Just how fireproof is drywall/sheetrock?
elliot
| Posted in Construction Techniques on
Hi All:
FHB just ran an article that explained the moisture and mold properties of the different types of drywall/sheetrock. Good stuff to know.
But what about fire? Just how fireproof are these drywall/sheetrock products? “Meets code” doesn’t carry much weight with me, since houses that meet code burn down every day. What other material could I use for the interior walls of my own house to be as fire safe as possible?
Much obliged!
Elliot
Replies
Are you talking about fire ratings of dry wall?
Well, I'm not up on the terminology -- I'm here to learn. I'd love to hear about the ratings, but I am also concerned about what I think of as "real life".
Let me put it this way. I saw the remains of a burned down house and I did not see any intact, just sooty, sheets of dry wall.
The structure will be steel and concrete, and the insulation probably rockwool. So I'm looking for an interior finish to match. I live in Northern California wildfire country, and my parents house (which I grew up in, yes) once caught fire from an electrical connection arcing, so i'm just a bit paranoid on this!
Appreciate your help!
Elliot
Are you worrying about fire started inside the house or wildfire from the outside? Or both?
There was a discussion in FHB I believe may be couple of years ago about exterior house design that stood up in real test of California wildfire. There were pictures of houses that survived after the fire swept through while the surrounding houses were turned into ashes.
You might want to look into to using a residential sprinkler system.But if you are in fire country you have a much larger concern with external fire.In the last year FHB (or maybe JLC, but I think that it was FHB) had a good article on reducing losting from wild fires.
This is great -- you guys are answering faster than I can read and respond!
Both external and inside fires are a concern, but I think I have the outside figured out.
I'm down to eliminating interior "tinder".
Hey, my Dad was right! Dad was an engineer specializing in wood construction, and he tought me about wood beams vs steel beams in a fire.( And he was sitting in the living room when his beloved wood caught fire behind the fuse box in the attic. (Big thanks here to the FD!)) The idea now is to make darn sure on MY house that the place doesn't get hot enough for it to make any difference.
Edited 1/29/2005 12:31 am ET by Elliot
If you can keep the fuse panel out of the attic, you should be OK.
"I cut this piece four times and it's still too short."
I have studied California wildfires a fair bit and found that the most important design element is to eliminate fuel near the structure exterior - including your firewood storage, propane tank, vehicles, outbuildings, and vegetation. I am installing an underground propane tank for fire safety and the planning department will allow it outside of my building envelope.
The second most important is to use roofing and siding that is non-combustible AND make the structure as close to monolithic as possible. High thermal mass also helps. There have been plenty of stucco houses with tile roofs that survive wildfires and burn down well after the firestorm passes. Apparently, burning embers are blown under tiles, into vents, and under siding that smolder unseen and burn the house down from the inside hours later.
In this case a residential fire system would be of some value if you also protected attics. It is also useful if a window fails during the relatively sort time it takes for a firestorm to pass.
Monolithic features also make good energy efficiency. Casement windows, HRVs, and good sealing practices around penetrations.
The most wildfire resistant structures have:* A high mass exterior like conventional stucco. The stucco will have to absorb a lot of heat energy before studs would ignite. Adobe, rammed earth, ICF, underground, gunited concrete domes, and concrete block are also good. Rigid insulation like EPS will melt in a low oxygen environment rather than burn, but has to get very hot. I am using ICF.
* A mechanically interlocked metal roof (like a double-lock standing seam) on top of an unvented vaulted roof structure (like SIPs)
* A slab or sealed crawl space.
* Oh yeah, and sit in the middle of a concrete parking lot about this size of Costco's. Can you get a clear cut permit? ;-)
Edited 1/29/2005 1:10 pm ET by CJD
Hi CJD:
I'm not far from you, in Clearlake, Lake County.
As I read your post I went "yep", "yes", "that's it", "you know it", and so forth on each item. I watched the Oakland Hills burn and I looked at the aftermath of the Laurel Canyon fire in So Cal a couple of decades ago. There was just no need for all those houses to burn. Wood is lovely stuff to work with, look at and touch, but it is a FUEL, for heavens sake! Yep.
At this point, I'm thinking red iron frame and concrete block walls on a concrete pad -- a 720 sq. ft. Costco building. Plus standing seam steel roof. The frame and roof seem to be common commercial "metal building" hardware.
One of my goals is to minimize mechanical systems (and get rid of the propane tank!), so there will be LOTS of thermal mass. Frankly, I'm considering TWO concrete block walls, with rockwool insulation in the middle. Then I might go with plaster on the inside, eliminating the drywall issue altogether. Overkill, yes. I like overkill.
The roof overhangs will need special attention. They will be long. There will need to be absolutely no penetrations under those eaves. One way to do that is, as you say, to use an unvented vaulted roof. With two or three red iron "bents", I might achieve the look of a post-and-beam chalet, even in my little cabin.
Some of these ideas will be more expensive than "necessary", but I already own the lot free and clear and live here, so I think I can afford to endulge my personal priorities in the new house.
I have looked at some house types that are even more unconventional, such as the domes of Monolithic Dome Co. in... Texas, I think. But that might be a bit too radical, even for me.
""Casement windows, HRVs, and good sealing..."" What is HRV?
You mention rammed earth. I have read about it -- I went on a book-buying spree at Real Goods last year. (Stand clear -- I'm about to criticize something! ;-)) First, they say, eliminate clay and use sand and gravel instead. Then "stabilize" the mix with portland-cement. Sounds to me like it winds up being simply a poor grade of concrete, mixed very dry and thus requiring a great deal of manual labor to install. (I feel better now!)
I think we have drifted away from the drywall flammability question I originally posted! Once I gather my thoughts, maybe I'll launch a new thread about the whole project. See you around!
Elliot
Elliot, a HRV is a Heat Recovery Ventilator. HRVs are basically air-air heat exchangers. In incoming fresh air and outgoing stale air transfer heat to minimize energy loss.
Houses like we are discussing can be very air tight and will not have enough ventilation through normal air infiltration. An HRV has two small fans and take in air from a duct outside that can be protected from flying embers. There are a lot of them on the market but I am partial to aluminum core units like: http://www.lifebreath.com/pr_hrv01.htm
Have you noticed that mold has become such a huge problem since the energy crisis? Tighter houses don't leak as much air so humidity stays inside and grows microscopic critters. Not a problem in old leaky houses, they just cost lots to heat.
I agree with you on the rammed earth, but the look and super thick walls have their place.
Have you looked into pouring a concrete roof? See http://www.insul-deck.org/ and http://www.insul-deck.org/. They do work on moderate pitch roof designs. I am using it on the second floor deck and SIPs for the roof. My location is not as wooded as yours so the duration of a fire storm would be much less.
Not kidding. Strawbale walls with lime plaster have a VERY long fire rating. Something like 4 hours, and at that, the code official had to make an excuse to cut the test short. (A chunk of plaster fell off.)
Several have survive california fires.
Drywall's job is to delay the fire long enough so that people can get out. It is not intentded to make the building fireproof.
Most people killed in fires are not burned to death,but are killed by materials in the house outgassing. Carpet is evil. Upholstery foam is bad.
If wildfire is a concern, you also want shiny shutters for the windows. Lots of fires are started INSIDE the house from radiant energy passing though the window.
White metal roof.
Big cistern under/adjacent to the house. (It can double as a pool. Sprinklers mounted under the eaves, and on the ridge peak.
A 15 x 30 foot pool, with average depth of 6 feet contains 2700 cubic feet of water = 20+ thousand gallons of water. If you have a pump that can spray 100 gallons of water a minute onto your house, you have 3 hours of protection. Bigger pool = longer protection. May have problems keeping the pump running. May not be enough oxygen to keep a gas fired pump running.
When the fire is coming, start watering teh area around your house. Ideally you want to change it from a crown fire to a slow brush fire.
1/2 inch reg gyp = 15 minutes
1/2 inch ceiling board [type x] = 30 minutes
5/8 type x = 45 minutes .
Tim Mooney
There's not much that's totally fireproof. Even rocks melt if they're hot enough. Drywall that meets code just means it takes a certain amount of time for the fire to go through the wall. Gypsum is hygroscopic, meaning that it takes on and gives off moisture. When it gets hot, it gives off whatever moisture is in it, helping it remain intact. Thicker drywall means more time till the fire gets through. If you want a house that won't burn, use stone, concrete, cementitious shingles and just about anything other than wood, plastic or anything else that burns. Or, don't live in a place where the houses are exposed to forest fires on a regular basis.
"I cut this piece four times and it's still too short."
Thanks, Highfigh!
Appreciate the "hygroscopic" knowledge!
I know what you mean about nothing being totally safe from everything.
I actually live in a town, but we get no rain for eight months and temperatures sometimes above 100F, so fire is an unavoidable hazard. Steel, concrete and such it will be, indeed.
But the dry wall question is more about an electrical malfunction setting the inside of the house on fire -- which happened in my childhood home, although that was bare wood. For example, I wouldn't dream of having long cloth window curtains -- the classic villain in "frayed extension cord" scenarios. So I'm trying to take that one step further and eliminate all possible forms of "tinder and kindling" near electrical wiring. Sure, at some point, I will have to say "good enough" and build the silly thing. But I still have time to plan and learn.
Elliot
As Jeff said, wooden beams will still support whatever is above them long after the steel sags and fails. Wood can be treated to be less flammable. If the house that burned was wired with aluminum 14ga, it was doomed anyway. The insulation back then sucked, too and I suspect that it had a lot to do with the fire starting.
"I cut this piece four times and it's still too short."
Highfigh, I detect your affection for wood, and I don't disagree. Wood is a lovely material. There will certainly be wood inside my house -- just not around wiring.
"My Father's fire" was judged to have been started by a loosened connection, and this was attributed to the subway trains that rattled right past the house several times per hour 24/7. We were used to it, so it didn't bother us that we were aware of, but yes, the house did shake.
I like wood, but in a fire, I'm not gonna have steel beams and trusses. They will definitely fail in a fire before the wooden ones burn through.
"I cut this piece four times and it's still too short."
Actually, the classic villain isn't a frayed extension cord, it's an overloaded one. The plastic insulation melts and you have live wires and melted plastic -- perfect combo for a fire. I've seen this happen with just the lights on a Christmas tree, all plugged into a standard "lamp extension".The best way to avoid an electrical fire is to be conscientious about never overloading an extension, never overloading a circuit, etc.
Oh, and never put a bulb larger than the rated wattage into a lighting fixture.
SteelBuddha and DanH:
That's great news. I didn't know about water being chemically bound up in the dry wall. Sounds like that makes the performance of the dry wall independent of the climate.
I'm less sceptical about dry wall now. Thanks!
Elliot,The type X drywall has more water bound up in it per cubic inch than the regular drywall does. Type X drywall is also made with glass fibers all through the core so that the core will stay in place longer after the facing paper burns away.If you really want fire resistance, look into a Rastra-type ICF construction. The 10" walls on my shop had a 4-hour rating before any plaster was applied. The roof can be done that way, too, or use heavy timber.As others have said, get a good electrician, and run everything in metal conduit, trenched into your non-flammable Rastra wall, and sleep soundly.One other thing that few have mentioned here is clutter. It is a great contributor to fires in homes and shops. Too much junk in the building. Personal belongings are the tinder/kindling in many structure fires. A Zen house with proper wiring and site clearing makes for a pretty safe scene.Build safe, live wisely, sleep securely.Bill
Another thing not mentioned is animals. They like to chew on wires. They may not like it when those wires are live, but when the wires are obscured by drapes and when things move so they can cover the wires, the chewing isn't necessarily visible.
"I cut this piece four times and it's still too short."
If you're really worried about electrical fire safety, the most important thing to do is hire a good, conscientious electrician: one that won't do things like bury junction boxes, for example. ;)
As an extreme, you could have the house wired to commerical standards: EMT conduit and metal J-boxes. Depending on what style you're doing, I suppose you could even have it exposed in places as an architectural element.
BarryO: I'll be hiring pros for the big tasks like concrete and steel, but the wiring I'll be doing myself. Steel conduit, home runs, code+ sizes -- the good stuff, yes. I'd never sleep well otherwise. The house will be only 720 Sq. ft., so it's doable. Thanks!
Thanks. I take it that refers to a specified "test flame".
But I'm worried about a fire starting in the first place. The word "paper" in "paper facing" scares me. The fiberglass in the GP DensArmor Plus also, since the resin that binds the glass fibers can perhaps burn. Is the facing material rated in any way for catch-on-fireability, or am I worrying about a non issue?
Elliot
Thanks. I take it that refers to a specified "test flame".
No it doesnt . Its referring to fire containment in minutes. Some sructures are fire rated for containing a structure till the fire department gets there. Normally it is used between two occupancies or an unsafe room joining a occupant room. For example a garage stores cars and gasoline that has to be protected from the living quaters. The code there is 15 minutes .
Test flame would be known as flame spread which is the period of time an object holds up structurally under heat and fire untill its lost its rigid unity. They are rated in an index. In residential no sealing panel may be used that has a greater flame spread of greater than the index of 25.
Tim Mooney
I understand about containment while waiting for the FD.
Now I need to learn about the flame spread index. By the time I start building the house, I'll almost know what I'm doing!
Thanks!
15 minutes for a firewall? Sounds kinda light. What's the point of having a one or two hour firedoor between a garage and living space?
"I cut this piece four times and it's still too short."
"15 minutes for a firewall? Sounds kinda light. What's the point of having a one or two hour firedoor between a garage and living space?"
I didnt write the code , just enforced it." All garage ceiling and walls in such a garage that ajoins living quarters shall have a minumum of 1/2 inch drywall. "
The ceiling actually gets a rating of an hour. I think they had to do that becuse of commercial ceilings . I dont think it makes it so to call 1/2 drywall or ceiling tile an hour rating when it takes 1 5/8s and a regular 1/2 to get an hour rating on the wall.
On the wall , reg 1/2 is worth 15 minutes.
USG puts out a complete book on it . Thats the book in the office in use.
Tim Mooney
Why not talk to a building inspector so you can find out the code requirements, then take them a couple/few steps further?
"I cut this piece four times and it's still too short."
Highfigh:
""...find out the code requirements, then take them a couple/few steps further?""
Great minds think alike -- that's exactly what I want to do. The house will be tiny and the utilities are already here (I'm living in the old house on the property), so I can afford to upgrade where it matters most to me.
here's something else to think about ...
"wood beams" ... are more "fire proof" ... than steel.
houses with wooden main beams tend to stand longer in a fire than houses with a steel main beam.
the wood "chars" ... which insulates the inner fibers from farther damage ... to a certain extent ...
while the steel heats and weakens in a fire.
Jeff
Buck Construction
Artistry in Carpentry
Pgh, PA
A good reference that can be had for $20.00 is the Fire Resistance Design Manual
from the Gypsum Association. THe address and phone number is.
810 First St Ne #510
Washington DC 20002
202-289-5440
This breaks out all steel and wood structures form 15 min to 4 hours and how to construct them.
mike
No good deed goes unpunished
Thanks, Mike -- that's one I'll be reading.
Elliot
As much as I hate hanging 5/8" board, it's significantly better than 1/2" in a fire.
My dad put in 40 years with one of the Big 2 drywall manufacturers, and he recently told me about a test they did in their research facility. 5/8" Fire Code board will actually throw off enough moisture to knock down a fire started in a room, based on their tests. I'm sure if enough accelerants were present this wouldn't work so well, but it's an interesting point.
-Jonathan Ward
Elliot:
You might want to check out a publication called UL Fire Resistance Directory. It's got a lot of information that may be helpful to you. It talks about how resistive individual materials are as well as "fire resistive assemblies". I believe it's available on the web at an outfit called Constructionbooks.com, or something like that.
BILL
As highfigh said, standard drywall contains a substantial amount of water. It's chemically bound up in the gypsum. Before the fire can burn through the drywall it's got to boil off all the water. It'll happen eventually in a hot enough fire, but not for a fairly long time. This is essentially the same stuff used in fireproof safes.
Note that in commercial structures the steel girders are often wrapped in drywall to protect them from fire. Steel gets soft pretty quickly in a hot fire.
Not sure what the situation is with some of the more exotic wallboards. They would have to be lab tested to certify their fire resistance.
Really expensive but hardly anything better that wire lath and true plaster walls.
Will, I have been reading about the "natural" building materials movement and even bought a book on natural plasters. Since my house will be small, it may be doable. Thanks!
I did not read the 36 replies before me, so forgive me if I repeat someone else.
Regular drywall is non-combustible, but it will crumble when exposed to fire. Fire rated drywall is treated and reinforced so that it will not crumble. Fire rated wall assemblies require fire rated drywall so that they hold up to a fire for some substantial period of time, for example, 1 hour (depending on the rating required), keeping the fire from burning through to the rest of the structure.
If you want to be as fire safe as possible, masonry is one way to go, but in my opinion, if you used fire rated drywall in place of regular drywall, you are plenty safe with your walls at a reasonable cost. Masonry has it's own hazards in earthquake country. Then pay attention to all the other details, such as roofing, siding, windows, and so forth. In reading about resistance to exterior fires, the way the soffits and roof are vented is critical. It has to do with burning embers getting inside the attic. You'll have to research those details if you wish to be sure you are doing them right.
kc
Can't help you out with finding the article, but this will bring your post to the top and maybe someone will have an answer.
You can find the article by doing a search on the Fine Homebuilding Website itself. All the articles are up there, some you might have to pay to access.
5 seconds of typing found this:
https://www.finehomebuilding.com/how-to/articles/fire-resistant-details.aspx
My comments are not addressed to any particular person, but are of a general nature. They are derived from participation in a large number of indusry standard fire tests, both of materials and complete assemblies.
First off, it's not so much a specific part as an entire assembly that makes a 'fire wall.' Like a chain, it's all up to the weakest link.
Results from these fire tests have been supported by actual results from real fires. Sometimes the results are not what you think they would be. The 'time" is based upon how long before either the assembly fails - OR the protected side gets hot enough to light a new fire. Half-inch steel might survive the worst fire - but it passes enough heat to start a new fire after about 12 minutes. Thus, you don't see steel firewalls.
The primary factor in fire resistance is the simple thickness lof the drywall. Double the thickness and you double the time it will take for the fire to burn through. It's that simple. That's pretty much the same for any manner of gypsum product. When you get a 'listed' product, what you're really paying for is the testimony of an outside firm that they have actually tested the product, and that they monitor the continued production of it.
Does such certification matter? A few years ago I might have said "no,' ... but that all changed when we began receiving Chinese 'drywall' that contained all manner of things besides gypsum.
Attention to assembly details matters. Where do you think the nailing schedules come from? In a similar manner, another thread asks about re-mounting a piece using the same screw holes. Fire tests tell us "DON'T do it." The re-attached panel is much less secure than it was before. This is also why we stagger seams, etc. One fine detail that needs to be pointed out is that ALL fire tests are done with the drywall 'standing up,' rather than horizontal.
Others have listed various places where you can find detailed information about various assemblies. Follow those. Do NOT use the code book as an 'instruction manual.'
Finally, I will sneer at the remark that 'houses burn down every day.' Darn few fires 'burn down' any type of house. Far more are the fires whose scale is reduced because they were restrained by various protective measures - and drywall is one of our most versatile tools in reducing fire damage.
Naturally, it doesn't help when we pack our homes with drapes and furniture that practically explode into flame at the first opportunity.
"One fine detail that needs
"One fine detail that needs to be pointed out is that ALL fire tests are done with the drywall 'standing up,' rather than horizontal."
Out of curiosity, why would the orientation of the drywall matter during the flame test?
Probably would affect how quickly the taped seam fails, and to what extent the fire then "shines through" the resulting slot.
Does the direction the board lays matter? Well, we have no information on which to base a factual answer. It's left to guessing and speculation. A fine point, but one that matters if you're going to ask whether something was built as designed.
The primary reason for the concern, on the part of the testing folks, is that drywall is most clearly stiffer in one direction than in the other- similar to plywood.
This is clearly one area where the testing procedures differ from the way things are done in the real world.
reno-
The primary reason for the concern, on the part of the testing folks, is that drywall is most clearly stiffer in one direction than in the other- similar to plywood.
This is always a topic that's nebulous. Most never think of the strength of drywall in the same manner as plywood with it's directional layers (more going in the long direction).
And correct me if I'm wrong, when drywall strength is talked about it too is considered stronger in the long direction (hence-why many people claim it's true when talking hanging across the studs or joists rather than with them)
In this fire discussion I think the direction with the framing is considered stronger is because you have solid framing behind the long seam as well as on the ends (plates). No joint is not backed up-no flex etc.
When we hang and finish for a "firetaped' wall-it's paper and one coat of compound. Two layers, all taped and staggered.
Drywall direction? IMO, it doesn't matter. That's just my opinion, I can't say I "know" because I have never seen a test assembly where the board was laid 'sideways.' Yet, it's just the sort of thing an inspector will flag.
Speaking of rated assemblies ... there is absolutely NO difference between wood and light steel in the fire tests. NO difference, whether the assembly is loaded or not. Oh, I've heard all the theories and speculation, but the fact remains that replacing the steel with wood, or vise-versa, will not change how long the wall survives in the test. That's one variation I have seen tested, repeatedly.
Yet, it's just the sort of thing an inspector will flag.
What is the inspector going to flag?
Fireresistant Gypboard
I've use gypboard behiind wordburning stoves in corners. I cut scaps of gypboard into two inch strips. Only 1/2" gypboard is used in solid panels. The scrap spaces gypboard out from the wall by 1" and 3" coarse thread screws are used. The panel is raised about 1 1/2" off the floor. Heat from the wood stove makes the area behind the gypboard act like a chimney. Air is drawn in the botton and exits the top (4'). Only heat transfer is through the screws (too small) Try it with concrete board like Durabond.
Could be adapted to exterior use. Thor
Apart from code requirements, you're required to build what your plans specify. If your plans specify a fire-rated assembly, you'll be required to follow ALL of the details and specifications of that assembly. If the plan shows the drywall vertical, that's how it needs to be hung.
I have never seen vertical drywall detailed on any plan.
And I don't think any rated assemblies that would be listed on a site like USG has them either....................
but then again, I've never seen them nor had occasion to look.
Since you had experience with these tests, do you know of anything written that would clear up the question?
thanks.