Query on timber sizing - and converting imperial to metric.

[CmdrBond]

Could someone please explain timber size conversions in a way that I can understand?

I am looking at possibly building a shed, a lot of people are recommending 3x2. When I go looking for 3x2 (which I presume is 3"x2") I find 63mm x 38mm - which is 2.5"x1.5".

Is this what is meant by 3x2, or should I be looking out for 75mm x 50mm?

 

[Belboz]

Lot of timber yards will quote 47 x 75 or 47 x 100 as 3 x 2 or 4 x 2 (47 x 150 for 6 x 2)

Don't take the conversion size as a literal. Nearest approximate size in mm will be fine.

I don't know Dorset but, as an example, see below.

You will note the 47mm thickness and various widths


http://www.sydenhams.co.uk/treated-timber.aspx

 

[Newboy]

Timber sizes refer to the original sawn size. When the timber is machined to produce 'smooth' finishes (PAR - planed all round or PSE - planed square edge for example) then the finished size is smaller than the original size.

If you go to a timber merchants then you are likely to have a wider selection of sizes and you may find imperial sizes as well as metric.

 

[JBR]

Timber sizes refer to the original sawn size. When the timber is machined to produce 'smooth' finishes (PAR - planed all round or PSE - planed square edge for example) then the finished size is smaller than the original size.

If you go to a timber merchants then you are likely to have a wider selection of sizes and you may find imperial sizes as well as metric.

And take a tape measure with you!

To me, 3 x 2 = 75 x 50. An inch is just about 25mm.

 

[Bosswhite]

it is quirk that came in when metrication was introduced, ( a bit like asking for a pint of beer)
timber was always known as 3x2 or 4x2 (imperial measurements) and its seems to have stuck
So a builder now asks for a 3 metre length of 4x2

 

[CmdrBond]

it is quirk that came in when metrication was introduced, ( a bit like asking for a pint of beer)
timber was always known as 3x2 or 4x2 (imperial measurements) and its seems to have stuck
So a builder now asks for a 3 metre length of 4x2

Which is kind of my point, if you ask for a size based on imperial measurements you could end up with the wrong size timber due to the different metric specifications.

I suppose that is negated a little with PAR, PSE, CLS, &c... however it is still bloody confusing.

In the building of a (very basic) garden shed where 3x2 is recommended, would you use 75x50(47) or 63x38?

 

[ntb]

Either is going to be stronger than that used in mass produced sheds so take your pick.

 

[Newboy]

Use 3x2 treated, for example
http://www.jewson.co.uk/timber/carc...aded-timber/standard-c16-regularised-treated/

 

[CmdrBond]

Either is going to be stronger than that used in mass produced sheds so take your pick.

In that case, what about 47x47?

The 63x38 has a surface area of 23.94 cm² and the 47x47 had an area of 22.09 cm².

I'm just thinking the squarer profile would be easier to work with.

 

[Belboz]

Depends on the size of the intended shed. For a small shed, 47 x 47 will be fine for carcassing.

I would definitely check pricing though because you would be surprised by the variations in prices out there.

 

[ntb]

Yep, will be fine for a basic shed.

 

[big-all]

ask for actual sizes you will then get the finished size
also remember wet wood can be swollen by up to 10% but not in length

 

[CmdrBond]

Use 3x2 treated, for example
http://www.jewson.co.uk/timber/carc...aded-timber/standard-c16-regularised-treated/

That link directs to 4x2 (100x47)

 

[Belboz]

Yep because he said 'as an example'.

However, having seen your post on this subject in another topic, don't use 47 x 47 for your LARGE shed. I suggest 4 x2 (100 x 47)

 

[CmdrBond]

Yep because he said 'as an example'.

However, having seen your post on this subject in another topic, don't use 47 x 47 for your LARGE shed. I suggest 4 x2 (100 x 47)

Thank you for your advice on the matter. But isn't that going to be overkill?

The existing 8'x10' shed is built out of 38x38mm at 600mm centres, and having had a look at a local shed "specialists" (Stable Structures and Broomhill Garden Buildings), they are all using 47x47/47x50 and 38x63 at a push - even for their 16'x12' sheds.

Even an online shed builder I was looking at is only using 38x63.