I’m going to make a short story long…..I am in the process of doing some reno’s in one room upstairs of our house that was built in the 1860’s in Eastern Ontario. It has log walls with the log creating about a 3′ knee wall and then full 3″X5″ rafters about 32″ OC to a 9/12 pitch. Knee walls were strapped with vertical 1X3’s then covered with lath and plaster (no insulation). Rafters appear to have 4/4 boards as the roof decking on the outside and also on the inside of the sloped portions of the room to form the ceiling. The ceiling boards were strapped vertically with lath to create some spacing and then regular lath and plaster was installed (no vapour barrier). Some of the rafter bays have faced batt insulation but it is definitly not a ‘tight’ fit. I have removed all the lath and plaster and will build new regular stud knee walls and use batt insulation. On the sloped portion of the ceiling I may try to pour some loose insulation into the empty areas. I was then considering fastening 1″ foam board insulation to the inside of the ceiling planks (to help insulate and vapour barrier) and then drywalling over that. Finally here is my question….Is there a problem installing drywall over the board insulation and if not, what type of screws should I use as I haven’t seen any ‘drywall’ screws longer than about 1.25″. There is about 6’X 9′ of flat ceiling in the room that I left the lath and plaster on. I was considering also just covering the L&P with foam board and then drywalling that as well. Also, is the foam board sufficient vapour barrier or should I use polyethylene as well??
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
You don't have to sacrifice historical elements of a house in the name of energy efficiency.
Featured Video
Highlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Give Dave Palmer from Perth a call and he will spray foam the ceiling for you and you will have the best for your renovation. You'll be so cozy, you want your whole house done.
Gabe
hiya wood- you can use decking screws if you can't find the drywall screws at your desired length. I would recommend calling around to different stores. You should be able to find the length you need.
It would be a good idea to get rid of the plaster on the ceiling too but I understand summer, sweat, dust, alkalii, etc.
The foam baord is a good idea and it's OK to apply it directly over the boards with SR directly on it. SR screws come in many lungths. 1.25" is probably the shortest that I have seen. 1-5/8" is standard for ceilings. 2-1/2" or so should do you with one inch foam board. Tape the seams in the foam board to make it a decent vapour bar.
But the very best would be to spray urethene foam if you can afford it.
Excellence is its own reward!
In foam board/sheetrock situations like yours, my first choice is to use foil-faced polyisocyanate RFBI (R7.2 per inch), in a 4' by 8' sheet. When installing the sheets, I gap them by about 3/8ths of an inch. The sheets don't have to break over a rafter or stud. After hanging, I foam the gaps with a foam gun. You could use canned foam. That'll give you a very tight installation.
Over the foam I do furr out before sheetrocking. The reason is that on several occasions where sheetrock is screwed directly to the foam, I've seen the screw pull the sheetrock so tightly against the foam that the foam is somewhat "compressed." What I'm really saying is that the screw, and the gypsum core and face paper, are really under a lot of tension.
It may be a few minutes or a few seasons later, but eventually the gypsum paper/core lets go, and the sheetrock pops off the foam a bit, burying the head of the screw in the middle of the sheetrock.
Result? Usually, a hole in the face of the sheetrock...after it's been painted, of course.
In the end, I prefer to furr out 16" oc, then screw the sheetrock to the furring strips with standard length screws. I think the furring strips give a flatter plane as well. The furring strips also make easy targets for the rockers. No hunting for framing members through an inch or two of foam. The 3/4" air space from the furring strips adds another bit to the R-value of the wall as well.
I too will be installing 1/2" foil-faced polyisocyanate over studs under drywall, just on the walls not ceiling. Installing drywall in ceiling I know to use screws, but in walls is it not common to nail. Nailing should keep drywall from popping leaving holes or dimples in your finished walls, right?
Actually , that is not right. A hammer breaks the feild in the drywall , making it weaker. Good drywallers have loose rock nailing . A good finisher will screw off a nailed job. The screws pull the rock down tight with out bothering the feild of drywall, thus making the drywall stronger, unless the rock cant settle against a stopping surface . This happens many times when cripples arent flush to framers. Im sure you all have seen that happen . Also , it happens when the top plates are not flush . Thats why there are dimple nails at the top of the wall. It is not a good idea to rock over foam in any application. The only way you can " get by with it " is using a spanish texture. That texture shows a hi -low effect , thus hiding loose nails. That is why its popular in apartments. [cheap work ] I would never want to own a set of apartments with spanish texture because of the prep, and labor involved with repairing it. I have made good money repairing it for others though , so I guess it depends whose hand is fed. Many have tried to staple insulation on top of the studs , and joists . I would walk out when I was hanging , because I was the finisher. My rockers will walk out now , if its done .
Guys you may not like what Im saying . I wouldnt like having to fur a job out either especially on the walls , changing jams and the like. But Im giving you information that is dead on . Call your finishers , and they will join in with my words on this subject . Try asking the USG rep. Or believe it is so by your own common sense.
Tim Mooney
I know what you're saying Tim, now I know why I see all those nail pops at the top plates in houses. In my situation the other hassles aren't an issue (ie: changing jams, etc.). The only part that would be foam and furred would be the sloped portions of the ceiling neither of which have any casework at all. The knee walls would be new standard framing and insulation installation so that base boards won't be affected (I've already pulled them off as well.....3" cut nails sure hold well!!!).
Tim, having done some framing before and plus not being able to pay custom top dollar framers to build my house, their is nothing 100% flush about my walls. Top plates to jack studs off as much as 1/4" . I would think most likely what causes drywall popping around screws (or nails) is exactly this uneven walls. So if you fasten too tight against a uneven surface behind your drywall you most likely have problems. 2nd would be movement within the wall ie: moisture and air currents. If the hanger is aware that he is going against a flat smooth suface ( foamboard) he should adjust his fastening screws to only dimple enough as needed. JMHO, Roger
I made the example to show that nailing , or screwing drywall with out solid back stop would end up loose , today or a year from now.
Tim Mooney
First I thought you said install the foam board in between the lath , then you said over the lath. Assuming you want to sr over the foam board.
The problem is finishing the drywall. You must have the drywall tight against a hard surface , other wise it will show dimples that will be loose after one heating season. It will be like that when finishig if its not screwed tight in installation. Most times when this is tried , its never right . Texture ends up covering the loose screws ,; not good. I dont recomend this at all.
Here is two options to do it right ;
urethane spray
foam in between the lath , using 2 bys , then rocking to the lath .
That would then be exellence is its own reward [had to do that pif ]
Tim Mooney
or eliminate the screw popping scenerio by applying a different final surface besides mud and paint such as a thick wallpaper, thin t&g pine or cedar or any undisclosed wall covering to hide the drywall seams and screws if you are pressed for height in an upstairs.
Half of good living is staying out of bad situations.
Edited 7/9/2002 12:19:36 AM ET by rez
Hmmmmm....
I usually use strapping/furring over the foam on ceilings anyway for the wiring chase, etc. but have placed SR directly on foam for walls. Never a problem with depressions on walls but I can see it more likely on ceilings.Excellence is its own reward!
Hi Tim,
Actually the lath is all removed and the cut nails pulled out as well (anyone have ideas of what you can do with a whack of 100+ yr old lath??). I was going to put the foam directly on the plank ceiling and then strap as has been suggested and then drywall. I'm trying to track down the guy Gabe suggested to investigate the foam option, but so far no luck.
Two of you have used the word" strap. " Piffin was the other one. This is no compredee to me [lol]. But however , you have told me that you have a plank ceiling , thats good . Apply the foam board over the plank ceiling then , and then use a 16 nailer, and run cheap studs On 16 inch centers on your ceiling. Fill in at the ends of the room so you have a nailer completely around the room. Your ready for 1/2 inch drywall. Glue and screw .
It doesnt get any better than that !!
Tim Mooney
PS. tomato stakes or kindling
100 year old lath makes startlingly good kindling.
That's what the short pieces are destined for.....kinda feel bad about condeming the nice 4' lengths to the kindling box though. Got them stored in the barn now awaiting some sort of devine inspiration...or at least until winter hits!!
I E-mailed you his tel number and address, let me know if you didn't get it.
Gabe
Is this a cathdral ceiling application and is there adequate eave to ridge ventilation?
makes a big difference in your R-value
HUH??????????????
How does ventilation effect R-Value?Excellence is its own reward!
How does the ventilation affect R value??? I'm under the impression that the ventilation is to create a cold roof deck (at least in this part of the world) so that you don't get any snow melting leading to ice dams. I don't want to start a war between the 'cold roof' and 'hot roof' camps because in my situation it's kinda moot. This isn't a cathedral ceiling in the modern sense....140 yr old house where the top floor had kneewalls, sloped ceiling and flat ceiling at the top (creating a bit of an attic space above). The house has been added onto a number of times, so that what was origionally outside walls (and soffits) is now inside walls so there is no longer a soffit to allow air to enter the roof deck thereby preventing any sort of ventilation on that side of the room. On the other side, I'm really suspicious (haven't had a chance to really look yet) that there is also not a way for ventilation air to enter. So basically I'm figuring that at this time I'll fill the entire space between the roof deck and ceiling planks with insulation and then when it comes time to re-roof, will create ventilation space between the old and new roof deck. Right now, all the roof structure is in great shape...my biggest fear is that this is due to all the air leaks in the old house creating passive ventilation and that sealing all this up with foam insulation may actually cause a problem that doesn't presently exist. Might be one of those 'damned if you do, and damned if you don't' situations.
Insulation is good
Ventilation is good
Cold roofs are great in extreme conditions
But R-Value is a(n imperfect) way of measureing resistance to heat loss, generally through the insulation.
So, technicly ventilation doesn't effect this except in that it reduces the amt of moisture in the insulation and on a practical basis, maintains the intended R- Value as installed. I don't think that it adds to it but it is a proper part of the overall package.
Insulation is its own reward!