Adding a Timber Porch

[ballen]

I am in the process of designing a barn conversion (into a home).  I'd like it to be well insulated with no thermal bridging to the outside. How do folks add a wrap a rap around porch (probably 3 sides of the house) without attaching to the main beams (that would be a thermal bridge which is a no-no when it comes to PassiveHouses.)?
Thanks
Bill

[Thehardway]

Make the entire porch on piers/posts, freestanding next to the barn/house. To most people this would not be practical but to you it may be. Another more practical way would be to use a thermal break on the inside rather than outside.

How do you intend to insulate the walls? wattle and daub, wrap and strap, SIP's?

Depending on the thickness of the wood you use and it's species, thermal bridging might not be that big of an issue even in a passive house.  If done right, an all wood passive house can be built with wood used for thermal mass and buffering.  This has been demonstrated successfully by Enertia Homes.  http://www.enertia.com/Science/HowItWorks/tabid/68/Default.aspx

EWP is not a real good thermal conductor but it is fairly decent thermal mass, especially when it is greater than 6" thick/deep.  This made evident in solid log homes and is why they perform fairly well thermally without any conventional insulation material being added. 

[ballen]

Wow, that's some design....basically using the whole "inner house" as the absorber and thermal mass in a giant solar air heater.  My barn frame is just the right size for my planned home so I would have to find another, larger frame to put around it....seems like a lot of work and resources.
I do not yet know how I am going to enclose my frame.  SIPS seem the easiest but I suspect there is a lot of petroleum and foreign money in the foam?
If I did a free standing porch, you still need to tie in the roof to the main house. How do you ensure it stays put and doesn't move separately from the house?

[Thehardway]

Foam can actually be quite environmetally friendly.  Many of them are made from "recycled" products or are soy or vegetable based.  Water based spray in place foam is probably one of the most energy efficient ways to stay warm/cool when considering total life cycle and the energy saved by its superior insulating performance.  You could sheath the inside of your barn siding with plyboard and then literally spray the foam to it. 2.5" of Polyurethane foam would give you an airtight envelope with a rated R-value of R-13+ and would perform closer to an R-21 or better wall.  It is not the cheapest initially but will pay itself back in 3-5 years with no performance deterioration down the road unlike many other products.

Other interesting options would be infill such as AAC block, strawbale, ecoblock, Cob. etc.

Log home building has to deal with movement and settlement all the time. A free standing porch is much the same. To allow the porch to move you simply use a system of overlapping flashing.  The exterior finish is stopped short of the roof and flashing installed to cover a second flashing affixed to the roof floats against the building under this preventing water and ice from reaching the building.  Ideally you would place the posts for the porch on the same footing as the building which would eliminate unlike movement.

Is the barn being re-constructed on a new foundation or are you using it as is where is?

[ballen]

Thanks,

In my ideal world, I want to see all of the frame and barn siding from the inside so any insulation will have to be outside of that (just like SIPs).  I suppose I will have to frame some sort of cavity on the outside to contain the foam against the outside of the barn siding.  I hope to finish the outside with another layer of barn siding.  Can you offer any names or other specifics for the environmentally friendly foam you mention?

I am moving the barn frame to a new site (just down the road) and hope to build a new, whole basement foundation.  I could easily design in footings for the porch and handle the roof line the way you suggest. Thanks!

[witterbound]

I just cut pockets into my outer walls for my porch ridge beam and plates to fit into.  They then got spray foamed on the inside, along with the rest of my walls.  It seems like a lot of extra work (posts, mortises, tenons, footings, connections to footing, etc), and something that isn't structurally necessary it doesn't seem, just to avoid having to cut a few pockets in your outer walls to hold up the house end.

[Thehardway]

Ballen,

It should be no problem to put siding on the outside, the distance off the existing wall that you want and then foam in between with the insulation. Not sure what your inspector will think though ;D



There is a lot of hype about green building and green building materials.  I think it needs to be approached with open eyes and an armored pocketbook.  Some will give you a song and dance about how terrible foams are and how they are made from imported oil and you should use wood.  The next group will tell you how bad micro-toxins are and that they come from mold and mildew which thrives on wood and cellulose, the next bunch will tell you that you should live in a canvas yurt because it uses less material and resources and can move with you if you move.  They will also be the first ones knocking on my ICF home door when the tornado comes through seeking a safe shelter.The bottom line in my book is green is local and green is what it saves more energy over its life cycle than it took to produce .  Everything is toxic if not properly handled and used or cared for.  I have read books where on opposing pages two parties claimed they were more ecologically responsible and "green" than the other (wood vs. steel framing and roofing)
Has your barn ever been painted inside or out?  It probably has lead in it. If the siding wasn't painted it probably is housing mold spores that are just waiting to dry out and go airborne. If you chose to replace it with new siding you are cutting down trees and using fossil fuels to transport and mill the materials and steel for nails to secure it.  I bought 50# of nails the other day at Home Depot and after getting it home looked at the place of origin.  I expected it to say China or India as no one is willing to make nails in the US.   Guess what, it was the United Arab Emirates.  I guess they have plenty of dead tanks sitting in the desert to melt down and make nails out of and plenty of oil to run their smelters. 

Here are a couple sites with info on the foam.

http://www.biobased.net/

http://www.hgtvpro.com/hpro/nws_ind_nws_trends/article/0,2624,HPRO_26519_3679395,00.html

[frwinks]

looks like the PH is catching on 8)
I too wanted to limit as many openings in the external envelope as possible...heck if it weren't for my g/f I prolly would've installed two windows and called it done ;D
We've opted for a standalone porch as well, tied in as per Thehardways's description.

I chose the REMOTE wall system (also known as the wrapn'strap), which I modified slightly to reflect materials used.  The product I used was IKO Enerfoil Polyiso. 
You probably know this already, polyisocyanurate insulation has the highest thermal resistance per inch out of anything that's offered to the market today.  It's also one of the cleanest out of the bunch. 
The REMOTE wall system allows you to keep ALL of the insulation of the wall cavities, where it belongs, the polyiso provides the VB and the Enerfoil also acts as WRB and excellent RB.  Depending on the material used for the curtain walls, in my case 2x4, the 3.5" of airspace really lets the foil facing do its thing ;D
details on my modded REMOTE wall (also includes a link to CCHRC manual on REMOTE):
http://www.tfguild.org/forums/ubbthreads.php?ubb=showflat&Number=22170#Post22170





opening detail with REMOTE

[ballen]

Why was it neccessary to put up a 2x4 wall first?  Why not just begin the Remote wall on the timber frame (or just outside what ever interior surface you want to see)?

[mmhailey]

Not to hijack the thread, I'll send FRWINKs a PM. I want to know how the bottom of his wall that overhangs the stem wall is protected from insects, water, etc;

[frwinks]

Why was it neccessary to put up a 2x4 wall first? 

to make the "powers to be" happy... and it makes attaching the foam/siding/kitchen cabinets a lil' easier ;D
You could run horizontal "strapping" 2' OC and just frame in your doors and windows and still have good attachment points for drywall, foam and siding....