Joist and Rafters - actual vs nominal values.

[ab12]

I'm a little bit confused. Have had a new extension built with pitched roof and 7 by 2 joists were use.

When I measured the joist the other day to work out what insulation will fully fit the joits depth they weren't fully measuring 175mm but about 165mm.  So technically theyre not truely 7 inches.

Is this normal?

Looks like real value is different from the nominal stated value.

Does the same sort of things go for other timber e.g. studs. 

Bit confused

[SteamyTea]

3 hours ago, ab12 said:

Is this normal

Yes. I think the sizes are based on the rough sawn size, not the finished size.

 

https://www.ryedaletimber.co.uk/blog/regularised-timber-sizes-uk-guide-to-nominal-vs-finished-dimensions/