Floor joists and metal restraining straps.

Has anyone any experience of installing a suspended timber floor into a new building / extension ? I understand that according to UK building regulations, new joists have to be tied into the new wall using galvanised restraining straps at max 2000 centres and these have to be taken over at least 3 joists with tight packing between. I also understand that this is normally achieved using what is in effect an 'L' shaped strap with the short edged pulled up tightly behind and built into the block wall and the longer end secured on the top of each joist.
All well and good, but what can you do if the top of the joist doesn't align with the horizontal mortar beds in the block wall ? Can they be installed on the bottom of the joist ?
What if it still doesn't align, is there some other method to achieve the same thing ? I have been wondering about the possibilty of obtaining a strap which can be intalled in a vertical mortar gap with a bend to pull it up against the back of the block and then a twist at the front of the block so it still sits on top of the joist.
Does any of this make any sense to anybody?
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Hi Kevin,
Try this site for some answers :
http://www.diydoctor.org.uk/projects/load-bearing_walls.htm
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BigWallop wrote:

Use appropriately sized joist hangers then your joists will align with the mortar joints. Should this not be possible use a smaller block one course below. The strap must go over an uncut block. It can be fastened either above or below the joist and noggins. The gap between the last joist and wall needs suitable packing.
Toby.
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Toby, Thanks for the advice, joist hangers aren't actually going to help as I am actually talking about an extension and the new joists need to align with the top of the existing joists in the house otherwise there will be a difference in floor level. I should be able to work something out with cut blocks in order to bring the mortar beds in line though. Are my thoughts on a twisted bent strap impractical then ?
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Kevin wrote:

The hangers give you the opportunity to fine tune the floor height (packing / notching).

No, I thought you were spot on. The requirement is the strap must be of durable metal, 30mm x 5mm minimum section, spanning 3 joists. Bang the noggins in between the joists and run the strap above or below these and then over a _full_ block. Although I can't see any written guidance, I believe the bend should always be downward rather than upward.
Toby.
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Good link thanks. I got the impression he was talking about the straps that are set in the gable to stop the roof blowing away.
It does happen that when the bricklayers don't know what they are doing, or don't care, that the courses run out of level. If it's a new house you can insist that the builder put it right. Take some litigation that though. Renovations are bound to hit that snag as buildings settle. The trick there is to notch the joists to suit.
It is the thickness of the joist at the centre that is crucial so you might get away with quite deep notches at the ends. You can always underpin them with a cross member at the wall? Or notch the joists to go over a 3"x 2" at either end fixed to the wall securely?
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