want to do that could/should be done
at the same time (e.g. extending electric circuits,
checking/insulating/changing central heating pipes, network cables).

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org
  #4  
Old May 20th 08, 04:19 PM posted to uk.d-i-y
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Posts: 9,356
Default How to prop up floor joists

On Tue, 20 May 2008 07:11:46 -0700 (PDT), RobertL wrote:

One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.


The normal solution would ne to build a sleeper wall under the joists and
pack up to the underside of the joists with a DPC (a bit of slate is
strong in compression). Props will work but you'll have to think of a way
of stopping the wedges working loose over time and possibly some means of
spreading the load on the soil so they don't sink in.

--
Cheers
Dave.



  #5  
Old May 20th 08, 04:30 PM posted to uk.d-i-y
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Posts: 1,105
Default How to prop up floor joists

On May 20, 4:35*pm, Tony Bryer wrote:
On Tue, 20 May 2008 07:11:46 -0700 (PDT) RobertL wrote :

Under the house the gap between the earth to underside of each joist
is about 50cm. *This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. *It's too small for an ACROW
prop.


You want trench props.http://www.toptower.co.uk/builders_props.htmwas
the first source thrown up by Google but there may be cheaper options.
As you only want to use them the once, a hire shop might sell some used
ones.



thank you all for your suggestions. Tony was right on the nail
though. TRENCH PROPS are exactly what I need. they come in just the
right sizes.

It is a permanent installation, but I might decide to move them around
if the piano is moved.

Rod's comments about doing otehr work down there at the same time it
well taken, but I have good access via a trap door so I can get down
there without too much effort.

Many thanks,

Robert

Robert

  #6  
Old May 20th 08, 04:35 PM posted to uk.d-i-y
external usenet poster
 
Posts: 1,211
Default How to prop up floor joists

On Tue, 20 May 2008 07:11:46 -0700 (PDT) RobertL wrote :
Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.


You want trench props. http://www.toptower.co.uk/builders_props.htm was
the first source thrown up by Google but there may be cheaper options.
As you only want to use them the once, a hire shop might sell some used
ones.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk

  #7  
Old May 20th 08, 05:44 PM posted to uk.d-i-y
external usenet poster
 
Posts: 4,807
Default How to prop up floor joists

Dave Liquorice wrote:
On Tue, 20 May 2008 07:11:46 -0700 (PDT), RobertL wrote:

One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.


The normal solution would ne to build a sleeper wall under the joists and
pack up to the underside of the joists with a DPC (a bit of slate is
strong in compression). Props will work but you'll have to think of a way
of stopping the wedges working loose over time and possibly some means of
spreading the load on the soil so they don't sink in.


How much does this piano weigh? A Yamaha grand is only 250kgs. Ten bags
of sand isn't going to do much to any floor. People are quite heavy
these days as well.
  #8  
Old May 20th 08, 06:41 PM posted to uk.d-i-y
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Posts: 19,203
Default How to prop up floor joists

In article
,
RobertL wrote:
Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.


One simple solution is to use some wooden 4"x2" props with carpenter's
wedges to adjust the height. But I am worried about creating a damp-
conducting path up to the joists even if I stand the base on damp
proofing membrane.


The ground floor in my Victorian house was changed from sitting on wood
wall plates to 'floating' as part of damp and wood treatment. They built
brick piers and columns in the cellar with minimal footings which the
joists now rest on - via a cross joist or two. A simple damp proof
membrane between brick and wood.

--
*If one synchronized swimmer drowns, do the rest have to drown too?

Dave Plowman London SW
To e-mail, change noise into sound.
  #9  
Old May 20th 08, 09:40 PM posted to uk.d-i-y
external usenet poster
 
Posts: 146
Default How to prop up floor joists

George wrote:
"RobertL" wrote in message
...

I want to support my ground floor joists. This is partly to take the
weight of a piano and also because the joists do deflect rather a
lot anyway when weight is put on them (such as bookcases, cookers
etc.
The joists in these houses (8"x2" at 18" centres) are, apparently,
of rather poor quality and have shrunk and bent in every house in
eth development. They were built in 1964 - part of the "Span House"
movement. When the floor deflects the walls that are built on it
(of block) move and crack which is not nice.

Under the house the gap between the earth to underside of each joist
is about 50cm. This is too big for a car scissor jack - I had
imagined using a row of scissor jacks. It's too small for an ACROW
prop.

One simple solution is to use some wooden 4"x2" props with
carpenter's wedges to adjust the height. But I am worried about
creating a damp- conducting path up to the joists even if I stand
the base on damp proofing membrane.

Does anyone have any other suggestions?

Robert


House bricks and put a piece of insulation in between the joist and
the top brick ie plastic sheeting doubled over.


Might also be worth putting some noggins/dwangs in between the joists at
regular intervals to stop the joists twisting as they get loaded. Our
builder did this when sorting out our wonky dining room floor.

Tim


  #10  
Old May 20th 08, 10:04 PM posted to uk.d-i-y
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Posts: 9,356
Default How to prop up floor joists

On Tue, 20 May 2008 17:44:37 +0100, stuart noble wrote:

How much does this piano weigh? A Yamaha grand is only 250kgs. Ten bags
of sand isn't going to do much to any floor.


Not if you spread 'em out but pile 'em all in a heap at one side... The OP
has already stated the the floor and walls move enough to cause cracking
in normal use. 8 x 2 at 18" is, IMHO, a pretty light weight bouncy floor.
10 x 3 at 12 would be a good strong a floor.

--
Cheers
Dave.



 




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