Give me your wisdom: how is plasterboard used in your practice? 2

[Greenalleycat]

Hopefully I'm not pushing the boundaries here. I'm writing my Master's project which relates to plasterboard usage in construction (very simplified, it's a part of a much larger project ongoing for my client).

As part of this, I am comparing New Zealand practice to international practice, primarily in Europe & USA (lol we use it as our primary wind and seismic bracing system).

The main uses for plasterboard here are 'standard' (substrate for plaster and paint), wet area, bracing, fire, and noise. For us, bracing is all based on a standardised test, and fire and noise systems are all tested systems with details provided by manufacturers. Standard and wet area boards have a manufacturing standard.

I have dug around on Google to compare, but I know this only ever teaches you so much. So I'm hoping the smart minds on here wouldn't mind sharing their 20s summary of how plasterboard is used in your industry.

 

[Eng16080]

Assuming "plasterboard" is what we normally refer to here (in the US) as drywall, sheetrock, or gypsum, for most structural project I'm involved in I generally don't consider it contributing to the overall strength of the building. One exception, I suppose, is that if I have an interior load bearing wall, I will consider it as bracing the wall studs in the weak direction against column buckling. Same deal for floor or ceiling members where bracing along the bottom is needed to resist lateral buckling.

On rare occasions I will design such walls as shear walls, although I usually avoid this. One reason is that in my particular geographic region, seismic loads usually don't control assuming I'm using wood structural panel shear walls. In that case the R value for seismic load calcs. is 7 whereas if sheetrock is used instead, it's 2.5, the end result being that the seismic response is much worse.

Despite my specific practice, I know it's not uncommon for it to be used as a structural material. Beyond structural uses, it's a great material in terms of fire protection, sound isolation, etc. In the US, despite few people being aware of this, I-joist floor systems are required to be protected with sheetrock (or other means) in basement areas where they would otherwise be exposed.

 

[human909]

As part of this, I am comparing New Zealand practice to international practice, primarily in Europe & USA (lol we use it as our primary wind and seismic bracing system).

Do you mean We here as in NZ? Seriously? For multi-storey as well or just single story?

I was in Christchurch (NZ) about 3 weeks ago and it was honestly quite fascinating observing all the newly complete builds and the builds in progress. The seismic detailing was pretty impressive and obviously much more extensive than across the ditch in Aus.

 

[XR250]

I'm involved in I generally don't consider it contributing to the overall strength of the building.

The reality is that in most residential structures, the sheetrock is probably doing the heavy lifting.

 

[Eng16080]

The reality is that in most residential structures, the sheetrock is probably doing the heavy lifting.

I think that's probably accurate, but I generally prefer alternative load paths which don't rely on it. Most of the time, with exterior walls sheathed with plywood (and not 2" thick Zip-R sheathing) with a reasonable amount of window/door openings, I can usually get lateral to work without relying much on interior walls. Of course, these conditions are not always the reality. When I do need interior shear walls, I usually have plywood along one side. Besides getting significantly better shear strength, I also figure there's a better chance somebody doing a future renovation might consider the wall as being important once they see the plywood and perhaps some hold-downs at the ends.

For the right application, sheetrock shear walls can certainly be a good cost-effective solution. I also think other engineers doing similar residential work probably rely on them more than I do.

 

[SE2607]

The reality is that in most residential structures, the sheetrock is probably doing the heavy lifting.

That might be true in non-high seismic regions. The problem with GWB is that isn't very ductile. R for GWB is 2 vs 6.5 for wood structural panels.

 

[XR250]

I don't typically count on them but i realize they are doing a lot more than we think. Especially in tract houses with that thin, "cardboard" "energy brace" stapled sheathing. I am in a nom-seismic region though.

 

[human909]

The reality is that in most residential structures, the sheetrock is probably doing the heavy lifting.

Like, others, I agree. But also like others, I don't rely on it and it isn't common. As far as I'm aware it isn't allowed (or just not part of the recommendations) of the AS codes.

 

[hokie66]

I call the way houses are built 'trickle theory'. If one load path doesn't work, another one will.

 

[NorthCivil]

i am in NZ now but used to practice in Canada

last i was in canada, maybe 10 years ago, i think the standard was CSA O-86? had provisions in there that 20% of the lateral force resisting system could be provided by the "GIB" or drywall as we called it. the remaining 80% had to be provided by OSB or plywood. please someone correct me if i am wrong.

that said, in practice, no engineer in practice considered the drywall to be providing anything (this was in BC anyway, (high seismic)).

I always thought it was a bit crazy that in NZ, they rely on GIB only for bracing. especially in areas with frequent quakes. it does seem to work though. also, and not to be ignored - the reason for this is probably because of the big and entrenched industry that monopolizes the supply of the GIB, and its compliance.

it fits in with the kiwi way of doing things (#8 wire mentality, doing things on a shoestring with as little as possible).

The biggest problem i think, is the lack of exterior sheathing on kiwi houses really contributes to the dampness/weathertightness problems. (for those who are unaware, in NZ they dont sheath their framing to the exterior. they just drape a sheet of building paper over the studs and staple it to the framing) this is not really great for holding the insulation in place, for airtightness, or for general "robustness" or "well built-ness"

minor weather ingress past cladding that i saw in canada, might dampen or cause mould to the sheathing. the sheathing can be relatively easily replaced (that is, if you already have the claddings off). in NZ, minor moisture ingress wets and moulds the face of the stud and the insulation. not great,

the detailing of their buildings without sheathing has knock on effects, like the way they design their windows in NZ. absolutely crazy IMO and also an example of #8 wire mentality.

Ive seen some really silly things before also. because NZ gets a lot of strong wind in most places, the amount of times i have seen half built houses with the paper up over studs, and a bunch of plywood temporarily fixed over it to stop the paper from being blown away by the wind... which will need be taken down later...

like... think about it guys... you could just sheath the building in the first place, and save a lot of work...

 

[Greenalleycat]

Do you mean We here as in NZ? Seriously? For multi-storey as well or just single story?

I was in Christchurch (NZ) about 3 weeks ago and it was honestly quite fascinating observing all the newly complete builds and the builds in progress. The seismic detailing was pretty impressive and obviously much more extensive than across the ditch in Aus.

We as in NZ yep. Are you NZ or Aussie based? Plasterboard is the primary bracing for almost all 2 story houses here, and often pushed to 3 (though technically this is a bit dubious). Beyond 3 it won't really work, and analysis requirements get too onerous to use plasterboard anyway

 

[Greenalleycat]

Assuming "plasterboard" is what we normally refer to here (in the US) as drywall, sheetrock, or gypsum, for most structural project I'm involved in I generally don't consider it contributing to the overall strength of the building. One exception, I suppose, is that if I have an interior load bearing wall, I will consider it as bracing the wall studs in the weak direction against column buckling. Same deal for floor or ceiling members where bracing along the bottom is needed to resist lateral buckling.

On rare occasions I will design such walls as shear walls, although I usually avoid this. One reason is that in my particular geographic region, seismic loads usually don't control assuming I'm using wood structural panel shear walls. In that case the R value for seismic load calcs. is 7 whereas if sheetrock is used instead, it's 2.5, the end result being that the seismic response is much worse.

Despite my specific practice, I know it's not uncommon for it to be used as a structural material. Beyond structural uses, it's a great material in terms of fire protection, sound isolation, etc. In the US, despite few people being aware of this, I-joist floor systems are required to be protected with sheetrock (or other means) in basement areas where they would otherwise be exposed.

Yep plasterboard = gyprock etc, you're on the money. This js a very helpful response, thank you. Where do you get the bracing values for plasterboard - manufacturers or code?

 

[human909]

We as in NZ yep. Are you NZ or Aussie based? Plasterboard is the primary bracing for almost all 2 story houses here, and often pushed to 3 (though technically this is a bit dubious). Beyond 3 it won't really work, and analysis requirements get too onerous to use plasterboard anyway

Wow. But like others have said I don't see it not working except in cyclonic winds that we do get here in Aus. Up in Darwin the lateral and especially uplift load paths are considered extremely important and for good reason!

Back in more normal areas. I can't say I've ever really heard of issues or lawsuits concerning lateral issues in our builds. Foundation movement and moisture issue however.....

the detailing of their buildings without sheathing has knock on effects, like the way they design their windows in NZ. absolutely crazy IMO and also an example of #8 wire mentality.

I had no idea what you were referring to when you said #8 wire mentality... But Google was my friend.

The Genesis of Kiwi Ingenuity - 'Number Eight Wire'

Many of you reading this would have heard of 'Number Eight Wire'. A common phrase as familiar as the old kiwi favourite, pavlova.

www.motovated.co.nz

I'm in Australia. And Australians like to think we have a "can do" attitude and are "laid back". But we lost that many decades ago. New Zealand has kept that. I especially NZ approach to enjoying the outdoors and nature. Australia has now become a nanny state. But I digress.

In a slightly more related topic. NZ tradespeople are suggested to be much better than those here in Aus. We have had such generous pay for trades that you don't need to be particularly competent to still make a good buck.

 

[Eng16080]

for those who are unaware, in NZ they dont sheath their framing to the exterior. they just drape a sheet of building paper over the studs and staple it to the framing

I can't be reading this right. They attach building paper to the exterior wall studs and then siding over that? That seems insane.

Where do you get the bracing values for plasterboard - manufacturers or code?

Our wood design code has a side code for wind and seismic design (NDS SDPWS). In it they provide unit shear values for shear walls and floor/roof diaphragms. So, for example, for a wall with 1/2" thick sheetrock and #6 drywall screws fastened at 4" o.c. at panel edges and 16" o.c. elsewhere with wood studs spaced at 24" o.c. max and fully blocked, the nominal unit shear strength is 320 plf. This nominal value then must be adjusted by a safety factor to get an allowable capacity. For wind loads, the factor is 2.0 and for seismic 2.8.

In general, you get penalized rather heavily in a number of ways using sheetrock for shear strength. A comparable wall with plywood is generally at least 3 times stronger. You're also limited by the maximum aspect ratio for walls/wall sections with a plywood wall having a ratio of 3.5:1 and sheetrock 2:1 with the additional requirement that the sheetrock wall must also be fully blocked if this ratio exceeds 1.5:1.

I'll assume seismic loads are low in NZ. The biggest issue, perhaps, with using sheetrock shear walls versus wood structural panel shear walls is that for seismic load calculations, due to the R factor being much smaller (as noted above), the design loads end up much greater (which is essentially accounting for the limited ductility of the sheetrock).

So, at the end of the day, for seismic loads, you essentially end up with a shear wall with roughly 1/3 the capacity of a structural panel wall with loads that are roughly 2.5 times higher. Even in situations where seismic wouldn't normally control, using sheetrock shear walls will often make it control.

 

[NorthCivil]

I can't be reading this right. They attach building paper to the exterior wall studs and then siding over that? That seems insane.

yes you are reading it right
yes, it is a little bit insane.
because you effectively cant get any water in that opening, because it has 0 weather protection, they push the windows right outside of the opening, so the glass is proud of the cladding.
the craziest part though and the completion of the #8 wire miracle, is the window also comes prefitted with the interior finishing trim (timber liner), that doubles as a structural connection for the window, which gets stapled to the trim
here is a link for a typical detail
ive seen windows like these 12 stories up in the city centre (which is far beyond where this detail was meant to live, lol)

https://www.eboss.co.nz/assets/literature/165/14240/VRAWBB.pdf

 

[NorthCivil]

I'm in Australia. And Australians like to think we have a "can do" attitude and are "laid back". But we lost that many decades ago. New Zealand has kept that. I especially NZ approach to enjoying the outdoors and nature. Australia has now become a nanny state. But I digress.

In a slightly more related topic. NZ tradespeople are suggested to be much better than those here in Aus. We have had such generous pay for trades that you don't need to be particularly competent to still make a good buck.

yes, i love Australia, but way too uptight, too many rules and fines.
my mate went to queensland for holiday and got $6000 worth of speeding tickets in the mail upon his return!
kiwis love to gloat that they are far better tradies than the australians... but to be honest, i thought trades in canada were far more skilled and took much more pride in their work, compared to NZ.

 

[XR250]

my mate went to queensland for holiday and got $6000 worth of speeding tickets in the mail upon his return!

Funny, I have a friend visiting there now. Says you get a ticket if you have a cell phone in your lap while driving via cameras. Also said, you get tickets for 3 mph over.
He mentioned this is the perfect place for self driving vehicles.

 

[Greenalleycat]

yes you are reading it right
yes, it is a little bit insane.
because you effectively cant get any water in that opening, because it has 0 weather protection, they push the windows right outside of the opening, so the glass is proud of the cladding.
the craziest part though and the completion of the #8 wire miracle, is the window also comes prefitted with the interior finishing trim (timber liner), that doubles as a structural connection for the window, which gets stapled to the trim
here is a link for a typical detail
ive seen windows like these 12 stories up in the city centre (which is far beyond where this detail was meant to live, lol)

https://www.eboss.co.nz/assets/literature/165/14240/VRAWBB.pdf

There is a great BRANZ (industry resarch/testing report) where they investigated a bunch of windows falling out due to wind pressure. They concluded that we needed more staples to hold them in......

 

[Greenalleycat]

yes, i love Australia, but way too uptight, too many rules and fines.
my mate went to queensland for holiday and got $6000 worth of speeding tickets in the mail upon his return!
kiwis love to gloat that they are far better tradies than the australians... but to be honest, i thought trades in canada were far more skilled and took much more pride in their work, compared to NZ.

Engineers in NZ are very involved in construction, which I think isn't typical for most places in the world (USA/Aus in particular?). I can assure you that 10% of our tradies are world-class and 90% are muppets. Maybe 5%/95%. Tradies talking about the quality of NZ tradespeople are lying - in my experience, the good tradies don't brag about their quality, they spend their time bitching about the rest of the industry giving them a bad name.

That said, at least the quality of our basic codes seems to be OK structurally. I love watching Grand Designs (NZ, Aus, UK versions)....the amount of completely unreinforced foundation trenches filled with soupy concrete is terrifying. I don't understand how these guys aren't getting lawsuits left right and centre

 

[Tomfh]

Says you get a ticket if you have a cell phone in your lap while driving via cameras.

In general I oppose the nanny state. But mobile phone cameras is one thing I don't have a problem with. To me it's no different to random breath tests. People using their phone whilst driving kill a lot of people.