Comments requested proposed modification plans for attic

I have a 1928 Craftsman which has a full attic (about 28 x 24) with a fairly new standing seam roof (with a little cap on the top of the roof where the two sides meet). A previous owner had foam (probably icynene) sprayed in the floor of the attic/top of bedroom (6 inch depth), but this is crumbling and has cracks so does not do much.

The attic has soffit vents, and two gable vents (but currently no ridge vents). Right now the house is super leaky so attic insulation is plan #1. Rafter depths are 6 inches with 16 inch centers.

After lots of reading and talking with different contractors the plan is (also driven by local code) to make a ventilated attic with an insulation of about R 80

The plan
- cut ridge vents in roof
- put a 1 inch spacer on the inside of the roof
- install 2 inch blue board inside rafters on the spacer (so have the 1 inch as ventilation from the soffits to the ridge)
- extend rafters to about 21 inches total
- put straps and netting in place to give a grid with about 16 x 16 inches gridsize
- blow in dense packed cellulose (about 18 inches)
- put 5/8 drywall in

I will be doing most of this myself, with a contractor emplacing the dense packed cellulose and providing some guidance on an hourly basis. As the design is a bit non standard, I was wondering if someone sees any red flags or has words of caution (the ventilated attic is driven by local code requirements) before I embark on this project.

Thanks!

 

As long as air can flow & moisture doesn't get trapped, it should be okay.

 

Hi rversteeg and welcome to the forum. Some questions:

1. Are the soffit vents continuous and do they provide sufficient lower vent area?
2. Are you planning to utilize the attic space, ie close off the old gable vents and allow just venting below the roof deck?
3. The blue board will need to be perfectly sealed so it does not allow air flow up through the insulation to a colder surface.
4. Any vapor barrier?
5. Will there be heat and air conditioning provided to the remaining attic space? Or will this just be a void between the ceiling below and the new well insulated roof above?
6. Have you verified that this approach meets local codes?

Bud

 

I can't deny a certain fondness for insulating not the floor of the attic, but the underside of the actual roof. But, that means that the HVAC has to provide for the added space of the attic in addition to the volume of the rest of the house. But, it means that whatever you store up there doesn't get baked or frozen.

 

 

Why do you want to use blowin insulation as opposed to Kraft-faced rolls?

 

Determine the net free area of the soffit vents and your total ridge and soffit area should be 1 ft� for every 300 ft� of attic floor. How you fudge that for the sloped ceiling, I don't know. Half high and half low is the general guideline. Since you will be extremely well insulated and air sealed, all of your moisture problems should be from the outside, ie moist air venting in or a leak getting to those raters. In any case it would need enough air flow to dry to the outside.

Be sure to insulate those gable wall.

Intuition says a closed attic space will end up musty and maybe some mold. The connection to the house for heat and moisture is unknown, but a backup plan to be able to exchange some of the air up there wouldn't be bad, other than having to go up and open a window. A supply and return vent wouldn't cost a lot with all of that insulation. Again, just intuition.

Since you are new to ridge vents, do some reading. I have seen water and snow blowing in on many occasions in many attics. Some brands claim to be much better than the others, but I'll bet the others are cheaper. Don't settle for cheap as you will not be able to see the leaks.

You are also probably new to a metal roof. In snow country, under the right conditions, they can unload like an earthquake, if you don't have the provisions to hold the snow. Under the eaves is not a good place for small children to play in the snow.

Bud

 

I did not really consider fiberglass rolls. It seems that blowin would get me better airtightness than fiberglass, but I can of course be wrong, and there are lots of horror stories about fiberglass. Also, might be hard to get the R value I am shooting for (would need to do double layer), but I will look at it again

 

Bud - thanks - that really helps a lot. As an alternate/complement to ridge vents, would a fan (say a 4 inch duct fan which vents to the outside) be a better solution? My main concern is cutting ridge vents, especially as I can not easily get under the existing roof (so I would have to cut from the inside, which will be non ideal)

 

As far as I know, it would be R21, nothing would be doubled.

 

Ok - I see. R21 would not meet my local code requirements, so maybe that's why I took it off the list (even adding some blue/pink board would not get it to meet code)

 

I thought NY was tough on code. NH seems top be worse.

 

A fan is not useful for exhausting an attic with an insulated floor - the ceiling of the floor below - and is even worse for one where you are insulating the underside of the roof.

Just saw the "complement." A fan would not only not complement the function of the ridge vent, it would interfere with it.

Is that "little cap on the top of the roof where the two sides meet" the standard ridge finish for a standing seam roof? That is, a taller standing seam with the seams from each side of the roof rolled down to lay into it, and no air passage? If so, can you get a quote from the company that installed the roof for cutting it and installing a ridge vent? A ridge vent cannot be installed from inside, AFAIK.

 

rversteeg, are you going to R-80 because of code or just the desire to go extreme? I see R-80 in the opening and may have missed something in between.

Bud

 

Code requires R-38. The R-80 is the strong suggestion from the insulation contractor. It may be that this is too extreme, but partly this is a "if I do it, may as well do it good" approach - but I am open for suggestions and comments.
I am still trying to get a comprehensive understanding of what my options are, how much I can do myself (most of it apart from either spraying foam or installing dense packed cellulose) and what is the best approach to do this

 

At r-38, there is a certain amount of heat ($) exiting through your ceiling/roof. We can easily calculate that number for you. Then you can consider the added cost of going to r-60 or r-80 and at each level you again calculate the reduced dollars going out the roof. I can even give you the equation if you are a numbers geek like me, it's not hard.

Here is a quick example. If your ceiling at r-38 is going to lose $200 over the heating season, then increasing it to r-76 (double) would reduce your heat loss to $100 (half). Skipping the little details, is the added cost (and labor) of going double justified by the added savings of $100 per year. Now, things don't always have to be justified based upon dollar savings. Sometimes you just want to save as much as you can while you are there. But other times, there are other places where those dollars and effort can produce much greater savings.

My wife wanted new windows and we needed new siding so while I'm there I'm adding 3.5" of rigid foam to the outside. This is a case that "now" is a good time for the extreme upgrade. If r-38 is good, but r-whatever is much better, while your doing this it's a lot easier to go extreme than coming back. I understand that our glut of natural gas has currently suppressed energy costs, but don't plan on that lasting. Locally produced energy vs imported is always better, but world demand will drive the cost.

Since you are still at the drawing board, feel free to toss around other ideas.

Bud

 

I realize that I am not completely clear (happens more often to me). So, here are some pictures of the design which should hopefully clarify what I want to do.

The reason I am shying away from spray foam is the potential for cracking (my house is sort of old and moves a lot, and with the recent New England earthquake that may be an issue), but maybe I should go back to the drawing board and do a simple design with an unvented attic with layers of pink board directly on the roof sheathing and just bring it up to R40 and call it a day.

What I meant by the fan (figure 3) is to install a fan which would be venting the uninsulated airspace just below the roof cap and which would vent through the gable. This would avoid me having to cut ridge vents, which I do not feel that warm and fuzzy about.

 

A ridge vent is the best exhaust vent because it is passive, continuous and in-kine with the airflow. How will you power the fans and how much will it cost to run them. How will you control them? Since ventilation is more critical in winter than in summer, and keeping the insulation dry is the goal of attic insulation, thermostats are pretty much useless. A humidistat might work. And how will you get to the wiring, the controls and the fans themselves if (when!) something needs to be fixed?

I can't believe I haven't said this before: To determine the optimum level of insulation for your house, plug your location and house-specific information into the ORNL's ZIP-Code Insulation Program, an online calculator.

 

Thanks again for all the info. I am contacting the roofing company to see how they installed the roof and to see if a ridge vent is even possible, and then will think some more about what to do. It may be that I may end up doing 6 inches of closed cell spray foam and then sheetrock that (so go with an unvented attic) , but from what I have read the thermal bridging from the rafters would negatively affect the performance. In the meantime it's slowly getting colder. On the plus side I am learning a lot - especially that insulation is a heck of a lot harder than I thought.

 

What are you doing with the gable end walls, code or more than code?

Bud