Rethinking my attic insulation...

[RatLabGuy]

The Duke Energy thread and discussion there got me really thinking about my insulation situation again.

BLUF: what problem would I have adding a 2nd layer of insulation in between my rafters, in addition nto the R13 already between the joists?

Details:
House built in '67, fairly typical 1-story ranch style, with attached garage under the same main roof. Altogether it's something like 90'x28 of roof/attic.
The ceiling joists are only 2x4s and the original insulation is R13.
One oddity - it has a walk-up stairway for the attic that runs parallel to the basement stairwell in the center of the house, so that there's a door in the back corner of the den that puts you at the base of the stairs and you walk up into the center. This means (1) there are two walls and a door that aren't insulated but are losing heat up into the attic and (2) people see this as a convenient feature for easy access to lots of storage space; there's plywood sheets running the middle of the whole house up there.

Because of this "feature" I've been loath to just blow in a whole new layer like most folks would.

A couple years ago I got a great deal on a snotpile (maybe 100 rolls) of unfaced pink fiber, the kind that is wrapped on both sides w/ perforated plastic so it supposedly can breath. I started putting them in the attic, running perpendicular as a 2nd layer across the joists from the eaves up to the plywood, leaving just enough clearance space to still walk around. To leave some access to be able to get across them later if needed, I laid 2x8s across the joists between every 2 rows of fiber.
Boy, getting all those 2x8s up there was a PITA and expensive, and in the end I only got 3/4 of the main part of the house covered, still had to leave a 3-4' center strip open for walking/storage, and didn't have any coverage for the stair/stair walls space. Don't feel like it was worth it since it wasn't done right.

As much as I hate giving him credit @shawn had a good idea of mactually covert he whole saking a sort of belco door covering the stairs that hinges up when you walk up, which I may look into.

But really I'm wondering - would I be better off just moving all that insulation (and finishing it all) up into the rafter space? That way I could actually get complete coverage and still maintain walking/storage access.
The one challenge is that the R30 is like 8" deep but the rafters are only 3.5". So the usual insulation hangars won't cut it. I'm sure I can find a creative solution to that.

Now I know normally you want airflow in an attic - but I already don't have any soffit vents (all the soffit space is solid, unvented), no ridge vent, no fan, and the eve vents are really small (and 90' feet apart). So it seems prime to just cover the eves and make it an unvented space.

My understanding is the big problem with insulated rafters is potential ice dams under the roofing from the area under them being warm. But how is this avoided on homes with a finished attic or vaulted ceilings?

 

[R Q]

''mactually" If that's not a real word, it should be! lol

 

[rockcity]

Why couldn't you insulate the portion of the staircase walls above the ceiling joists and put an insulated door with weatherstripping in? That should help. And then finish insulating the rest of the attic like you started.

You may need to pull the plywood floor up and insulate there and then reinstall. May need to crib the plywood up after more insulation is installed.

 

[BigClay]

Good timing of this thread for me. Yesterday I noticed that portions of my roof were showing through the snow as all of my neighbors roofs were still all covered in snow. My house was also built in 1967 and it is the original insulation.

I do have this over the attic stairs which has helped keep the draft down. Attic Tent AT-2 Attic Cover / Insulator 25" x 54" x 7"

 

[drkelly]

I don't work in the construction business professionally or as a hobby, and am not familiar with building codes, so...

My first thought would be to set another set of 2x4's on top of the existing 2x4's making it now 7" tall. Stick pieces of 2x8's perpendicular to the ceiling joists every so often to help support the new 2x4's from moving. Install insulation between the new 2x4's, then lay OSB flooring down. You could possibly only do 1/2 the attic like that or 1/3, or whatever amount you determine to be needed for storage space.

It would be a good early spring or late fall project.

I like Rockcity's idea for insulating the walls of the stairwell and buying an insulated door.

 

[shawn]

Why couldn't you insulate the portion of the staircase walls above the ceiling joists and put an insulated door with weatherstripping in?

You don't get as much insulation value. The R value of an insulated door is shit, and you aren't likely to get more than R15 in the walls. Then there's the whole question of the air barrier and what's happening with the stairs themselves. If you put a lid over the stair opening, now you have an air and thermal barrier that's in plane with the air and thermal barrier in the rest of the house.

@RatLabGuy - blown fill? Easier and faster than batts. You don't want to put insulation against the roof sheathing because of wetting due to the location of the dew point.

 

[Fabrik8]

I used to rent a 1960s house with a layout just like yours about 20 years ago with some friends. We built a climbing/bouldering wall in the attic with a cave around the chimney. I think it was insulated with a mix of new loose fill fiberglass and old vermiculite.

Like @shawn says, The easy solution for the insulation is blow-in filled to a proper depth, but you'll lose the storage space. The door and staircase are not so easy.

 

[shawn]

but you'll lose the storage space

Not necessarily. Frame a floor section around the stairs to 12" deep, fill it, then install plywood over. Just do a couple hundred SF that way, then leave the rest unfinished.

If the ceiling joists are 2x4s, they're too shallow for storage or occupancy.

 

[Fabrik8]

If the ceiling joists are 2x4s, they're too shallow for storage or occupancy.

I missed that detail. I was kinda wondering why there would be a subfloor and storage over a 2x4 joist section.... So out of curiosity, how would you retrofit with a 2x12? Sister it, or cut out and replace the 2x4 in those areas?

So what's the current joist depth under the floored section?

 

[rockcity]

@shawn i agree that the insulation on an insulated door isn't that great and the walls won't net much R value, but considering what he's got, it's better without a ton of work or $. Could always add insulation on the attic side of the door to help further improve the insulating factor.


@RatLabGuy maybe add a door on the first level and close off the attic stairs from the first level? You'd still need to do some insulation on the stairwell walls of some sort.

Pics of what you have may help.

 

[shawn]

but considering what he's got, it's better without a ton of work or $

I'm talking about a piece of plywood with a bunch of XPS screwed to it. That's easier. And actually, I'm recommending adding the plywood for safety (fall protection) and weight to help seal the air barrier. I've built several similar hatch covers that were just XPS built up with coarse-thread sheetrock screws until they're ~4" thick. But those were all 36x60" ish overall over folding stairs, not over permanent stairs with a ~36"x12' floor opening. The smaller ones only take an hour or so to build and install.

I'm not really a fan of the walk-up attic at all, but that seems like a reasonable fix, given what he has to work with.

 

[Fabrik8]

I'm talking about a piece of plywood with a bunch of XPS screwed to it. That's easier. And actually, I'm recommending adding the plywood for safety (fall protection) and weight to help seal the air barrier. I've built several similar hatch covers that were just XPS built up with coarse-thread sheetrock screws until they're ~4" thick. But those were all 36x60" ish overall over folding stairs, not over permanent stairs with a ~36"x12' floor opening. The smaller ones only take an hour or so to build and install.

I'm not really a fan of the walk-up attic at all, but that seems like a reasonable fix, given what he has to work with.

If his house is like the one I rented, the attic opening is just clear space above the entire stairway. Depending on the stair pitch, it may be possible to close some of that opening off to a smaller size and still maintain the 6'8" headroom. I'm not even sure if there is a headroom requirement per code for attic stairs in non-conditioned space.

Anyway, the idea of adding a flange to the opening and a large hatch cover should work much better than the open staircase and door. The hatch cover could be hinged at the back edge and could include gas struts or counterweights for load assist, and a simple hardware latch or two to hold it shut against the compression of foam weatherstrip around the perimeter.
I know that sounds like overkill, but if the solution is a large insulated hatch cover, there are some easy ways to make a large insulated hatch cover and deal with the weight of it.

 

[RatLabGuy]

OK maybe I didn't emphasize the important point here.
The attic ceiling is not high - I'm only 5'9 and can just barely stand up straight in the center where the apex of the roof is with my head between rafters.
If I crib across the whole floor, anywhere I'll want to lay plywood down on top will have to be 2x10s. That dramatically reduces the height. You can really tell in the areas I've already done (used 2x8s just to separate them and provide access to shimmy across if necessary).
I'm really not hot on that.

Plus, it means hauling a shit ton more wood up there. Something like 30-40 boards, plus bracketry for every one. Not cheap either.. I didn't realize how that would add up until I'd started doing the part already done. Also, most of the original house electrical is run up there and maintaining some way to get to it would be nice.

Going between the rafters instead still looses overhead room, but not as much, and won't require adding plywood, wood or brackets.

So what are the problems associated with insulating between rafters? If it's moisture on the underside of the roof wood, I can add the cheap foam vent spacers to offset the insulation. I'm sure I can deal with the rafters being shorter than the batts, and come up with some way to hold them in place.

If the educated opinion is that is still a bad idea, then to deal with the stair way I will build a giant hatch cover for the stairs. It will have to be like 10' long and 3.5' wide (that is the size of the stairs + stair walls) and insulate that with XPS, hinge it at the bottom, and add a spring (?) to assist opening. Moving the 2nd layer of insulation to the rafters mostly negates the need for that.

@shawn
@RatLabGuy maybe add a door on the first level and close off the attic stairs from the first level? You'd still need to do some insulation on the stairwell walls of some sort.

Pics of what you have may help.

There is a door now. Well it used to be a door, I replaced it with homemade shelves to hide it a little, it looked really weird being there. I put XPS on the back of the shelf-door.
i'll get pics a little later.

I missed that detail. I was kinda wondering why there would be a subfloor and storage over a 2x4 joist section.... So out of curiosity, how would you retrofit with a 2x12? Sister it, or cut out and replace the 2x4 in those areas?

So what's the current joist depth under the floored section?

Yep, 2x4s top and bottom. So, little space for insulation in floor, currently filled with 50 y/o R13 rolls, and only way to add more is to lay on top.

 

[josh m]

Find some poly ISO foam boards and tack them up to the underside of your rafters. If you look on Craigslist there is often some that have been salvaged from a built up roof or stuff that's dented. Layer a couple 1-2 inch sheets, stager joints and make it a conditioned (somewhat) attic.


Sent from my iPhone using Tapatalk

 

[paradisePWoffrd]

OK maybe I didn't emphasize the important point here.
The attic ceiling is not high - I'm only 5'9 and can just barely stand up straight in the center where the apex of the roof is with my head between rafters.
If I crib across the whole floor, anywhere I'll want to lay plywood down on top will have to be 2x10s. That dramatically reduces the height. You can really tell in the areas I've already done (used 2x8s just to separate them and provide access to shimmy across if necessary).
I'm really not hot on that.

Plus, it means hauling a shit ton more wood up there. Something like 30-40 boards, plus bracketry for every one. Not cheap either.. I didn't realize how that would add up until I'd started doing the part already done. Also, most of the original house electrical is run up there and maintaining some way to get to it would be nice.

Going between the rafters instead still looses overhead room, but not as much, and won't require adding plywood, wood or brackets.

So what are the problems associated with insulating between rafters? If it's moisture on the underside of the roof wood, I can add the cheap foam vent spacers to offset the insulation. I'm sure I can deal with the rafters being shorter than the batts, and come up with some way to hold them in place.

If the educated opinion is that is still a bad idea, then to deal with the stair way I will build a giant hatch cover for the stairs. It will have to be like 10' long and 3.5' wide (that is the size of the stairs + stair walls) and insulate that with XPS, hinge it at the bottom, and add a spring (?) to assist opening. Moving the 2nd layer of insulation to the rafters mostly negates the need for that.

There is a door now. Well it used to be a door, I replaced it with homemade shelves to hide it a little, it looked really weird being there. I put XPS on the back of the shelf-door.
i'll get pics a little later.

Yep, 2x4s top and bottom. So, little space for insulation in floor, currently filled with 50 y/o R13 rolls, and only way to add more is to lay on top.

It doesn't have to be 10ft long. Fix the lower part and just hinge the section where head clearance is an issue.

 

[RatLabGuy]

It doesn't have to be 10ft long. Fix the lower part and just hinge the section where head clearance is an issue.

Actually I just took a look, there's a;ready a short fixed portion, would only need to cover ~7'. So totally doable w/ a sheet of plywood. Then just have to deal with the weight.

 

[RatLabGuy]

Pics. The hinged shelves on tbe right are the door, so the stairs run a diagonal from lower right to upper left behind that wall.

Oh, yeah, it's about time to put away the Christmas crap.

 

[WARRIORWELDING]

Insulate like crazy. Make the hatch usable but only in an emergency......build storage building. With the low ceiling and challenges I would put my material dollars in better storage else where......if it's in another less climate controlled space it can't be much different then the attic in the summer or winter.
I have an attic space similar in a rent house. The biggest difference is the roof has a stupid pitch and the space is litterally a bonus room. Blown insulation. Raised sub floor. Pull down ladder. Only thing I would add is a glued up frame/ lid for the ladder out of blueboard. The house is pretty tight otherwise so I haven't bothered.
My mom's house is like yours. A very insulated crawl space on the top.....I hate crawl spaces the older I get.

 

[RatLabGuy]

My mom's house is like yours. A very insulated crawl space on the top.....I hate crawl spaces the older I get.

Thats what I'm trying to avoid this attic turning into if possible.

looking at the cost of continuing cribbing a 2nd layer, it's going to be at least another $300 in wood and brackets. 2x10s aren't cheap. Thats the part I overlooked when I first started this.

After doing a lot more reading, it seems the biggest issue with the insulation between rafters is moisture permeability into the fiberglass. So the preferred solution is instead closed-cell spray insulation on the sheathing/rafters to seal them, then if that itself isn't enough, add the fiberglass behind that. But that stuff is bookoo expensive.

Bonus fun: I just realized all my batts are 15" wide, but I have 24" rafters. Doh.

 

[shawn]

I'm pretty sure I spend $300 at Home Depot every weekend.

2x10s are probably unnecessary, but without a framing drawing, it's impossible to say. I had 2x6" ceiling joists, so went R19 between, then set a new floor above that framed perpendicular on blocks over load bearing walls and insulated that with R19. So it's a bit different, but that's a good strategy that keeps you out of the existing electrical and won't break or cause nail pops in the GWB. The plywood floor is just tacked down, and comes up quickly if there's a need.

Not worried about ceiling height because it's an attic, and you get what you get.

 

[peewee]

This is something I've looked in to pretty extensively. There are many benefits to insulating your roof instead of your celing. But it is nessicary to insure air flow to your shingles ,or under them, to avoid overheating them and voiding warrenties and "curling the edges". They make a styrofoam insert that goes against the bottom of your roof from your eves to your center vent cap. Your insulation would go under this. If any part of your hvac system is in your attic you'll benefit from this greatly.