osb subfloor

owen85

what thickness osb should i lay if my joists are spaced at 12inch on center?

sky6

15mm should be fine, or 18 mm if you have the room to match the finished height.

agusta

18mm

cork2

15mm is perfectly strong enough 18mm if you're matching in as already said, but if you can get the t and g version of either get it. Most builders providers will have it and glue all the joints. Some people think it's over kill but t and g and glue isn't much of an extra cost at all and it's such a superior floor!! No contest. Much less chance of squeaks too.

650gs

the reg is 18mm with 15 mm it will sag with time

sky6

cork2 wrote: »

15mm is perfectly strong enough 18mm if you're matching in as already said, but if you can get the t and g version of either get it. Most builders providers will have it and glue all the joints. Some people think it's over kill but t and g and glue isn't much of an extra cost at all and it's such a superior floor!! No contest. Much less chance of squeaks too.

i totally agree.

sky6

650gs wrote: »

the reg is 18mm with 15 mm it will sag with time

Unlikely to sag at 300 mm centres, especially if it's T & G.

North West

Hi Owen 85
I used 18mm t&G 2440 x 610mm sheets. Solid as a rock. I screwed them down. A bit more expensive than full sheet, but well worth it.
NW

650gs

sky6 wrote: »

Unlikely to sag at 300 mm centres, especially if it's T & G.

even at 100mm walking on it will make it sag

Boiled-egg

650gs wrote: »

even at 100mm walking on it will make it sag

Very unlikely

650gs

100%

cork2

650gs wrote: »

even at 100mm walking on it will make it sag

This is basically arguing what if, no real point to it. How many millimetres did it sag at 100 mm centres and what was the weight of the individual walking on it?? 15mm osb is plenty strong enough, if it wasn't osb smartply wouldn't be selling it specifically as a flooring board nor would engineers be signing off on it! I've used it many times including in my own house and it's a brilliant floor when fitted properly.

650gs

engineers cant sign off on it read up on the building reg's

cork2

Well they do..............and I've seen one specify it as a subfloor.

cork2

Also I'm failing to find in the regs where it says this does not comply, I'm not questioning you or starting a fight at all I'm genuinely interested. If you could tell me where to look that'd be great. Thanks.

agusta

cork2 wrote: »

Well they do..............and I've seen one specify it as a subfloor.

well id love to know any engineer in this who specify a 15 mm osb subfloor,silly statement,

cork2

agusta wrote: »

well id love to know any engineer in this who specify a 15 mm osb subfloor,silly statement,

NO no, it'd be a silly statement if it were untrue. But last summer a project I was on had a large first floor area, all of which was specified in eco joists and 15mm osb. It also had 5 flat roof areas, all of which were specified in 9x2 and 15mm osb. I'm not arguing here what is or is not regulation, if ye tell me it's not up to regulation I believe ye but it is being done! I won't lie either it escapes me as to why it wouldn't meet a regulation, as No.1 osb smartply are selling the product onto the Irish market for this exact purpose and secondly 15mm osb with all 4 sides glued, and nailed ever 150mm with 63mm ring shank nails is a brilliant floor. In my opinion it's superior to 18mm wbp!! But again as I say Point out in the regs where it says it doesn't comply, not starting a fight just trying to educate myself a little

650gs

If you check the building regs it doesn't say you cant used 6mm as a floor or it doesn't say you cant use 6mm for a roof what it does say is a spect of 18mm

cork2

All I can see in the regs is a standard for flooring as apposed to a thickness and 15mm osb by smartply meets the standard. Again if you can show me that in the regs do, I'm genuinely interested. I find when you research things like this it sticks in your mind for the future.

owen85

great to see so many replies.
i like your floor plan cork2.
id be interested to see where you saw that 650gs.

what ive got from reg. BS: 8103 -3
Thickness of OSB floor panels for domestic loading:

Maximum centers of Minimum thickness (mm)
support members (mm)
450 max center... 15mm thickness
600 max center.... 18mm thickness
600 max center..... 22mm (where enhanced floor performance is required)

considering my spacing is 300...im edging a lot closer towards the 15mm side.... of course the place in dublin where i thought i was going to buy the osb from only does 11mm and 18mm where cost was :
18mm 8ftx2ft (unconditioned, t&g) €11.69 and 18mm 8x4ft (conditioned but no t&g) €18.82

Pms welcome for any places supplying 15mm at a lower cost than this.

next question is have any of you a preference if the osb3 is conditioned or not? and if more than usual ring bat screws are put in would a t&g really matter

650gs

reg. BS: 8103 you do know that is from the UK not irish reg's

owen85

i do, i couldnt find any specific thickness required in the irish reg so i had a look at what the brits said.
not many places stock the 15mm stuff and the saving is minimal.
the place i got the best quote from only has 18mm so i reckon ill end up just going with it. most people i talked to say they use 18mm for subfloor. hopefully get my final quote tomorrow for 18mm no t&g, (couldnt justify the extra cost for t&g) along with the rest to fit out the shell of a house.


the plan: glue and nail osb to joists every 150mm with 63mm ring shank nails, while leaving a gap of 3mm between each sheet of osb. i want to fill these gaps with some kind of flexible adhesive. any recommendations?

cork2

owen85 wrote: »

great to see so many replies.
i like your floor plan cork2.
id be interested to see where you saw that 650gs.

what ive got from reg. BS: 8103 -3
Thickness of OSB floor panels for domestic loading:

Maximum centers of Minimum thickness (mm)
support members (mm)
450 max center... 15mm thickness
600 max center.... 18mm thickness
600 max center..... 22mm (where enhanced floor performance is required)

considering my spacing is 300...im edging a lot closer towards the 15mm side.... of course the place in dublin where i thought i was going to buy the osb from only does 11mm and 18mm where cost was :
18mm 8ftx2ft (unconditioned, t&g) €11.69 and 18mm 8x4ft (conditioned but no t&g) €18.82

Pms welcome for any places supplying 15mm at a lower cost than this.

next question is have any of you a preference if the osb3 is conditioned or not? and if more than usual ring bat screws are put in would a t&g really matter

Ya I found the same regs as you did. Don't worry about the British Standard because I found it too. God only knows why they print British standards in Irish regs but it doesn't really matter it is what it is.

When we used 15mm the quantity of sheets was very big, we were talking bales as apposed to sheets, therefore the saving was worth it. 63mm ringshank nails and glue is good and the reason I always use the t and g is to stop squeaks. What you're proposing should work too. I've never done it but I've seen it done, using washers as spacers and then they pulled the washers afterwards and filled all the joints with silicone to prevent rubbing.