Furring out walls and Rafters

[shelby27604]

I had to open up some walls and ceilings, now the man says insulation needs to be brought up to code.
Rafters are 2x6 @ 24" o.c. and need to be 2x10's, thinking sistering up the rafters with screws and glue us my best option, past experience tells me 2x4's won't take that many screws down the skinny side, and it would probably crack the rafters.

The walls need 2+ inches added, I think if I pre-drill ripped 2x4's I can get away with slapping them right up against the existing 2x4's to furr the wall out to 6"....

thoughts, ideas, suggestions from past experience? This is all old growth, 2x's as my house is 70+ years old.

 

[Fabrik8]

For adding that much depth for insulation, I've seen people commonly put the 2x4 on edge against the rafter edge, and then put plywood/OSB gusset plates on the sides, of whatever size and whatever spacing (I don't know what that would need to be).
It's not structural, you're just supporting the distributed weight of the drywall, furring strips, and whatever insulation. Whatever you can do with a table saw and a nail gun and some adhesive (gusset plates) I'd do that. You can pre-install the plates onto the 2x4s on the ground as well, or pre-install onto the rafter depending on what's easier.

If you sister everything instead, that will make a lot more thermal bridging, will make you have to compress or cut all the insulation to fit the double-width rafters, and will cost more because of the deeper sistered lumber. With the gusset plates, the plate material is cheap and you use commodity 2x4s.

The way you're talking about doing the walls, make a top and bottom plate, then set the furring strips on top of that (like adding an additional, narrow depth wall). You're going to need top and bottom plates anyway to fasten/support your drywall at the edges. You'll only need a few screws or nails per furring strip to hold to the wall. Remember that you may have to relocate all of your switch/outlet boxes to align with the furring strips, if that is too much depth to add extension rings to all the boxes.

Probably no need to pre-drill anything on the walls if the screws have the right amount of un-threaded shank on them, and the screws only need to be pretty small diameter so not much risk of splitting. Again, furring strips for drywall/insulation aren't structural. There are also long screws that have self-drilling points, which takes away that pre-drilling step and the splitting risk. Or, nail them.


Who is telling you that you need to upgrade everything? Building inspector?

I think you can just keep your 2x4 walls and use R15 (high density) fiberglass to meet code (Climate Zone 3 and 4). I think that's what they must be doing in the subdivision being built down the street here, because it's all 2x4 walls with kraft-faced fiberglass and I don't see any exterior sheet insulation (they're obviously not doing the R13 cavity + R2.5 exterior alternative). Or you could use mineral wool, which is R-15 by default for a 2x4 wall, but more expensive than high density fiberglass (and massively overpriced at Lowes and HD).

 

[jeepinmatt]

If its just for insulation properties, can you not just use spray foam?

 

[shelby27604]

I had an insulation contractor in here, to keep cost at a minimum he said furring out the rafters to 10" was the easiest and cheapest option. as for the walls, the rest of the addition is R19, so I assumed that was code minimum (been a few years since I built the addition)

 

[jyaks]

Cut 2x4 blocks and nail/screw into side of rafter then add your 2x4 stacked on the rafter. That's what my framers always did to fur out for insulation.

 

[Fabrik8]

I had an insulation contractor in here, to keep cost at a minimum he said furring out the rafters to 10" was the easiest and cheapest option. as for the walls, the rest of the addition is R19, so I assumed that was code minimum (been a few years since I built the addition)

As far as I understand, the current NC Energy Code says either R-13+2.5, or R15. If I remember correctly, I think the difference between R13 (2x4) and R19 (2x6) ends up being about 25%, once you factor in the thermal bridging of the wood studs, etc. That gap closes up even more if you go with the R-15 (current code minimum without exterior insulation). I'm not sure if I'd spend the time/money/effort to fur out the walls because of that; it's a lot of work to gain probably less than 20% over R-15. If you're doing a whole-house retrofit for energy savings, maybe a different story.

The rafters though.... that's where more of the heat loss/gain comes from. That's why current code is R38 for ceiling insulation, with R30 for space-limited cathedral ceilings (with max 500 sqft).

 

[RatLabGuy]

I had an insulation contractor in here, to keep cost at a minimum he said furring out the rafters to 10" was the easiest and cheapest option. as for the walls, the rest of the addition is R19, so I assumed that was code minimum (been a few years since I built the addition)

It may be the cheapest, b/c labor on nailing on those stubs is cheaper than spray insulation, but it's definitely not the easiest. I wonder what it's like to be a guy whose time is worth less than some exanding foam.
I'm guessing the loss of the space/height isn't an issue for you too.

 

[jeepinmatt]

I wonder what it's like to be a guy whose time is worth less than some exanding foam.

This is a very profound statement actually.

 

[Loganwayne]

I had an insulation contractor in here, to keep cost at a minimum he said furring out the rafters to 10" was the easiest and cheapest option. as for the walls, the rest of the addition is R19, so I assumed that was code minimum (been a few years since I built the addition)

did said contractor do spray? if not he is just trying to keep the job. Doing the roof rafters is min. 2 guy job. 10.00 is way low but for talks sake start there how many rafts do they have to do? estimate the time then double it, it will be slower than you think.

EDIT: also think about the weight of the ceiling that will be pulling down on whatever you scab on to the 2x6 plus the weight of the extra materials to scab. at some point it makes since to just slap a 2x10 against the existing notch the bottom so that it is bearing weight on the wall and hang it to the ridge. (this is the most correct way in my book but also the slowest and most labor involved. if the roof or rafters have any sag you will find it installing the new rafters.

 

[RatLabGuy]

This is a very profound statement actually.

Believe it or not, I have those occasionally. Some of them even come from profound thoughts.