Adding sleepers to rafters?

[krogers]

I am finishing an attic space. My rafters are 2x6 with 1x sheathing and slate roof tiles on the outside. My plan is to use clipvent and rigid foam to create an air channel. In order to get adequate insulation in the space it has been recommended that I add sleepers to the current rafters. What is the best way to add sleepers? My thought is to add a 2x4 on on edge and then secure with squares of 1/2" ply or osb. I thought 5"x5" squares every 4' on both sides. Does that sound right?

[scorrpio]

I take it you want to extend the width of rafters so that more insulation can be put in. I would chuck a 3/8" bit in a drill, mark 1.5" depth and drill blind holes roughly every 2' into the edges of 2x4s. Then, use 3.5" deck screws in the holes to fasten the 2x4s to the rafters.

[crokett]

Those ply gussets, construction adhesive and a finish nailer might be faster than the screws.

[krogers]

Thanks for the ideas.

Scorrpio, yes that is exactly my intention. 2x4 on edge to add depth and more insulation. This is the recommendation I received from 2 contractors. But now one told me exactly how to do it.

Crokett, I was thinking of a framing nailer instead of a finish nailer. I have both. HF framing or PC 15 gauge. Would the framing nailer be overkill? Would all of those larger holes weaken my rafters? Would 15 ga with construction adhesive be enough to hold the 2x4 and weight of sheetrock, tape etc? And do you think 5"x5" ply is about the right size. Is every 4' enough or should I go every 2'?

Does anyone have any experience with either method? By the time I cut all the plywood gussets, I wonder if I am using the same amount of time as scorrpio's suggestion to drill and screw.

[crokett]

The construction adhesive is holding the gussets and 2x4s. The brads are just there to hold things until it dries. Also put glue along the edge of the 2x4. Considering when I mistakenly glued a 2x4 to my basement floor last year and the 2x4 split before the glue let go I'd say the glue will hold.

The difference between cutting gussets and drilling and screwing is most of your time is spent in the shop cutting gussets and fixing them to 2x4s. With drilling and screwing most of your time is spent in a possibly cramped, probably hot and certainly dirty attic. Your call.

[siliconbauhaus]

A couple of thoughts:

I'm assuming your rafters are at 16"centres so by the time you add 3" of 2X will you have enough room to get a framing nailer in there?

What about using the paper backed insulation? You just tack it with a stapler to the rafters you already have. I would think the cost difference between insulation with backing and plain would be less than buying all the materials to frame is out?

[scorrpio]

The difference between cutting gussets and drilling and screwing is most of your time is spent in the shop cutting gussets and fixing them to 2x4s. With drilling and screwing most of your time is spent in a possibly cramped, probably hot and certainly dirty attic. Your call.

Err, not so. I'd drill the holes in 2x4's on my drill press in my shop, then pre-install the screws in holes ALSO in the shop. The only thing left to do in the attic would be squeezing on the adhesive (which I also recommend using) and then driving the preinstalled screws all the way in.

Besides, if the attic is being made into finished space, it can't be that cramped. And given it's middle of March, hot is not likely as well.

Again, this is how I would go about it.

P.S. A thought: if your rafters have standard spacing and you plan to put rigid foam between them, (which also comes in standard width) those 1/2" ply gussets will cut the bay width by an inch - an inch you'll have to trim off every foam board you install. And what about the space between the squares?

[LarryG]

The fact is that this is one of those jobs that there's no truly good or easy way to do; it's a PITA no matter how you do it. So every person's take on what is "easiest" or "best" will be colored by his own prejudices.

I personally would get some 3-5/8" x 25 ga steel studs, lay a bead of construction adhesive down one flange, and attach them to the existing rafters with self-tapping screws about 24" OC. The screws would be driven at a slight angle (similar to toe nailing) but the stud being open on one wide side will give direct access to where the screws need to go. No gussets, no drilling holes, no advance prep of any kind. Just glue, screw, and done.

[JeremyM]

And we have a winner with Larry's suggestion!

I was thinking along the gusset ideas but MUCH prefer the steel stud idea. Likely lighter in weight, but truly easier to get done and still very strong. The self tapping screws will be the secondary connector to back up the Liq Nail you squeeze very liberally all over the place.

Just like Larry said, IMO.

Jeremy

[BrianWillan]

I personally would get some 3-5/8" x 25 ga steel studs, lay a bead of construction adhesive down one flange, and attach them to the existing rafters with self-tapping screws about 24" OC. The screws would be driven at a slight angle (similar to toe nailing) but the stud being open on one wide side will give direct access to where the screws need to go. No gussets, no drilling holes, no advance prep of any kind. Just glue, screw, and done.

I am not entirely sure this would be the best way to do this. Usually with steel studs, for walls at least, there is a top and bottom track to prevent the steel stud from twisting before the installation of the drywall.

I think that the drywall attached to the steel studs in this manner would cause a weight issue.

Insulating a cathedral ceiling to insure proper ventilation requires some attention to detail. I personally think it would be better/easier to use spray foam directly against the underside of the roof sheathing for 5 inches (R7 per inch). This elimates ventilation and vapour barrier issues and also gives you a few more inches of headroom in the space.

Of course check with your local building officials for code requirements.

Cheers

Brian

[LarryG]

The tracks at the top and bottom of lightgage steel framing do keep the individual studs from rotating, to a degree, but they're mainly there to hold them in a straight line (i.e., to define a wall) and to provide a means of attaching the individual studs to the supporting structure. With tall partitions, one can grasp the studs at mid-span and twist them to a considerable degree. Some view this as alarming but it's entirely normal and NBD. When the gypsum board is applied, it serves as a diaphragm that holds the flanges in alignment.

I don't underside the "weight issue" comment. We use steel studs in horizontal applications in virtually every project we do (the ones that use lightgage steel framing at all, anyway), never with a problem.

All that said, I concur with the suggestion to use foamed-in-place insulation. If this were mine, I'd have a spray-foam insulation company come out and shoot the rafter spaces full (there must be NO voids left ... in this case the depth of the rafters looks to be about 5-5/8", must be a pretty old house), with the excess trimmed off flush before the gypsum board is applied. The only downsides of this approach is that it moves this portion of the job out of the DIY realm, and it will probably cost more. Still, it's what I choose to do because it's a lot less fooling around, it conserves space in the finished room, and it'll ultimately be a better finished job.

[krogers]

More answers and questions

I have to comment that this discussion is why I really like this community. I can always count on you to provide good feedback, ideas and discussion.

Scorrpio you are correct. The attic space is not cramped and it is still pretty cool up there. I am trying to get this project finished before it gets too hot up there. And David called it dirty. It may not be Kirby-esque up there, but the working conditions are not too bad.

Steel studs are a new idea. I wonder about the insulation installation. My plan was to use kraft faced fiberglass. It is easy to stable the kraft paper to wood studs. But how would you attach the paper to a steel stud? Is there another way or another insulation product you would use if I go the steel stud route?

Brian you mention spray foam insulation. I have been considered it and like the idea. But you said to spray up against the sheathing. My understanding is that you want an air channed in the rafter bay for airflow, heat and moisture control. Two of my neighbors have the same house design of the same vintage. (1929) They have both finished their attic space with just insulation and drywall. No problems reported with lack of air channels. I have the chance to do anything and I want to do it the right way.

I chose clip vent (see clip-vent.com) because the rafter spacing is unique. Most are 19" to 23" wide. One or two are even smaller. There isn't a lot of consistency. Clip vent with rigid foam would use 2.5 inches. 1.5 inch air space and 1" of foam. That leaves about 3" free. I didn't think this was enough insulation for a third floor ceiling. Tell me if you disagree. With sleepers I could have 6.5" of insulation. I am not against hiring a spray foam contractor if you think this is the way to go.

Can you spray foam insulation on steel studs and get the same results? Will the foam cause the steel to rust or fail over time?

Thanks for your help and opinions. - Kevin

[BrianWillan]

Brian you mention spray foam insulation. I have been considered it and like the idea. But you said to spray up against the sheathing. My understanding is that you want an air channed in the rafter bay for airflow, heat and moisture control.

Actually ventilation is not required with spray foam insulation. Spray foam seals pretty much air tight as it gets to all the nooks and crannies. Since it is air tight for all practical purposes there is no moisture that gets in and thus it doesn't need to be dealt with.

Here is a link to a spec sheet for 1 manufacturers' closed cell polyureathane spray foam.

http://www.basf.com/urethanechemical...f/Walltite.pdf

In there it states that the product meets all standards for an air barrier and vapour barrier.

This product also has an isulation value of R 6.7 per inch. So in essence with a 2x6 rafter you would get a net R value of almost 37 (6.7x5.5). Or if you use its Design value of R6 (after 28 days) you still get R33 by just filling to the depth of the 2x6 rafter. So going this route, I wouldn't bother with adding sleepers to give more insulation space. This results in a few more inches of head room in your attic space.

Remember do check with local building code officials for requirements in your area.

Cheers

Brian

[LarryG]

There is batt insulation sized for steel stud framing; i.e., either a full 16" or full 24" wide, rather than the 1-1/2" narrower equivalents for wood framing. It can either be friction fit (unfaced version) or the flanges of the vapor barrier can be taped to the steel studs. The tape only has to hold long enough to get the gypsum board in place.

Brian is correct about sprayed foam not needing to be vented. Given the varied spacing of your roof framing, and that sprayed foam would negate the need to furr out the roof any deeper, it may well be your best solution overall.

[krogers]

foam options

Okay, so if I choose spray foam what do I do about the peak? My original plan was to use the are channel to connect the area behind the knee-wall to the area under the peak and above the roof. The space is about 10.5' at the peak. The current plan is to add a flat ceiling at 8.5'. This would give me surface for ceiling lights and a fan. If spray foam with no air channel should I install the foam all the way to the peak and over the other side? Will the air trapped between the insulated peak and the drywall ceiling become a problem? Similar question for the space behind the knee-wall, should I insulate it?

Thanks for you help on this discussion. I am looking for spray foam installer to see if I can get some quotes.