Floor on joists sinking

I am building a new house and my building inspector warned me that the floor joists can shrink with time and the floor will sink accordingly. He says that he has seen vertical gaps of up to 10mm between the skirting board and the floor a few years after the house was built.
I recently rented a house where I was able to see this. Half way on the first floor walls there is a gap big enough to pass notepads under the skirting board from one room to another. Towards the ends of the walls the gap is minimal.
That the inspector was right is fine but what is the solution while you are still building the floor?
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I'm not sure I buy the inspectors opinion. If the joists shrank, wouldn't everything come down 10 mm? I think it is more likely shrinkage in the base trim. If it is the joists, the only solution I can think of is to either use engineered lumber or else somehow be sure that the wood is kiln dried and that it stays dry before trim goes on--not really a real world solution. At any rate, this isn't a big problem. I would just use a base shoe, which is a secondary peice of trim that can be nailed to the floor. If you are doing it yourself, you could even hold off on the base shoe through a heating season or whatever until things have stabilized a bit.
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wrote:

Marson's right. You won't see that much on the first floor of a balloon-frame or western frame building due to the joist shrinkage (alone). Something else is at work, though I don't think baseboard shrinkage could explain it either. Depending on the local climate, much of the normal shrinkage will occur early in the first heating season, and can often happen during construction itself, before final finishing.
Always use dry lumber, and keep it as dry as you can while exposed to minimize shrinkage.
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MichaelB
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First, the condition in the unit you rented seems more likely to be sagging floor joists, than any thing else. Materials and their storage seems important to shrinking. If the wood is 'green' or 'treated' and not given time to dry to local conditions, it may well change dimension. T
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Floor joists do shrink; from green to final moisture content
In California worst case is about 1/28 of an inch per inch.....so a 2x12 shrinks about 10mm
The problem we get out here is that the building are framed & finished while framing material is not dry
When the floor joists shrink, you get "wow" in the plywood sheathing under the stucco layer.....often times this results in a buldge in the stucco.
Previous advice about engineered members or dry wood is good.
IMO your situation with the base is not joist shrinkage related, joist shrinkage causes the entire floor system to "get thinner"....uniformly.
Does every wall exhibit this behavior or are perpendicular tones different?
cheers Bob
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Are you talking about "green" lumber? We have building codes that say:
"(1) Moisture content of lumber shall be not more than 19% at the time of installation." That's basically Kiln Dried that's been rained on.
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No the walls perpendicular to the ones that are sagging or shrinking are not bad so it must be to do with the orientation of the joists but I do not know for sure which way the joists are placed in this house. I suspect the joists are parallel to the walls where the gaps show.
Yes, the inspector told me that the material for joists is now kiln dried but I have seen it in building materials yards well exposed to the weather.

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Bobk207 wrote:

It looks like my messages are not getting through. Anyway, I was saying on a previous message that the walls perpendicualr to the one where the floors are sinking are not shoiwng sinking. So it must be to do with the orientation of the joists. I suspect that the joists are parallel to the walls where sinking shows
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