Helpful? 0

New Construction

This site has been invaluable as I attempt to educate myself with respect to designing and hopefully building (with plenty o' help) a 1500 sq. ft. passive solar home.

Here are some details of the current design. See conceptual pictures.

> Climate Zone 5A (Rochester, NY)
> Shed roof. Standing Seam Metal roof with air gap/rain screen
> OSB-SIP walls and roof (R=52 for both)
> Frost-protected shallow foundation, concrete slab on grade
> South windows triple-glazed, high SHGC>0.5, fiberglass (not sure on manufacturer)
> Lunos e2 ductless HRV (2 or 3 pair)
>: Main floor with loft

This may be greedy, but after reading for a few month (along with many other sites - particularly Building Science Consultants), I have a few questions.

1: I am paranoid about moisture condensation/retention, especially under roof panels, rotting the OSB sheathing on SIPS. I am thinking of using a liquid applied air barrier for roof and walls, along with a rain screen/air gap for roof and walls. I assume I should use a vapor permeable product in this case. Correct?

2: Should the slab be a monolithic poor with a thickened edge or some other method?

3: I am totally clueless on heating methods. I quick and dirty web calculation revealed a max heating load of ~9500 BTU/hr (design temp 5F). I have looked at WarmFloor (low voltage radiant heat mats) for slab. I am trying to eliminate any needs for ducts in design. I had also considered a wood/pellet stove but want to minimize my SIP penetrations. Any help here? Space heaters? Mini-splits?

4: Martin H......you mentioned in previous posts a dislike of shed roofs....rationale?

5: Martin H. again.....you mentioned in a previous post that you preferred exposed fastener metal roofs vs. hidden....why?

6: Should I be considering other wall/roof designs besides SIPS for super-insulation? If so, why?

7: Siding material is undecided. Considering Cor-ten (weathering steel) but am open to suggestions.

8: Are triple glazed, fiberglass windows from Canada my best bet? If I was made out of money I would consider German windows.....

9: I realize there is an abundance of south facing windows. I plan to use Window Quilts or insulated shades (both sealed) to provide shading in summer and to prevent heat loss in winter.

Thanks in advance and thanks again for all of the wisdom and experiences shared here.

Dave

House 1.jpg963.04 KB
House 2.jpg888.77 KB
Asked by David Mancuso
Posted Sat, 01/04/2014 - 19:55
Edited Sun, 01/05/2014 - 15:29

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7 Answers

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1.
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Dave,

Shed roofs look like a shed, and where's your PV going to be installed in the future?

Please install the Lunos e2s as soon as possible and provide a detailed report about their installation and performance to this site. They are really expensive, and I have never seen anyone express any detailed experience with them on this site.

Unless you have natural gas distribution, use one, or maybe two, ductless minisplits. I call them electronic woodstoves, because they are point sources of heating (also cooling). Just make sure you have/want a nice open floor plan if you decide to use them. I think it takes away the beauty of minisplits if you use a lot of them or use ducts with them. Open floor plans seem very much en vogue these days, anyway.

I have Accurate Dorwin with triple glaze on the north and double glaze (approx. 0.6 SHGC) on the south. I like them ok--just had trouble with them getting my order right and trouble with the shipper they used in US (MD). You might have a lot of trouble finding >0.5 SHGC in a triple pane window.

Answered by Sonny Chatum
Posted Sun, 01/05/2014 - 07:37
Edited Sun, 01/05/2014 - 07:44.

2.
Helpful? 0

Sonny,

Thanks for your reply.

I plan to use a pole mounted PV array.

I have access to natural gas service. Are you suggesting a heating method other than the ductless mini-split?

Accurate Dorwin has been at the top of my list of window manufacturers.

Dave

Answered by David Mancuso
Posted Sun, 01/05/2014 - 12:50

3.
Helpful? 0

David,
My main objection to shed roofs is aesthetic. Functionally, they are fine.

You referred to triple-glazed windows for your south side, implying (perhaps) that your east and west windows might not be triple-glazed. But if you can't afford triple glazing for all 3 (or all 4) orientations, the triple-glazed windows go everywhere BUT the south side, and the south side gets double-glazed windows (because of the higher SHGC).

A monolithic slab is certainly one way to build a foundation, but my no means the only way. If you can afford it, a basement is certainly handy.

Ductless minsiplits provide both heating and cooling, but if you have access to natural gas, then you can certainly heat your home inexpensively with a small gas furnace or one or two gas space heaters.

Most builders have concluded that SIP walls cost more than double-stud walls filled with cellulose or 2x6 walls with exterior rigid foam. If you decide to use a liquid-applied air barrier, it should be vapor-permeable.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 01/06/2014 - 09:06

4.
Helpful? 0

Martin,

Thanks!

1) I plan on using triple glazed on all four sides.

2) I agree on basement being handy. I am trying to a) manage my budget and b) attempt to live a simpler lifestyle

3) As I am trying to avoid ductwork, what is your opinion on gas space heaters vs. mini-splits?

4) My paranoia about OSB faced SIPS has led me to consider SIPS faced with fiber cement board (both roof and walls).. Any thoughts/opinions?

5) Can you recommend any sites or documents that describe penetration barrier details to a newbie? I listened to the podcast by Joe L. and understand the concept of wall, slab, and roof having continuous water, air, vapor and insulating layers, in order of decreasing importance, but the details of installation and product select overwhelm me.

I really appreciate all the wisdom and knowledge you offer.

Dave

Answered by David Mancuso
Posted Mon, 01/06/2014 - 10:23

5.
Helpful? 0

David,
Natural gas is cheap right now. If you don't need air conditioning, you can buy a wall-mounted space heater with through the wall venting for $1,000 or less.

In the future, natural gas might become more expensive. If you plan to install a PV system, you may prefer an all-electric house. Electricity is the fuel of the future, for sure. If you want air conditioning, get the minisplits.

I haven't had any experience with SIPs faced with fiber-cement, but I imagine that there are less expensive ways to build a wall.

I don't know what you mean by "penetration barrier," but if you are talking about thermal barriers, water-resistive barriers (WRBs), and air barriers, you might want to read these articles:

All About Water-Resistive Barriers

Using Rigid Foam As a Water-Resistive Barrier

All About Rainscreens

How Risky Is Cold OSB Wall Sheathing?

Housewrap in a Can: Liquid-Applied WRBs

Questions and Answers About Air Barriers

Vapor Retarders and Vapor Barriers

One Air Barrier or Two?

Airtight Wall and Roof Sheathing

All About Wall Rot

Answered by Martin Holladay, GBA Advisor
Posted Mon, 01/06/2014 - 10:39
Edited Mon, 01/06/2014 - 10:42.

6.
Helpful? 0

Martin,

I've read most of the links you posted and they have all been very helpful. What I meant by penetrations is window and door openings (or any other wall penetrations). I will continue to read the posts and links you mentioned.

Dave

Answered by David Mancuso
Posted Mon, 01/06/2014 - 12:14

7.
Helpful? 0

David,

I found the same thing when I started designing my own build, it can be overwhelming. Here a few sites I found helpful.

http://bldgtypblog.blogspot.ca (I found this site especially illustrative)
http://uphillhouse.wordpress.com/
http://ourhouseuponmoosehill.blogspot.ca/p/details.html

All of these sites include illustrative details on window/door penetrations, and usually a well written explanation as to what they did, and why. They may not fit your design goals exactly but it's a starting point.

I found it really helpful to look at different project blogs. Also, if you find a useful detail, whether text or an image, save it.

Sites like BuildingScience are invaluable as I am sure you know, but for me it took looking at pictures of real people, building real homes (often their own) to finally "get it" for some details. After that moment of understanding comes, more general details you previously found daunting become a resource.

The last blog-like site I suggest is this one. To me, GBA has struck a balance between providing detailed information on an array of critical, often difficult to understand topics and being a website that welcomes anyone who has the good grace to be polite. Thats all that is asked of us, and look what we get in return. I realize I am preaching to the choir, but it's still my best advice.

Best of luck.

Answered by Jason Hyde, Peterborough 6A
Posted Tue, 01/07/2014 - 10:37

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