Remodeling of our 100+ year old house (in southern Wisconsin) is proceeding well, including the new superinsulated sidewall assembly. We adapted new construction practices outlined in a VERY useful Building Science Corp. technical report on exterior insulation techniques to this remodel. Our GC, A Better Home, did a masterful job (in my humble opinion!) of building out the 21st century construction techniques we designed for this 1912 story-and-a-half house.
After we stripped the siding, ABH bucked out all the openings and added 3 1/2 inches of polyiso foam outside the old 1x sheathing. Combined with the existing dense-pack cellulose in the 2x4 cavity wall, the result is a functional sidewall R-value of 40. The furring strips that lock the foam to the sheathing also create a full pressure-equalized rainscreen cavity. If there is a building on our block that is basically immune from rot/mold/moisture problems, this is that house! Energy models indicate that the wall retrofit reduces the space heating consumption to half of the pre-retrofit condition.
I can't wait to get interior details completed so I can throw a blower door in and see what the infiltration looks like. The goal is 1,000 CFM50, which would put us at about 0.2 ACHn.
If you'd like to learn more, Jeff A and I will be presenting on this project at the Better Buildings, Better Business conference in March, at Wisconsin Dells. Come see us at: Bringing a 100 year Old Home to the 21st Century -- Thursday, March 3 at 3:15-4:30 PM
Nice job Don!!!
What is the R-value of the roof, and basement?
Well, the roof and foundation are the weak spots left. The roof can get fixed, but I think I am stuck with the foundation.
The flat attic areas (center of house and above the dormers) are R-60 loose-fill cellulose, but the four slopes are 2x4 rafters with dense-pack cellulose. The slopes still melt snow in a hurry. And I still get little ice dams halfway up the slopes every winter, where interior wall plates intersect with the rafters and the thermal bridging is pretty strong. They will get fixed when the roof gets done next -- a new layer of foam on top of the sheathing, then a metal roof that will last for decades.
The foundation got R-10 to about 1 foot below grade. Fitting in more than 2 inches of foundation foam with the wall assembly above got messy, so R-10 was the best choice we could make there. And the old foundation was formed about three feet deep, then the rest was trench-poured. So we couldn't get effective insulation any deeper. The basement is a lot better that it was, but there's still a lot of foundation heat loss.
Placing horizontal R-10 slightly sloping away from the building (for drainage purposes) and near the bottom (not below) of the 1'-0" vertical insulation on your foundation walls would help immensely. I understand that such placement is almost as good as going 4'-0" vertical below grade, which for many reasons can be impossible to do in a retrofit.
The heating system is now wildly over-sized. The 60K NG sealed combustion FA furnace is more than twice as big as the current heat loss calc. We had a huge stratification problem this winter!
But I had attended a couple of John Straub presentations about HVAC systems in low-load houses, and knew that was coming. I warned my wife that it would be an issue, so I bought myself a year's grace to re-engineer.
We will probably replace the current FA furnace with a modulating FA furnace, using the existing duct work. When I figure out a safe way to circulate heat from the wood stove in the basement, we can probably be essentially fossil-fuel-free most of most winters.
derate the furnace then test with a flue gas meter. I find most nat gas and LP gas furnaces are 3-4 times over sized. After the building is sealed and R-60 is added - most gas furnaces will go off high limit with low air flow and small filter. I take a burner or two out and plug them. MUST test CO - O2 - temp rise after you adjust a gas furnace. If done wrong very bad thing happen but if you know what to do then works well. I find most teck will just lower the gas presser and this will if to low will soot up a heat exchanger, 1/8" of soot on steel heat exchanger will cut down 30% of heat exchanged and then high limit will open.
I have thought about that...
I am not a furnace tech, so the idea of rooting around right on the manifold seems like it's pushing my luck. But I know how to test a furnace and test for gas leaks. So maybe a little furnace surgery is in order.
If you have done this sort of thing, detailed info would be useful -- and maybe as a direct message, rather than in this forum.
to derate a furnace takes a very good teck. Top 10% teck and a master in combustion. In Kansas City there is less than 50. Most maker of furnaces do not want derating done. If you need 4-5 ton AC but just 40,000 BTU's heat Then must use high end furnace 2-4 stage heat or just derate. I saw a gas leak take out a house after derating, you MUST test after work is done. Most burners are 25,000 BTU's each and I get most heat where the air is most.
New Update -- House ALMOST met my air sealing target! This weekend's blower door test came in at 1,060 CFM50.
We finally got interior ceiling work complete enough for a blower door test yesterday.
Nice work. Great to see you doing something that makes long-term sense with regard to energy and durability
if you are not already a 000Home Challenge Applicant you should be.
Don - Good work! Can you add more detail to what windows/doors you used? Maybe one of the reasons you did not test out as tight as expected was the use of double-hung windows (I see nine in the above photo which is just 2 sides) versus casement, awning or just fixed style. Double-hung units always leak; the others would have given a better seal. Also - what kind of bug shield did you use between the foundation insulation and the wall assemblies above?
You are probably right, but there were multiple levels of decision-making on the window issue. First of all, it was really hard to keep the Department of the Treasury (my wife) on line with simple Anderson 400 series windows. I finally had to pull rank -- "Honey, I do energy cost-effectiveness assessments all the time. We are not doing those $200 vinyl sliders!!"
Also, I am not an absolute belier in casements and awning windows, even though they can seal pretty doggone tight. At least half of the 100 year old existing windows in our house worked just fine, but I have not seen very many 40 year old casements that work well at all. Retrofit for the long run takes on lots of levels.
The rainscreen cavities are dammed top and bottom with "Cor-a vent" siding venting. It's a corrugated polypropylene filler with a fibrous filtration layer to keep out bugs and such. I bought seven cases, and used only four. You need some??