Addition Framing/Insulation Questions

[Dmm698]

Adding an addition onto an existing 30x30, will be replacing the 6/12 commons currently installed on the existing building with 8/12 attics. The new 24' addition to the rear gable will follow the existing ridge line and also be 8/12 attics. Overall the building will be 30x54.

I've got two questions that i'm trying to decide the best approach to.
1) Bumped from 20' to 24' addition so that I could put the stairs inside. I plan to install the gable, skip a truss, and double up the next one, and stick frame between them. This will alleviate having to cut out and box in the truss that would be installed at 2' off the gable. Top / Bottom chords are 2x8 on the trusses. Would you stick frame the roughly 4' between the gable and the double truss with 2x8 as well? 2x6? 2x4? The reason I ask is because I fear that when going 2x8 , you'll end up with fully closed off "squares" along the top chord where the ceiling tappers in the attic room, essentially having no venting once the ceiling is sheetrocked (or OSB'd).

2) Plan to blow in Cellulose, and just repurpose all the existing batts that are up there. Doesnt seem like it makes sense to insulate between the ceiling, and Attic floor for the width of the attic? Seems like it would make more sense to place some rigid foam down the side of the attic knee walls at the bottom so the cellulose has a hard stop, and then just "wrap" the attic area with batts, and the rest would be cellulose. I'd like to insulate the attic somewhat (it will be storage, not livign space) to minimize the temp swings as best as I can, so it seems silly to insulate between garage ceiling and attic floor, if the walls/ceiling of the attic space will be insulated.

 

[Dmm698]

Anyone have any thoughts on this?

 

[duneslider]

How are you ordering the trusses? The truss companies I work with would put the whole detail together for what you are wanting to do and provide the engineering to show that it is good (which is required where I am) We can't just willy nilly decide to move a truss over and stick frame how we want, the inspector wants to see the details.

The truss designer should be able to put this detail together for you.

I'm not totally following all your questions on insulation but in my garage with attic trusses, I have blown in fiberglass type on the ceiling of the garage, batts between ceiling and floor of liveable attic space. "knee walls of liveable space are batts (r-19) and batts in the liveable space of the ceiling. This was done by the insulation contractor. If I were to do it again (which isn't gonna happen) I would have done the ceiling of the liveable space with rigid foam to get a bit more R-value out of it. I also would have put a little more on the walls, moved to r-21. It getts pretty hot here in the summer and I think a little more would help. It isn't hard to keep it conditioned now though, pretty happy with it.

If you did the WHOLE ceiling of the area instead you could omit the walls and floor of the liveable space but I think that will cost more and be more difficult that the route I went. It might be a better way to go in the long run though.

 

[TurnipTruck]

I also had a four foot gap in my trusses. The truss designer doubled the common truss, but the attic truss only required larger nailplates to handle the load.
Regarding insulation: I bracketed in 2x12 rafters and totally filled the bays with fiberglas.

I have a ton of pics in my link if unclear, or if applicable to your situation.

 

[Dmm698]

I also had a four foot gap in my trusses. The truss designer doubled the common truss, but the attic truss only required larger nailplates to handle the load.
Regarding insulation: I bracketed in 2x12 rafters and totally filled the bays with fiberglas.

I have a ton of pics in my link if unclear, or if applicable to your situation.

Thanks! I think the situation is a little different. I've included a screen grab of a drawing I created to help clarify.

Trying to decide the best way to stick frame between the gable and then doubled truss (since i'll be skipping one to allow for stairs). This is shown in red circle. If I utilize 2x8 to match the Top chord, i'll end up with isolated cavities once I put OSB or sheetrock up on the "ceiling" of the attic.

Screen grab with blue will show what i'm talking about as far as creating "cavities" where air will be stagnant and not able to vent up from the soffit continuing on to the ridge vent.

As far as the truss placement, the bottom chord I'll stick frame with 2x8 and they'll tie into the gable truss as well as the doubled truss , and on the gable end also be sitting partially on the top of the top plate.

 

[billconner]

If you insulated between rafters to eave, instead of down knee wall and across floor - less area of heat loss and less sf of insulation.

If venting eave to ridge, why not drop 2x4s flush with bottom of top chord, and set a 2x4 on top parallel with trusses to support roof sheathing? You might have to shim 1/4" or rip it from a 2x6.

 

[Dmm698]

If you insulated between rafters to eave, instead of down knee wall and across floor - less area of heat loss and less sf of insulation.

If venting eave to ridge, why not drop 2x4s flush with bottom of top chord, and set a 2x4 on top parallel with trusses to support roof sheathing? You might have to shim 1/4" or rip it from a 2x6.

You’re correct, venting is from eaves up to ride vent.

I hadn’t considered the layout you mentioned but seems like it would absolutely work. Basically run 2x4 flush with the bottom of the top chord, then run a 2x4 as if it was a top cord toe nailed in. I think I’ll probably go this route.

Ideally I just want the 8 feet outside the attic space insulated, and then the knee walls/ceiling of the attic. I don’t plan to use a door at either end of the stairs as it will make getting stuff up there a PIA. So I wanted it somewhat insulated.

Still on the fence of weather or not to insulate between attic floor and the sheet rock below. Cellulose will blow in on the 8 feet on either side of the attic.

Thanks for the feedback!!

 

[billconner]

If the stair is open between ground floor and attic (no doors), and you heat ground floor, you are heating the attic. I see no use for insulation in ground floor ceiling. What am I not seeing?

 

[duneslider]

From experience, if you don't have a door between the upper and lower the heat will all rise to the top and it will be much warmer up than down. The door helps slow that stack effect and warm air rising, not to mention fumes wanting to move up there too. Unless you are planning to run hvac in the building the door is needed in my opinion and if you put it at the bottom it seems to work better. Then you can just open it all the way when you are needing to go up and down with stuff.

 

[duneslider]

Also, from experience, consider what you will be taking up the stairs. With the landing at the bottom as small as it is you may have issues with longer items. I made some miscalculations on one of my sets of stairs and I can't get 4x8 sheet good around it, I goofed up by a mear inch...

 

[Dmm698]

Also, from experience, consider what you will be taking up the stairs. With the landing at the bottom as small as it is you may have issues with longer items. I made some miscalculations on one of my sets of stairs and I can't get 4x8 sheet good around it, I goofed up by a mear inch...

I missed your original post.

Yes, I have stamped plans for the trusses.

I see no issue doubling up the truss and stick framing between them. my day job is engineering but I don’t have a PE so the plans are from the truss manufacturer.

What I was saying about insulation , you described. You have insulation up the knee walls of your attic, and then across the “ceiling “ of the attic. You have blown in on top of the ceiling outside your attic space.
It also seems like you have Batts between the attic floor and lower level ceiling. This was my question. I’m not sure if I should do this or not as the usable attic space envelope is insulated.


I’d prefer not to insulate the underside of the roof and end up with a hot roof. Going to utilize soffit / ridge vent.

I don’t plan to install a traditional door to the attic. I plan to have a hatch that’ll open up and then lay flat over the opening with insulation on the back side.

This attic space won’t be used as a man cave hang out. It’s purely for storage. I just want to put some bare bones insulation around the space in an attempt to keep it a bit more regulated.

Heat source will be the wood stove I’ve already got / been using. Being in NYS we don’t get a ton of overly hot weather.

 

[duneslider]

If your space is conditioned below the attic space you shouldn't need the insulation in the floor of the attic space. My garage is technically not conditioned and does get colder in the winter and the attic space is liveable so I needed to insulate it. The bit of roof over the attic space has batts and there is a 1" ish air gap, so not totally packed tight.

Lately, with the weather pretty cool here we aren't running the heat or ac and have doors/windows open during the day. Main level area stays 70-72 like the outside but the attic space is probably 80ish due to the heat rising up the stairs to that space. If I open a window up there and put a fan in to pull air out of the room it stays much better but even with just windows open we don't get enough air flow to keep the temps the same as the lower level. If it is just storage for you then it will probably be fine but I am positive the wood stove is going to make the temp up there way warmer in the winter.

 

[KenC]

Another framing option that include positive vent space. Use a 2x8 with a notch in the middle top large enough to accommodate a vent channel. Cut the notches before installing and they can all be done with a circular saw quickly. Use the foam panels designed for this. I'd install from the top, just before doing the roof sheathing. that way your not constrained on the type of insulation you can use. And you will have an open path from eave to ridge.