Will these ideas work in Zone 5a?
Hopefully this questions won’t be to all encompassing and broad so that it won’t make any sense.
I’m trying to build a home in Southern Connecticut to be as energy-efficient and cost-effective as possible. My Dad is a Carpenter / Contractor so we will be doing it ourselves. He has never done anything “green” or energy efficient before, so I have been researching as much as possible to find the most cost-effective and energy-saving way possible.
What I want to do so far:
Home will be Colonial, Gambrel style roof, 36 X 30, no garage.
Basement will be concrete forms, floor poured over 4″ XPS foam. Will seal basement walls with Spray insulation, 2 – 4″.
Framing walls will be double 2 X 4 stud, spray insulation inside wall, minimum 2 inches to form vapor barrier, rest will be filled with cellulose. Wall thickness will be 12 inches, should result in a R value of near 40.
Roof thickness will follow the same values as walls, utilizing gambrel roof style to save on Lumber and materials.
Exterior siding will be vinyl, due to cost. Housewrap will not be vapor barrier due to it existing inside the home sheathing.
Hoping to accomplish heating and cooling with a mini split system with upstairs and downstairs units. I think I will also need a HRV due to the house envelope being very tight.
Now for the questions, is anything im doing totally wrong? Is there a cheaper, more effective way to do this? I think ive addressed most everything I can think of in ways that I can handle, and from browsing other projects that have been done on the site.
Thanks in advance
Denis
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Replies
Denis,
Yes, there is a cheaper way to do it. Don't use spray foam. Instead, just use dense-packed cellulose in your walls. You can insulate the interior of your basement walls with rigid polyiso.
I would use plywood wall sheathing instead of OSB because of the risk that cold OSB is subject to moisture accumulation and rot.
Your sentence, "Housewrap will not be vapor barrier due to it existing inside the home sheathing" is confusing. Housewrap is never a vapor barrier. All brands of housewrap are vapor-permeable.
Gambrel style roof:
You said: "Roof thickness will follow the same values as walls, utilizing gambrel roof style to save on Lumber and materials." Are you using the gambrel style to have living space above the top plates of the first floor? If so, what is your strategy to insulate the sloped sections of the gambrel roof? If no living area above the top plates, a gable roof is much more cost effective.
John,
The plan is to have living area above on the gambrel style, just to save on walls and use the roof as my exterior walls, I should have been more specific and said we sould be shed dormering the back of the home. I was hoping to insulate the sloped sections with a couple inches of spray foam, then dense pack cellulose, but that leads me to Martin's comment.
Martin,
Sorry for the confusion on the housewrap, probably the wrong term, I know there are ways to create a vapor barrier besides using spray foam, I just dont know what would be a viable alternative to me. Im trying to read / learn as fast as i can.
Denis,
You don't need an interior vapor barrier; however, you do need an interior vapor retarder.
In most cases, vapor-retarder paint is all you need.
Thanks again Martin,
So how does that change my exterior solution? If from inside out Im
Vapor Retarding Paint, drywall, 2X4 interior, Cellulose, 2X4 Exterior, Plywood, ??, Vinyl SIding
Thanks so much for the help, its giving me some good stuff to read up on.
Denis
There has been no mention of how to create an air barrier....
Or roof venting
I think you need a local contractor or coach who understands air barriers and roof venting(or how to properly build an unvented roof)
Isnt that what this site is for? To ask questions and get info? Obviously without the closed cell spray foam i dont have an air barrier, hence the question.
I would suggest you choose a design with a vented attic
http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting/view
and start reading about Airtight Drywall and Airtight Sheathing
I still suggest a local coach
Denis,
If your first slope up from the top plates will be your roof/walls, will you then have ceiling joists at the break of the second slope? If you are creating an attic at the intersection of the two roof slopes (by installing ceiling joists) you will need very careful detailing at that intersection if you are venting the roof. Or will you be treating the entire gambrel roof as a conditioned space? As John B points out, you may want to consult with somebody locally that is experienced in energy design. You will need more than a spray foam contractor to get it right (and spray foam is not always the best solution).
Denis,
If you are planning to insulate a sloped roof, I suggest you read this article: Creating a Conditioned Attic.
This might be an area im not sure on. I was really planning on making an "attic" per say, no storage or anything was ever going to go up there. The space from the ceiling joist to the ridge should be not that large of an area.
I believe my intial line of thought was to keep that as conditioned space, because the spray foam was my air barrier, everything inside of it was inside the house. Maybe that line of thinking is completely wrong and I need to go back to researching. Its tough finding examples of gambrel houses on this site or any other.
Denis
"Its tough finding examples of gambrel houses on this site or any other."
This is probably because gambrel roof two-story homes are perniciously difficult to detail properly, and especially so when it comes to energy performance. And yes, roof shingles are cheaper than siding but you'll more than make up for it with the extra complexity of the dormers etc. Of course if you just have a hankering for the look of a gambrel it's possible to do a decent job. But don't expect it to cost less than a simple two-story with vented attic and cellulose insulation as Martin suggests: it'll certainly cost you more.
Well, the long and short of it is the wife wants a gambrel. If any of you guys are married you know what that means.
I know the front dormers will be a little difficult, but im hoping with the shed in the back it will alleviate some of the problem.
I read the linked article and see what you guys are talking about, im giong to have to do some kind of hybrid between the rafters and either above or below them to make this work, and that seems like a total pain. Thats the only way of trying to avoid thermal bridging or some sort of hybrid rafter system where I add on to make them have the same depth as the exterior walls.
I see where the costs are gonna expand greatly.
I was reading through the thread and noticed I didnt get one answer on a questions i asked. If I go full cellulose in the walls, what kind of product should I do to make an air barrier on the exterior walls? Barring spray foam that is.
Im sure the dormers will be difficult, but Im going to have to do the best that I can with the design thats been put on me :)
Thanks again everyone for your help, its already changed some of the things I want to do.
Have you read up on airtight Drywall Approach?
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/19744/airtight-drywall-anyone
Or Airtght Sheathing?
https://www.greenbuildingadvisor.com/blogs/dept/musings/airtight-wall-and-roof-sheathing
Contact the local Energy raters (RESNET)and find out who is building tight houses...you might get some local advice
http://www.resnet.us/directory/raters
Dennis,
I second the idea that you consider the benefits of ADA for both air and vapor management. It's already on site and doesn't require an additional contractor.
If the "rigors" of ADA seem a bit tall for you guys... Consider the simple solution of an air & vapor control layer on the face of your interior stud walls. This would be in the form of a membrane like Certainteed Membrain http://www.certainteed.com/products/insulation/mold-prevention/317391, or SIGA Majpell http://www.siga.ch/Majpell-detail.61.0.html?&L=1&frage=501&keyword=majpell&lang=en. Both would be fairly simple to install and create a good airseal.
Working with your Dad on a project... Enjoy it. Wish i could :)
Denis,
how about posting a wish-picture that Illustrates the style?
Even if you get yourself a snappy looking vest ...Some Euro-Tape.. and a video :--)
This is going to be Not-So-Simple
Just razzing you Albert ... I like the video
do you have a link to one that shows the partition wall intersections,dormers and Rim Joist etc?
Denis,
It's certainly doable. A builder with air-sealing experience and insulation experience can make a tight insulated gambrel roof. If you're not sure how to do it, however, you may want to hire a consultant to help you.
I feel like im going to make my own thread here to confusing, but what the heck.
Back to the walls, If I got
Vinyl -> Plywood sheathing - > Intial 2X4 wall - > Cellulose insulation in bays and filled to - > Interior 2X4 wall - > MemBrain or Airtight drywayll - > Paint
Is that a good enough system? Should I have some sort of vapor / air barrier between my sheething and the insulation? not just on the inside?
Since getting off the spray foam against the sheathing im a little lost on the complete wall construction.
Denis
Something like this style, ignore the hug porch, just look at the roofline
http://www.remodeling4dumbbells.com/Roof_Design/Gambrel_roof_photo.php
In my surfing around, what if to accomplish this I used I - Joists for the rafters? I know they are legal in normal roof applicatiosn but I dont know in a gambrel. The only other way it looksl like from reading martins article would be to insulate the bays and then put sheets either on top or under the rafters to supplement the insulation and get it up high enough.
I joists look nice because I think ive seen them used in applications to cut down on thermal bridging since the center of the joists are thinner and transfer less heat.
I would appreciate any ideas that you guys have on doing this kind of roof, my wife is married to this house "looking like a barn"
thanks for the membrain link Albert, that looks doable
Denis,
It sounds like you need to read up on air barriers. Here are two introductory articles to get you started:
Questions and Answers About Air Barriers
One Air Barrier or Two?
Thanks alot for the links Martin, good information there, Ill keep going with it.
From reading the comments, it seems like your a fan of One good external side air barrier. Very interesting article though thank you.
Denis
Denis,
thanks for posting the link ... I think it helps to visualize what you are talking about.
you may get some better feedback now
John,
Studies show that wearing the "snappy looking vest" improves job site skills by 12.3%. The hard part is to find the matching tool belt (not shown)... Back at ya! :)
Dennis,
There is nothing wrong with relying on an external air barrier. It does seem like it might be a challenge considering your "warm roof" is twice the surface area and will wind up being full of penetrations (I'm guessing here...) from roofing.
The Interior air barrier is perhaps an upgrade since it can also prevent moisture laden air from entering your wall and roof cavities.
I like your chances of ADA on this project. Working the finished drywall surface might be the most practical. Obviously I'm going back and forth and can't make up my mind. Take the cue and pick one (...or two). You guy's will figure it out. Having local experience will help a lot: This job may spark a few "Father & Son disagreements". Consider having a local family therapist on site too.
Still Jealous... Have a blast.
Albert, kidding aside... I respect the Europeans and I think we can learn a lot from them.
I did like your video links
You have a good point about "the warm roof"
My current thinking is that a double stud wall with the primary air barrier at the sheathing(Marc Rosenbaum) CONNECTED to a good ole air-tight drywall ceiling and vented attic(see Lstiburek's current blog) is a damn good track for Buildable & Affordable.
This particular project has a complication with the gambrel and the dormers that will take some head-scratching and careful detailing.
It's not fair to say don't build gambrels and dormers ... because the fashion/style choices of homeowners and designers are almost impossible to overcome.
I think for cold climates ....the 2 air barrier approach would be wise.
Primary at the sheathing and the best you can do at the drywall with all framing cracks and cavities fully filled
John,
"It's not fair to say don't build gambrels and dormers ... because the fashion/style choices of homeowners and designers are almost impossible to overcome."
Agreed. What would we do without a challenge? Perhaps it's a luxury, but it's much more fun to figure out how to build things that you don't know how to build than things that you do.
The two barrier wall should be ok. There are more problematic connections, but essentially a gambrel is just an out of plumb wall with roofing on it. An odd duck, but certainly an important iconic style.
Dennis's wife is doing him ( & his Dad) a favor by making them stretch their abilities. I think it's within their means.
Thanks again for all the continued input guys, giving me alot of strong ideas that I can hopefully put into practice here.
Would Vinyl over external taped foam, either 2 layers or one with taped sheathing, with a double stud wall filled with cellulose, with something like membrain on the external side of the internal double stud wall be a good idea? Or ami I overcomplicating it.
Im thinking that by using the membrain on the inside edge of that 2nd stud wall, Id have that space between the drywall and the membrain for wire chases etc, and wouldnt have to worry about air tight electical outlets etc.
Does that make any sense? Ill try to draw a picture tomorrow.
Thanks so much again guys
Denis
Denis,
If you are building a double-stud wall, and if you want to keep the inner wall free of insulation so that it can easily be used as a wiring chase, the best air barrier and vapor retarder on the exterior side of the inner 2x4 wall is OSB or plywood.
You could also use InsulWeb, which is the standard membrane used when blowing cellulose, but installation details are complicated. I would use OSB. Forget the MemBrain. (Remember, OSB is a vapor retarder.)
Lessons Learned from the Habitat for Humanity Westford House
Even with some of the best consultants in the country overseeing this project...
Those "darn" dormers were a hassle and a major source of air leakage.
Denis:"I'm trying to build a home in Southern Connecticut to be as energy-efficient and cost-effective as possible. My Dad is a Carpenter / Contractor so we will be doing it ourselves. He has never done anything "green" or energy efficient before, so I have been researching as much as possible to find the most cost-effective and energy-saving way possible."
Ok, so far ... this is admirable
Denis, I probably won't win this battle...
I think you and your Dad could build a straight up 2 story house that is extremely energy-efficient,durable and cost-effective... no problem
The problem is the Architecture.
Maybe Albert or someone else will volunteer their time and help you work through the CHALLENGE... Otherwise I think you need to Invest in a very good Consultant.
If I were building a house with my Dad (or Mom)... I know what I would do.
Dennis,
I second Martin's advice. If you create a service cavity as you describe, OSB is the best choice. I really do like a service cavity, but I don't mean to make ADA sound to hard at all. ADA seems like the simplest approach for such a complicated frame since it allows you to work on the interior face for airsealing and vapor control.
Also... Now that I imagine myself working through the "challenges" of a Gambrel... John has pointed out that it's easy to underestimate how "challenging" it will be. It would be a REALLY GOOD IDEA, to have someone with double stud wall experience to design & work the framing with you two.
So... A good consultant, a good therapist, and a "snappy vest" will take you far.
But seriously, don't let my light heartedness suggest that you don't need a consultant. You really ought to make sure that you've got: A plan that can be built, know how to build it, and who to ask onsite when things are not "adding up". Third party review can help to keep you out of trouble.
Life's short. Make your wife happy and "go for the Gambrel".
Life is short ... full 2 story homes are not-so-awful
finish early, save consultant fee... with money left over to take Dad and Wife to Ireland
some constructive advice
If you want to research high performance homes with compact roofs and dormers...
Join the JLC Magazine Online Archive (a great resource)
Look for recent articles by John Abrams, David Joyce and Dan Kolbert.
Not-So-Simple and Not-So-Affordable ...
I've always hated dormers. To me, they are evidence that the architect got confused and had to cut a hole in the roof as an afterthought.
I think like a roofer. You design a house the size you want -- one story or two stories, your choice. Make sure you have just the right amount of area. Ideally, make the house a rectangle.
Then put a roof on top. Under the roof is an area called your attic. Don't condition it and don't put anything up there but Christmas ornaments.
A rectangle with a hat on top. Now, is that complicated?
Martin,
"I think like a roofer".
I'm not sure that's to your credit.
I'm going to laugh if I find out that you live in a geodesic dome way up there and off the grid!
Dennis... They are right. As far as energy efficiency goes... Simple compact forms are the most efficient and "greenest" when looked at from an energy consumption standpoint. Adding dormers or bump-outs inevitably adds air leakage and thermal bridging. Therefore they will add cost in consumption for the duration. Not to mention that the cost to the project will be significant.
Just so I'm on record as admitting that both John's and Martin's logic is absolutely faultless. Their taste in styles however is not proven.
Perhaps your wife would like to spend the energy savings on a trip to Ireland... I hear it's beautiful.
Albert,
I did not expect to win this one.
I like simple Architecture and Homes without Garages.
I also think Fireplaces are pretty dumb in Texas.... But it is very rare for me to find clients who will agree with me....
So your point is understood.
I like simple...but I don't think every house should look like a Monopoly House Token.
or a Monopoly Hotel.
Or that a house should be designed from the outside IN.
The site,the sun, the owners, the program(functions),the climate,the budget,the neighborhood,aging in place and the builder AND Delight should ALL be considered.
Denis, sorry for the diversion