Sourcing materials according to Engineers Specification?

10 May 2020
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United Kingdom
Hi there,

I have a silly question (or three). My structural engineer has specified various beams and joists etc for the loft conversion.

For example, TR1 is specified to be "2No.50x125dp C24 Timber Joists".

But when I google that I can't find those exact dimensions and matching C rating.

What does one do? Am I not looking hard enough or am I supposed to just go one size up? For example, this is what I could find. But it is 3mm narrower and 25mm too tall.

Does the "2No." mean that 2 timbers are fixed together to form one joist?

What does "dp" mean?

Many thanks in advance.


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3 Sep 2006
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West Mids
United Kingdom
Most timber now is regularised (smoothed), not rough so it comes in a few mm less than stated once its planed at the mill. Thats a 5x2 in old money so you can use anything near to that.

d = deep
No = number

If he is specifying two timbers joined to form a beam, then he should be specifying how they are to be fixed together - what with, what fixing size, how many, what spacing and where along the axis.

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