Odd sized boards

[Jupiter01]

A simple job turned out to be a handful today and I am feeling annoyed. Perhaps you can tell me this is normal.

I spaced the floor joists of my garden room at 400 centre (5x2s). Ordered full sized OSB boards and when I went to fit them, I noticed that they were all around 2.44m x 1.24m. I had to cut every one of them! I thought 2.4x1.2 is the standard size?

 

[big-all]

sheet material is mostly imperial as in 8ft by 4ft or 1220x2440 so 406/610mm centres

have a look at your tape it will often be marked at 16" 406mm centres and 400mm centres with a diamond or triangle

planks on the other hand tend to metric lengths

 

[endecotp]

Until the 1960s, building products in the UK were measured in feet and inches.

In the mid 60s, a decision was made to change to metric. Let’s take as an example the long side of a sheet of plasterboard. That had been 8 feet, which is 2438.4 mm. There were two proposals for how to convert to metric. One option was to round to the nearest 10 mm, another option was to round to the nearest 100 mm. In the former case that would give a dimension of 2440 mm, in the latter case it would be 2400 mm.

Some people preferred one option, some preferred the other. The sensible thing to do would have been to choose one or the other and make half the people unhappy. But no. The chosen “compromise” solution was to use one option for some products and the other option for others - thereby making no-one happy, and resulting in people like you making these mistakes sixty years later.

It’s interesting that some people believe that it’s a difference between metric products and imperial products. That’s not true; all of the product sizes are metric, but they are different metric sizes.

Note that in the case of OSB, the sheets you’re using are 2440 long - but the tongue-and-groove OSB boards are 2400 long (excluding tongues).

If you want to learn more about this fascinating subject, note that “Building Metrication News” - part of “Building” magazine published from 1967 to 1969 - is available online: https://ukma.org.uk/what-is-metric/uk-progress/building-industry/ . Here’s a quote from the first edition:

“In fifteen months’ time [from Sept 67] architects are to start designing in metric and a year later contractors will start the first metric buildings on the ground. Three years after that at the end of 1972 the bulk of the metric change, as far as the construction industry is concerned, will be complete. The count down has started but are we prepared?”

This was happening around the same time as the change to decimal currency, from pounds/shillings/pence, which happened in February 1971.

 

[Jupiter01]

sheet material is mostly imperial as in 8ft by 4ft or 1220x2440 so 406/610mm centres

have a look at your tape it will often be marked at 16" 406mm centres and 400mm centres with a diamond or triangle

planks on the other hand tend to metric lengths

I think plasterboard is metric and therefore requires 400 centres?

 

[Jupiter01]

Until the 1960s, building products in the UK were measured in feet and inches.

In the mid 60s, a decision was made to change to metric. Let’s take as an example the long side of a sheet of plasterboard. That had been 8 feet, which is 2438.4 mm. There were two proposals for how to convert to metric. One option was to round to the nearest 10 mm, another option was to round to the nearest 100 mm. In the former case that would give a dimension of 2440 mm, in the latter case it would be 2400 mm.

Some people preferred one option, some preferred the other. The sensible thing to do would have been to choose one or the other and make half the people unhappy. But no. The chosen “compromise” solution was to use one option for some products and the other option for others - thereby making no-one happy, and resulting in people like you making these mistakes sixty years later.

It’s interesting that some people believe that it’s a difference between metric products and imperial products. That’s not true; all of the product sizes are metric, but they are different metric sizes.

Note that in the case of OSB, the sheets you’re using are 2440 long - but the tongue-and-groove OSB boards are 2400 long (excluding tongues).

If you want to learn more about this fascinating subject, note that “Building Metrication News” - part of “Building” magazine published from 1967 to 1969 - is available online: https://ukma.org.uk/what-is-metric/uk-progress/building-industry/ . Here’s a quote from the first edition:



This was happening around the same time as the change to decimal currency, from pounds/shillings/pence, which happened in February 1971.

That’s very useful context. Won’t assume 400 centres for everything.

 

[Charlie George]

I think plasterboard is metric and therefore requires 400 centres?

It is, just to confuse.

 

[Jupiter01]

Oh and…
When I build my stud wall, which will be lined externally with osb and internally with plasterboard, where do I place the studs? How do I centre these when both sheets are different measurements…

 

[big-all]

I think plasterboard is metric and therefore requires 400 centres?

indeed it is ....sometimes you can do noggins at 400mm and studs at 406 or visa versa to accomodate imperial sheet material one side and metric the other to reduce strips cut off for example outside shiplap so 400 studs inside8x4 ply/osb sheets so 406 noggins or on a roof with plasterboard underneath and osb on top

although it can frazzle the brain trying to keep up with picking up and supporting the loose ends between board iff you get it wrong

 

[Jupiter01]

My stud wall will have one set of noggins half way up. That wouldn’t be sufficient to catch the whole edge of the “oversized osb”?

 

[stevie888]

Oh and…
When I build my stud wall, which will be lined externally with osb and internally with plasterboard, where do I place the studs? How do I centre these when both sheets are different measurements…

I'd suggest it's easier to rip 40mm off each OSB sheet than mess around adding additional support for plasterboard edges.

You set your studs according to what you're putting on them, so with osb or ply but no p/b go with divisors of 2440 ie 16", but otherwise 2400 ie 400mm.

I think it's well worth planning ahead of time to see the best way to use materials efficiently. I'm currently putting up several bits of studwall at home and because my ceilings are a tad over 2600 high it's more economic to use 900x1800 plasterboard even though it's dearer per sqm. All the walls are short lengths so simple enough to set the studs accordingly. Also a whole lot easier to get smaller boards upstairs as the body creaks more eaxh day!!

In a similar vain we would often use 1800x3600 sheeps of mesh rather than the normal 2400x4800 if it suited the slab dimensions better.