Big picture planning for house build
My parents have purchased land in Idaho (zone 6B) where their retirement home will be built. I have been doing some research on different home options that might work for them within their limited budget.
One option that seems promising is a company that does post and beam kits with 2×6 framed walls between the posts. Their standard roof system would likely consist of 2×12 rafters on 24″/16″/12″ spacings (depending on snow load requirements) with 2×4 strapping over those and 7/16 sheathing. The post and beam structure uses 4×8 timber horizontally along the base of the exterior walls, and then the vertical posts are placed above those.
I have some questions:
1. I am thinking of a heated rift slab-on-grade. Any issues I should be aware of? I am intrigued by the Legalett system with air-based in-floor heat. It sounds like such a nice simple system. But I suppose I could be open to something like a Radiantec water-based in-floor heating system as well, using Bygghouse WarmFörm or Iso-Slab foam forms. What would you advise regarding this slab foundation stuff?
2. Is there any concern using the 4×8 douglas fir timber horizontally at the base of the exterior walls? There would be the strip of whatever membrane between the concrete and the wood. The inside of the 4×8 would be revealed to the interior and would sort of negate the need for baseboard along those walls. A pressure treated 2x can be placed below the 4×8, depending on what sort of flooring is used. But if we were to go with polished or etched concrete floors, it would be just the 4×8 on a membrane. Any water staining/rotting concerns there?
3. With the post/2×6 exterior walls, I am interested in using the Zip R system of sheathing/vapor barrier (the type with the layer of foam insulation attached on the inside). This would help to reduce thermal bridging through the studs and posts, as well as help to create a pretty airtight wall. Any suggestions with this? I guess going this route would include batt insulation in the stud cavities, right? Would using Zip R outside of 2×6 studded walls complicate window installation? Any suggestions?
4. Any suggestions for the roof? I would like some rigid foam. I am also somewhat interested in using Zip roof sheathing. Any suggestions for how to integrate these things properly? Would it simplify things to have the roof system changed out to larger timber rafters with 2x T&G over that? I’m not necessarily looking to go full-on with SIPs. But I would like more than just traditional batt insulation. The roofing will likely be clip style standing-seam metal roofing.
5. Any experience with Zip system 2.o (as described on Matt Risinger videos)? Does using the sealant in the tubes actually create a better seal than the Zip tape? Does it affect the Zip warranty or anything like that? Or am I better off giving up on the Zip stuff and going with plywood and Tyvec?
6. With a slab-on-grade rift foundation, is it going to be a pain to create tiled showers without much of a lip getting in? I want this house to be age-in-place/universal friendly for my parents.
7. Does drywall need to be installed behind T&G wood ceiling boards? Does it make a difference whether they are 2x over the top of rafters vs. 1x installed to the bottom side of rafters?
Thanks for any advice you can give on any or all of the above points! I know this is a lot. I am a detailed perfectionist type of person and want to make sure stuff is done right.
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Replies
Brent,
You might want to start individual threads for your questions. As a general suggestion, you might want to search on "the pretty good house" concept. I think that is what you are trying to do.
On Q1, in-slab heating is generally a waste of budget on energy-efficient new builds. Experts on this site usually advise focusing on air sealing and insulation to create a tight enclosure. That way you can use a relatively small system to maintain indoor temperatures.
Yeah, I should probably break these out to separate posts. Thanks for the lead on "the pretty good house" concept. Seems like the sort of concept I want to pursue with this build.
There are no real advantages to using air as the working fluid in a radiant slab. It takes a lot more energy to move heat with air than with water. And until the house is designed, with preliminary heat load calculations it's not clear if ANY radiant floor heating solution would make sense.
A 2x6 wall in zone 6B would require >R11.25 out of the ZIP-R for dew point control on the batt insulation. That means only the fattest 2.5"/R12.6 ZIP-R will do:
https://up.codes/viewer/washington/irc-2015/chapter/7/wall-covering#R702.7.1
https://www.huberwood.com/assets/user/library/ZIP_System_R-Sheathing_-_Product_Data_Sheet_(R3-12)_v1.pdf
It would probably be cheaper to install standard ZIP and a couple inches of exterior side polyiso.
That would beat code, but it's not a very high performance assembly.
Can I assume that what you mean by "...rift foundation..." is actually a RAFT foundation?
The ceiling needs to be air-tight, whether its a cathedral ceiling or above/below attic floor joists. That air barrier could be a layer of drywall. I need a clearer description of what you're going for.
Would there be any benefit in using Zip R on the walls when that system places the foam inside the sheathing/vapor barrier?
How does polyiso insulation do with various temperatures? Does it lose R-value in extreme cold?
What would be the best (but still economical) insulation/sheathing/vapor barrier system to use on 2x6 exterior walls?
Yes, RAFT foundation!
Regarding the ceiling - this would be an a-frame/chalet/cathedral type ceiling. So a traditional ventilated attic would not be an option. What would the best (but still relatively economical) system on this roof system that uses 2x12 rafters with 2x4 strapping over those?
Hi! I think you should contact professional builders to get answers to your questions. You want to learn quite a lot, so I concluded that you do not understand construction specifics. So it's better to ask for advice from professionals. The only thing I can advise you is to print out many family pictures to remember pleasant moments with your family. You can pick up stylish photo frames for them on https://www.frameshow.com.au and give them to my parents. I'm sure they'll be very happy.
The way I see it your words and your to do list are total at odds with each other and almost oxymorons.
Limited budget and new construction.
Budget and heated floors.
Post frame and 2x6 with Zip.
In terms of dollars per square foot almost every existing home on the MLS listing will be priced lower than any similar new construction.
Heated floors are luxury option and not part budget builds.
Sloped ceiling tend to be complicated trying to fit to much stuff in too little space driving you to use the most expensive materials and end up with a lower R value roof.
My guess is you have decided you like the low cost of a pole barn and have set your mind to making a high performance building out of a pole barn. I say every pole barn is a sow’s ear and if you spend the time and money to make it into a silk purse of a real building you could build a much better building for less money without the poles.
I understand everyone wants to own the custom home of their dreams and hopes they can do it for short money. Do yourself a favor and admit to yourself this is luxury dream build and you are going to spend the money to build it, if not trim the luxury items and put them out of your mind the sooner the better.
Walt
Walta,
This is a three year old thread, which was only revived by the troll in post #5.