Timber joists shrinkage or structural defect?

[klmtig]

Hi,

The new extension in a new conversion that I bought is showing some rather large gaps between the flooring and skirting board and parts of the flooring feels like it has dropped. In some places the gap is about 17-18mm and I can insert my fingers through the gap. The builder is claiming that it is shrinkage of the joists and this is considered normal. However, from speaking to timber specialists they pretty much laughed at the story and said wood doesn't shrink that much, or they would be getting some serious complaints for joists used in roofing work.

Is it true that the joists (made from tanalised timber) would not shrink this much?

Has anyone come across anything like this and if so what is the best course of action?

Thanks in advance.

 

[Deleted member 174758]

With tanalised timbers you can get some shrinkage, especially if they are installed soaking wet in the middle of winter, however I've never seen 17 to 18mm shrinkage across the width of a joist in my life. Your builder is talking rowlocks!

 

[KenGMac]

klmtig, good evening.

As this is your first post and if no one else does, welcome to the board.

OK gaps such as you have are not occasioned by "joist shrinkage"

I have seen such deformity when wood rot has either rotted the "Joist End" when the joist end is embedded in the external wall, but? this generally only occurs in older [Victorian / Georgian] ground floor properties. Can also occur when the timber wall plate rots down in similar aged properties when the joist is not built into the external wall but the joists rest on a wall plate.

Is the floor "Bouncing?"

Do you know how the joist ends are supported? on a wall plate? built into the external walls? on joist hangers?

Ken

 

[Deleted member 174758]

Do you know how the joist ends are supported? on a wall plate? built into the external walls? on joist hangers?

OP quoted new extension, so i'd expect wall plates/ledgers or direct to masonry hangers (ZIP hangers). Can't see anyone ending the joists inside the masonry these days (or the BCO accepting it). but maybe I have that wrong

 

[foxhole]

The joist hangers may not have been seated securely allowing slippage, or timbers may not have been secured firmly in hangers which could also allow them to drop .

 

[Deleted member 174758]

Sounds like it may be worth the OP either lifting a section of floor to inspect, or maybe drilling and getting an inspection camera in there to ascertain what's what beneath the floor at the wall joint

 

[tony1851]

Is it 17-18mm? On the rule, it looks more like 12-13mm.
Some timbers are prone to relatively large shrinkage, depending on how they were cut from the log, and shrinkage across the grain can vary from 3-10%.
If you have large floor joists (eg 8x2s) which were maybe stored outside for a period, it's not inconceivable that you could get considerable shrinkage once in a centrally-heated environment.
Not saying that's the issue here, but the gap does seem to be level, suggesting that all the joists are down by the same amount.
It seems odd that the floor seems to have dropped evenly.

 

[klmtig]

Thank you all for taking the time to reply. that's helpful to know.

The measurement on the ruler doesn't start until about 4 mm in which is why it seems less. The gap isn't even all along the wall either.