(Long post - sorry)

This year I had a double-storey extension done on my house. It was
started in April, finished in August.

Part of the extension includes an en-suite shower upstairs, and in
October I got round to tiling the floor and installing the shower.

However, since then, it has become obvious that the upstairs floor is
sinking. By looking at the level of the floor tiles against the
skirting boards (screwed to the wall) I can see that the floor in the
corner of the en-suite has dropped by about 6-7mm so far. While this is
not a huge problem with the floor (the grouting is still intact),
unfortunately the shower tray has also dropped by a few mm and the
waterproof seal along the edges is starting to crack and break as a result.

As far as I can tell, the settling is not happening to the same degree
across the whole of the extension's first floor. I haven't got an easy
way to tell elsewhere (no flooring yet!), but I am reasonably sure that
any other settling is only around a couple of mm, if at all.

The floor's construction is pretty standard - 2x10 (or 12? not sure)
wooden joists, laid on 40cm centres, one end bedded into the inner
blockwork leaf of the new wall, the other end suspended on joist hangers
from the existing wall. The end that's dropping is the one bedded into
the new wall. The flooring surface is sheets of T+G flooring grade
chipboard, screwed to the joists at approx 30xm intervals.

Inspecting the ceiling on the ground floor below (plasterboard screwed
to the underside of the joists) shows no signs of the ceiling dropping
or any other movement.

So as far as I can tell, this floor movement can only be explained by
some of the joists actually shrinking by about 2-3% on their vertical
axis. What do others think? Is this normal, and if so, how much
shrinkage can I expect? How long will it last - i.e. how long should I
wait before starting to repair the tiling and shower tray waterproofing?

--
Tony

On Fri, 24 Dec 2004 09:55:13 +0000, Tony Eva wrote:

(Long post - sorry)

This year I had a double-storey extension done on my house. It was
started in April, finished in August.

Part of the extension includes an en-suite shower upstairs, and in
October I got round to tiling the floor and installing the shower.

However, since then, it has become obvious that the upstairs floor is
sinking. By looking at the level of the floor tiles against the
skirting boards (screwed to the wall) I can see that the floor in the
corner of the en-suite has dropped by about 6-7mm so far. While this is
not a huge problem with the floor (the grouting is still intact),
unfortunately the shower tray has also dropped by a few mm and the
waterproof seal along the edges is starting to crack and break as a result.

As far as I can tell, the settling is not happening to the same degree
across the whole of the extension's first floor. I haven't got an easy
way to tell elsewhere (no flooring yet!), but I am reasonably sure that
any other settling is only around a couple of mm, if at all.

The floor's construction is pretty standard - 2x10 (or 12? not sure)
wooden joists, laid on 40cm centres, one end bedded into the inner
blockwork leaf of the new wall, the other end suspended on joist hangers
from the existing wall. The end that's dropping is the one bedded into
the new wall. The flooring surface is sheets of T+G flooring grade
chipboard, screwed to the joists at approx 30xm intervals.

Inspecting the ceiling on the ground floor below (plasterboard screwed
to the underside of the joists) shows no signs of the ceiling dropping
or any other movement.

So as far as I can tell, this floor movement can only be explained by
some of the joists actually shrinking by about 2-3% on their vertical
axis. What do others think? Is this normal, and if so, how much
shrinkage can I expect? How long will it last - i.e. how long should I
wait before starting to repair the tiling and shower tray waterproofing?


The joists should nto shrink as they dry, cause they should have been
kiln dried before installing.

What I think is that the packer put under the joist to hold them level
has either come out, or crushed. I would put a straight edge on the
ceiling below, to see if its no longer straight.

Rick

"Tony Eva" wrote in message ...
(Long post - sorry)

This year I had a double-storey extension done on my house. It was
started in April, finished in August.


snipped
wait before starting to repair the tiling and shower tray waterproofing?

Tony


It might just be the timbers shrinking in the cold weather Tony. The small
spaces are appearing normally for a new build, that's why builders come back
after months not weeks to do any snagging work on a new build. Small gaps
could appear in plasterboard joints over the next few months. Skirting
boards may appear to have lifted off the floor by a few millimetres.
Chipboard flooring may show signs of opening up at the joints by a couple of
millimetres. These are all perfectly normal on something as new and heavy
as an extension.

If you'd said that the skirting board had fallen off, or that it had risen
up the wall by a few centimetres, then I would have worried about your
build. But for a couple of millimetres of movement over such a short period
of time after completion, it's nothing un-normal about it.

BigWallop wrote:

But for a couple of millimetres of movement over such a short period
of time after completion, it's nothing un-normal about it.

OK, thanks for that. I suppose what I also need to know is how long I
can expect this to continue for? There's no point in my doing a full
repair job on the shower if it's yet to get significantly worse.

--
Tony

Rick Dipper wrote:

The joists should nto shrink as they dry, cause they should have been
kiln dried before installing.

What I think is that the packer put under the joist to hold them level
has either come out, or crushed. I would put a straight edge on the
ceiling below, to see if its no longer straight.

The ceiling below is still 100% level with no signs of movement.

The other reply suggests that joist shrinkage *is* normal, though I must
admit I am surprised by the extent (6-7mm over 25-30cm) of it.

--
Tony

"Tony Eva" wrote in message

So as far as I can tell, this floor movement can only be explained by
some of the joists actually shrinking by about 2-3% on their vertical
axis. What do others think? Is this normal, and if so, how much
shrinkage can I expect? How long will it last - i.e. how long should I
wait before starting to repair the tiling and shower tray waterproofing?

The other explanation is that the wall is rising. If it is a stud wall I
imagine it has. Have a look in the loft to try an see if the trusses
have been pushed up at the spot.

I have no idea how that might be overcome, if it is the problem.



--
Posted via Mailgate.ORG Server - http://www.Mailgate.ORG

"Tony Eva" wrote in message ...
BigWallop wrote:

But for a couple of millimetres of movement over such a short period
of time after completion, it's nothing un-normal about it.

OK, thanks for that. I suppose what I also need to know is how long I
can expect this to continue for? There's no point in my doing a full
repair job on the shower if it's yet to get significantly worse.

Tony


It is normal Tony. Most new builds move and settle for years after the main
build completion. I live in a tenement that's over one hundred years old,
and it's still moving slightly here and there. The difference in
temperatures inside and out can also create shrinking and expanding of the
building, so if the timbers were installed in summer hot weather they will
shrink slightly in the colder winter months. It's a natural process for
everything and everybody. If the building were moving by huge centimetre
amounts at a time, then you start to worry, but a few millimetres here and
there is natural.

The shower should have a base seal which allows for millimetre movement at
any time. The weight of a body in the shower will cause the base to move
anytime it's used, and this should always be allowed for in the type of
sealant used. A skirting should always allow for movement against the floor
to stop it forcing when the temperatures change in and around the house, so
this to should be allowed for when fitted.

Believe me, it's nothing to worry about unless the movement is huge amounts
at a time.

Tony Eva wrote:


However, since then, it has become obvious that the upstairs floor is
sinking. By looking at the level of the floor tiles against the

The floor's construction is pretty standard - 2x10 (or 12? not sure)
wooden joists, laid on 40cm centres, one end bedded into the inner
blockwork leaf of the new wall, the other end suspended on joist hangers
from the existing wall. The end that's dropping is the one bedded into
the new wall. The flooring surface is sheets of T+G flooring grade
chipboard, screwed to the joists at approx 30xm intervals.

There are a few clues in there. The fact the the floor is moving
relative to the skirting would suggest it is *not* the whole wall that
is moving since the joists are presumably being supported by the same
wall. So that does lend weight to the shrinkage theory. Also the fact
that the joists are in hangers at one end might also go some way to
explain why you are not seeing the same (or as much) movement at that
end. Depending on the hanger design it may well have a row of nails down
both sides for most of the depth of the joist, this would tend to
restrict the shrinkage a little, and also maintain the centre of the
joist in its original position, causing the shrinkage to be shared
partly above and partly below. The other end however the joist is simply
sat on a wall plate and hence all shrinkage will appear as a loss of
height of the joist.

You may also see some variation as the centre of the span sags a little
as it will over time. If the builder was careful then he will have
placed all the joists with their natural camber rising, so they settle
towards level.

While in theory the timber is kiln dried, I know from recent experience
that is only part of the story! What happens to it after it leaves the
lumber yard is another matter. Many builders merchants seem to keep
constructional timber outside in the rain. (I know I had some bits of
4x2" delivered that were so wet you could almost wring them out!)

Did you start to notice more movement after the weather got colder and
the heating came on?


--
Cheers,

John.

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In article , Tony Eva wrote:
So as far as I can tell, this floor movement can only be explained
by some of the joists actually shrinking by about 2-3% on their
vertical axis. What do others think? Is this normal, and if so,
how much shrinkage can I expect?

http://www.turningtools.co.uk/howdry/howdry.html suggests 1.5-2%
shrinkage across the grain for a 5% change in moisture content,
air-dried timber will have a MC of 18-20% and in a centrally heated
house this may drop to 10%, so what you're seeing is not unexpected.
Traditional joinery practice when making panelled doors or panelling
a room is to put the panels into grooves with no glue so that they
can move with the changing humidity.

--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
Free SEDBUK boiler database browser http://www.sda.co.uk/qsedbuk.htm

John Rumm wrote:
While in theory the timber is kiln dried, I know from recent experience
that is only part of the story! What happens to it after it leaves the
lumber yard is another matter. Many builders merchants seem to keep
constructional timber outside in the rain. (I know I had some bits of
4x2" delivered that were so wet you could almost wring them out!)

We were lucky this year - over the period that the joists were on site
(delivery to roof completed) there was no rain. What happened to them in
the yard is another story, of course - April was *very* wet.

Did you start to notice more movement after the weather got colder and
the heating came on?

I couldn't really say... I didn't pay any attention to floor movement
until after I'd tiled the floor around Sep-Oct, which was about the time
the heating came on.

However another post suggests that I can expect around 3-4% shrinkage as
the joists reach their stable moisture content, with a smaller seasonal
fluctuation after that. So I might well have seen the worst of it by now.

Thanks for all the responses.

--
Tony