We have a single storey extension about 7m x 4m and were wondering about
making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground upwards?

Any thoughts welcome!
--
John Alexander,

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John wrote:
We have a single storey extension about 7m x 4m and were wondering about
making it two storey.

How would we find out if the foundations were adequate?

Dig trial holes down the side. They almost certainly will not be, as
regulations have got more stringent in this area.



If not what options are there?

1/. Demolish and rebuild.

2/. Underpin at about £1000 per linear meter.


A simple calculator will show which is the cheaper option.

Exetsnion work to a bare shell is about £60 per sq foot.

If you have an abutted extesnion of X x X feet (square) then total floor
are is X squared, whereas outside walls are 3X.

Cost of rebuild is about 60x^2, cost to underpin is about 3000X.

so the break even point is where X is about 50 feet. Or 2500 sq ft.

i.e. in almost all cases its cheaper to knock down and start again.
Takes about 3-4 days to demolish, and dig new footings.

And that way the extension gets to be really well built and of
cosnisetnt brickwork from top to bottom.



What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground upwards?


very little different. The largest costs come not from the structural
work, if its 'new build' but from fixtures and fittings. I.e. carpets
curtains, wiring, plumbing heating painting plastering etc etc.

Unless the current extension is likely to remain undamaged (hardly
likely) you have to redo all that anyway.

Demolition costs are not too high..probably couple of thou for a small
extension.

I would get trial holes dig and the BCO onsite or structural engiuneers,
and if the answer is 'no way are those foundatins up to snuff' then bite
the bullet, get planning permission for a totally new edifice, get the
site cleared completely and think about access for machinery, and dig
yourself a new set of foundations. This also means you have the
opportunity to sort out drains - VERY important - and soakaway type stuff.

Expect the garden for at least 6 ft around the extension to be totally
trashed, remove any plants you want to keep, get the skips on and then
trash it.

BUT builders LIKE 'new build' - there are a lot of unexpected costs
fettling new stuff to fit old stuff.



Any thoughts welcome!

John wrote:
We have a single storey extension about 7m x 4m and were wondering about
making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground upwards?

Any thoughts welcome!
--
John Alexander,

Remove NOSPAM if replying by e-mail

Do you have the plans for the original extension, if not do your local
planning office, specs and inspections should be held there. Otherwise
dig down and have a peep !!

John wrote:
We have a single storey extension about 7m x 4m and were wondering about
making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground upwards?

Any thoughts welcome!
--
John Alexander,

Remove NOSPAM if replying by e-mail

Price wise, for a rebuild ball park figures, DIY £15K (slate roof)
Builder £30 - £35K,
Prices for builders seem extortionate but remember they have to shell
out for the sparky plumber and chippy quite often, and the cost soon
mounts up !!.
My extension is 5 X 4 metres two storey, slate roof. I've done most
myself with a lot of help and advice, lots of it lateley on here ( I
wish I found this group when I started!!)
And its looking to be around £20K but thats including the kitchen.
Not too bad really for a good sized fourth bedroom and a decnt size
kitchen. :-)
When doing it DIY you'll be amazed how quickly the "little" things you
need to do a job soon mount up :-(
The only no go area for me is plastering, but one day........

John wrote:
We have a single storey extension about 7m x 4m and were wondering
about making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground
upwards?

Any thoughts welcome!

How old is the extension?

Our single-storey extension was built 10 years ago and the builder said that
Building Regs required foundations to be adequate for two storeys even
though - for other reasons - that's extremely unlikely to happen in our
case.

--
LSR

LSR wrote:
John wrote:
We have a single storey extension about 7m x 4m and were wondering
about making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground
upwards?

Any thoughts welcome!

How old is the extension?

Our single-storey extension was built 10 years ago and the builder said that
Building Regs required foundations to be adequate for two storeys even
though - for other reasons - that's extremely unlikely to happen in our
case.


Thats true, 600mm X 600mm minimum if I remember. my foundation is 600mm
deep at one side going down to 1200mm !!! this was due to me finding
granite at 600mm and the BCO insisted I carry the foundations along the
face of the granite to avoid differential settlement, unfortunatley for
me the granite dropped away sharply !, lots of readymix!! I chose to
fill it all instead of stepping it.

John wrote:
We have a single storey extension about 7m x 4m and were wondering
about making it two storey.

How would we find out if the foundations were adequate?

Dig a hole down the side of the wall until you find the concrete it's
sitting on, then dig down the side of that until you find the bottom, the
BCO will insist on these test holes prior to any work commencing and you
will probably need them before plans are submitted, which means they could
be left open for a long while, or filled in with soft material like sand for
easier removal next time, you only really need one hole but two won't do any
harm.


If not what options are there?

You either live with the extension you have, or knock it down and start
again, underpinning will cost more than the last war, but as long as the
extension is on at least 250mm of concrete and the concrete is on a firm sub
base like clay or stone, then it's 90% certain that it'll be ok to go
ahead....it may even be on a raft, which again will probably be OK.


What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground
upwards?

Any thoughts welcome!

knocking down and rebuilding is obviously the most expensive - new
extensions start in the region of £600 - £800 per square metre (outside
measurements - walls included!), but demolition will set you back a few
grand too, probably around 5-6K.
So a new double storey would set you back:
7.5m X 4.5 metres = 33.75m2 + 33.75m2 (upstairs floor area) =
67.5m2....times this by £700 and add on 5K for demolition, grand total =
£52,250 is probably about the lowest price you'll get.

The price for extending upwards only (provided foundations are OK) is much
less, because A) there's no digging or concreting involved or any associated
groundworks (relocating drains, manholes, water, gas and electricity mains
etc)
B) some of the existing roof timbers may be used as joists for the upper
floor or provide support to new ones.
C) There's no concrete floor to lay - this is a major factor in many
extensions and accounts for about 10% of the total cost once excavation,
insulation and screed is factored in.
D) it's much easier!

It works out around £400 per m2, so 33.75 X £400 = £13,500, ish....as you
can see there's a difference of about 40K, so you'd better hope and pray
that the foundations are good!!

On Thu, 28 Sep 2006 09:12:22 +0100 The Natural Philosopher wrote :
Dig trial holes down the side. They almost certainly will not be,
as regulations have got more stringent in this area.

We were insisting on 1m min deep foundations back in the late 1970s and
I would have thought these OK for most two-storey extensions

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

Tony Bryer wrote:
On Thu, 28 Sep 2006 09:12:22 +0100 The Natural Philosopher wrote :
Dig trial holes down the side. They almost certainly will not be,
as regulations have got more stringent in this area.

We were insisting on 1m min deep foundations back in the late 1970s
and I would have thought these OK for most two-storey extensions

It's not the depth of the footings that matters, they can be 2m deep but if
they are only sitting on 100mm of concrete, they aren't suitable.

Today's trend is to mass fill the footing with concrete, given that premixed
is coming down in price and trench blocks (and brickie's prices) are going
up, the last one we did was 600mm wide and over a metre deep of solid
concrete and it was only single storey.
I dropped 8m3 into a footing yesterday, but it was 33m long and 600mm wide,
it's around 400mm deep at it's shallowest and a metre deep where we came
across a bad patch and had to dig further down....the days of crouching down
in a hole to lay bricks and blocks have long gone!

Phil L wrote:
John wrote:
We have a single storey extension about 7m x 4m and were wondering
about making it two storey.

How would we find out if the foundations were adequate?

Dig a hole down the side of the wall until you find the concrete it's
sitting on, then dig down the side of that until you find the bottom, the
BCO will insist on these test holes prior to any work commencing and you
will probably need them before plans are submitted, which means they could
be left open for a long while, or filled in with soft material like sand for
easier removal next time, you only really need one hole but two won't do any
harm.

If not what options are there?

You either live with the extension you have, or knock it down and start
again, underpinning will cost more than the last war, but as long as the
extension is on at least 250mm of concrete and the concrete is on a firm sub
base like clay or stone, then it's 90% certain that it'll be ok to go
ahead....it may even be on a raft, which again will probably be OK.


What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground
upwards?

Any thoughts welcome!

knocking down and rebuilding is obviously the most expensive - new
extensions start in the region of £600 - £800 per square metre (outside
measurements - walls included!), but demolition will set you back a few
grand too, probably around 5-6K.
So a new double storey would set you back:
7.5m X 4.5 metres = 33.75m2 + 33.75m2 (upstairs floor area) =
67.5m2....times this by £700 and add on 5K for demolition, grand total =
£52,250 is probably about the lowest price you'll get.

The price for extending upwards only (provided foundations are OK) is much
less, because A) there's no digging or concreting involved or any associated
groundworks (relocating drains, manholes, water, gas and electricity mains
etc)
B) some of the existing roof timbers may be used as joists for the upper
floor or provide support to new ones.
C) There's no concrete floor to lay - this is a major factor in many
extensions and accounts for about 10% of the total cost once excavation,
insulation and screed is factored in.
D) it's much easier!

It works out around £400 per m2, so 33.75 X £400 = £13,500, ish....as you
can see there's a difference of about 40K, so you'd better hope and pray
that the foundations are good!!


I disagree. Demolition and groundwork were the smallest part of my
rebuild here.

The time is all spent in te fiddly bits and the money is all spent on
the fittings.

Tony Bryer wrote:
On Thu, 28 Sep 2006 09:12:22 +0100 The Natural Philosopher wrote :
Dig trial holes down the side. They almost certainly will not be,
as regulations have got more stringent in this area.

We were insisting on 1m min deep foundations back in the late 1970s and
I would have thought these OK for most two-storey extensions


YOU might have been insisting, but my niece recently underpinned a whole
length of 1970s extension that had been tre-rooted as it were, and apart
from the 500mm strip foundations and the rotting wooden lintels over the
windows, I can say the general standard of construction was utter crap.

They insisted here on a minimum of 1.5meters, and up to 2.5 meters in
places on similar soil with tree roots.

John wrote:
We have a single storey extension about 7m x 4m and were wondering about
making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground upwards?

Any thoughts welcome!

Just undertook the exact same task, for the same reason too! I phoned
the local BCO who were extremely helpful. They identified the original
plans were now on the microfiche archive. They found them, and found the
then inspectors note, who had stated the foundations were 1.2m deep :-)
With that information I was then informed by the BCO that any plans
I submit should reference the original extension plans, and reference
the inspector's note. They will then be accepted as OK. Total cost of
this, £0.00. I must admit the council guy I spoke with was really helpful.

That saved a load of £££'s in knock-down and rebuilding, or underpinning
costs.

IHTH

Gavin

On Thu, 28 Sep 2006 22:13:19 GMT Phil L wrote :
It's not the depth of the footings that matters, they can be 2m deep
but if they are only sitting on 100mm of concrete, they aren't suitable.

Today's trend is to mass fill the footing with concrete

In my BCO patch that was the norma 30 years back: trying to do traditional
strip footings and lay bricks in a trench whose sides wanted to fall in
would have been no fun. And on the sort of clay we had, even 400mm wide
trench fill foundations are OK for two storeys.

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

In article , Gavin
writes
John wrote:
We have a single storey extension about 7m x 4m and were wondering about
making it two storey.

How would we find out if the foundations were adequate?

If not what options are there?

What are the "order of magnitude" costs for either putting on a second
level and extending the pitched roof, or rebuilding from ground upwards?

Any thoughts welcome!

Just undertook the exact same task, for the same reason too! I phoned
the local BCO who were extremely helpful. They identified the original
plans were now on the microfiche archive. They found them, and found the
then inspectors note, who had stated the foundations were 1.2m deep :-)
With that information I was then informed by the BCO that any plans
I submit should reference the original extension plans, and reference
the inspector's note. They will then be accepted as OK. Total cost of
this, £0.00. I must admit the council guy I spoke with was really helpful.

That saved a load of £££'s in knock-down and rebuilding, or underpinning
costs.

IHTH

Gavin
Thanks to everyone for all the thoughts, experience, etc. At the moment
it is only an idea, but before we start trial holes it is good to know
what we might be looking at in the end.


--
John Alexander,

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