A question for the energy nerds out there…
My 1600 sq. ft., 7-year-old, 2-storey home in the Pacific Northwest has cathedral ceilings insulated with fiberglass batts and covered with cedar-faced plywood panels. The joints are covered with 1×3 fir. A recent energy audit showed immense heat loss through these joints and the auditor recommended air sealing the ceilings by covering the plywood with drywall. Bids for this are coming in around $4000.
The house is heated by radiant tubing in the floors. One not-very-efficient propane water heater provides the hot water for the radiant and for DHW, and I pay about $2400/year for propane. A more efficient boiler would run about $8000 installed or an electric heat-pump water heater around $3000 installed.
My questions: What’s the best investment to bring my energy costs down on my very limited budget? Should I drywall the ceilings or invest in a more efficient water heating system? And are there any easy-to-use energy modeling tools out there to help me decide?
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Replies
E.,
There is no simple answer to your question, because air sealing work and added insulation will last longer than new heating equipment, and it's hard to predict how long each measure will last. To do a full analysis, we'd have to know more about the characteristics of your house.
I recommend starting with ceiling repairs, and delaying the equipment replacement until you can afford to do it. Instead of just adding drywall to your ceiling, why not add 6 inches of rigid insulation first, and then strapping and drywall? Then you'll actually have some R-value as well as better air sealing.
I know... more money .. the bid keeps going up. But it costs money to do the job right, and shortcuts lead to later regrets.
Not sure where you are in the region, but here in NW Washington the cost of electric heat or hot water is significantly less than the cost of propane (.07 per kWh versus $3/gallon in my immediate area). If a water heater of a given capacity is adequate for your heating and hot water needs, I would consider removing the propane heater and installing an electric unit instead. Obviously a calculation like this has to take into account your specific fuel costs. I'm not at all sold on heat pump water heaters in this climate, since we're often heating anyway.
Re the ceiling, I see a lot of situations like that and usually have to tell folks that covering their ceiling with drywall, or better yet a layer of foam insulation and then drywall, is the way to reduce heat loss. In theory you could re-install the plywood over foam insulation if you like the look, but in any case you need a real air barrier at the ceiling. Actually, I would be hesitant to go over the plywood directly... I would probably want to remove it, see if the insulation above can be improved, then simply install drywall (or foam + drywall) directly to the framing.
I'll second both of the above approaches. Begin by limiting the heat loss, then when ready move to more efficient delivery. A ceiling is the right area to focus on.
I really like David's idea. It makes great sense if the plywood could be removed and then replaced.
The sequence I would consider is: Remove plywood. Bring any lighting down below this level for later re-instalation. Leave the batts where they are, Establish an air-barrier (the most important step) by a membrane (vapor semi permeable), new insulation layer, of 2.75 " of Foam (or mineral wool) + Battens. Replace the lighting in this layer. Then add the plywood and 1x3's back.
When completed, you'll have an long term and protected air barrier with the lighting (if any) below and not penetrating the air barrier. That to me is the most significant step. Although perhaps not critical, the vapor management profile of a semi permeable (less than 1 perm) air-barier (and no foam) would let the both sides dry if and when they need to. By using mineral wool in place of foam (again), you'll have a vapor permeable insulation that has more mass that EPS. This should reduce heat transfer by radiation on hot sunny days over foam.
I have to admit that this last statement is a bit of a reach for mineral wool. It's based on European studies on performance of Wood Fibre Board insulation compared to Foam boards. The studies show that the wood fibre material stores the radiated heat longer because of their mass vs. the low mass foam boards. It was also a shared opinion by Thorsten Clupp in a conversation about dense pack cellulose insulation vs. foam boards and radiation cycle time while at the international passive house conference (nerd heaven) in Innsbruck Austria last month. The crossover being that dense pack cellulose has a much higher storage capacity over foam of the same value.
The benefit for you E Coe, is that since you are working on your ceiling, you'll have reduced over heating on the 2 or 3 days that we do actually get sun in the PNW.
Albert is right. There are only 2-3 days (per year) that we get sun up here. On top of that, it's usually raining, the people are mainly extremists of one sort or another, there are no jobs, the attractive single people have all left, there are no outdoor recreation opportunities, housing costs are exorbitant, and taxes are off the charts. You would definitely not want to move here!!
The starting point should be improving the shell. As you noticed with the audit that the insulation still allowed the air leaks to easily pass through the insulation. Fiberglass insulation is the most air pourus insualtion and is the least effective in leaky cavities. You also have the factor of radiant heat flow through the insulation from the hot roof deck above in summer months.
I would question if the roof is adequatley vented with a chathedral cieling. I think a good starting point for energy efficiency would be removed the existing ceiling and insulation.Use rigid insulation spaced 1 inch below the roof deck. This would provide a vented roof. Seal around the edges to the rigid insulation. Then dense pack the rest of the cavity with fiberglass or cellulose. Install drywall.
If you like the looks of the wood ceiling maybe it could be salvaged and reinstalled on the drywall. If you do that make sure the seams are taped and mudded.
Thanks for all the answers. It sounds like the consensus is to start with the ceiling. I don't mind replacing the plywood with drywall, so will probably go with the suggestions of adding extra rigid insulation, firring strips, then drywall.
Albert, thanks for pointing out the need to drop the can lights down. When you suggest using mineral wool in place of foam, do you mean a rigid board? I think Roxul makes something like that. Would that be as effective as the EPS? While I believe that insulation is the best use for foam, I'd prefer to use a non-petroleum based product if it's effective and affordable.
E Coe,
My preference is still the Mineral Wool board. The product that I'm familiar with is rockboard 80. I said my preference is "still with mineral wool"... See another GBA posting that you might find interesting re: insulation materials https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/20958/styrene-and-epsxps-rigid-foam-insulation.
btw.. The rockboard 80 is pretty high density at 8lb per cu ft. As I was pointing out before, I believe that due to it's higher mass, it will perform better than EPS in reducing sunny day heat transfer into your envelope.
David Meiland's comments about the realities of Zone 4C are accurate. Temperate is not the word for it. "Grating" is by far the more accurate. The reduced overheating in your application will reduce the "false hope syndrome" most common in zone 4C. For those not familiar with the area, the "FH syndrome" is the depression that follows after the 2 annual sunny days are over and the reality that the climate is really "not livable" returns. I hear that the San Juan Islands are worse.
E Coe: Should you choose the rock wool route, there is plenty of it in the area though it can sometimes be hard to find where to buy. If you need help finding a local source, drop me a line through http://www.smallplanetworkshop.com. Be happy to help...
Only thing I'd add to the excellent advice already offered is to toss the can lights completely. In addition to being hard to air-seal they are hopelessly inefficient as light sources. Use suspended track instead. There are some really good-looking fixtures out there, including some great LED options for not too much money.