Framing lumber sizes

[Jimbo]

Hey folks, I've been using Sketchup to visualise a couple of garden projects I've got coming up - first a large lean-to type shed to replace my battered old 5'x7' relic; and secondly a pretty sizeable garden room.

The garden room is next year's project most likely. In terms of the shed, I'm planning on framing using 2x4. However, I'm not sure whether the US 2x4 actual dimensions (I've been watching mainly US Youtube vids on framing) also apply in the UK. If I ask for 2x4 at my local building supplier, will I get 1.5" x 3.5" (which is what I've based my Sketchup models on), or is it some other actual size? Or can I specify which I want?

I'm planning on visiting the building supplier on Saturday to see what's available but in the meantime, any advice on UK standard sizes for pressure treated and untreated lumber would be useful for planning.

Thanks
J

 

[Newboy]

The 'size' of timber usually refers to the original cut size - 4x2 is the sawn size.

Each time the timber is processed some of the original dimensions will be lost in the finishing so:

To take your example of 4x2,

Sawn timber will still be approx 4x2 - 100mmx50mm (also available as 'sawn & treated)
Regularised timber will be approx. 3-4 mm smaller on each face - e.g. 97x47
Planed timber (also call Planed All Round - PAR/ Planed Square Edge - PSE) will be approx 5mm smaller on each face e.g. 95x45

There is also CLS (Canadian Lumber Size)available in two common sizes - 38mm x 63mm & 89mm x 38mm

You may also come across 'SCANT' with a finished size of 42mm x 69mm - low grade timber to be avoided!

Timber grading indicates it's suitability for structural work - C16 will meet your requirements.

It's probably worth avoiding 'americanisms' when you visit the merchants

UK = timber not lumber
UK = 4x2 not 2x4
UK = carcassing not framing





Edited - to amend conversion errors (my bad!)

 

[Notch7]

The majority of merchants, esp builders merchants now mostly have standard stock which is regularised, treated, strength graded timber

So 4 x 2 will be around 95mm x 45mm finish. 3 x2 is 70mm x 45mm

Its often eased edge as well.

CLS are odd sizes, much smaller than the nominal size.

A small shed could be done in CLS 63mm x 38mm or carcassing 70mm x 45mm

A garden office 95mm x 45mm

 

[Jimbo]

Thanks NSNB and Notch, both really helpful answers. Point taken on the Americanisms, I've struggled to find much UK-based content on Youtube which always bothered me a little.

 

[big-all]

whilst cls does seem odd sizes its canadian lumber standards so imperial as in 1 x1/2"[38mm] 2x1/2"[s 63mm]3x1/2"[89mm]