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Rim Joist (wall plate) marking out: towards a check list


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Example: I give my recently-acquired beard a quick brush when I get out of the shower, in front of a mirror that's temporarily sitting on a chest of drawers against a wall in our bedroom. The movement of my hand is enough to make the mirror wobble.

 

I suspect part of the issue is that the posi-joists in this area span between an outer wall and a very long steel beam.

 

It may be that I happen to brush at a resonant frequency of the system as a whole!

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Interesting to hear what difference the joist spacing can make to the floor deflection. I've got 300x63 JJI joists, 4.8m span, at 600 centres. I wonder if it would have been worth the extra couple of hundred quid to switch to 400. Oh well, a bit late now... I didn't want a tiled floor anyway...

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22 hours ago, MikeSharp01 said:

@recoveringacademic TOC is top of concrete and the value is the 27.255 height from your drawing. I assume the 27.255 dimension is to the bottom of the piles because if it is from some other survey datum point it may be worth verifying it so you can be sure everything is correct in relation to the datum if it is not the bottom of the piles.

 

If the piles are 27 metres (90 ft) long I'd be gobsmacked.

I assume the datum is taken from the Ordnance Survey standard datum. https://en.wikipedia.org/wiki/Ordnance_datum

Edited by RichS
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32 minutes ago, RichS said:

If the piles are 27 metres (90 ft) long I'd be gobsmacked.

Me to! but if a standard OS datum I wonder how it was transfered to the site and why it is so prominent on the drawing. One might expect a single datum zero on the site tracked back to OS datum this way it just feels confusing and you need a vastly long tape to measure heights.

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14 hours ago, Crofter said:

Interesting to hear what difference the joist spacing can make to the floor deflection. I've got 300x63 JJI joists, 4.8m span, at 600 centres. I wonder if it would have been worth the extra couple of hundred quid to switch to 400. Oh well, a bit late now... I didn't want a tiled floor anyway...

It's not only the spacing but also the size of the flange. I have, 122mm flange, metal web joists spanning 5.9m at 400mm centres and there is no deflection at all.

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I had a visit yesterday from a member and his wife who, in fairness to them both, must remain nameless. 

 

He took a huge weight off my shoulders by explaining how to mark out for the wall plate properly. And when he had explained it, he showed me how. Since he does this job commercially, I am not left wondering whether competence was an issue. I feel like I have had a bag of cement taken off my back.

 

I thought that to ascertain wall plate level, all I needed to do was to measure from the existing level (DPC) to the bottom of the wall plate (rim joist). I had the odd niggling naggling doubt though. What would happen if the subfloor was not level? (It isn't)

 

Ya just can't know what ya don't know.  And that's why I spend hours 'wasting time' reading round the subject, hoping to hit a gold mine of information. But 'Tinternet is full of shared ignorance, misinformation and waffle. So, I'll stop waffling for now and post pics and method a bit later today.

 

A big thank you to the big lad from Preston and his wife and his HILTI laser.

 

 

 

 

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On 29/09/2017 at 19:47, MikeSharp01 said:

Me to! but if a standard OS datum I wonder how it was transfered to the site and why it is so prominent on the drawing. One might expect a single datum zero on the site tracked back to OS datum this way it just feels confusing and you need a vastly long tape to measure heights.

 

 

Every height on our main drawings is referenced to ordnance datum.  The standard abbreviation when this is the case is to put AOD after the height, for Above Ordnance Datum. 

 

If drawings don't have this, then there should be a note somewhere saying where the datum is located.  For example, the working copies of our ground works drawings were referenced to a datum nail in the lane that was at 81.48m AOD.  It was easy to then just use relative heights to this point as far as the guys on site were concerned, because they could just do a very quick check from that datum nail, without needing to subtract the height above ordnance datum.

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1 hour ago, JSHarris said:

 

If drawings don't have this, then there should be a note somewhere saying where the datum is located. 

Yes we have a datum based upon a survey nail in a sunken brick with two fixed back sights all set by our surveyor I think we do know the AOD of the brick but it us not used anywhere and our PP gives the FFL of the ground floor as 500mm above the datum and everything is linked back to that as the architects 0 datum.  Looks like Ian has sorted his issue out, thanks to ANON - this is exactly the sort of thing this place can faciliate so all praise to them, but I was not sure how his AOD heights link back to his planning permission or if some other datum, in the way ours does, defines the heights. Given the drawings it looks like it is the OS so all should be well. 

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9 hours ago, recoveringacademic said:

I had a visit yesterday from a member and his wife who, in fairness to them both, must remain nameless. 

 

He took a huge weight off my shoulders by explaining how to mark out for the wall plate properly. And when he had explained it, he showed me how. Since he does this job commercially, I am not left wondering whether competence was an issue. I feel like I have had a bag of cement taken off my back.

 

I thought that to ascertain wall plate level, all I needed to do was to measure from the existing level (DPC) to the bottom of the wall plate (rim joist). I had the odd niggling naggling doubt though. What would happen if the subfloor was not level? (It isn't)

 

Ya just can't know what ya don't know.  And that's why I spend hours 'wasting time' reading round the subject, hoping to hit a gold mine of information. But 'Tinternet is full of shared ignorance, misinformation and waffle. So, I'll stop waffling for now and post pics and method a bit later today.

 

A big thank you to the big lad from Preston and his wife and his HILTI laser.

 

 

 

 

?

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