I have several cathedral ceilings in new construction framed with 2 x 12s. I ran a level accross teh bottom of several of these rafters and they are not in plain. How flat is flat when it comes to having a clean drywalled surface in teh end? If the rafters very by a 1/8 or an inch, or 3/16 or 1/4 of an inche between rafters on 24 OC will that be noticable as light reflects off the painted surface?
Should I shim the rafters to flatten the ceiling (and again what amount of out of flat do I need to worry about?)
Would it be easier or better to strap the rafters? and if so how is that done? ie place 1 x 2 or 3 or 4 againt the be bottom of the rafters and shiming the gaps????
Thanks all.
Replies
it's an eyeball thing...
I suppose it takes a little experience to sight down rafters or joists or whatever to see if they are "flat enough." Perfect is for fairy tales. Rafters can be in "perfect" plane say 6' from a wall then wonky at another point in the span. In fact you can rest assured that'll happen. Also they can be all in alignment today and not next week. There will be some changes as they dry from 12 or 15% to the final MC. All the more reason to minimize the agonizing.
Pressed for a measurement i would consider 1/4" between 24" oc to result in a good finish. Even more variance would be hard to see unless you can sight right down the finished product in which case you're just too close to the ceiling.....
Strapping will help even out a wonky joist system and makes it easy to shim a really bad framing member if required.
really? you can get away with 1/4 inch? In other words if I use say a level and span three rafters and the center rafter is low by 1/4 inch you would say good to go? I was figureing I could get away with an 1/8.
I'd strap it with 16' 1x3 furring strips spaced 16" oc.
What exactly do I ask for at the lumber yard if ..
if I am intersest in 1 x 3. I have never seen a 1 x 3. 2 x3 yes 1 x3 no. And I would think I am looking for low grade junk, right?
Steel resiliant channel makes a good substitue for 1x3, and is inexpensive. 12 ft long and straight.
Find the low spot in your ceiling, pull some string level with that, and shim the channel at the joists. Easy way to get a flat, and level ceiling. Carefull shimming and you can hold 1/16" from true.
Sound reduction is extra if you wish.
Yes DR, Suppliers here in New England sell "strapping" as 1"x3" spruce. It is usually pretty wet and not very pretty.... sold in bundles of 10 and lengths to 16 feet
On a cathedral ceiling it is unlikely your eye will ever catch the angle to see 1/8 to 1/4 inch. maybe on a second floor walkway or climbing the stairs you would.
Drywall mud regularly builds out around a 1/16 inch in 8 to 10 inches and you don't notice it. at the butt joints it can be a solid 1/16 or a little more, spread out over 12 to 16 inches.
Think about lighting too. Any place a light like a sky light has a line close to parallel with the wall it will emphasize any flaws.
I would 1) use a moisture meter to confirm it is close to equilibrium moisture content 2) use a string to see the difference. 3) use a power planer to shave off rafters that may stand too proud and 4) scab on something (plywood b/c it doesn't split out under a fastener) 3/4 to 1 inch thick along the side of the rafter if absolutely necessary to extend any rafters that are short.
putting shims in on the 1.5 inch face of the rafter seems like a really tedious and inaccurate and SLOW way to work. And how will you know where to drive your screw to catch the shims when they're covered with drywall? If you don't catch the shim with your fastener you're guaranteed a lot of nail/screw pops.
Hey DoRight,
We always strap flat and cathedral ceilings in my neck of the woods. After we nail it all up, we sight down each run of strapping and adjust as needed. We tap high spots down with a hammer, insert a shim, then run a screw through everything. Low spots we handle a couple of different ways. For slight adjustments we tap the strapping down and chisel a recess for the strapping to sit in. This usually takes only one or 2 chisel chops. Then we nail it back up tight or add a screw. Really bad low spots (these are usually limited to old house remodeling situatons), we will cut the strapping on either side of the low rafter or joist. Then the strapping will spring up to where it wants to be and we put a block on either side of the framing member and nail off the newly cut ends of the strapping to the blocking after sighting it down the line for straight. This extra step of straightening everything up doesn't take long, but sure makes a big difference in the finish quality. Happy Halloween
They make stuff for shimming prior to sheetrock. It comes in a roll. Looks like the same stuff as felt paper.
I'd take a power plane to the 1/4" out one. Get it down a bit, then use the asphalt shim material.