Year: 2012

Bump Out

One of the things we’ve been talking about for a while now is what to do about the second floor “bump out”. Despite our initial impressions, a survey of the attic shows this to be part of the original structure. Despite this, my inclination is to lop it off. Over the years it’s developed leaks and sags, and sealing it properly seems like a challenge. In addition, it goes right to the property line on the south side of the house, which will prove a challenge for getting zoning and permit approval to keep it. Its proximity to the neighbors house resulted in a broken window last summer during a hail storm because it ricocheted off the nearby pitched roof. While it brings in a lot of light in its current form, the floor plans for the second floor I’ve come up with put the bedrooms at the front, making it somewhat unnecessary. It adds a whopping 27 square feet of space, so it’s not exactly a big contributor to the size of the house.

However, my recent change of heart on double walls has raised the question of the importance of square footage. We’re eventually adding a finished attic, so we’re definitely not suffering for want of space, but keeping it with a bit of rearranging of room layout would increase bedroom sizes noticeably, and in the current plan they aren’t exactly generous. One of the architects noted that if we remove it, the city would never let us put it back, something that doesn’t really sell it for me, but it’s worth contemplating that reducing the size of the house in any dimension isn’t necessarily a smart move. Like so many other decisions, it isn’t an easy one.

Double Wall Section

We’ve met with several architects and we’re waiting for a couple of proposals. One of the common themes in talking with them is the suggestion that we should insulate with spray foam. We’ve been talking about building a double wall with rockwool insulation, and the architects are almost unanimous in saying that spray foam insulation in the walls is the way to go.

Now they are the experts, but I come back to the reasons we planned to do this in the first place: the insulation value of the double wall with rock wool is 25% better and costs less than half as much. There are other factors though: spray foam is an air barrier, and it would seal up gaps in our leaky old house. Not having to build the double wall would save a lot of work plus we wouldn’t be making an already narrow house even more so. On the other hand, we’re planning to replace the exterior sheathing after we remodel the inside, so using spray foam would mean adding some new layer to the inside before applying, so we don’t break the foam seal when we remove the exterior boards. When we do the exterior we’ll be using a house wrap and taping all seams, which should seal the house nicely, without the expense of spray foam.

I’ve been referencing BuildingScience.com, which has some R-Value Recommendations for walls based on climate zone. In Chicago, which is Zone 5, they recommend an R-30 wall. Closed-cell spray foam yields an R-value of  6 per inch. Filling the 3 3/4″ thick outside walls would give us R-22.5. In addition, we’re planning a 1″ layer of insulation on the outside of the sheathing, which will give us another R-4. Adding the minimal contributions of drywall and sheathing and we’re up to about R-28. Compare that to the double wall, as in the diagram. Each 3 1/2″ thick batt of rockwool provides R-14. Adding the exterior insulation and the rest of the wall brings that total to R-33 while also reducing thermal bridging. Of course, there’s another option that’s kind of the worst of both worlds: do both. We could spray foam the outer wall and then still build the inner wall, insulating it with rockwool. The insulation value would be a stunning R-42, but carries the highest cost by far as well as the most work.

Deciding the right course can often be tricky, but in this case it can be done with straight economics. Using houses on the market in our area today I can estimate the value of the square footage I would lose with the double wall. Then I subtract the extra cost of spray foam and the increased cost of heating and cooling. The numbers come out in favor of spray foam. So despite my inclination toward the double wall, I’m open minded enough to see the better decision and change my mind.

House Model

I’ve been working on my 3D SketchUp model of the house for quite a while. This isn’t finished by any stretch, but it’s starting to look rather presentable, so I’m sharing it now. I have a laundry list of things to add to the design, like the spiral stair down from the second floor on the back porch and slew of minor tweaks here and there. That said, this is what I hope the house looks like from the outside. It may not happen: there are zoning setback requirements that may prevent us from having the front porch span the whole house. If that winds up being an insurmountable permit challenge, we’ll have to revise the porch to only be on the side with the door, and not protrude out as far.

Some of our design decisions may help for unintended reasons. We removed the windows from the North side on the plan because they just overlook the neighbors house and don’t bring in a lot of light. As it happens, because our house is on the property line that may help us for fire code reasons. Apparently houses are no longer permitted to be so close to the line, but we can get a waiver because it’s an existing structure.

The other thing I’ve been working on (aside from scheduling architects as Sarah posted about) is working on our Chicago Green Homes plan. We want to apply for the city’s Green Permit Program, which would save us a lot of money on permits for things we’re planning to do all ready. However, in order to qualify, the plans you submit have to reach a variety of criteria, including a minimum of a two star rating on the Chicago Green Homes guide, as well as two items from their “menu” of green design elements. My thinking is that by figuring all of this out now, I’ll  save a lot of work (and money) for our architect.

I went through 162 pages of guide fun, selecting items and tallying up their point total. I mostly picked items that we were already planning to do and things that wouldn’t cost us a ton of extra money, since spending money on air pressure tests to save money on permits doesn’t make a ton of sense. I’m not in this for the certification itself. The energy efficiency is its own reward, and I doubt the resale value of the home would go up dramatically just because of the certification, though I could be mistaken. Since we’re not planning to sell anytime soon anyway, it’s not a strong motivator. The two required menu items for the Green Permit program could be accomplished with additional points from the Green Homes guide, so I elected for the three star rating, along with 200 points from the Energy Efficiency category. The majority of these we need to include as a specification on our submitted plans and we’re good to go. Some of them will require some calculations and software. Chicago already has a whole list of requirements for Energy Efficiency that’s required by normal code, so we’ll need to do a lot of it regardless. Then we just need to make sure the elements we’re adding, like highly insulated walls, high-efficiency windows, heating, and cooling exceed those requirements. Whichever architect we wind up with we’ll need to go through all of this I’m sure, but having done a once over ahead of time will probably help a lot.