What ply thickness?

[ashthekid]

I have to put structural ply onto my exterior stud wall but I'm not sure what is best to use before it becomes a waste of time and money.

I was thinking 9mm but a carpenter said it's really not thick enough to make any benefit. He suggested 12mm.

 

And how about areas where I'm hanging a towel rail for example, a wall hung TV, a big heavy picture frame, kitchen high wall units etc.

9mm, 12mm, 18mm?

I'm obviously plasterboarding over the top but want to make sure I have a strong enough base to fix upon.

 

The original plan was stud wall, 100mm PIR in between the studs, then 12mm ply on top, 25mm PIR, 25mm battens to allow for services, then 12.5mm plasterboard.

Now I'm thinking just 9mm ply, 20mm PIR(or none at all), 19mm batten(or none at all) then 12.5mm plasterboard. But where I need the extra base strength to fix to I replace the batten with 12 or 18mm ply although that won't balance depth wise.

[SteamyTea]

No idea what thickness, but my shelves hang off the plasterboard only.

But this may be worth a read:

 

[Jenki]

54 minutes ago, ashthekid said:

I have to put structural ply onto my exterior stud wall but I'm not sure what is best to use before it becomes a waste of time and money.

I was thinking 9mm but a carpenter said it's really not thick enough to make any benefit. He suggested 12mm.

Is this on the inside of the exterior wall or outside. If outside that will be part of the structural calculations for the build. (racking forces etc.)

57 minutes ago, ashthekid said:

And how about areas where I'm hanging a towel rail for example, a wall hung TV, a big heavy picture frame, kitchen high wall units etc.

9mm, 12mm, 18mm?

In Scotland, for areas in Bathrooms you need to install 18mm to cater for hand rails etc.

 

For kitchen wall units, usually 5x2 noggins added to the studs at about 2050 high would be enough - check the kitchen tall cupboard heights to be sure. 

 

[ProDave]

So this is a timber frame with no external blockwork?  So the skin you are talking about is the racking layer to stop the building collapsing in string winds?

 

What you need depends on your location and exposure and would normally be calculated by a structural engineer. e,g, in my case the SE called for 2 layers of 13mm OSB3 with the joints staggered and specified the type and spacing of the nails used to attach it to the frame.

[saveasteading]

1 hour ago, ashthekid said:

I have to put structural ply onto my exterior stud wall

If this has been formally designed, then the sheathing material and fixings should have been specified already.

[nod]

2 hours ago, ashthekid said:

I have to put structural ply onto my exterior stud wall but I'm not sure what is best to use before it becomes a waste of time and money.

I was thinking 9mm but a carpenter said it's really not thick enough to make any benefit. He suggested 12mm.

 

And how about areas where I'm hanging a towel rail for example, a wall hung TV, a big heavy picture frame, kitchen high wall units etc.

9mm, 12mm, 18mm?

I'm obviously plasterboarding over the top but want to make sure I have a strong enough base to fix upon.

 

The original plan was stud wall, 100mm PIR in between the studs, then 12mm ply on top, 25mm PIR, 25mm battens to allow for services, then 12.5mm plasterboard.

Now I'm thinking just 9mm ply, 20mm PIR(or none at all), 19mm batten(or none at all) then 12.5mm plasterboard. But where I need the extra base strength to fix to I replace the batten with 12 or 18mm ply although that won't balance depth wise.

The TF homes in working on 

are using 6 mil ply on the internal Structual wall 

Nailed every 100 mil

[ashthekid]

It's a timber frame new build within the walls of an old 200yr old property so essentially the new timber frame is creating the second skin inside so no direct weathering or forces from that but it is of course load bearing as it's now taking the majority of the weight of the roof etc. it's all been signed off my Building Control but I believe it was my initial contractor (who's disappeared on me) who started putting the OSB on the inside of the stud work saying it helps to reinforce the structure of the building which makes sense. it's been done of 70% of the property but since he has disappeared and a few people have asked me why I was still doing it when it wasn't essential, I'm now doubting whether to do it. Especially when you consider thing like mould and mildew as mention above.

[saveasteading]

4 hours ago, nod said:

a carpenter said it's really not thick enough

 

I meant who decided to propose 9mm in the first place?

The building inspector only has an overview and has not necessarily approved this element.

 

As there is no wind then that is a major element removed. The lining is still helping to stop buckling or domino-ing.

 

Other than that, we don't know your construction in any detail so can't say much more.

[Temp]

 

2 hours ago, ashthekid said:

It's a timber frame new build within the walls of an old 200yr old property so essentially the new timber frame is creating the second skin inside so no direct weathering or forces from that but it is of course load bearing as it's now taking the majority of the weight of the roof etc. it's all been signed off my Building Control but I believe it was my initial contractor (who's disappeared on me) who started putting the OSB on the inside of the stud work saying it helps to reinforce the structure of the building which makes sense. it's been done of 70% of the property but since he has disappeared and a few people have asked me why I was still doing it when it wasn't essential, I'm now doubting whether to do it. Especially when you consider thing like mould and mildew as mention above.

 

As its load bearing/structural it should be designed by someone like an SE. Bit surprised the BCO didn't insist.

 

It's not uncommon to have something like OSB or WBP in load bearing TF structures to prevent racking. I used 12mm WBP on an outbuilding with a tiled roof.

 

 

[nod]

I was surprised at how thin the Structual ply is that they are using But it is housing association 

Three Clark’s of works High spec 

I worked on TF for around 40 years 

I’ get the speed and convenience I also get the superior heat retention But I wouldn’t have one Nothing is straight or square 

Every site manager I speak to loves them 

But asked would you build one for yourself 

They answer no 

[saveasteading]

9 hours ago, Temp said:

Bit surprised the BCO didn't insist.

The BCO may not have noticed that it is structural. Their job is not to do 100% check.

What does the stud wall sit on?

[ashthekid]

Studwall sits on new solid top grade concrete base foundation of approx 1m depth. 

[saveasteading]

12 minutes ago, ashthekid said:

foundation of approx 1m depth

so it is structural. 9mm is normal enough to stiffen the wall, so all good

[ashthekid]

Now comes the question of ply or OSB?

[Gus Potter]

On 23/02/2022 at 17:10, ashthekid said:

I have to put structural ply onto my exterior stud wall but I'm not sure what is best to use before it becomes a waste of time and money.

I was thinking 9mm but a carpenter said it's really not thick enough to make any benefit. He suggested 12mm.

 

And how about areas where I'm hanging a towel rail for example, a wall hung TV, a big heavy picture frame, kitchen high wall units etc.

9mm, 12mm, 18mm?

I'm obviously plasterboarding over the top but want to make sure I have a strong enough base to fix upon.

 

The original plan was stud wall, 100mm PIR in between the studs, then 12mm ply on top, 25mm PIR, 25mm battens to allow for services, then 12.5mm plasterboard.

Now I'm thinking just 9mm ply, 20mm PIR(or none at all), 19mm batten(or none at all) then 12.5mm plasterboard. But where I need the extra base strength to fix to I replace the batten with 12 or 18mm ply although that won't balance depth wise.

Hiya.

 

Hope this helps and for a bit of fun (please excuse my grammer / spelling) I have added in some other stuff later to do with timber framed structures and thickness of ply / OSB boards in a structural context.

 

Internally.. towel rails.. future provision for grab rails in bathrooms etc. The Scottish Building Standards talk about robust details. Below is a screenshot from clause 3.12.3 from the domestic handbook. 18mm ply is considered to be robust.

 

Next turning to timber frame and what the structural sheeting does. Your vertical timbers generally hold up load. But at the top and bottom they are often just nailed with 2 to 4 nails to the top and bottom rail. Thus if you put up a TF panel with no sheeting it's easy for the wind say to push it sideways.. your house will then fall over. If you nail a sheet of ply to the frame it stiffens it all up. The sideways (horizontal forces are transferred from the timbers through the nails and into the sheet. The sheet then transfers these loads to another part of the sheet that is connected via other nails at the bottom say and back into the timbers. The sheet acts like an exoskeleton. SE's call this diaphragm action. The nails carry mainly shear ( sideways loading), they do other thinks but I'll leave that out for now.

 

Now remember where the load goes. From the timber, into the nails, into the sheet, into other nails and back into the timber. Now if the sheet is thin it will buckle and also fail where the nails are transferring the shear loads. To mitigate we can make the sheet thicker.. thus spreading the shear loads at the nailed connection.

 

Below is a screen shot of part of a TF panel design, one I made earlier today in the oven. Its a bit abbreviated and there are some post and later calcs that go with it. Also I have manipulated the calcs to suit this panel so please don't do this at home. If you are browsing then please don't read on. If keen then the following is a fly through to give you a flavour of what it is all about and the things you need to look out for.

 

 

The above is based on BS 5268.. it's a bit less lengthy than the Eurocodes.

 

Rows 529 to 533 are the basic parmeters showing the basic strength of a typical TF panel. You can see here that you can add another sheet of structural board on the inside. Row 531. We do this if we get stuck.. BH members like to put big holes in walls and fill them with glass. Now we take the basic strength and start to modify it depending on the following:

 

Row 536 to 541. Here we are looking at the spacing and diameter of the nails. Be aware the nails and spacing are important!

 

At row 543 we take into account the board thickness. The base line for this code is a 9.0mm thick sheet. if we make it thicker we get a positive increase in resistance. Rows 549 to 551 take into acount the shape of the panel. A long low one will carry more horizontal load than a tall thin one.

 

Row 554 takes into account the size of the windows / doors. Cut openings in the panel and it get weaker.

 

Row 561 looks simplistically how many other panels are attaching.. this requires an essay / book to explain.

 

Row 566 recognises that the TF and masonry interact.

 

Row 575.. if the applied load is less than the resistanc we crack open a beer!

 

Lastly you'll see that this panel appears to be over designed. It's not as the later checks on global stabilty are the critical ones.

 

 

 

 

 

 

 

Edited February 26, 2022 by Gus Potter
worst of typos corrected

[SteamyTea]

2 hours ago, Gus Potter said:

If you are browsing then please don't read on

I read on.

So many questions to ask, where is the free version of codes/regs.  The arithmetic looks manageable, but the devil is in the detail.

[redtop]

Has it been determined this is structural and not just for hanging heavy stuff off. I wont comment on the former but for the later we have very heavy Radiators hanging of plasterboard screwed to the timber stud walls. Load spreading screws (the ones that you use a tool to spread the arms out). They can take a lot of weight and don't forget you are usually trying to stop them dropping down not tipping forward, if that makes sense. For kitchen wall hung cudboards i would just use noggins behind the plasterboard.