Major Thermal Upgrade
I am an owner-builder (1991) of a timber frame house in north central Massachusetts (zone 5). To enclose my frame (made of 100% timber from the land where the house now sits), I purchased Winter Panels outside of Brattleboro, Vt. At the time they were called double chip (i.e., osb on both sides of foam) stress skins (now named SIPS). I installed double pane Pella windows, a double roof and a central Finnish fireplace that heats the entire building ( 32′ x 32′ two floors, a half attic and fully bermed basement) with between 1 1/2 cords and 2 cords each heating system.
So, what’s the problem? The windows have lost a good deal of their R-value as has the polyisocyanurate insulation, which originally was around R-36. Finally, I am no longer in my 30’s (how did that happen?) which means I need to do the work now. Here are my comments and questions about doing a major thermal upgrade for my house.
1. Replace all windows (except for a Hurd picture window which still holds its heat) with triple pane casements from Inline (Toronto, Canada). Will very much read everything you have on GBA for flashing “outies”.
2. Replace siding which is cedar shingles, with horizontal clapboard. Have to do this – we are in a woodpecker hot spot and NOTHING keeps them away in the fall. (If you have this problem, try Cornell University’s agri. center. – great info. on woodpeckers.)
3. Repair outer skin of SIPS where needed.
4. Then apply liquid WRB to outer skin of SIP. (Any tips on doing this correctly?)
5. Add R-15 to 20 foam panels to outside of outer SIP skin. (Is Phenolic foam board a possibility in the U.S.?)
6. What is the best way to seal the insulation board seams? (Do not trust tape in the long run.)
5. Put in 3/4 inch plywood strapping to hold in foam and create a rain screen. (Something never considered in the early 1990’s.)
6. Use s.s. screws to attach strapping to SIP outer skin.
7. Install new clapboards with s.s. nails.
I am doing this work predominantly by myself, so it will likely take 2- 3 years.
Any tips or information GBA can steer me to would be very much appreciated.
I think the GBA site and the incredible amount of expertise, information and informed opinion that can be found here is an incredible treasure to those of us interested in highly efficient building. THANKS!
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Replies
I'm not sure how much improvement you can really make here. Aged polyiso is around R5.5/in, so what you have is still R25+. In Zone 5, most of your energy savings is had with an R20 assembly, so you are well above that already.
If the windows are starting to bend/warp and leak, replacing them makes sense. Otherwise, you can buy new IGUs with modern coatings and argon fill and swap just the glass out. You can probably swap a half dozen IGUs out in a day if you get into the groove, much less work and cost than replacing the whole window.
Since the siding work will have to happen, it might be a good idea to check your air sealing. Getting the place air tight will make a noticeable comfort improvement. Adding extra insulation is doable but I don't think you'll notice it.
Double pane windows don't really lose R value over time unless the seal fails. How can you tell if the seal has failed? There will be fog and haze inside the IGU from moisture intrusion. If you don't have any moisture inside, the seal is almost surely intact, in which case the R value is pretty nearly exactly the same as it was when the unit was brand new.
Polyiso also doesn't really lose much R value over time. Even worst case, it will stabilize at around R5 or so at minimum. It should always be a tiny bit better than the best EPS out there in terms of R per inch.
If you seem to be loosing more heat than you used to, my first thought is that you have some air leaks that have developed over time. Sealants can and do sometimes fail over time, and small shifts in the structure along with temperature and humidity related expansion and contraction of structural elements can open up gaps that can be hard to see. I suspect this is much more of the problem you're seeing than degrading R value in the insulating materials.
Fiber cement siding is probably the most critter proof option out there aside from brick. If you have woodpecker problems, I'd absolutely go with fiber cement siding. I'm planning to replace the T1-11 on my own home with fiber cement for that very reason.
Bill
Bill,
My house started out 25 years ago clad entirely in cedar. After the ravages of our damp climate, and a carpenter ant infestation, it's now fairly evenly split between cedar shingles, corrugated galvalum and Hardi panels.